It’s Not the Media, It’s the Message

To hear The Wildlife Society’s staunch opponents of TNR tell it, the media’s just not interested in stories about “the impacts of free-ranging and feral cats on wildlife.”

“This January when thousands of blackbirds fell from the sky in Arkansas, articles about mass extinctions and bird conservation were a dime-a-dozen. When the Deepwater Horizon oil spill killed 6,000 birds between April to October 2010, news organizations ran ‘Breaking News’ about the negative impacts on the environment. Meanwhile it is estimated that one million birds are killed everyday by cats, and the only news organizations covering it are small, local branches. The bigger problem is being shuffled to the backburner for more sensational news.”

According to The Wildlife Society (TWS), however, “the bigger problem” is “greater than almost any other single-issue.”

In their effort to get the issue on the front burner, TWS has “gathered the facts about these cats, and published them in the Spring Issue of The Wildlife Professional in a special section called ‘The Impact of Free Ranging Cats.’” (available free via issuu.com)

Thus armed, readers are expected to, as it says on the cover, “Pick One: Outdoor Cats or Conservation”

Back Burner or Hot Topic?
Before we get to the “facts,” it’s worth looking back over the past 15 months to see just how neglectful the media have been re: “the bigger problem.”

  • January 9, 2010: Travis Longcore, science director for the Urban Wildlands Group, tells Southern California Public Radio: “Feral cats are documented predators of native wildlife. We do not support release of this non-native predator into our open spaces and neighborhoods, where they kill birds and other wildlife.”
  • January 17, 2010 Longcore, whose Urban Wildlands Group was lead plaintiff in a lawsuit aimed to put an end to publicly supported TNR in Los Angeles, tells the L.A. Times: “It’s ugly; it’s gotten very vicious. It’s not like we’ve got a vendetta here. This is a real environmental issue, a real public health issue.” In the same story, American Bird Conservancy’s Senior Policy Advisor, Steve Holmer, tells the Times: “The latest estimates are that there are about . . . 160 million feral cats [nationwide]… It’s conservatively estimated that they kill about 500 million birds a year.”

  • September 30, 2010: “Scientists are quietly raging about the effects that cats, both owned and stray, are having on bird populations,” claims Washington Post columnist Adrian Higgins. “It’s not an issue that has received much attention, but with an estimated 90 million pet cats in the United States, two-thirds of them allowed outdoors, the cumulative effect on birds is significant, according to experts.” Higgins’ story is riddled with misinformation, courtesy of the American Bird Conservancy (ABC), The Wildlife Society, and Dauphine and Cooper’s 2009 Partners in Flight paper.

“Palmer said one of the most ‘heartbreaking’ scenes during filming was at a volunteer spay-neuter clinic in Los Angeles that sterilized 80 ferals a day. She said most of the cats had infections that never healed, as well as broken bones, large abscesses around their teeth and mange.” (A claim easily discredited, if only the reporters had bothered to check.)

  • January 2011: Utah Representative Curtis Oda sponsors HB 210, which would permit “the humane shooting of an animal in an unincorporated area of a county, where hunting is not prohibited, if the person doing the shooting has a reasonable belief that the animal is a feral animal.”

Yet, the folks at TWS would have us believe that “the only news organizations covering [the cat-bird issue] are small, local branches.” As is often the case, their story doesn’t hold up well alongside the facts.

Indeed, other than when Higgins got Executive Director/CEO Michael Hutchins’ name wrong, it’s hard to see what TWS has to complain about.

The Art of Selling Science
“After years of arguments,” laments Nico Dauphine and Robert Cooper, recalling last year’s decision by Athens, GA, to adopt TNR, “the vote was cast: 9–1 in favor of the ordinance, with an additional 7–3 vote establishing a $10,000 annual budget to support the TNR program.”

“How could this happen in a progressive community like Athens, Georgia, home to one of the nation’s finest university programs in wildlife science? The answer is a complex mix of money, politics, intense emotions, and deeply divergent perspectives on animal welfare… If we’re going to win the battle to save wildlife from cats, then we’ll need to be smarter about how we communicate the science.” [1]

Something tells me this “smarter” communication doesn’t allow for much in the way of honesty and transparency—attributes already in short supply.

Old Habits
“The Impact of Free Ranging Cats” has given its contributors the opportunity to revive and reinforce a range of dubious claims, including the ever-popular exaggerations about the number of free-roaming cats in the environment.

According to Dauphine and Cooper, “The number of outdoor pet cats, strays, and feral cats in the U.S. alone now totals approximately 117 to 157 million,” [1] an estimate rooted in their earlier creative accounting. Colin Gillin, president of the American Association of Wildlife Veterinarians, who penned this issue’s “Leadership Letter” (more on that later), follows suit, claiming  “60 million or more pet cats are allowed outdoors to roam free.” [2]

The American Pet Products Association 2008 National Pet Owners Survey, though, indicates that 64 percent of pet cats are indoor-only during the daytime, and 69 percent are kept in at night [3]. Of those that are allowed outdoors, approximately half are outside for less than three hours each day. [4, 5]

This information is widely available—and has been for years—yet many TNR opponents continue to inflate by a factor of two the number of free-roaming pet cats.

And it only gets worse from here.

Dense and Denser
Not content to inflate absolute cat numbers, Dauphine and Cooper go on to misrepresent research into population demographics as well. “Local densities can be extremely high,” they write, “reaching up to 1,580 cats per square kilometer in urban areas.” [1] In fact, the very paper they cite paints a rather different picture. For one thing, there’s quite a range involved: 132–1,579 cats per square kilometer (a point recognized by Yolanda van Heezik, another contributor to the special issue [6].)

Also, this is a highly skewed distribution—there are lots of instances of low/medium density, while high densities are far less common. As a result, the median (417) is used “as a measure of central tendency” [7] rather than the mean (856). So, although densities “reaching up to 1,580 cats per square kilometer in urban areas” were observed, more than half fell between 132 and 417 cats per square kilometer (or 51–161 cats per square mile).

Even more interesting, however, are what Sims et al. learned when they compared bird density and cat density: in many cases, there were more birds in the very areas where there were more cats—even species considered especially vulnerable to predation by cats. It may be, suggest Sims et al., that, because high cat density corresponds closely to high housing density, this measure is also an indication of those areas “where humans provide more supplementary food for birds.” [7]

Another explanation: “consistently high cat densities in our study areas… and thus uniformly high impacts of cat populations on urban avian assemblages.” [7] (Interestingly, the authors never consider that they might be observing uniformly low impacts.)

The bottom line? It’s difficult enough to show a direct link between observed predation and population impacts; suggesting a causal connection between high cat densities and declining bird populations is misleading and irresponsible. (Not that Dauphine and Cooper are the only ones to attempt it; recall that no predation data from Coleman and Temple’s “Wisconsin Study” were ever published, despite numerous news stories in which Temple referred to their existence in some detail [8–10].)

Predation Pressure
Dauphine and Cooper make a similar leap when, to buttress their claim that “TNR does not reduce predation pressure on native wildlife,” [1] they cite a study not about predation, but about the home ranges of 27 feral cats on Catalina Island.

While it’s true that the researchers found “no significant differences… in home-range areas or overlap between sterilized and intact cats,” [11] this has as much due to their tiny sample size as anything else. And the difference in range size between the four intact males and the four sterilized males was—while not statistically significant—revealing.

The range of intact males was 33–116 percent larger during the non-breeding season, and 68–80 percent larger during the breeding season. In his study of “house-bound” cats, Liberg, too, found differences: “breeding males had ranges of 350–380 hectares; ranges of subordinate, non-breeding males were around 80 hectares, or not much larger than those of females.” [12]

All of which suggests smaller ranges for males that are part of TNR programs. What any of this has to do with “predation pressure on native wildlife,” however, remains an open question.

On the other hand, Castillo and Clarke (whose paper Dauphine and Cooper cite) actually documented remarkably little predation among the TNR colonies they studied. In fact, over the course of approximately 300 hours of observation (this, in addition to “several months identifying, describing, and photographing each of the cats living in the colonies” [13] prior to beginning their research), Castillo and Clarke “saw cats kill a juvenile common yellowthroat and a blue jay. Cats also caught and ate green anoles, bark anoles, and brown anoles. In addition, we found the carcasses of a gray catbird and a juvenile opossum in the feeding area” [13].

Another of Dauphine and Cooper’s “facts”—that “TNR does not typically reduce feral cat populations”—is contradicted by another one of the studies they cite. Contrary to what the authors suggest, Felicia Nutter’s PhD thesis work showed that “colonies managed by trap-neuter-return were stable in composition and declining in size throughout the seven year follow-up period.” [14]

Indeed, Nutter observed a mean decrease of 36 percent (range: 30–89 percent) in the six TNR colonies they studied over two years. By contrast, the three control colonies increased in size an average of 47 percent. [15]

Additional TNR success stories Dauphine and Cooper fail to acknowledge:

  • Natoli et al. reported a 16–32 percent decrease in population size over a 10-year period across 103 colonies in Rome—despite a 21 percent rate of “cat immigration.” [16]
  • As of 2004, ORCAT, run by the Ocean Reef Community Associa­tion (in the Florida Keys), had reduced its “overall population from approximately 2,000 cats to 500 cats.” [17] Accord­ing to the ORCAT Website, the population today is approximately 350, of which only about 250 are free-roaming.

Toxoplasma gondii
In recent years, Toxoplasma gondii has been linked to the illness and death of marine life, primarily sea otters [18], prompting investigation into the possible role of free-roaming (both owned and feral) cats. [19, 20] But if, as the authors claim, “the science points to cats,” then it does so rather obliquely, an acknowledgement Jessup and Miller make begrudgingly:

“Based on proximity and sheer numbers, outdoor pet and feral domestic cats may be the most important source of T. gondii oocysts in near-shore marine waters. Mountain lions and bobcats rarely dwell near the ocean or in areas of high human population density, where sea otter infections are more common.” [21, emphasis mine]

Correlation, however, is not the same as causation. And not all T. gondii is the same.

In a study of southern sea otters from coastal California, conducted between 1998 and 2004, a team of researches—including Jessup and Miller—found that 36 of 50 otters were infected with the Type X strain of T. gondii, one of at least four known strains. [22] Jessup and Miller were also among 14 co-authors of a 2008 paper (referenced in their contribution to “The Impact of Free Ranging Cats”) in which the Type X strain was linked not to domestic cats, but to wild felids:

“Three of the Type X-infected carnivores were wild felids (two mountain lions and a bobcat), but no domestic cats were Type X-positive. Examination of larger samples of wild and domestic felids will help clarify these initial findings. If Type X strains are detected more commonly from wild felids in subsequent studies, this could suggest that these animals are more important land-based sources of T. gondii for marine wildlife than are domestic cats.” [20, emphasis mine]

Combining the results of the two studies, then, nearly three-quarters of the sea otters examined as part of the 1998–2004 study were infected with a strain of T. gondii that hasn’t been traced to domestic cats. (I found this to be such surprising news that, months ago, I tried to contact Miller about it. Was I missing something? What studies were being conducted that might confirm or refute these finings? Etc. I never received a reply.)

As Miller et al. note, “subsequent studies” are in order. And it’s important to keep in mind their sample size was quite small: three bobcats, 26 mountain lions, and seven domestic cats (although the authors suggest at one point that only five domestic cats were included).

Still, a recently published study from Germany seems to support the hypothesis that the Type X strain isn’t found in domestic cats. Herrmann et al. analyzed 68 T. gondii-positive fecal samples (all from pet cats) and found no Type X strain. [23] (It’s interesting to note, too, that only 0.25 percent of the 18,259 samples tested positive for T. gondii.)

This is not to say that there’s no connection between domestic cats and Toxoplasmosis in sea otters, but that any “trickle-down effect,” as Jessup and Miller describe it, is not nearly as well understood as they imply. There’s too much we simply don’t know.

Money and Politics
I agree with Dauphine and Cooper that science is only part of the TNR debate—that it also involves “a complex mix of money, politics, intense emotions, and deeply divergent perspectives on animal welfare.” And I agree with their assessment of the progress being made by TNR supporters:

“Advocates of TNR have gained tremendous political strength in the U.S. in recent years. With millions of dollars in donor funding, they are influencing legislation and the policies of major animal-oriented nonprofit organizations.” [1]

What I find puzzling is Dauphine’s rather David-and-Goliath portrayal of the “cat lobby” (my term, not hers) they’re up against—in particular, her complaint, “promotion of TNR is big business, with such large amounts of money in play that conservation scientists opposing TNR can’t begin to compete.” [24]

The Cat Lobby
In “Follow the Money: The Economics of TNR Advocacy,” she notes that Best Friends Animal Society, “one of the largest organizations promoting TNR, took in over $40 million in revenue in 2009.” [24] Fair enough, but this needs to be weighed against expenses of $35.6 million—of which $15.5 million was spent on “animal care activities.”

But Dauphine’s got it wrong when she claims that Best Friends “spent more than $11 million on cat advocacy campaigns that year.” [24] Their financials—spelled out in the same document Dauphine cites—are unambiguous: $11.7 million in expenditures went to all “campaigns and other national outreach.” Indeed, there is no breakdown for “cat advocacy campaigns.”

Dauphine does a better job describing Alley Cat Allies’ 2010 financials: of the $5.2 million they took in, $3.3 million was spent in public outreach. But she’s overreaching in suggesting that their “Every Kitty, Every City” campaign is nationwide. For now, at least, it’s up and running in just “five major U.S. cities.”

Echoing Dauphine’s concerns, Florida attorney Pamela Jo Hatley decries ORCAT’s resources: “At a meeting hosted by the Ocean Reef Resort in June 2004,” recalls Hatley, “I learned that the ORCAT colony then had about 500 free-ranging cats, several paid employees, and an annual operating budget of some $100,000.” [25]

What Hatley fails to mention is how those resources have been used to make ORCAT a model for the rest of the country—using private donations. Hatley doesn’t seem to object to the U.S. Fish and Wildlife Service shelling out $50,000—of tax dollars—in 2007 to round up fewer than 20 cats (some of which were clearly not feral) along with 81 raccoons (53 of which were released alive) in the Florida Keys. [26, 27]

Following the Money
According to their 2008 Form 990, ORCAT took in about $278,000 in revenue, compared to $310,000 in expenses. How does that compare to some of the organizations opposing TNR? A quick visit to Guidestar.com helps put things in perspective.

  • In 2009, ABC took in just under $6 million, slightly more than their expenses.
  • TWS had $2.3 million in revenue in 2009, which was more than offset by expenses of $2.5 million.
  • Friends of the National Zoo, which oversees the Smithsonian Migratory Bird Center, showed $15 million in revenue, just exceeding their 2009 expenses of $14.7 million. (The Smithsonian Institute topped $1 billion in both the revenue and expense categories.)
  • And the National Audubon Society took in $61.6 million in 2008 (the most recent year for which information is available). And, despite expenses in excess of $86 million, finished the year with more than $255 million in net assets.

These numbers clearly don’t reflect the funding each organization dedicates to opposing TNR—but neither do they offer any evidence that, as Dauphine argues, “conservation scientists opposing TNR can’t begin to compete.”

Intense Emotions
Nobody familiar with the TNR debate would suggest that it’s not highly emotional. How can it be otherwise? Indeed, the very idea of decoupling our emotions from such important discourse is rather absurd.

Having an emotional investment in the debate does not, however, make one irrational or stupid.

“On the surface,” suggest Dauphine and Cooper, their tone unmistakably condescending, “TNR may sound reasonable, even logical.” [1] Gillin, for his part, bemoans the way the TNR debate “quickly shifts from statistics to politics to emotional arguments.” [2]

What’s particularly fascinating about all of this—the way TNR supporters are made out to be irrational (if not mentally ill—as in a letter to Conservation Biology last year, when several TNR opponents, including four contributors to “The Impact of Free Ranging Cats,” compared TNR to hoarding [28])—is just how emotionally charged the appeal of TNR opponents is.

Witness the “gruesome gallery of images,” for example, in which “one cat lies dead with a broken leg, one lies dying in a coat of maggots, and another suffers as ticks and ear mites plague its face.” [1] The idea, of course, is that these cats would have been better off if they’d been rounded up and killed “humanely.” A preemptive strike against the inevitability of “short, brutal lives.” (This phrase, which I first saw used by Jessup, [28] has become remarkably popular among TNR opponents.)

But is it that simple? Applying the same logic (if that’s what it is) to pelicans covered in oil, for instance, would we suggest that these birds should either be in captivity or “humanely euthanized”? Obviously not.

Divergent Perspectives on Animal Welfare
While I disagree that “the debate is predominately about whether cats should be allowed to run wild across the landscape and, if not, how to effectively and humanely manage them,” [29] I tend to agree with Lepczyk et al. when they write:

“It’s much more about human views and perceptions than science—a classic case where understanding the human dimensions of an issue is the key to mitigating the problem.” [29]

But, like Dauphine and Cooper, Lepczyk et al. seem more interested in broadcasting their message—loudly, ad nauseam—than in listening. “We need to understand whether people are even aware,” they write, “of the cumulative impact that their actions—choosing to let cats outdoors—can have on wildlife populations.” [29]

Although it’s packaged somewhat “softly,” we’re back to the same old speculative connections between predation and population impacts (familiar terrain for Lepczyk, who tried to connect these same dots in his PhD research). But how much of a connection is there, really? In their review of 61 predation studies, Mike Fitzgerald and Dennis Turner are unambiguous:

“We consider that we do not have enough information yet to attempt to estimate on average how many birds a cat kills each year. And there are few, if any studies apart from island ones that actually demonstrate that cats have reduced bird populations.” [30]

While the tone used by Lepczyk et al. is very much “we’re all in this together,” their prescription for “moving forward” suggests little common ground. (They actually cite that 2010 letter to Conservation Biology [28]—not much of an olive branch.)

“One approach is exemplified in Hawaii,” explain the authors, “where we’ve become part of a large coalition of stakeholders working together with the shared goal of reducing and eventually removing feral cats from the landscape.” [29] So, who’s involved?

“Our diverse group includes individuals from the Humane Society of the United States, the Hawaiian Humane Society, the U.S. Fish and Wildlife Service, the National Park Service, Hawaii’s Department of Land and Natural Resources, and the University of Hawaii. Our team also regularly interacts with other groups around the nation such as regional Audubon Societies and the American Bird Conservancy. Several stakeholders in the group have differing views, such as on whether or not euthanasia or culling is appropriate, or whether people should feed feral cats.” [29]

Other than the Humane Society organizations (whose position on TNR I don’t take for granted, considering they were early supporters of ABC’s Cats Indoors! campaign [31]), I don’t see a real diversity of views in this coalition.

I suppose it’s easy to make room at the table when you’re offering so few seats.

For Dauphine, though, any such collaboration approaches treason. Or selling out, at least.

“In some cases,” she explains, “conservation groups accept funding to join in efforts promoting TNR. The New Jersey Audubon Society, for example, had previously rejected TNR but began supporting it in 2005, acknowledging funding from the Frankenberg and Dodge Foundations for collaboration with TNR groups.” [24]

Dauphine doesn’t go into detail about the amount of funding, and it’s not clear what, if any, role it played in the decision by NJAS (which took in $6.8 million in 2008) to participate in the New Jersey Feral Cat-Wildlife Coalition—the kind of collaborative effort that should be encouraged, not derided:

“From 2002 to 2005, NJAS had actively opposed the practice of TNR in New Jersey. Despite this opposition, municipalities continued to adopt TNR ordinances. In 2005, NJAS, American Bird Conservancy, Neighborhood Cats and Burlington Feral Cat Initiative began exploratory dialogue about implementing standards to protect rare wildlife vulnerable to cat predation in towns which have already adopted TNR programs.” [32]

Message Received, Loud and Clear
Rather than wringing their hands over how to “better communicate the science” [1] or how to better facilitate “legal or policy changes, incentives, and increased education,” [29] TNR opponents might want to reconsider the message itself.

What they are proposing is the killing—on an unprecedented scale—of this country’s most popular pet.

I don’t imagine this tests well with focus groups and donors, of course, but there it is.

These people seem perplexed by a community’s willingness to adopt TNR (“In the end,” lament Lepczyk et al., referring to the decision in Athens, GA, “the professional opinion of wildlife biologists counted no more than that of any other citizen, a major reason for the defeat.” [29]) but fail to recognize how profoundly unpalatable their alternative is.

And, unworkable, too.

Which may explain why it’s virtually impossible to get them to discuss their “plan” in any detail. (I was unsuccessful, for example, in pinning down Travis Longcore during our back-and-forth on the Audubon magazine’s blog and couldn’t get Jessup or Hutchins to bite when I asked the same question during an online discussion of public health risks.)

In light of what’s involved with “successful” eradication programs, I’m not surprised by their eagerness to change the subject.

  • On Marion Island, it took 19 years to eradicate something like 2,200 cats—using disease (feline distemper), poisoning, intensive hunting and trapping, and dogs. This on an island that’s only 115 square miles in total area, barren, and uninhabited. [33, 34] The cost, I’m sure, was astronomical.
  • On the sparsely populated (fewer than 1,000, according to Wikipedia) Ascension Island (less than 34 total square miles), a 2003 eradication effort cost nearly $950,000 (adjusted to 2009 dollars). [35]
  • A 2000 effort on Tuhua (essentially uninhabited, and just 4.9 square miles) ran $78,591 (again, adjusted to 2009 dollars). [35]
  • Efforts on Macquarie Island (also small—47.3 square miles—and essentially uninhabited) proved particularly costly: $2.7 million in U.S. (2009) dollars. And still counting. The resulting rebound in rabbit and rodent numbers prompted “Federal and State governments in Australia [to commit] AU$24 million for an integrated rabbit, rat and mouse eradication programme.” [36] (To put this into context, Macquarie Island is about one-third the size of the Florida Keys.)

These examples represent, in many ways, low-hanging fruit. By contrast, “the presence of non-target species and the need to safely mitigate for possible harmful effects, along with substantial environmental compliance requirements raised the cost of the eradication.” [37] Eradicating rodents from Anacapa Island, “a small [1.2-square-mile] island just 80 miles from Los Angeles International Airport, cost about $2 million.” [38]

Now—setting aside the horrors involved—how exactly do TNR opponents propose to rid the U.S. of it’s millions of feral cats? [cue the sound track of crickets chirping]

I think the general public is starting to catch on. Even if they fall for the outlandish claims about predation, wildlife impacts, and all the rest—they don’t see anything in the way of a real solution. As Mark Kumpf, former president of the National Animal Control Association, put it in an interview with Animal Sheltering magazine, “the traditional methods that many communities use… are not necessarily the ones that communities are looking for today.” [39]

“Traditional” approaches to feral cat management (i.e., trap-and-kill) are, says Kumpf, akin to “bailing the ocean with a thimble.” [39]

For all their apparent interest—22 pages in the current issue of The Wildlife Professional alone—TWS might as well be handing out thimbles to its members. Although Gillin’s “Leadership Letter” invites “dialogue among all stakeholders,” it offers nothing substantive to advance the discussion:

“If removal and euthanasia of unadoptable feral cats is not acceptable to TNR proponents, then they need to offer the conservation community a logical, science-based proposal that will solve the problem of this invasive species and its effect on wildlife and the environment.” [2]

So much for leadership.

Literature Cited
1. Dauphine, N. and Cooper, R.J., “Pick One: Outdoor Cats or Conservation.” The Wildlife Professional. 2011. 5(1): p. 50–56.

2. Gillin, C., “The Cat Conundrum.” The Wildlife Professional. 2011. 5(1): p. 10, 12.

3. APPA, 2009–2010 APPA National Pet Owners Survey. 2009, American Pet Products Association: Greenwich, CT. http://www.americanpetproducts.org/pubs_survey.asp

4. Lord, L.K., “Attitudes toward and perceptions of free-roaming cats among individuals living in Ohio.” Journal of the American Veterinary Medical Association. 2008. 232(8): p. 1159-1167. http://www.avma.org/avmacollections/feral_cats/javma_232_8_1159.pdf

5. Clancy, E.A., Moore, A.S., and Bertone, E.R., “Evaluation of cat and owner characteristics and their relationships to outdoor access of owned cats.” Journal of the American Veterinary Medical Association. 2003. 222(11): p. 1541-1545. http://avmajournals.avma.org/doi/abs/10.2460/javma.2003.222.1541

6. van Heezik, Y., “A New Zealand Perspective.” The Wildlife Professional. 2011. 5(1): p. 70.

7. Sims, V., et al., “Avian assemblage structure and domestic cat densities in urban environments.” Diversity and Distributions. 2008. 14(2): p. 387–399. http://dx.doi.org/10.1111/j.1472-4642.2007.00444.x

8. Wilson, M. (1997). Cats Roaming Free Take a Toll on Songbirds. Boston Globe, p. 11.

9. Seppa, N. (1993, July 22). Millions of Songbirds, Rabbits Disappearing. Wisconsin State Journal, p. 1A.

10.  Wozniak, M.D. (1993, August 3). Feline felons: Barn cats are just murder on songbirds. The Milwaukee Journal, p. A1.

11. Guttilla, D.A. and Stapp, P., “Effects of sterilization on movements of feral cats at a wildland-urban interface.”Journal of Mammalogy. 2010. 91(2): p. 482–489. http://dx.doi.org/10.1644/09-MAMM-A-111.1

12. Liberg, O. and Sandell, M., Spatial organisation and reproductive tactics in the domestic cat and other felids, in The Domestic cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 1988, Cambridge University Press: Cambridge; New York. p. 83–98.

13. Castillo, D. and Clarke, A.L., “Trap/Neuter/Release Methods Ineffective in Controlling Domestic Cat “Colonies” on Public Lands.” Natural Areas Journal. 2003. 23: p. 247–253.

14. Nutter, F.B., Evaluation of a Trap-Neuter-Return Management Program for Feral Cat Colonies: Population Dynamics, Home Ranges, and Potentially Zoonotic Diseases, in Comparative Biomedical Department. 2005, North Carolina State University: Raleigh, NC. p. 224.

15. Stoskopf, M.K. and Nutter, F.B., “Analyzing approaches to feral cat management—one size does not fit all.”Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1361–1364. http://www.ncbi.nlm.nih.gov/pubmed/15552309

www.avma.org/avmacollections/feral_cats/javma_225_9_1361.pdf

16.  Natoli, E., et al., “Management of feral domestic cats in the urban environment of Rome (Italy).” Preventive Veterinary Medicine. 2006. 77(3-4): p. 180-185. http://www.sciencedirect.com/science/article/B6TBK-4M33VSW-1/2/0abfc80f245ab50e602f93060f88e6f9

www.kiccc.org.au/pics/FeralCatsRome2006.pdf

17. Levy, J.K. and Crawford, P.C., “Humane strategies for controlling feral cat populations.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1354–1360. http://www.avma.org/avmacollections/feral_cats/default.asp

http://www.avma.org/avmacollections/feral_cats/javma_225_9_1354.pdf

18. Jones, J.L. and Dubey, J.P., “Waterborne toxoplasmosis – Recent developments.” Experimental Parasitology. 124(1): p. 10-25. http://www.sciencedirect.com/science/article/B6WFH-4VXB8YT-2/2/8f9562f64497fe1a30513ba3f000c8dc

19. Dabritz, H.A., et al., “Outdoor fecal deposition by free-roaming cats and attitudes of cat owners and nonowners toward stray pets, wildlife, and water pollution.” Journal of the American Veterinary Medical Association. 2006. 229(1): p. 74-81. http://www.avma.org/avmacollections/feral_cats/javma_229_1_74.pdf

20. Miller, M.A., et al., “Type X Toxoplasma gondii in a wild mussel and terrestrial carnivores from coastal California: New linkages between terrestrial mammals, runoff and toxoplasmosis of sea otters.” International Journal for Parasitology. 2008. 38(11): p. 1319-1328. http://www.sciencedirect.com/science/article/B6T7F-4RXJYTT-2/2/32d387fa3048882d7bd91083e7566117

21. Jessup, D.A. and Miller, M.A., “The Trickle-Down Effect.” The Wildlife Professional. 2011. 5(1): p. 62–64.

22. Conrad, P.A., et al., “Transmission of Toxoplasma: Clues from the study of sea otters as sentinels of Toxoplasma gondii flow into the marine environment.” International Journal for Parasitology. 2005. 35(11-12): p. 1155-1168. http://www.sciencedirect.com/science/article/B6T7F-4GWC8KV-2/2/2845abdbb0fd82c37b952f18ce9d0a5f

23. Herrmann, D.C., et al., “Atypical Toxoplasma gondii genotypes identified in oocysts shed by cats in Germany.”International Journal for Parasitology. 2010. 40(3): p. 285–292. http://www.sciencedirect.com/science/article/B6T7F-4X1J771-2/2/dc32f5bba34a6cce28041d144acf1e7c

24. Dauphine, N., “Follow the Money: The Economics of TNR Advocacy.” The Wildlife Professional. 2011. 5(1): p. 54.

25. Hatley, P.J., “Incompatible Neighbors in the Florida Keys.” The Wildlife Professional. 2011. 5(1): p. 52–53.

26. O’Hara, T. (2007, April 3). Fish & Wildlife Service to begin removing cats from Keys refuges. The Key West Citizen, from http://keysnews.com/archives

27. n.a., Lower Florida Keys National Wildlife Refuges Comprehensive Conservation Plan. 2009, U.S. Department of the Interior, Fish and Wildlife Service: Atlanta, GA. http://www.fws.gov/nationalkeydeer/

http://www.fws.gov/southeast/planning/PDFdocuments/Florida%20Keys%20FINAL/TheKeysFinalCCPFormatted.pdf

28. Jessup, D.A., “The welfare of feral cats and wildlife.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1377-1383. http://www.ncbi.nlm.nih.gov/pubmed/15552312

http://www.avma.org/avmacollections/feral_cats/javma_225_9_1377.pdf

29. Lepczyk, C.A., van Heezik, Y., and Cooper, R.J., “An Issue with All-Too-Human Dimensions.” The Wildlife Professional. 2011. 5(1): p. 68–70.

30. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

31. Berkeley, E.P., TNR Past present and future: A history of the trap-neuter-return movement. 2004, Bethesda, MD: Alley Cat Allies.

32. Stiles, E., NJAS Works with Coalition to Reduce Bird Mortality from Outdoor Cats. 2008, New Jersey Audubon Society. http://www.njaudubon.org/Portals/10/Conservation/PDF/ConsReportSpring08.pdf

33. Bester, M.N., et al., “A review of the successful eradication of feral cats from sub-Antarctic Marion Island, Southern Indian Ocean.” South African Journal of Wildlife Research. 2002. 32(1): p. 65–73.

http://www.ceru.up.ac.za/downloads/A_review_successful_eradication_feralcats.pdf

34. Bloomer, J.P. and Bester, M.N., “Control of feral cats on sub-Antarctic Marion Island, Indian Ocean.” Biological Conservation. 1992. 60(3): p. 211-219. http://www.sciencedirect.com/science/article/B6V5X-48XKBM6-T0/2/06492dd3a022e4a4f9e437a943dd1d8b

35. Martins, T.L.F., et al., “Costing eradications of alien mammals from islands.” Animal Conservation. 2006. 9(4): p. 439–444. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-1795.2006.00058.x/abstract

http://i3n.iabin.net/documents/pdf/Costingeradicationsofalienmammalsfromislands.pdf

36. Bergstrom, D.M., et al., “Indirect effects of invasive species removal devastate World Heritage Island.” Journal of Applied Ecology. 2009. 46(1): p. 73-81. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2008.01601.x/abstract

http://eprints.utas.edu.au/8384/4/JAppEcol_Bergstrom_etal_journal.pdf

37. Donlan, C.J. and Heneman, B., Maximizing Return on Investments for Island Restoration with a Focus on Seabird Conservation. 2007, Advanced Conservation Strategies: Santa Cruz, CA. http://www.advancedconservation.org/roi/ACS_Seabird_ROI_Report.pdf

38. Donlan, C.J. and Wilcox, C., Complexities of costing eradications, in Animal Conservation. 2007, Wiley-Blackwell. p. 154–156. http://onlinelibrary.wiley.com/doi/10.1111/j.1469-1795.2007.00101.x/abstract

http://www.advancedconservation.org/library/donlan_&_wilcox_2007a.pdf

39. Hettinger, J., Taking a Broader View of Cats in the Community, in Animal Sheltering. 2008. p. 8–9. http://www.animalsheltering.org/resource_library/magazine_articles/sep_oct_2008/taking_a_broader_view_of_cats.html

http://www.animalsheltering.org/resource_library/magazine_articles/sep_oct_2008/broader_view_of_cats.pdf

Best Available Science?

After a while, I suppose, such things will no longer surprise me.

A couple weeks ago, the American Bird Conservancy released a statement in support of the Florida Keys National Wildlife Refuges Complex Integrated Predator Management Plan/Draft Environmental Assessment proposed by the U.S. Fish and Wildlife Service (USFWS):

“American Bird Conservancy, the nation’s leading bird conservation organization, and 27 additional science and conservation organizations have signed a letter to the Florida Keys National Wildlife Refuge supporting their plans to remove cats and cat feeding stations found on refuge lands in the Keys because of the harm they are causing to birds and other wildlife, including endangered species.”

No surprise there, really. It’s the following paragraph that caught my eye:

“The U.S. Fish and Wildlife Service deserves credit for bringing the best available science to bear on the management of exotic predators inhabiting National Wildlife Refuge lands regardless of the emotional aspects of the issue,” said Steve Holmer, Senior Policy Advisor for American Bird Conservancy. “Given the overwhelming evidence of harm to native birds inhabiting and migrating through the Keys, this predator management plan offers hope for healthier environment.”

“Best available science”? Are we talking about the same document here?

Granted, this is Steve Holmer—the same guy who, a year ago, told the Los Angeles Times that there are 160 million feral cats in the U.S. (a figure he arrived at by “reinterpreting” the already inflated figure proposed by Dauphine and Cooper).

In other words, consider the source.

Among the letter’s highlights (the letter itself doesn’t seem to be available, which is a shame, as I’m very interested in knowing which other “science and conservation organizations” are supporters):

“…cat predation accounted for 50 percent and 77 percent of mortality of two endangered species—the Lower Keys Marsh Rabbit and the Key Largo Woodrat.”

Lower Keys Marsh Rabbit
ABC’s claim about cats being responsible for half the mortality of marsh rabbits doesn’t actually correspond with what’s in the USFWS plan:

“Free-roaming domestic cat predation accounted for 50 percent of adult Lower Keys marsh rabbit mortality during radio telemetry studies and was cited as the largest factor limiting their population viability in the 1990s (Forys and Humphrey 1999).” [1]

During her PhD dissertation work, Elizabeth Forys’ found that 13 of 24 rabbits monitored over the course of her research were killed by cats, [2] findings she described four years later (in the paper cited by USFWS) this way:

“Twenty-seven (18 M, 9 F) of the 43 radiocollared individuals died during our 2.5-year study. Domestic cats killed the most marsh rabbits (53 percent of all mortality), killing nearly an equal number of both juvenile and adult marsh rabbits.” [3]

ABC misrepresents both Forys’ work and the USFWS plan by transforming those 13 marsh rabbits into “50 percent of mortality of [this] endangered species.” And this is too straightforward to be an accident.

For what it’s worth, this has been done before.

Impact of Cats on Marsh Rabbits
The Multi-Species Recovery Plan (MSRP) for South Florida, published in 1999 by USFWS, refers repeatedly to Forys’ work, noting, for example:

“Although habitat loss is responsible for the original decline of the Lower Keys marsh rabbit, high mortality from cats may be the greatest current threat to the persistence of the Lower Keys marsh rabbit [4].”

The report’s authors alternate between concessions and allegations, the latter of which are based on what can only be considered—even in the most generous light—circumstantial evidence. They acknowledge, for instance, that “a detailed study of cat diets in the Keys has not been conducted,” but then point out that “rabbits were the largest component of feral cat diets in several studies that have been conducted elsewhere (Jones and Coman 1981, Liberg 1985).” [5]

Let’s set aside for the moment the debate about whether or not two is considered “several” (and the fact that they got the year wrong on the Liberg study). Where exactly were those studies conducted? “Victorian Mallee, Kinchega National Park in western New South Wales, and the Victorian eastern highlands” [6] and “Revinge area in southern Sweden.” [7]

None of which, it’s safe to say, could be mistaken for the Florida Keys.

USFWS also acknowledges that “the exact extent [of predation by cats] cannot be determined,” though they imply that it must be increasing: “the number of cats present in the Lower Keys has increased over the past 20 years with the increase in the residential population.” [5]

(In fact, a number of studies have shown that cats will shift their “preferences” according to prey availability [see, for example, the review in 8]. Indeed, this was the case in the study from southern Sweden cited by USFWS: “Wild rabbits were the most important prey, and cats responded functionally to changes in abundance and availability of this prey.” [7])

The less common the rabbits, the less likely they are to fall prey to free-roaming cats.

Telling Stories
Somewhere along the line, though, the marsh rabbit story began to change.

An article in The Key West Citizen describing USFWS’s 2007 effort to round up cats in the Keys [9, 10] is a clear reference to—and equally clear misrepresentation of—Forys’ work:

“According to a 1999 U.S. Fish and Wildlife report, feral cats have killed 53 percent of marsh rabbits in the Lower Keys.” [9]

Contributors to the 2008 South Florida Environmental Report claim, “feral cats… have contributed to a 50 percent decline in populations of Hugh Hefner’s rabbits (Sylvilagus palustris hefneri, an endangered subspecies of marsh rabbit named for Hefner’s contributions to their research) on Big Pine Key (CNN.com, accessed May 20, 2007).” [11] I was unable to find anything at the CNN site, but suspect the story was nothing more than a pick-up of the story that ran in The Key West Citizen. (Florida residents will no doubt take great comfort in knowing that the South Florida Water Management District, publisher of the report, is unwilling to look any further than CNN.com for its science.)

In the 2009 book Invasive Species: Detection, Impact and Control, the story is much the same:

“[cats] have been a factor in the 50 percent decline in populations of the endangered Lower Keys marsh rabbit (Forys and Humphrey 1999).” [12]

In fact, Forys and Humphrey have little to say about the declining population:

“During the 1970s and 1980s, a period of intense habitat destruction, a decline in marsh rabbits was reported (Lazell 1984).” [3]

And Lazell? Nothing at all about the marsh rabbit population. I did, however, find this interesting:

“In 1980 I live-trapped five specimens on Lower Sugarloaf Key under Florida Game and Fresh Water Fish Commission (FGFWFC) permit 28. Three were prepared as skins and skeletons; two were released after physiological studies (Dunson and Lazell, 1982).” [13]

Not that Lazell was the only scientist taking marsh rabbits. North of the Keys, 10 years earlier, Nicholas Holler and Clinton Conaway were studying the reproduction of this now-endangered species.

“From September 1968 through August 1969, 610 marsh rabbits were collected by hand or with a .22 caliber rifle in sugarcane plantations south and west of Belle Glade, Palm Beach and Hendry counties, Florida, at the southern edge of Lake Okeechobee. Rabbits were readily obtained except in July, August, and September…. After collection, rabbits were weighed and one eye and one front paw were preserved in 10 percent formalin.” [14]

To put this into perspective, the MSRP (published 30 years after Holler and Conway’s research) suggests that there may be only 100–300 marsh rabbits left. [5]

How’s that for irony? It seems the best evidence of a declining population comes from two scientists who killed several hundred marsh rabbits 40 years ago.

Key Largo Woodrat
ABC’s reference to Key Largo woodrat mortality is actually an accurate recounting of what’s in the USFWS plan:

“In addition, cats accounted for 77 percent of the mortality during a recent re-introduction of the Key Largo woodrat (S. Klett, Refuge Manager, personal communication).” [1]

Such personal communications—even by knowledgeable, honest professionals—are no substitute for rigorous, science-based reporting. What kind of sample size are we talking about? Over what duration? Under what conditions? Where? Etc.

More to the point, though: here is ABC once again blatantly misrepresenting the science (or the closest thing we’ve got to science, in this case). USFWS is talking about a portion of the population, while ABC is talking about the entire population. And I have to think the people responsible are smart enough to know the difference—which, of course, can mean only one thing: it’s not the intelligence that’s lacking here, but the integrity.

The Rest of the Best
But what about all the rest of the science—the “best available,” according to Holmer, don’t forget—that USFWS including in its Integrated Predator Management Plan/Draft Environmental Assessment? Among the more egregious errors and misinterpretations I cited in my comments to USFWS:

  • Another of the papers cited by USFWS has nothing to do with extinctions at all. As the authors describe it, their study was an evaluation of “whether a collar-worn pounce protector, the CatBib, reduces the number of vertebrates caught by pet cats and whether its effectiveness was influenced by colour or adding a bell.” [17]
  • Listed among the “evidence” of island extinctions were studies that—in addition to having nothing to do with extinctions—were not conducted on islands. Coleman and Temple’s 1993 survey, for example, involved rural Wisconsin residents and their outdoor cats, [18] while Churcher and Lawton surveyed residents of a small English village. [19]
  • Among the evidence that “free-roaming cats kill at least one billion birds every year in the U.S., representing one of the largest single sources of human-influenced mortality for small native wildlife,” [1] is Rich Stallcup’s 1991 article from the Observer, a publication of the Point Reyes Bird Observatory. In fact, “A Reversible Catastrophe” is little more than Stallcup’s advice—at once both folksy and sinister—about defending one’s garden from neighborhood cats (“…try a B-B or pellet gun. There is no need to kill or shoot toward the head, but a good sting on the rump seems memorable for most felines, and they seldom return for a third experience.” [21]).
  • Another of the studies cited by FWS—a 2008 paper by Sax and Gaines—isn’t about cats at all. Or even invasive animals. It’s about invasive plants. [22]
  • Citing the Centers for Disease Control and Prevention’s website, USFWS argues: “…free-roaming cats not only threaten wildlife through direct predation but also serve as vectors for a number of diseases including rabies, cat scratch fever, hookworms, roundworms and toxoplasmosis. Some of these diseases can be transmitted to other domestic animals, native wildlife, and in some cases, humans.”

    In fact, the CDC site makes no mention of cats being a threat to wildlife. And humans? “Although cats can carry diseases and pass them to people, you are not likely to get sick from touching or owning a cat.” And, notes the CDC, “People are probably more likely to get toxoplasmosis from gardening or eating raw meat than from having a pet cat.”

    (Unwilling to do their own research and writing, ABC uses exactly the same language and cites the same CDC website as USFWS. Had they simply clicked on the link, they might have avoided the blunder—which, I think, speaks volumes about little scrutiny they gave the USFWS plan before backing it.)

This is what Holmer is referring to when he says USFWS “deserves credit for bringing the best available science to bear on the management of exotic predators inhabiting National Wildlife Refuge lands regardless of the emotional aspects of the issue.”

What’s Missing
In addition to everything USFWS gets wrong, though, there’s also everything they overlooked or ignored (again, each point is covered in detail in my comments to USFWS). For example:

Mesopredator Release
“In the absence of large, dominant predators,” write Soulé et al., “smaller omnivores and predators undergo population explosions, sometimes becoming four to 10 times more abundant than normal.” [23] Several studies have demonstrated such an “explosion” of non-native rat populations as a result of cat populations being eliminated. [24–27]

As Courchamp et al. explain, “although counter-intuitive, eradication of introduced superpredators, such as feral domestic cats, is not always the best solution to protect endemic prey when introduced mesopredators, such as rats, are also present.” [26] Fan et al. warn of the risks involved with such eradication efforts: “In some cases, it may cause a disastrous impact to managed or natural ecosystems.” [25]

But USFWS doesn’t even mention the risk of mesopredator release, despite the fact that—should the population of free-roaming cats be sufficiently reduced—the situation in the Keys suggests that such an outcome is actually quite likely. And controlling these rats is complicated considerably by the need to protect Lower Keys marsh rabbits. Indeed, the MSRP warns of these rabbits coming into contact with pesticides and “poisons used to control black rats.” [5]

Based on evidence cited by USFWS itself, it’s clear that a dramatic reduction in the number of free-roaming cats in the Keys (assuming it’s possible—see below) will very likely have a negative impact on the marsh rabbit population—and may well lead to their extirpation from any Key where these rats are present.

Such impacts would also likely affect the Key Largo cotton mouse [28–29], Key Largo woodrat [30–31], and silver rice rat [32–33], all of which USFWS identifies as species of particular concern, and which are threatened—either through predation or competition—by non-native rats such as the black rat.

Removing Cats
Reports indicate that USFWS has a rather poor track record when it comes to trapping cats. Its 2003 contract with USDA, for example, yielded just 23 cats over 31 days of trapping. [34] Their efforts four years later—at a cost of $50,000—were equally ineffective. [9–10]

None of which should surprise USFWS. “Successful” eradication efforts require both extraordinary resources and profound cruelty. For example:

  • Nogales et al., describing the “success” of Marion Island, note, “it took about 15 years of intense effort to eradicate the cats, combining several methods such as trapping, hunting, poisoning, and disease introduction… The use of disease agents or targeted poisoning campaigns hold promise for an initial population reduction in eradication programs on large islands—such an approach may save effort, time, and money.” [35]
  • Cruz and Cruz point out that, of all the non-native mammals there, cats were “the most difficult to control or eliminate on Floreana Island.” Although “hunting with dogs was the single most effective method employed and it gave a sure body count,” the authors warn that “the method was costly and with the limited manpower available was only useful over small areas. Both poisoning and trapping were effective and the combination of the three methods is probably the most effective approach, as well as being the best use of time and materials.” [15]
  • Veitch describes efforts on 11-square-mile Little Barrier Island as “a determined [cat] eradication attempt” involving “cage traps, leg-hold traps, dogs and 1080 poison were used, but leg-hold traps and 1080 poison were the only effective methods.” [36] Four cats were also infected with Feline enteritis, but “because of the poor reaction to the virus no other cats were dosed and none were released… Altogether, 151 cats were known to have been killed before the eradication was declared complete. Important lessons learnt can be transferred to other feral cat eradication programmes.” [36] (By way of comparison, the Keys are approximately 137 square miles in total area.)

As USFWS admits, such methods are “not… socially acceptable” and “inconsistent with the points of consensus developed by the stakeholder group.” Yet, they offer nothing in the way of a feasible alternative; their latest plan is just more of what’s been done—and proven ineffective—in the past.

Because it’s extremely doubtful that USFWS will be able to remove the cats quickly enough to keep up with reproduction rates (again, consider the “success” stories outlined above), the most likely outcome of their plan is an increase in the number of feral cats in the Keys—and, of course, a corresponding increase in the negative impacts they have on the area’s wildlife and environment.

•     •     •

I fully expected ABC to support the USFWS plan. And, come to think of it, I should have expected them to blindly embrace the underlying science. After all, this is the same organization that’s been trying, since at least 1997, to sell the Wisconsin Study as valid research.

And, more recently, ABC endorsed “Feral Cats and Their Management” (also known as the University of Nebraska report) as if it were valid research.

Perhaps this is what ABC President and CEO George Fenwick meant when he wrote, in the preface to The American Bird Conservancy Guide to Bird Conservation, “every point of view has its own science.” [37]

Literature Cited
1. n.a., Draft Environmental Assessment: Florida Keys National Wildlife Refuges Complex Integrated Predator Management Plan. 2011, U.S. Fish & Wildlife Service: Big Pine Key, FL. http://www.fws.gov/nationalkeydeer/predatormgmt.html

http://www.fws.gov/nationalkeydeer/pdfs/USFWS%20FL%20Keys%20Refuges%20Integrated%20Predator%20Mgmt%20Plan%20&%20EA%20FINAL%20DRAFT.pdf

2. Forys, E.A., Metapopulations of marsh rabbits: A population viability analysis of the Lower Keys marsh rabbit (Sylvilagus palustris hefneri), in Department of Wildlife Ecology and Conservation. 1995, University of Florida: Gainesville. p. 244.

3. Forys, E.A. and Humphrey, S.R., “Use of Population Viability Analysis to Evaluate Management Options for the Endangered Lower Keys Marsh Rabbit.” The Journal of Wildlife Management. 1999. 63(1): p. 251–260. http://www.jstor.org/stable/3802507

4. Forys, E.A. and Humphrey, S.R., “Home Range and Movements of the Lower Keys Marsh Rabbit in a Highly Fragmented Habitat.” Journal of Mammalogy. 1996. 77(4): p. 1042-1048. http://www.jstor.org/stable/1382784

5. n.a., Multi-Species Recovery Plan for South Florida: Lower Keys Rabbit. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 151–171. http://www.fws.gov/verobeach/index.cfm?Method=programs&NavProgramCategoryID=3&programID=107&ProgramCategoryID=3

www.fws.gov/verobeach/images/pdflibrary/lkmr.pdf

6. Jones, E. and Coman, B.J., ” Ecology of the feral cat, Felis catus (L.), in southeastern Australia.” Australian Wildlife Research. 1981. 8: p. 537–547. http://www.publish.csiro.au/paper/WR9810537.htm

7. Liberg, O., “Food Habits and Prey Impact by Feral and House-Based Domestic Cats in a Rural Area in Southern Sweden.” Journal of Mammalogy. 1984. 65(3): p. 424-432. http://www.jstor.org/stable/1381089

8. Fitzgerald, B.M., Diet of domestic cats and their impact on prey populations, in The Domestic cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 1988, Cambridge University Press: Cambridge; New York. p. 123–147.

9. O’Hara, T. (2007, April 3). Fish & Wildlife Service to begin removing cats from Keys refuges. The Key West Citizen, from http://keysnews.com/archives

10. n.a., Lower Florida Keys National Wildlife Refuges Comprehensive Conservation Plan. 2009, U.S. Department of the Interior, Fish and Wildlife Service: Atlanta, GA. http://www.fws.gov/nationalkeydeer/

http://www.fws.gov/southeast/planning/PDFdocuments/Florida%20Keys%20FINAL/TheKeysFinalCCPFormatted.pdf

11. Ferriter, A., et al., The Status of Nonindigenous Species in the South Florida Environment, in 2008 South Florida Environmental Report. 2008, South Florida Water Management District.

12.  Engeman, R., Constantin, B., and Hardin, S., “Species Pollution” in Florida: A Cross Section of Invasive Vertebrate Issues and Management Responses, in Invasive Species: Detection, Impact and Control, C.P. Wilcox and R.B. Turpin, Editors. 2009. p. 179–197.

13. Lazell, J.D., Jr., “A New Marsh Rabbit (Sylvilagus palustris) from Florida’s Lower Keys.”Journal of Mammalogy. 1984. 65(1): p. 26–33. http://www.jstor.org/stable/1381196

14. Holler, N.R. and Clinton, H.C., “Reproduction of the Marsh Rabbit (Sylvilagus palustris) in South Florida.” Journal of Mammalogy. 1979. 60(4): p. 769–777. http://www.jstor.org/stable/1380192

15. Cruz, J.B. and Cruz, F., “Conservation of the dark-rumped petrel Pterodroma phaeopygia in the Galápagos Islands, Ecuador.” Biological Conservation. 1987. 42(4): p. 303-311. http://www.sciencedirect.com/science/article/B6V5X-48XKMBP-17J/2/f81b57e317f217802d9aca8b6927a88c

16. Kirkpatrick, R.D. and Rauzon, M.J., “Foods of Feral Cats Felis catus on Jarvis and Howland Islands, Central Pacific Ocean.” Biotropica. 1986. 18(1): p. 72-75. http://www.jstor.org/stable/2388365

17. Calver, M., et al., “Reducing the rate of predation on wildlife by pet cats: The efficacy and practicability of collar-mounted pounce protectors.” Biological Conservation. 2007. 137(3): p. 341-348. http://www.sciencedirect.com/science/article/B6V5X-4NGBB7H-3/2/456180347a2c3916d1ae99e220dd329e

18. Coleman, J.S. and Temple, S.A., “Rural Residents’ Free-Ranging Domestic Cats: A Survey.”Wildlife Society Bulletin. 1993. 21(4): p. 381–390. http://www.jstor.org/pss/3783408

19. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455. http://dx.doi.org/10.1111/j.1469-7998.1987.tb02915.x

20. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. 1998, Texas A&M University.

21. Stallcup, R., “A reversible catastrophe.” Observer 91. 1991(Spring/Summer): p. 8–9. http://www.prbo.org/cms/print.php?mid=530

http://www.prbo.org/cms/docs/observer/focus/focus29cats1991.pdf

22. Sax, D.F. and Gaines, S.D., Species invasions and extinction: The future of native biodiversity on islands, in In the Light of Evolution II: Biodiversity and Extinction,. 2008: Irvine, CA. p. 11490–11497. www.pnas.org/content/105/suppl.1/11490.full

http://www.pnas.org/content/105/suppl.1/11490.full.pdf

23. Soulé, M.E., et al., “Reconstructed Dynamics of Rapid Extinctions of Chaparral-Requiring Birds in Urban Habitat Islands.” Conservation Biology. 1988. 2(1): p. 75–92. http://www.jstor.org/pss/2386274

http://deepblue.lib.umich.edu/bitstream/2027.42/74761/1/j.1523-1739.1988.tb00337.x.pdf

24. Fitzgerald, B.M., Karl, B.J., and Veitch, C.R., “The diet of feral cat (Felis catus) on Raoul Island, Kermadec group.” New Zealand Journal of Ecology. 1991. 15(2): p. 123–129. http://www.feral.org.au/the-diet-of-feral-cats-felis-catus-on-raoul-island-kermadec-group/

www.newzealandecology.org.nz/nzje/free_issues/NZJEcol15_2_123.pdf

25. Fan, M., Kuang, Y., and Feng, Z., “Cats protecting birds revisited.” Bulletin of Mathematical Biology. 2005. 67(5): p. 1081–1106. http://www.springerlink.com/content/p0h5854n56183874/

26. Courchamp, F., Langlais, M., and Sugihara, G., “Cats protecting birds: modelling the mesopredator release effect.” Journal of Animal Ecology. 1999. 68(2): p. 282–292. http://dx.doi.org/10.1046/j.1365-2656.1999.00285.x

http://deepeco.ucsd.edu/~george/publications/99_cats_protecting.pdf

27. Bergstrom, D.M., et al., “Indirect effects of invasive species removal devastate World Heritage Island.” Journal of Applied Ecology. 2009. 46(1): p. 73-81. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2008.01601.x/abstract

http://eprints.utas.edu.au/8384/4/JAppEcol_Bergstrom_etal_journal.pdf

28. n.a., Key Largo Cotton Mouse (Peromyscus gossypinus allapaticola) 5-Year Review: Summary and Evaluation. 2009, U.S. Fish and Wildlife Service, Southeast Region, South Fiorida Ecological Services Office: Veero Beach, FL. p. 19. http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=A086

http://ecos.fws.gov/docs/five_year_review/doc2378.pdf

29. n.a., Multi-Species Recovery Plan for South Florida: Key Largo Cotton Mouse. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 79–96. http://www.fws.gov/verobeach/index.cfm?Method=programs&NavProgramCategoryID=3&programID=107&ProgramCategoryID=3

http://www.fws.gov/verobeach/images/pdflibrary/klcm.pdf

30. n.a., Key Largo Woodrat (Neotomafloridana smalli) 5-Year Review: Summary and Evaluation. 2008, U.S. Fish and Wildlife Service, Southeast Region, South Fiorida Ecological Services Office: Vero Beach, FL. http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=A087

http://ecos.fws.gov/docs/five_year_review/doc1985.pdf

31. n.a., Multi-Species Recovery Plan for South Florida: Key Largo Woodrat. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 195–216. http://www.fws.gov/verobeach/index.cfm?Method=programs&NavProgramCategoryID=3&programID=107&ProgramCategoryID=3

http://www.fws.gov/verobeach/images/pdflibrary/klwr.pdf

32. n.a., Multi-Species Recovery Plan for South Florida: Rice Rat. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 173–194. http://www.fws.gov/verobeach/index.cfm?Method=programs&NavProgramCategoryID=3&programID=107&ProgramCategoryID=3

http://www.fws.gov/verobeach/images/pdflibrary/srra.pdf

33. n.a., Rice rat (Oryzomys palustris natator) 5-Year Review: Summary and Evaluation. 2008, U.S. Fish and Wildlife Service, Southeast Region, South Florida Ecological Services Office: Vero Beach, FL. http://ecos.fws.gov/speciesProfile/profile/speciesProfile.action?spcode=A083

http://ecos.fws.gov/docs/five_year_review/doc1958.pdf

34. n.a., Feral and Free-Ranging Cat Trapping by the USDA, APHIS, Wildlife Services (WS) on North Key Largo. 2004, U.S. Department of Agriculture.

35. Nogales, M., et al., “A Review of Feral Cat Eradication on Islands.” Conservation Biology. 2004. 18(2): p. 310–319. http://onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2004.00442.x/abstract

36. Veitch, C.R., “The eradication of feral cats (Felis catus) from Little Barrier Island, New Zealand.” New Zealand Journal of Zoology. 2001. 28: p. 1–12. http://www.royalsociety.org.nz/publications/journals/nzjz/2001/001/

http://www.royalsociety.org.nz/media/publications-journals-nzjz-2001-001.pdf

37. Lebbin, D.J., Parr, M.J., and Fenwick, G.H., The American Bird Conservancy Guide to Bird Conservation. 2010, London: University of Chicago Press.

Reviving a Classic

“The cat, of all animals, is in some respects the most intimate companion of man… Nevertheless, it leads a dual existence. ‘The fireside sphinx,’ the pet of the children, the admired habitué of the drawing-room or the salon by day, may become at night a wild animal, pursuing, striking down and torturing its prey, frequently making night hideous with its cries, sneaking into dark, filthy, noisome retreats, or taking to the woods and fields, where it perpetrates untold mischief. Now it ravages the dovecote; now it steals on the mother bird asleep on her nest, striking bird, nest and young to the ground. In the darkness of night it turns poacher. No animal that it can reach and master is safe from its ravenous clutches.” —Edward Howe Forbush, The Domestic Cat: Bird Killer, Mouser and Destroyer of Wild Life; Means of Utilizing and Controlling It (1916)

Among the numerous criticisms of “Feral Cats and Their Management,” we can now add lack of originality.

In the January/February issue of Animal People, editor Merritt Clifton confirms his “hunch that ‘Feral Cats and Their Management’ is little more than a paraphrased and condensed update of the 1916 tract The Domestic Cat: Bird Killer, Mouser and Destroyer of Wild Life; Means of Utilizing and Controlling It, authored by then-Massachusetts state ornithologist Edward Howe Forbush.”

After a careful re-reading of the 1916 work (available online), Clifton (whose comprehensive article, “Where Cats Belong—and Where They Don’t,” I have quoted repeatedly) concludes:

“…the University of Nebraska paper and the Forbush work follow almost identical outlines from beginning to end, making similar allegations, arriving at the same recommendations in closely parallel language.” [1]

The Domestic Cat: Bird Killer, Mouser and Destroyer of Wild Life; Means of Utilizing and Controlling It

“The major structural difference,” writes Clifton, has to do with the sources involved. Whereas Forbush relied largely on “anecdotal testimony from more than 200 individual correspondents” (much of it from hunters who were after the same birds the cats were pursuing), Hildreth, Vantassel, and Hygnstrom provide “no firsthand testimony.” [1]

Instead, notes Clifton, they “plugged in references to more recent studies… in support of essentially the same claims, including that cats devastate populations of birds who would otherwise be hunted.” [1]

Among the similarities described in Clifton’s article:

Fecundity
Like Forbush, the authors of “Feral Cats and Their Management” use “outlandishly high claims about feline fecundity” [1] to drum up support for their eradication (“Hence the necessity for checking such increase promptly by killing all superfluous kittens soon after birth,” [2, p. 19] as Forbush put it).

For their reprise of Bird Killer, Mouser and Destroyer of Wild Life, Hildreth, Vantassel, and Hygnstrom turn to a frequently cited—but bogus—figure:

“The Humane Society of the United States estimates that a pair of breeding cats and their offspring can produce over 400,000 cats in seven years under ideal conditions, assuming none die.” [3]

But of course, feral cats—like all animals, and especially those living outdoors—don’t live “under ideal conditions.” And kittens do die. (The fact that Hildreth, Vantassel, and Hygnstrom leave it that is telling: their intent has nothing whatsoever to do with science, or research of any kind.)

In fact, the Wall Street Journal’s “Numbers Guy,” Carl Bialik, discredited this myth four years earlier in his column. What’s more, John Snyder, Vice President, Companion Animals, told Bialik then that HSUS wasn’t the source, adding, “that number is flawed.” (I’ve searched the HSUS website and can find no mention of it.)

Predation and Impact
Clifton points out that Forbush ignored reliable information indicating that free-roaming cats kill, on average 10 or 11 birds annually, and instead “dwelt on the claims of 15 people that their cats killed 20.4 birds per month, and the claims of six people that their cats killed about 50 birds per year.”

It’s not clear what information Hildreth, Vantassel, and Hygnstrom relied on, as they didn’t bother with in-text citations. Whatever the source, the authors settled on a surprisingly conservative annual predation rate of eight birds per year, and used 60 million as the estimated number of feral cats in the U.S. This, too, might be considered conservative in light of other “estimates,” (the American Bird Conservancy, for example, claims—without citing any source—that the population is 120 million) though Clifton himself estimated, in 2003, that “the winter feral cat population may now be as low as 13 million and the summer peak is probably no more than 24 million.” [4]

Rather than relying on inflated predation rates to justify the eradication of feral cats, Hildreth, Vantassel, and Hygnstrom misrepresent well-known scientific studies of their impact on wildlife. Their “interpretation” of Olof Liberg’s 1984 paper, for example, and convenient omission of sample size (26 rodents, 21 birds, and 11 lizards) in their reference to Crooks and Soulé’s 1999 paper. [5]

And, not surprisingly, “Feral Cats and Their Management” makes no mention of compensatory predation.

Public Health Threats
“As a carrier of disease,” argued Forbush, “especially to children, no animal has greater opportunities [than the domestic cat].”

Among the threats suggested by Hildreth, Vantassel, and Hygnstrom are cat scratch fever, plague, rabies, ringworm, salmonellosis, fleas, and ticks. And toxoplasmosis—of particular concern, apparently, because “in 3 separate studies, most feral cats (62 percent to 80 percent) tested positive for toxoplasmosis.” [3]

But the rate of cats testing positive—or seroprevalence—is not a useful measure of their ability to infect other animals or people. Indeed, according to the Centers for Disease Control and Prevention:

“Although cats can carry diseases and pass them to people, you are not likely to get sick from touching or owning a cat… People are probably more likely to get toxoplasmosis from gardening or eating raw meat than from having a pet cat.”

•     •     •

“Much of Forbush’s antipathy toward cats,” suggests Clifton, “might be ascribed to the context of the times.”

“His life coincided with the era in which New England wildlife was more depleted than at any time since. Logging, ploughing, damming, and unrestrained development depleted the forest cover, the grasslands, and the rivers. Precocious as Forbush was in his birding, which then was done chiefly with a shotgun, predatory mammals, fur-bearers, and most wild species considered edible had already been extirpated from most of Massachusetts before he had much chance to see or kill them.” [1]

That was 1916. How to explain “Feral Cats and Their Management,” written 94 years later—in, presumably, a very different context? The answer—part of it, anyhow—may lie with one of the paper’s co-authors, Stephen Vantassel, whose PhD dissertation was dedicated to:

“…fur trappers who, every winter, brave the harsh weather in continuance of America’s oldest industry. Regrettably, they must also endure the ravages of urban sprawl and the derision of an ungrateful and ignorant public.” [6]

Vantassel, it seems, would be more at home in the early twentieth century than in the twenty-first. (Though, by 1916, the American Society for the Prevention of Cruelty to Animals was already 50 years old, and the burgeoning animal welfare/right movement would surely have Vantassel longing for “the good old days.”)

Literature Cited
1. Clifton, M. (2011, January/February). The Domestic Cat: Bird Killer, Mouser and Destroyer of Wild Life; Means of Utilizing and Controlling It, by Edward Howe Forbush. Animal People, p. 17, from http://www.animalpeoplenews.org/11/1/Jan-Feb2011.zip%20Folder/Ho8j3PWe.html

http://www.animalpeoplenews.org/11/1/Jan-Feb2011.pdf

2. Forbush, E.H., The Domestic Cat: Bird Killer, Mouser and Destroyer of Wild Life; Means of Utilizing and Controlling It 1916, Boston: Wright and Potter Printing Company.

3. Hildreth, A.M., Vantassel, S.M., and Hygnstrom, S.E., Feral Cats and Their Managment. 2010, University of Nebraska-Lincoln Extension: Lincoln, NE. http://elkhorn.unl.edu/epublic/live/ec1781/build/ec1781.pdf

4. Clifton, M. Where cats belong—and where they don’t. Animal People, 2003.  http://www.animalpeoplenews.org/03/6/wherecatsBelong6.03.html.

5. Crooks, K.R. and Soulé, M.E., “Mesopredator release and avifaunal extinctions in a fragmented system.” Nature. 1999. 400(6744): p. 563–566. http://www.nature.com/nature/journal/v400/n6744/abs/400563a0.html

6. Vantassel, S.M., Dominion over Wildlife?: An Environmental Theology of Human-Wildlife Relations. 2009: Resource Publications.

Exceptional Predator

Photo of cat leaping after birdUsing Google to translate the page’s contents, it seems this bird—despite “mock[ing] the cat and with loud cries of diving at him from the branches of acacia”—was yet another one that got away.

In the third edition of his massive book Ornithology—“the classic text for the undergraduate ornithology course,” according to the description on Amazon.com—Frank Gill writes:

“Natural predators are a major source of annual mortality among birds, especially nestlings, incubating females, and young birds in their first year. Relentless predation is a driving force of natural selection for escape behaviors, camouflage plumage, and social behavior. With some conspicuous exceptions, however, predators don’t limit or regulate the bird populations on which they prey [1]. Instead, they take weak, sick, and young birds, many of which are part of the surplus that exceeds locally limiting food supplies.” [2, p 545]

For Gill, it seems, it’s all very straightforward; this, after all, is how Nature works. (It should be noted that, just one paragraph later, the author makes a clear distinction between islands and other habitats: “The endangerment and extinction of island birds by introduced predators is a conspicuous exception to the statement that predators don’t limit bird populations.”)

Unequal Treatment Under the (Natural) Law
Nobody opposed to TNR would deny that cats are predators—so why won’t they admit that the birds and other wildlife killed by cats are generally among, as Gill puts it, the “weak, sick, and young”?

The Carolina Raptor Center, for example, describes the role of predatory birds targeting bird feeders this way:

“Songbirds are part of the food chain just like other animals and their predators are going to look for the easiest targets. The birds that hawks are usually able to catch at feeders are the slow and sick ones. The strong and healthy ones escape, allowing their survival to produce more healthy babies.”

Cats, however, are a different matter altogether. According to the Carolina Raptor Center, they “kill a lot more birds then hawks do because hawks only kill for food, where cats kill for the sport of it.” I’ve never seen any scientific evidence to support such a claim, which may explain why so many have instead argued—again, without any support—that cats compete with raptors for food.

Who’s Crazed Now?
It wasn’t Gill’s book that got me thinking about this, though, but a comment posted last month on the Bountiful Films blog, following the release of their documentary Cat Crazed.

After listening to a CBC interview with director Maureen Palmer, whose “science” was clearly coming straight from the American Bird Conservancy, I posted a comment, stating in part:

“What you won’t find [from organizations opposing TNR] is any mention of the studies that show rather convincingly that birds killed by cats tend to be unhealthy compared to those killed by building collisions, say. Even high predation rates do not equate to population declines—as many scientists have noted.”

I also included a link to my “Predatory Blending” post. Which promptly drew fire from somebody calling him/herself “Catbird”:

“Where cats cause documented extinctions and extirpations, cat predation is additive (e.g., Hawkins 1998, Crooks and Soule 1999, Nogales et al. 2004). Researchers are interested in knowing if some cat predation is compensatory (that is, killing animals that would die anyway) (Beckerman et al. 2007, Baker et al. 2008, van Heezik et al. 2010). The purported evidence of compensatory predation is a study showing that cat-killed birds have larger spleens (indicating that they are less healthy) than birds killed by other sources (e.g., windows) (Moller and Erritzoe 2000). Other researchers found that birds killed by cats had less fat reserves and lower muscle mass than those killed in collisions (Baker et al. 2008), but warned against assuming that this corresponded with lower fitness of these individuals. In neither instance is it possible to conclude that individuals killed by cats would have died otherwise.”

Actually, Møller & Erritzoe don’t suggest that the birds captured by cats “would have died otherwise.” But, they are quite clear about the implications of their research:

“The present study has suggested that predators like the domestic cat may select against individuals with a weak immune system, leaving a disproportionate fraction of immunocompetent individuals as survivors.” [3]

What Møller & Erritzoe observed is very much in line with what Gill describes as typical predatory behavior.

Still, though, I’m not necessarily surprised with Catbird’s “interpretation” of the science, given his/her comments and tone elsewhere in the discussion. What’s far more troubling is that so few studies on the predatory habits of cats address the topic in any meaningful way.

Sins of Omission
Take that 2008 study by Baker et al., for example. The authors are, just as Catbird suggests, quite cautious about their findings:

“The distinction between compensatory and additive mortality does, however, become increasingly redundant as the number of birds killed in a given area increases: where large numbers of prey are killed, predators would probably be killing a combination of individuals with poor and good long-term survival chances. The predation rates estimated in this study would suggest that this was likely to have been the case for some species on some sites.” [4]

But, as I’ve pointed out previously, the authors’ predation rates are inflated—in part due to their unquestioning application of the dubious multiplier proposed by Kays and DeWan. [5] Baker et al. also use low estimates of breeding density—all of which combines to diminish the apparent level of compensatory predation. Were these estimates adjusted to better reflect the conditions at the site, the “redundancy” the authors refer to would be reduced considerably.

(Frankly, Baker and his colleagues seemed quite eager to demonstrate that Bristol’s cats were negatively affecting bird populations; in an earlier study, they suggested—based, I would argue, on insufficient information—that the area might be a “dispersal sink for more productive neighboring areas.” [6])

On the other hand, at least Baker et al. acknowledge Møller and Erritzoe’s work. Many other studies don’t even go that far.

Coleman and Temple, [7] for example, failed to consider the role of compensatory predation—despite the fact that they cite sources/studies that do. [8–10] And Temple himself addresses this very topic in his 1987 paper Do Predators Always Capture Substandard Individuals Disproportionately From Prey Populations?

Using a trained Red-tailed hawk to prey on eastern chipmunks, cottontail rabbits, and gray squirrels, Temple developed the “proposition that substandard individuals are captured disproportionately when the type of prey is relatively difficult to capture but not when it is relatively easy to capture.” [11]

Which seems a very fitting description for the general case of a cat attempting to capture an adult bird. (Ground-nesting and ground-feeding birds would likely be easier prey, though Hawkins’ PhD dissertation work [12] suggests that even this assumption deserves careful scrutiny.)

Longcore et al. never mention Møller and Erritzoe (one of many shortcomings I address in “Reassessment”); neither do Dauphine and Cooper. [13]

And ABC doesn’t go near the topic of compensatory predation. (Ironic since, unlike cats, most of the “threats to birds” listed by ABC (e.g., pesticides, pollution, oil spills, collisions with towers, buildings, wind turbines, and power lines, etc.) are clearly nondiscriminatory in terms of bird mortality.)

•     •     •

Is it any wonder that a reasonable discussion about the impacts of free-roaming cats on wildlife is so elusive? The same stakeholders that condemn these cats for their predatory nature too often refuse to acknowledge the nature of predation itself.

Literature Cited
1. Newton, I., Population limitation in birds. 1998, San Diego: Academic.

2. Gill, F.B., Ornithology. 3rd ed. 2007, New York: W.H. Freeman.

3.  Møller, A.P. and Erritzøe, J., “Predation against birds with low immunocompetence.” Oecologia. 2000. 122(4): p. 500–504. http://www.springerlink.com/content/ghnny9mcv016ljd8/

4. Baker, P.J., et al., “Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86-99. http://www.ingentaconnect.com/content/bsc/ibi/2008/00000150/A00101s1/art00008

5. Kays, R.W. and DeWan, A.A., “Ecological impact of inside/outside house cats around a suburban nature preserve.” Animal Conservation. 2004. 7(3): p. 273–283. http://dx.doi.org/10.1017/S1367943004001489

www.nysm.nysed.gov/staffpubs/docs/15128.pdf

6. Baker, P.J., et al., “Impact of predation by domestic cats Felis catus in an urban area.” Mammal Review. 2005. 35(3/4): p. 302-312. http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2907.2005.00071.x/abstract

7. Coleman, J.S. and Temple, S.A., How Many Birds Do Cats Kill?, in Wildlife Control Technology. 1995. p. 44. http://www.wctech.com/WCT/index99.htm

8. Fitzgerald, B.M., Diet of domestic cats and their impact on prey populations, in The Domestic cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 1988, Cambridge University Press: Cambridge; New York. p. 123–147.

9. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455. http://dx.doi.org/10.1111/j.1469-7998.1987.tb02915.x

10. Errington, P.L., “Notes on Food Habits of Southwestern Wisconsin House Cats.” Journal of Mammalogy. 1936. 17(1): p. 64–65. http://www.jstor.org/stable/1374554

11. Temple, S.A., “Do Predators Always Capture Substandard Individuals Disproportionately From Prey Populations? Ecology. 1987. 68(3): p. 669–674. http://www.esajournals.org/doi/abs/10.2307/1938472

12. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats  (Felis catus) on California birds and rodents. 1998, Texas A&M University

13. Dauphine, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2009. p. 205–219. http://www.pwrc.usgs.gov/pif/pubs/McAllenProc/articles/PIF09_Anthropogenic%20Impacts/Dauphine_1_PIF09.pdf

Operation Sisyphus

The draft environmental assessment (EA) for the Florida Keys National Wildlife Refuges Complex Integrated Predator Management Plan (download PDF), released last week by the U.S. Fish and Wildlife Service (FWS), aims to eliminate free-roaming cats in the Keys. Not that this is anything new—FWS (along with USDA, and some state agencies) has been trying to do this for years now.

Plans include the trapping/removal of free-roaming cats—owned and unowned alike—from refuge lands and other public lands nearby, as well as from other land (including private property) where cats may be considered a threat to vulnerable native species. TNR has been dismissed as an option, and FWS proposes to prohibit the feeding of feral cats wherever possible.

Unfortunately, the proposed plan is unlikely to be any more successful than previous efforts. There’s plenty to dislike about the FWS plan—including the risk that it may set a dangerous precedent nationwide. The deadline for public comments (see Plan for details) is February 3.

Justification or Rationalization?
In a section of the document called Justification for Management Action, FWS lays out their numerous grievances against “non-native species and human-subsidized populations of native predators.” [1] As a review of the relevant literature, the sub-section on domestic cats leaves much to be desired is a train wreck.

In fact, if this were a college-level term paper, it would likely receive a failing grade—followed, perhaps, by disciplinary action. (And, if it were allowed under the law, maybe a drug test, too.)

Science
Among the references cited here (about three-quarters of which I’m familiar; the rest I’m still chasing down) is, admittedly, some rather damning evidence. For example:

  • The near-extirpation of rock iguanas from Pine Cay in the Caicos Islands during the 1970s. “The decline, from an estimated adult lizard population of nearly 5,500, was due primarily to predation by domestic dogs and cats introduced to the island simultaneously with hotel construction.” [2] (Strangely, FWS cites Iverson’s paper not as an example of a near-miss, but of a global extinction. This, however, pales in comparison to the “strangeness” of many of their other citations.)
  • On Little Barrier Island, off the coast of New Zealand, cats “were considered to have been the sole cause of the local eradication of North Island saddleback and to have contributed to the extinction of the Little Barrier snipe, and to threaten, by their continued presence, grey-faced, black, and Cook’s petrels. Cats probably also contributed to the decline of tuatara and the 12 lizard species known to be present on Little Barrier Island.” [3]

Sci-Fi
On the other hand, much of the FWS’s evidence is, at best, circumstantial. Among the studies cited to support their claim that “free-roaming cats have been shown to be a major cause of 33 native species extinction [sic] globally,” is a 1987 paper by Cruz and Cruz, in which the authors, studying Galápagos Petrels, found that cats were hardly the only culprits:

“They are threatened by introduced rats, which attack eggs and young chicks… dogs and pigs which prey on eggs, nestlings and adults. Introduced goats, burros and cattle destroy nesting habitat and trample nests. A different combination of these pests and predators exists at each of the petrel nesting sites, while three of the islands are plagued by all of them.” [4]

And, as with the rock iguanas, the FWS would have the public believe the Galápagos Petrel is among those 33 extinctions. In fact, the birds are still there, though they are listed as Critically Endangered.

The story is similar for the 1986 paper by Kirkpatrick and Rauzon, another purported link between free-roaming cats and species extinctions. Kirkpatrick and Rauzon found that more than 90 percent of the diet of free-roaming cats on Jarvis Island and Howland Island was made up of Sooty Terns, Wedge-tailed Shearwaters, and Brown Noddies—each of which is listed as a species of Least Concern.

Another of the papers cited by FWS has nothing to do with extinctions at all. As the authors themselves describe it, their study was an evaluation of “whether a collar-worn pounce protector, the CatBib, reduces the number of vertebrates caught by pet cats and whether its effectiveness was influenced by colour or adding a bell.” [5]

FWS argues that “many of the species impacted by free-roaming cats are federally listed threatened or endangered species and federally protected migratory birds.” While probably true, this statement is also largely meaningless. According to the 2009 State of the Birds report, published by the Department of the Interior (which oversees FWS):

“The United States is home to a tremendous diversity of native birds, with more than 800 species inhabiting terrestrial, coastal, and ocean habitats, including Hawaii. Among these species, 67 are federally listed as endangered or threatened. An additional 184 are species of conservation concern because of their small distribution, high threats, or declining populations.” [6]

That translates to approximately 31 percent of all birds in this country being species of concern. FWS makes it sounds as if perhaps the cats are targeting these birds; in fact, they could just as easily have claimed that many of the species impacted by all forms of mortality are federally listed threatened or endangered species and federally protected migratory birds of these birds.

Hang in there, though—it gets better. I mean worse.

Fantasy
Also listed among the evidence of island extinctions were Coleman and Temple’s 1993 survey of rural Wisconsin residents about their outdoor cats [7], and Churcher and Lawton’s “English Village” study [8]. (While England is an island, it’s quite a stretch to suggest that Felmersham’s House sparrows are at risk of extinction.)

When it comes to the disruption caused by cats to “the abundance, diversity, and integrity of native ecosystems,” FWS turns to, among others, studies by Hawkins [9] and Jessup. [10]

As I’ve discussed previously, Hawkins’ dissertation work was plagued with problems that raise serious doubts about his rather triumphant conclusions—“the preference of ground feeding birds for the no-cat treatment was striking,” [9] for example. A closer look reveals that five of the nine ground-feeding birds showed no preference for either area of the study site. One could, based on Hawkins’ findings, just as easily conclude that more than half of the ground-feeding species studied were indifferent to the presence of cats.

Jessup cites some well-known predation studies, but his concern is the condemnation of “trap, neuter, and reabandon,” [10] as he calls it (“Abandonment of animals cannot be morally justified and is illegal under state humane laws… If it is illegal to abandon a cat once, how can it be legal to do it a second time? How can veterinarians justify being party to abandonment, an illegal act of animal cruelty?” [10])

FWS suggests that “free-roaming cats kill at least one billion birds every year in the U.S., representing one of the largest single sources of human-influenced mortality for small native wildlife,” [1] supporting their assertion with just three sources, one of which is Rich Stallcup’s 1991 article from the Observer, a publication of the Point Reyes Bird Observatory. But “A Reversible Catastrophe” is very light on science—and Stallcup gets most of that wrong. Mostly, the article is Stallcup’s manifesto regarding neighborhood cats:

“If you have a garden, why not proclaim it a wildlife sanctuary and protect it from non-native predators? If roaming cats come into your sanctuary to poach the wildlife under your stewardship, you have the right and perhaps even the duty to discourage them in a serious way.” [11]

Discourage them? Among Stallcup’s suggestions: “…try a B-B or pellet gun. There is no need to kill or shoot toward the head, but a good sting on the rump seems memorable for most felines, and they seldom return for a third experience.” [11]

No feral cat witch hunt would be complete without some public health threat fear-mongering, and FWS’s plan is no different:

“According to the Centers for Disease Control (CDC), free-roaming cats not only threaten wildlife through direct predation but also serve as vectors for a number of diseases including rabies, cat scratch fever, hookworms, roundworms and toxoplasmosis. Some of these diseases can be transmitted to other domestic animals, native wildlife, and in some cases, humans.” [1]

But the CDC site makes no mention of cats being a threat to wildlife. And humans? “Although cats can carry diseases and pass them to people, you are not likely to get sick from touching or owning a cat.” And, notes the CDC, “People are probably more likely to get toxoplasmosis from gardening or eating raw meat than from having a pet cat.”

There’s even a link to another page on the CDC’s site, called “Health Benefits of Pets.”

And finally, there’s the paper by Sax and Gaines. If the previous examples miss their mark, this one’s a full-blown non-sequitur. Though the authors do mention “the extinction of many native animal species on islands” [12] briefly in their introduction, the purpose of the paper is, as the authors state plainly enough, to “show that the number of naturalized plant species has increased linearly over time on many individual islands.” [12, emphasis mine]

•     •     •

FWS intends to eliminate free-roaming cats from the Florida Keys, and this is the best they can do? If so, well, perhaps they ought to be doing something else. If this is their “justification for action,” then any subsequent action can, I think, rightfully be considered unjustified.

Predator Management
Among the animals to be monitored throughout and/or removed from the four refuges that make up the Florida Keys National Wildlife Refuges Complex (National Key Deer Refuge, Key West National Wildlife Refuge, Great White Heron National Wildlife Refuge, and Crocodile Lake National Wildlife Refuge) are non-native reptiles and rodents, native raccoons, and, of course, the cats.

“Presence of exotic non-native iguanas, lizards, and large-bodied snakes will be detected through reports, incidental sightings, and the community-based interagency ‘Python Patrol’ network. Exotic reptiles will be immediately dispatched in accordance with AVMA guidelines for humane euthanasia.” [1]

“Any non-native opossum, armadillo, or rat caught incidentally in the live traps targeted for cats on Refuge lands will be immediately dispatched in accordance with the American Veterinary Medical Association (AVMA) guidelines for humane euthanasia. All native species will be immediately set free.” [1, emphasis mine]

“Raccoons trapped incidentally in live traps targeted for cats or other non-native predators will be released alive at the trap location… Raccoons that exhibit severe disease or other serious health issues will receive appropriate evaluation, which may include care by a state-certified wildlife rehabilitator or euthanasia as recommended by a qualified veterinarian or animal control services provider… If field studies and monitoring indicate that raccoon populations are having a negative impact on endangered species, the USFWS will reevaluate the need to implement more direct control by removal of raccoons from sensitive habitats. Removal could include, but not be limited to, transfer to a wildlife park or zoo, a state-certified wildlife rehabilitator, or euthanasia. Any decision by the Service to use lethal control measures on raccoons will trigger additional public notification and an amendment to this EA.” [1]

Free-roaming Cats
But, as I say, the cats are the real focus here: “The USFWS will remove all free-roaming cats found on Refuge lands through live trapping,” at which point, the cats will become of the responsibility of any one of three (currently, two; a third contractor is currently being sought) Monroe County animal control providers.

“The Monroe County animal control service provider will have the authority to determine the final disposition of the trapped cats according to county ordinances and standards, which may include returning to owner, adopting out, relocating to a long-term cat care facility on the mainland, or euthanizing.” [1]

Of course, it’s no secret what happens to the vast majority of feral cats brought into shelters. As Nathan Winograd writes in his book Redemption: The Myth of Pet Overpopulation and the No Kill Revolution in America, “there is no other animal entering a shelter whose prospects are so grim and outcome so certain.”

I asked Connie Christian, Executive Director of the Florida Keys SPCA, about this last week. “Every cat brought to our facility is assessed to determine their disposition,” Christian told me via e-mail. “Every attempt is made to return ‘non-feral’ cats to their owners or place for adoption.”

“Unfortunately,” she continued, “we do not have an outlet for feral cats that are brought to us without a request for return.” Which would likely be the case for cats unlucky enough to be trapped by FWS. (Interestingly, FKSPCA is involved with TNR, which FWS wants to eliminate—more on that in a moment.)

What about that “relocation to long-term facilities on the mainland” option? There was some discussion of this option during stakeholder meetings that took place in 2008. And local papers carried stories suggesting the possibility. [13, 14] Now it looks like FWS is dumping this is the laps of Monroe County animal control providers.

I guess they can say they tried.

Expanding Territory
But FWS isn’t stopping at their property line—and the four refuges included in the plan already make up, according to my calculations, more than 28 percent of the Keys’ total land mass. According to the South Florida Multi-Species Recovery Plan (MSRP), FWS has plans to use land acquisition and conservation easements or agreements to protect the endangered Lower Keys marsh rabbit. [15]

The MSRP, excerpts of which are included in the EA, also spells out FWS’s intention to “remove nuisance feral cats” from land “near rabbit habitat” in the Lower Keys. [1] Additional plans include deed restrictions “to prohibit free-roaming cats” [1] in areas where they might be a threat to the rabbits, the Key Largo Woodrat, or the Key Largo Cotton Mouse. And to “enforce deed restrictions of cat control in Ocean Reef Club and other areas.” [1]

The Ocean Reef Club, of course, is home to ORCAT, perhaps the best known—and certainly one of the most successful—TNR programs in the country. According to their website, ORCAT has reduced the island’s population of cats from approximately 2,000 cats, in the early 1990s, to about 350 today, “about 100 of which reside at the Grayvik Animal Care Center.”

Frankly, I’m not sure what FWS means by “enforce deed restrictions” (one of many follow-up items on my to-do list). Other aspects of their plan, however, are straightforward:

“Feral cat colonies and feeding stations on Refuge lands will be identified and removed. The USFWS will also coordinate with county and state agencies to assist in the identification and removal, where feasible and legal, cat colonies and feeding stations on other public properties that are adjacent to or near Refuge lands. Extensive public outreach will be conducted to encourage people who feed free-roaming cats to cease doing so, and to promote trapping and relocating those animals to long-term facilities on the mainland where they will no longer be a threat to Refuge’s wildlife.” [1]

Something else that’s clear: FWS is going after pet cats, too. The MSRP includes plans to “establish a program to license domestic cats, implement leash laws, eliminate cat-feeding stations, implement spay and neuter program, increase awareness through educational material, test diseases, and remove nuisance feral cats.” [15]

Is this mandatory spay/neuter (which has been shown to fail when implemented in the absence of adequate low- and no-cost services)? Does the FWS plan to test pets for, say FIV and FeLV? Lots of unanswered questions here, obviously.

Trap-Neuter-Return
It’s no surprise, then, given their plan for the removal of feeding stations—and cats—that FWS is staunchly opposed to TNR, which, they argue “does little to reduce cat predation on native wildlife.” [1]

Success Stories
“In addition,” argues FWS, “the TNR method has little valid scientific support for claims that it actually reduces cat colony numbers over time and often has been shown to attract people to release new cats into an area.” [1]

Ironically, some of the greatest TNR success stories are right there in the papers cited by FWS. Natoli, for example, reported a 16–32 percent decrease in population size over a 10-year period across 103 colonies in Rome—despite a 21 percent rate of “cat immigration.” [16]

Castillo and Clarke, though highly critical of TNR documented remarkably little predation in the two Florida parks they used for their study. In fact, over the course of approximately 300 hours of observation (this, in addition to “several months identifying, describing, and photographing each of the cats living in the colonies” [17] prior to beginning their research), Castillo and Clarke “saw cats kill a juvenile common yellowthroat and a blue jay.” [17]

“Cats also caught and ate green anoles, bark anoles, and brown anoles. In addition, we found the carcasses of a gray catbird and a juvenile opossum in the feeding area.” [17]

Any TNR program contends with the unfortunate (and illegal) dumping of cats. Still, it’s difficult to imagine that the presence or absence of a nearby TNR program would affect a person’s decision to abandon his/her pet cat(s). (If any studies had demonstrated such a connection, TNR opponents would surely cite them!) On the other hand, cats dumped near a managed colony are far more likely to be adopted and/or sterilized—thereby mitigating their potential impact on the overall population of unowned cats—as well any impacts to wildlife and the environment.

Moreover, FWS ignores the value of population stabilization. Julie Levy, Maddie’s Professor of Shelter Medicine in the University of Florida’s College of Veterinary Medicine, and one of the country’s foremost experts on feral cats, argues that “wildlife benefits when populations of cats that are trending rapidly upwards are at least stabilized” [18].

ESA and MBTA
Among the more perplexing aspects of FWS’s argument is their claim that “TNR practices are prohibited on National Wildlife Refuges, and violate the Endangered Species Act (ESA) and the Migratory Bird Treaty Act (MBTA) because they may result in the direct harm of protected species.” [1]

This is an argument that’s been thrown around since at least 2003, when Pamela Jo Hatley, then a law student, suggested the possibility. But that’s all it was—and, apparently, is—a possibility.

“It is quite obvious that cats can be lethal to birds,” writes Hatley, “and if the death of a migratory bird can be traced to a cat, or a cat colony, which can be further traced to an individual or organization, there may be strict liability for that person under the MBTA.” [19] Hatley’s argument for violations of the Endangered Species Act is similarly speculative: “…persons who release cats into the wild or who maintain feral cat colonies could be found liable for a take under section 9 of the ESA if maintenance of feral cats in the wild is found to kill or injure wildlife by degrading habitat.” [19]

It’s been nearly eight years now—a period during which TNR has undoubtedly increased substantially across the country—so where are all the court cases? If this were as black-and-white as FWS makes it sound, there wouldn’t even be a discussion about TNR (and the Urban Wildlands Group would likely have taken a very different tack in Los Angeles).

PETA
Finally—perhaps in a desperate attempt to appear as though their plan has the support of animal welfare organizations—FWS gives PETA a plug.

“Some animal advocates therefore often agree that traditional TNR programs are not the most appropriate choice, especially where cats are released near designated wildlife areas and at-risk wildlife populations (see the People for the Ethical Treatment of Animals’ Animal Rights Uncompromised fact sheets at www.peta.org/about/why-peta/default.aspx). For these reasons, TNR was considered but dismissed from further evaluation.” [1]

PETA, of course, is also opposed to caged birds, crating dogs, and zoos. When PETA is the only “animal advocate” you can get to endorse your approach, it’s time to rethink it.

Operation Sisyphus
The purpose of FWS’s Plan/EA “is to conserve and restore federally-listed species and protect all native fauna and flora on the [refuges] from population decline and potential extirpation or extinction due to predation by non-native species and human-subsidized populations of native predators.” [1]

Will the plan work? Only time will tell, of course—but there’s plenty of reason for skepticism. If their “literature review” is any indication, FWS either doesn’t have a particularly strong grasp of the issues involved—or they’re not interested in sharing that understanding with the public.

Nitpicking? I don’t think so. In their attempt to focus—however carelessly—on the impacts of cats, FWS overlooks some key factors.

Mesopredator Release
FWS refers to two often-cited papers [20, 21] as evidence of cats disrupting native ecosystems, but fails to acknowledge the larger point made by the authors: the mesopredator release phenomenon. “In the absence of large, dominant predators,” write Soulé et al., “smaller omnivores and predators undergo population explosions, sometimes becoming four to 10 times more abundant than normal.” [20]

In Soulé’s example, coyotes were the dominant predators, while cats were the mesopredators. In other contexts, however, cats have been shown to play the dominant predator role with rats becoming the mesopredators.

Mathematical modeling of the mesopredator release phenomenon illustrates the complexities involved in eradication efforts, even on small islands. As Courchamp et al. explain, “although counter-intuitive, eradication of introduced superpredators, such as feral domestic cats, is not always the best solution to protect endemic prey when introduced mesopredators, such as rats, are also present.” [22] Fan et al. warn of the risks involved with such eradication efforts: “In some cases, it may cause a disastrous impact to managed or natural ecosystems.” [23]

Macquarie Island, located roughly halfway between New Zealand and Antarctica, offers a well-documented example of such a disastrous impact. In 2000, cats were eradicated from this United Nations Educational, Scientific and Cultural Organization World Heritage Site in order to protect its seabird populations. The resulting rebound in rabbit and rodent numbers, however, has had its own disastrous impact. “In response, Federal and State governments in Australia have committed AU$24 million for an integrated rabbit, rat and mouse eradication programme.” [24]

Could something like this happen in the Florida Keys?

According to FWS, non-native rats are already “prevalent in residential and commercial areas.” [1] Should the removal of cats create a spike in their numbers, FWS suggests that they’re prepared to remove the rats, too: “Noticeable population increases based on reports, road kill, or other specific or auxiliary data may initiate targeted control and eradication efforts in addition to incidental capture…” [1]

But controlling these rats is complicated considerably by the need to protect Lower Keys marsh rabbits. The MSRP warns of these rabbits coming into contact with pesticides and “poisons used to control black rats.” [15]

“In a 1993 Biological Opinion, the FWS investigated the effects of vertebrate control agents on endangered and threatened species and determined that several chemicals (e.g., Pival) would jeopardize the continued existence of the Lower Keys marsh rabbit. Chemicals—such as Pival—a rodenticide used to kill rats, are lethal if ingested. The FWS also concluded that if development in the Keys continues to increase, the potential for these animals to come in contact with such chemicals also increases, as does the potential for their extinction. Based on these findings, the FWS believes the continued use of such chemicals will result in the deaths of Lower Keys marsh rabbits. Given that the majority of occupied habitat is adjacent to urbanized areas, and that urbanization continues to expand into their habitat, then it can reasonably be predicted that the use of such chemicals has had a negative impact upon the Lower Keys marsh rabbit that may prevent its recovery.” [15]

Removing Cats
It’s also not clear that FWS will be able to remove the free-roaming cats from the Keys. For one thing, they have no idea how many are there. Only now—after years of struggling with this issue—does FWS propose to “implement monitoring and conduct further research as needed to determine abundance and distribution of free-roaming cats throughout the Refuge, document effectiveness of management actions taken or not taken on cat populations, and determine the impacts on the ecosystems and native species to aid in the adaptive management process.” [1]

Plus, FWS has a rather poor track record when it comes to actually trapping cats.

In 2007, they “received $50,000 to remove cats from federal refuges on Big Pine Key and Key Largo, and to protect endangered marsh rabbits, silver rice rats and other animals and birds that call the refuges home.” [25] Reports (from what I can tell, nothing official has been issued) suggest that fewer than 20 cats were caught—some of which were returned to their owners (kudos to FWS and USDA)—along with 81 raccoons, 53 of which were released alive. [26]

I think it’s safe to say that the Keys’ wildlife reaped little or no benefit from this effort. Had that same money been used for TNR, on the other hand…

So what’s different this time around?

Déjà Vu
All the while I’ve been doing the research for this post, I’ve been haunted by two quotes I’ve used rather extensively in the past. Actually, the first is not a quote as such, but the title of Merritt Clifton’s excellent article: Where cats belong—and where they don’t. [27]

The second comes from Gary Patronek, who argues that “the release of cats into an environment where they would impact endangered or threatened species, or even into wildlife preserves or refuges, is inexcusable.” [28] Patronek, the former Director of the Center for Animals and Public Policy at the Cummings School, and one of the founders of the Hoarding of Animals Research Consortium, continues:

I do not believe that this is being advocated by cat protectors who see urban, managed colonies as an imperfect but still preferable alternative to the euthanasia of healthy animals. Abandoned pet cats whose own habitat has been reduced to colonies, and the wild species endangered by clear-cutting or beachfront development, are casualties of the same callous disregard for the lives of animals. I see little justification for shifting the role of cats to that of scapegoat.” [28, emphasis mine]

Well, isn’t this precisely what I’m advocating? I honestly don’t know.

Here’s what I do know:

There is no doubt that the Florida Keys are immensely valuable for their diversity of animal and plant life, some of which can be found nowhere else in the world. Due to a wide range of factors (most of them human-caused), this habitat has become quite fragile, with some animal and plant species on the brink of extinction. And, in such habitats, it’s been shown that free-roaming cats can have a significant negative impact.

I also know that where cats have been eradicated, the process is a horror. In fact, it’s spelled out in some of the papers cited by FWS (though, understandably, they don’t draw attention to that):

  • Nogales et al., describing the “success” of Marion Island, note, “it took about 15 years of intense effort to eradicate the cats, combining several methods such as trapping, hunting, poisoning, and disease introduction… The use of disease agents or targeted poisoning campaigns hold promise for an initial population reduction in eradication programs on large islands—such an approach may save effort, time, and money.” [29]
  • Cruz and Cruz point out that, of all the non-native mammals there, cats were “the most difficult to control or eliminate on Floreana Island.” Although “hunting with dogs was the single most effective method employed and it gave a sure body count,” the authors warn that “the method was costly and with the limited manpower available was only useful over small areas. Both poisoning and trapping were effective and the combination of the three methods is probably the most effective approach, as well as being the best use of time and materials.” [4]
  • Veitch describes efforts on 11-square-mile Little Barrier Island as “a determined [cat] eradication attempt” involving “cage traps, leg-hold traps, dogs and 1080 poison were used, but leg-hold traps and 1080 poison were the only effective methods.” [3] Four cats were also infected with Feline enteritis, but “because of the poor reaction to the virus no other cats were dosed and none were released… Altogether, 151 cats were known to have been killed before the eradication was declared complete. Important lessons learnt can be transferred to other feral cat eradication programmes.” [3] (By way of comparison, the Keys are approximately 137 square miles in total area.)

I know that ecosystems—especially those as fragile as the Keys—are incomprehensibly complex, and that tinkering with them is incredibly risky. And there’s plenty we simply do not know, and cannot—despite our best efforts—predict.

But I know, too, that time is short. And that we’ll never have all the answers we’d like to have before the need for action precludes further inquiry.

Implementation
Put another way: I’ve given this issue a lot of thought—and, here’s what I’m afraid will happen in the Keys:

FWS will proceed with their plan, rounding up cats—ferals and pets alike—on and “near” public lands. The pet cats will mostly be returned, but some mistakes—the risk of which will likely increase in an atmosphere of mass trapping—will surely be made. Feral cats will be killed.

Progress will move slowly, as these things often do—far too slowly to keep up with reproduction rates. If feeding and TNR are eliminated (to whatever extent possible) throughout the Keys, the cats will simply “go underground.” No more monitoring—and sterilizing—by the “foot soldiers” who currently care for colonies of cats.

Indeed, it’s quite likely that feral cat complaint calls to Monroe County, FWS, and the USDA would taper off considerably, as it becomes clear that such a call is essentially a death sentence. Thus, the cats become that much more difficult to locate—and sterilize. The population, therefore, increases.

Using a population model, Andersen, Martin, and Roemer have suggested that, in the absence of a sterilization program, 50 percent of cats would have to be removed in order for a colony to decrease 10 percent annually. [30] By contrast, the authors suggest that 75 percent of cats would need to be sterilized to achieve the same result.

This model has its flaws, as I’ve explained elsewhere, but the study is one many researchers are familiar with. And, frankly, it’s convenient for my purposes here.

Even if Andersen et al. are off by a factor of two, FWS would need to “remove” 25 percent of the free-roaming, unsterilized (and once they chase away the colony caretakers, it won’t be long before that’s the norm) cats continuously in order to achieve a 10 percent reduction in overall numbers.

Does anybody really think that’s going to happen? Where’s the evidence to suggest that it’s even possible?

FWS has—it seems—taken off the table the unspeakable methods so often employed on small, uninhabited islands.

“While lethal control is allowed by Refuge System policy, it is not a socially acceptable approach and is inconsistent with the points of consensus developed by the stakeholder group. This alternative would likely not be logistically feasible on a FKNWRC-wide basis and would not allow for adaptive management under a strategic habitat conservation approach.” [1]

But they’ve also taken TNR off the table. So, what’s left? We’re back to doing what we’ve been doing for years now—which, of course, is how we got into this mess in the first place.

From what I can tell, the FWS plan is nothing more than a warmed-over version of old-school trap-and-remove, an approach Mark Kumpf, president of the National Animal Control Association President from 2007 to 2008, describes as “bailing the ocean with a thimble.” [31] (There’s a metaphor that ought to resonate with people in the Keys!)

If so, it’s easy to imagine the losers in the deal—the cats, obviously, but also all of the wildlife FWS wants to protect. And the taxpayers, too, of course—not much of a return on investment for all of us, no matter what our position might be on feral cats, wildlife conservation, and the like.

The question is, where are the winners?

Literature Cited
1. n.a., Draft Environmental Assessment: Florida Keys National Wildlife Refuges Complex Integrated Predator Management Plan. 2011, U.S. Fish & Wildlife Service: Big Pine Key, FL.

2. Iverson, J.B., “The impact of feral cats and dogs on populations of the West Indian rock iguana, Cyclura carinata.” Biological Conservation. 1978. 14(1): p. 63–73. http://www.sciencedirect.com/science/article/B6V5X-48XKN72-1NN/2/bff9bfdeecb8ff6cec68527221b99a97

3. Veitch, C.R., “The eradication of feral cats (Felis catus) from Little Barrier Island, New Zealand.” New Zealand Journal of Zoology. 2001. 28: p. 1–12. http://www.royalsociety.org.nz/publications/journals/nzjz/2001/001/

4. Cruz, J.B. and Cruz, F., “Conservation of the dark-rumped petrel Pterodroma phaeopygia in the Galápagos Islands, Ecuador.” Biological Conservation. 1987. 42(4): p. 303–311. http://www.sciencedirect.com/science/article/B6V5X-48XKMBP-17J/2/f81b57e317f217802d9aca8b6927a88c

5. Calver, M., et al., “Reducing the rate of predation on wildlife by pet cats: The efficacy and practicability of collar-mounted pounce protectors.” Biological Conservation. 2007. 137(3): p. 341-348. http://www.sciencedirect.com/science/article/B6V5X-4NGBB7H-3/2/456180347a2c3916d1ae99e220dd329e

6. n.a., State of the Birds, United States of America, 2009. 2009, U.S. Department of Interior: Washington, DC. p. 36.

7. Coleman, J.S. and Temple, S.A., “Rural Residents’ Free-Ranging Domestic Cats: A Survey.” Wildlife Society Bulletin. 1993. 21(4): p. 381–390.

8. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455. http://dx.doi.org/10.1111/j.1469-7998.1987.tb02915.x

9. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. 1998, Texas A&M University.

10. Jessup, D.A., “The welfare of feral cats and wildlife.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1377-1383. http://www.avma.org/avmacollections/feral_cats/javma_225_9_1377.pdf

11. Stallcup, R., “A reversible catastrophe.” Observer 91. 1991(Spring/Summer): p. 8–9.

12. Sax, D.F. and Gaines, S.D., Species invasions and extinction: The future of native biodiversity on islands, in In the Light of Evolution II: Biodiversity and Extinction,. 2008: Irvine, CA. p. 11490–11497. www.pnas.org/content/105/suppl.1/11490.full

13. n.a. (2007, March 29). Key Deer Refuge wants to control feral cats: A plan to round up feral cats in the National Key Deer Refuge on Big Pine and No Name keys has animal-rights groups and area cat owners upset. The Reporter.

14. Busweiler, R. (2008, December 1). Feds begin drafting rabbit protection plan—BIG PINE KEY. The Key West Citizen.

15.  n.a., Multi-Species Recovery Plan for South Florida: Lower Keys Rabbit. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 151–171. www.fws.gov/verobeach/images/pdflibrary/lkmr.pdf

16. Natoli, E., et al., “Management of feral domestic cats in the urban environment of Rome (Italy).” Preventive Veterinary Medicine. 2006. 77(3-4): p. 180-185. www.kiccc.org.au/pics/FeralCatsRome2006.pdf

17. Castillo, D. and Clarke, A.L., “Trap/Neuter/Release Methods Ineffective in Controlling Domestic Cat “Colonies” on Public Lands.” Natural Areas Journal. 2003. 23: p. 247–253.

18. Levy, J.K., Personal communication, 2010.

19. Hatley, P.J., Feral Cat Colonies in Florida: The Fur and the Feathers Are Flying. 2003, University of Florida Conservation Clinic: Gainsville, FL. www.law.ufl.edu/conservation/pdf/feralcat.pdf

20. Soulé, M.E., et al., “Reconstructed Dynamics of Rapid Extinctions of Chaparral-Requiring Birds in Urban Habitat Islands.” Conservation Biology. 1988. 2(1): p. 75-92. http://deepblue.lib.umich.edu/bitstream/2027.42/74761/1/j.1523-1739.1988.tb00337.x.pdf

21. Crooks, K.R. and Soulé, M.E., “Mesopredator release and avifaunal extinctions in a fragmented system.” Nature. 1999. 400(6744): p. 563–566. http://www.nature.com/nature/journal/v400/n6744/abs/400563a0.html

22. Courchamp, F., Langlais, M., and Sugihara, G., “Cats protecting birds: modelling the mesopredator release effect.” Journal of Animal Ecology. 1999. 68(2): p. 282–292. http://deepeco.ucsd.edu/~george/publications/99_cats_protecting.pdf

23. Fan, M., Kuang, Y., and Feng, Z., “Cats protecting birds revisited.” Bulletin of Mathematical Biology. 2005. 67(5): p. 1081-1106. http://dx.doi.org/10.1016/j.bulm.2004.12.002

24. Bergstrom, D.M., et al., “Indirect effects of invasive species removal devastate World Heritage Island.” Journal of Applied Ecology. 2009. 46(1): p. 73-81. http://eprints.utas.edu.au/8384/4/JAppEcol_Bergstrom_etal_journal.pdf

25. O’Hara, T. (2007, April 3). Fish & Wildlife Service to begin removing cats from Keys refuges. The Key West Citizen.

26. n.a., Lower Florida Keys National Wildlife Refuges Comprehensive Conservation Plan. 2009, U.S. Department of the Interior, Fish and Wildlife Service: Atlanta, GA.

27. Clifton, M. Where cats belong—and where they don’t. Animal People 2003.  http://www.animalpeoplenews.org/03/6/wherecatsBelong6.03.html.

28. Patronek, G.J., “Letter to Editor.” Journal of the American Veterinary Medical Association. 1996. 209(10): p. 1686–1687.

29. Nogales, M., et al., “A Review of Feral Cat Eradication on Islands.” Conservation Biology. 2004. 18(2): p. 310-319. http://dx.doi.org/10.1111/j.1523-1739.2004.00442.x

30. Andersen, M.C., Martin, B.J., and Roemer, G.W., “Use of matrix population models to estimate the efficacy of euthanasia versus trap-neuter-return for management of free-roaming cats.” Journal of the American Veterinary Medical Association. 2004. 225(12): p. 1871-1876. http://www.avma.org/avmacollections/feral_cats/javma_225_12_1871.pdf

31. Hettinger, J., Taking a Broader View of Cats in the Community, in Animal Sheltering. 2008. p. 8–9. http://www.animalsheltering.org/resource_library/magazine_articles/sep_oct_2008/broader_view_of_cats.pdf

FWS – PDF = WTF

Last Monday, the U.S. Fish & Wildlife Service (FWS) released a draft environmental assessment associated with its Florida Keys National Wildlife Refuges Complex Integrated Predator Management Plan, giving the public 30 days to comment.

Just days later, the document became remarkably difficult to locate, as links to the PDF posted on the FWS website all seem to redirect to the agency’s home page. Later this week, I’ll post my initial impressions of the plan (hint: plan is probably too strong a word for it), but in the meantime, I’ve posted the original document for anybody interested: Download PDF

Adult Supervision Required III

As I dig deeper into “Feral Cats and Their Management,” I continue to undercover discrepancies between the story Hildreth, Vantassel, and Hygnstrom are telling and what’s actually in the literature.

As I pointed out in my first post on the topic, Olof Liberg did not differentiate between native and non-native prey, as Hildreth, Vantassel, and Hygnstrom suggest. In fact, his reference to “natural prey” [1] was only to distinguish between food provided by humans and any wildlife that cats might consume.

While revisiting Liberg’s paper, though, I found something far more intriguing: it appears Hildreth, Vantassel, and Hygnstrom never made it past the abstract.

In their report, the authors write: “The diets of well-fed house-based cats in Sweden consisted of 15 percent to 90 percent native prey, depending on availability.” [2] But what Liberg is describing here is merely the range of prey brought in by all of the cats in the study, 80–85 percent of which were “well-fed house-based” (the others feral).

Liberg (1984) Figure 1

Moving beyond the abstract, however, the story gets even better. Averaged annually, wildlife makes up just 25–30 percent of the diet of the owned cats (see Fig. 1). Rabbits, being abundant in the area, make up the bulk, with birds—which, we’re made to understand, are of greatest concern for Hildreth, Vantassel, and Hygnstrom—comprising a couple percent at most.

*     *     *

Considering the brevity of the report’s Issues and Impacts section (roughly the same space as was allotted to lethal control methods), the authors managed to squeeze in a surprising amount of misinformation.

Literature Cited
1. Liberg, O., “Food Habits and Prey Impact by Feral and House-Based Domestic Cats in a Rural Area in Southern Sweden.” Journal of Mammalogy. 1984. 65(3): p. 424-432. http://www.jstor.org/stable/1381089

2. Hildreth, A.M., Vantassel, S.M., and Hygnstrom, S.E., Feral Cats and Their Managment. 2010, University of Nebraska-Lincoln Extension: Lincoln, NE. http://elkhorn.unl.edu/epublic/live/ec1781/build/ec1781.pdf

Adult Supervision Required

“Have you seen this already? This is awful.”

That’s what somebody posted on the Vox Felina Facebook page late last night—along with a link to an MSNBC news story. The headline was an attention-getter, no doubt about it: “Report: Kill feral cats to control their colonies.”

But beyond that, MSNBC had practically no details. A little digging around, however, led me to New England Cable News (NECN), which has the complete story.

“The report began in an undergraduate wildlife management class, with students writing reports on feral cats based on existing research. The students’ professor and other [University of Nebraska] researchers then compiled the report from the students’ work.” [1]

“Feral Cats and Their Management” claims, straightforwardly enough, to provide “research-based information on the management of feral cats.” [2] Management, in this case, meaning—as is so often the case in such contexts—killing, extermination, eradication, and so forth. Detailed advice is provided (e.g., “Body-gripping traps and snares can be used to quickly kill feral cats”).

And research? In this case, nothing more than a cursory review of all of the usual suspects: Coleman and Temple, Pamela Jo Hatley, Cole Hawkins, The Wildlife Society, Linda Winter. In other words, lots of Kool-Aid drinking.

It’s Like Science, Only Different
Among the research misinterpreted and/or misrepresented (none of which is cited in the text):

“As instinctive hunters, feral cats pose a serious threat to native wildlife, particularly birds.”

It’s no surprise that the authors of the report offer no evidence to support such a sweeping claim. “There are few if any studies,” write Mike Fitzgerald and Dennis Turner in their contribution to The Domestic Cat: The biology of its behaviour, “apart from island ones that actually demonstrate that cats have reduced bird populations.” [3]

Biologist C.J. Mead, reviewing the deaths of “ringed” (banded) birds reported by the British public, suggests that cats may be responsible for 6.2–31.3% of bird deaths. “Overall,” writes Mead, “it is clear that cat predation is a significant cause of death for most of the species examined.” Nevertheless, Mead concludes, “there is no clear evidence of cats threatening to harm the overall population level of any particular species… Indeed, cats have been kept as pets for many years and hundreds of generations of birds breeding in suburban and rural areas have had to contend with their predatory intentions.” [4]

The German zoologist Paul Leyhausen (1916–1998), who spent the bulk of his career studying the behavior of cats, found that cats, frustrated by the difficulties of catching them, “may soon give up hunting birds.” [5]

“During years in the field,” wrote Leyhausen, “I have observed countless times how cats have caught a mouse or a rat and just as often how they have stalked a bird. But I never saw them catch a healthy songbird that was capable of flying. Certainly it does happen, but, as I have said, seldom. I should feel sorry for the average domestic cat that had to live solely on catching birds.” [5]

“Cats kill an estimated 480 million birds per year (assuming eight birds killed per feral cat per year).”

Fitzgerald and Turner (whose work is not referenced in the report) argue that “we do not have enough information yet to attempt to estimate on average how many birds a cat kills each year.” [3] Though, of course, many studies have tried to do exactly that—few, it should be said, involve feral cats.

Unfortunately—and as I have pointed out time and time again—such work typically suffers from a range of methodological and analytical problems (e.g., statistical errors, small sample sizes, and inappropriate/baseless assumptions).

And—as with the UNL report—obvious bias.

“Estimates from Wisconsin indicate that between 500,000 and 8 million birds are killed by rural cats each year in that state…”

How anybody could misquote the numbers from the Wisconsin Study—easily the most widely circulated work on the subject—is a mystery. (On the other hand, the figures were, as Stanley Temple has said, “not actual data” [6] in the first place, so I suppose that does allow for some rather liberal interpretation.)

“The diets of well-fed house-based cats in Sweden consisted of 15 percent to 90 percent native prey, depending on availability.”

How important is it that the prey of feral cats is native, versus non-native? That’s a point of some debate—but not in this case. See, what Liberg actually wrote was this: “Most cats (80-85%) were house-based and obtained from 15 to 90% of their food from natural prey, depending on abundance and availability of the latter.” [7, emphasis mine] He was merely drawing the distinction between food provided by humans and any prey that cats might eat as food.

Liberg goes on to point out that the predation he documented did not, justify a conclusive assessment of the effects of cats on their prey populations, but… indicate[s] that cats by themselves were not limiting any of their prey.” [7] Even high rates of predation do not equate to population declines.

“In California, 67 percent of rodents, 95 percent of birds, and 100 percent of lizards brought home by cats were native species, and native birds were twice as likely to be seen in areas without cats.”

What looks to be truly damning evidence loses much of its impact when it’s seen in context. The reference to Crooks and Soulé’s 1999 paper, for example, omitted the sample size involved: “Identification of 68 prey items returned by cats bordering the fragments indicated that 67% of 26 rodents, 95% of 21 birds and 100% of 11 lizards were native species.” [8] It’s important to note, too, that these researchers asked residents to recall what kind of prey their cats returned—no prey items were collected—thereby raising questions about the accuracy of species attribution.

Furthermore, the cats involved with Crooks and Soulé’s study were all pet cats. How their habits compare with those of feral cats is an open question. Merritt Clifton of Animal People, an independent newspaper dedicated to animal protection issues, suggests, “feral cats appear to hunt no more, and perhaps less, than free-roaming pet cats. This is because, like other wild predators, they hunt not for sport but for food, and hunting more prey than they can eat is a pointless waste of energy.”

The second portion of the quote refers to Cole Hawkins’ PhD dissertation. Hawkins’ research methods and analysis are so problematic that the suggestion of a causal relationship between the presence of cats and the absence of birds (native or otherwise) is highly inappropriate (indeed, Hawkins scarcely investigates predation at all).

Among the key issues: Hawkins had no idea what the “cat” area of his study site was like before the cats were there; he merely assumes it was identical to the “no cat” area in terms of its fauna (though the two landscapes are actually quite different). It’s also interesting to note Hawkins’ emphasis on “the preference of ground feeding birds for the no-cat treatment” while downplaying the fact that five of the nine ground-feeding species included in the study showed no preference for either area. (For a more comprehensive analysis, please see my previous post on the subject.)

“…cats are the most important species in the life cycle of the parasite responsible for toxoplasmosis, and in 3 separate studies, most feral cats (62 percent to 80 percent) tested positive for toxoplasmosis.”

While cats are the “definitive host,” it’s important to note that “wild game can be a source of T. gondii infection in humans, cats, and other carnivores. Serologic data show that a significant number of feral pigs, bears, and cervids are exposed to T. gondii.” [9]

“Humans,” write Elmore et al., “usually become infected through ingestion of oocyst-contaminated soil and water, tissue cysts in undercooked meat, or congenitally. Because of their fastidious nature, the passing of non-infective oocysts, and the short duration of oocyst shedding, direct contact with cats is not thought to be a primary risk for human infection.” [10]

Toxoplasma gondii has been linked to the illness and death of marine life, primarily sea otters [11], prompting investigation into the possible role of free-roaming (both owned and feral) cats. [12, 13] It’s generally thought that oocysts (the mature, infective form of the parasite) are transferred from soil contaminated with infected feces to coastal waterways by way of freshwater run-off. [13]

However, a 2005 study found that 36 of 50 sea otters from coastal California were infected with the Type X strain of T. gondii [14], a type linked to wild felids (mountain lions and a bobcat, in this case), but not to domestic cats. [13] A recently published study from Germany seems to corroborate these findings. Herrmann et al. analyzed 18,259 fecal samples (all from pet cats) for T. gondii and found no Type X strain.  (It’s interesting to note, too, that only 0.25% of the samples tested positive for T. gondii). [15]

[NOTE: Please see follow-up post for additional information about cats and T. gondii.]

“Predation by cats on birds has an economic impact of more than $17 billion dollars [sic] per year in the U.S. The estimated cost per bird is $30, based on literature citing that bird watchers spend $0.40 per bird observed, hunters spend $216 per bird shot, and bird rearers spend $800 per bird released.”

According to this bizarre form of accounting, hunters value an individual bird more than 500 times as much as a birdwatcher does—suggesting, it seems, that dead birds are far more valuable than live birds. This is the kind of estimate that can be developed only through university (or perhaps government) research efforts.

Public Indecency
Stephen Vantassel, a wildlife damage project coordinator who worked on the study, said researchers were aware that some people would be ‘very offended that we offered any type of lethal control method.’ But he said the report was written for public consumption and wasn’t submitted to any science journals for publication.” [1]

For the record, Dr. Vantassel, I’m more offended by the way you’ve allowed such sloppy, grossly irresponsible work to pass for “research.” And the idea that such an undertaking is somehow acceptable because it’s meant for a mass audience is simply absurd!

Naturally, the American Bird Conservancy (ABC) embraced the report immediately, “with one official calling it ‘a must read for any community or government official thinking about what to do about feral cats.’” [1]

“‘Not surprisingly, the report validates everything American Bird Conservancy has been saying about the feral cat issue for many years—namely, TNR doesn’t work in controlling feral cat populations,’ Darin Schroeder, vice president of the Conservation Advocacy for American Bird Conservancy, said Tuesday.”

But validation requires far more than this report provides—beginning with a real interest in scientific inquiry and some basic critical thinking skills. And while we’re at it, a refresher in ethics wouldn’t hurt, either.

*     *     *

In my previous post, I’d indicated that my next post—this post—was going to focus on The American Bird Conservancy Guide to Bird Conservation. Obviously, something came up. Anyhow, the book will keep for a few more days…

Literature Cited
1. n.a. (2010) Report: Kill feral cats to control their colonieshttp://www.necn.com/11/30/10/Report-Kill-feral-cats-to-control-their-/landing_scitech.html?&blockID=3&apID=95afccc4d9564caf8e264f9d087f5732 Accessed December 1, 2010.

2. Hildreth, A.M., Vantassel, S.M., and Hygnstrom, S.E., Feral Cats and Their Managment. 2010, University of Nebraska-Lincoln Extension: Lincoln, NE. http://elkhorn.unl.edu/epublic/live/ec1781/build/ec1781.pdf

3. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

4. Mead, C.J., “Ringed birds killed by cats.” Mammal Review. 1982. 12(4): p. 183-186. http://dx.doi.org/10.1111/j.1365-2907.1982.tb00014.x

5. Leyhausen, P., Cat behavior: The predatory and social behavior of domestic and wild cats. Garland series in ethology. 1979, New York: Garland STPM Press.

6. Elliott, J. (1994, March 3–16). The Accused. The Sonoma County Independent, pp. 1, 10

7. Liberg, O., “Food Habits and Prey Impact by Feral and House-Based Domestic Cats in a Rural Area in Southern Sweden.” Journal of Mammalogy. 1984. 65(3): p. 424-432. http://www.jstor.org/stable/1381089

8. Crooks, K.R. and Soule, M.E., “Mesopredator release and avifaunal extinctions in a fragmented system.” Nature. 1999. 400(6744): p. 563.

9. Hill, D.E., Chirukandoth, S., and Dubey, J.P., “Biology and epidemiology of Toxoplasma gondii in man and animals.” Animal Health Research Reviews. 2005. 6(01): p. 41-61. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=775956&fulltextType=RA&fileId=S1466252305000034

10. Elmore, S.A., et al., “Toxoplasma gondii: epidemiology, feline clinical aspects, and prevention.” Trends in Parasitology. 26(4): p. 190-196. http://www.sciencedirect.com/science/article/B6W7G-4YHFWNM-1/2/2a468a936eb06649fde0463deae4e92f

11. Jones, J.L. and Dubey, J.P., “Waterborne toxoplasmosis – Recent developments.” Experimental Parasitology. 124(1): p. 10-25. http://www.sciencedirect.com/science/article/B6WFH-4VXB8YT-2/2/8f9562f64497fe1a30513ba3f000c8dc

12. Dabritz, H.A., et al., “Outdoor fecal deposition by free-roaming cats and attitudes of cat owners and nonowners toward stray pets, wildlife, and water pollution.” Journal of the American Veterinary Medical Association. 2006. 229(1): p. 74-81. http://avmajournals.avma.org/doi/abs/10.2460/javma.229.1.74

13. Miller, M.A., et al., “Type X Toxoplasma gondii in a wild mussel and terrestrial carnivores from coastal California: New linkages between terrestrial mammals, runoff and toxoplasmosis of sea otters.” International Journal for Parasitology. 2008. 38(11): p. 1319-1328. http://www.sciencedirect.com/science/article/B6T7F-4RXJYTT-2/2/32d387fa3048882d7bd91083e7566117

14. Conrad, P.A., et al., “Transmission of Toxoplasma: Clues from the study of sea otters as sentinels of Toxoplasma gondii flow into the marine environment.” International Journal for Parasitology. 2005. 35(11-12): p. 1155-1168. http://www.sciencedirect.com/science/article/B6T7F-4GWC8KV-2/2/2845abdbb0fd82c37b952f18ce9d0a5f

15. Herrmann, D.C., et al., “Atypical Toxoplasma gondii genotypes identified in oocysts shed by cats in Germany.” International Journal for Parasitology. 2010. 40(3): p. 285–292. http://www.sciencedirect.com/science/article/B6T7F-4X1J771-2/2/dc32f5bba34a6cce28041d144acf1e7c

Rap(tor) Sheet

Perhaps it’s an act of desperation, this “kitchen sink” approach favored by some free-roaming cat/TNR opponents. Throw everything—including the kitchen sink—into the anti-cat argument, and perhaps something will stick. Their impact on wildlife and the environment, for instance, or their threat to public safety—it seems there’s something for everybody. (Surely it’s only a matter of time before beach erosion, ozone depletion, and climate change are added to this growing rap sheet.)

But for those of us willing to sort through this quantity-over-quality smokescreen, such arguments rarely prove substantive.

I touched on this point in one of my first Vox Felina posts, referring to how the now-classic predation study conducted by William G. George has been misread, misinterpreted, and misrepresented. This work, perhaps more than any other, has been used to suggest an indirect impact of free-roaming cats on raptors.

George was very cautious about drawing such a connection, acutely aware of the speculative nature of his own work. In recent years, however, the details of George’s work—and his well-tempered conclusions—have given way to a kind of mythology, having been co-opted by scientists more interested in their own agendas than in rigorous scientific inquiry.

The Study
Over four years, from January 1, 1968 through December 31, 1971, George monitored and recorded with meticulous care the various small mammals his three cats killed on his “fallow farmland” property in rural Cobden, Illinois. “As predators on rodents,” writes George, “cats inevitably compete for prey with many of our declining raptors, and therein may lie a serious problem.” (emphasis mine) [1].

“I am not suggesting a cause-and-effect relationship exists between the historical increase of cats and the historical decrease of raptors; however, cats, which are as efficient in their way as guns and DDT, accompany and add another dimension to man’s encroachment into wildlife areas.” [1]

The trouble, of course, is that so many scientists citing George’s work have suggested exactly that.

The Myth
“Cat predation on mammals,” write Longcore et al., is “cause for concern because of direct impacts to native species and competition with native predators (George 1974).” [2] “Human-subsidized cats,” warn Guttilla and Stapp, “can spill over into less densely populated wildland areas where they reduce prey for native predators (George 1974).” [3]

Of course anybody who grew up, as I did, watching Wild Kingdom, knows that competition is a central theme of many stories played out in the natural world. But competition for prey is one thing; having an impact on the population of competitors is something else altogether.

Which is precisely what Loyd and DeVore—citing only George’s research—suggest: “Feral cats can also have a considerable impact on the broader health of ecosystems by outcompeting native predators (George 1974)…” [4]

Dauphiné and Cooper, too, interpret George’s work rather loosely, but also seem to offer additional evidence of the indirect impacts about which he speculated:

“In addition to having direct impacts on prey, cats compete with avian predators, such as American Kestrels (Falco sparverius), Northern Harriers (Circus cyaneus), and Redtailed Hawks (Buteo jamaicensis) (George 1974, Mosher 1989, Lepczyk et al. 2004). George (1974) estimated that cats killed 5.5 million rodents and other vertebrates in a 26,000 square mile area in Illinois, effectively depleting the prey base for wintering raptors and other native predators.” [5]

What did Lepczyk add to the conversation? Nothing, actually; he merely cited George’s study:

“… cats may be directly competing with avian predators, such as American Kestrels (Falco sparverius), Northern Harriers (Circus cyaneus) and Red-tailed Hawks (Buteo jamaicensis; George, 1974).” [6]

And Mosher? This one’s far more interesting. According to Dauphiné and Cooper, Mosher’s research reveals some compelling evidence:

“In a study in Maryland of Cooper’s Hawks (Accipiter cooperii) that depended heavily on eastern chipmunks (Tamias striatus) to feed nestlings, Mosher (1989) found that these raptors altered their diet to prey more on songbirds in an area where chipmunks were eradicated by cats. The resulting increase in hunting time and difficulty for Cooper’s Hawks was associated with a decrease in nestling survival.” [5]

But Mosher’s paper includes no mention of cats at all. In fact, he suggests only “that reproductive performance, especially in studies encompassing relatively small areas, may reflect natural phenomena such as dependence on a particular prey species that undergoes population fluctuations.” [7] I found an earlier paper by Mosher, also mentioning chipmunks and Cooper’s Hawks [8]—but again, no mention of cats.

It’s possible this is an honest mistake, that Dauphiné and Cooper merely included the wrong reference. However, I was unable to find a hint of any such research in my (admittedly brief) online sleuthing. And, given the sloppiness and bias that permeates the rest of their paper, nothing these two might do would surprise me.

(If, as Dauphiné and Cooper suggest, the real problem is that raptors are preying on songbirds rather than chipmunks, then shouldn’t we be doing everything in our power to increase the chipmunk population? It’s an absurd suggestion, of course—but only slightly more so than many accepted wildlife “management” practices.)

Getting back to George’s research, the winner for most distorted version undoubtedly goes to David Jessup, who writes with a certitude generally reserved for politicians, marketers, and novelists. Gone is the trepidation George expressed—first, regarding the impact of cat predation on rodent and other prey populations; second, regarding the relationship between these populations and the raptors that feed on them. For Jessup, who offers no additional evidence, it’s all very straightforward:

“Feral cats also indirectly kill native predators by removing their food base.” [9]

Local/Regional Raptor Update
So, how have those raptors fared in the subsequent 40 years? Certainly there are factors other than cats that would likely contribute to their decline—habitat fragmentation and destruction, for instance. Such environmental impacts have the potential to affect the birds themselves, clearly, but also their prey.

Research into the population trends of Red-tailed Hawks, Northern Harriers, and American Kestrels—three raptors identified specifically by George—suggests that his concerns were largely unfounded.

BBS Routes and Data
Only one Breeding Bird Survey (BBS) route runs into Union County, Illinois, where George’s property was located. Unfortunately, count data for BBS Route 34080 go back only to 1993. However, data for neighboring routes are available from the time of George’s study through 2006. Surveys along two nearby routes in Illinois (34059 and 34061) began in 1970; surveys of two others, along the eastern edge of Missouri (52001 and 52007), date back to 1967.

Selected BBS Routes: Missouri and Illinois

No BBS count data from the routes in question are available for Northern Harriers, suggesting that perhaps this species was, for one reason or another, simply not included. Data sets for other birds—the Red-shouldered Hawk, for example—exist despite frequent counts of zero (in the case of the Red-shouldered Hawk, just one bird was recorded along Routes 52001 from 1967 through 2006).

BBS data for Red-tailed Hawks indicate a rather dramatic population increase for the two southwestern Illinois routes, and slight increases for the same period across the two eastern Missouri routes, as indicated in the following graphs.

Red-tailed Hawks Four BBS RoutesBBS Data: Red-tailed Hawks for two Illinois and two Missouri routes (adapted from North American Breeding Bird Survey website)

Populations of American Kestrels (along the same routes and for the same period) remained mostly stable.

American Kestrels Four BBS RoutesBBS Data: American Kestrels for two Illinois and two Missouri routes (adapted from North American Breeding Bird Survey website)

The bottom line? If the area’s cats are out-competing the raptors for prey, there’s no evidence in the BBS count data.

Prairie Voles
Of particular interest to George were prairie voles, which made up “more than 41 percent of all captured vertebrates and 45 percent of the captured mammals.” [1] And whose reduced numbers, suggested George, “could well pose the principal threat to the success of wintering hawks in my area of study.” [1] But maybe the voles weren’t as important as George surmised.

In Minnesota, the declining population of prairie voles—significant enough to warrant “special concern species” status beginning in 1984—seems to have had no effect on the populations of Northern Harriers, Red-tailed Hawks, and American Kestrels. Indeed, BBS data indicate that these raptors’ numbers have fluctuated little over the past 40 years or so. (And, according to the Minnesota Department of Natural Resources, the reason for the state’s declining vole numbers has nothing to do with cats, but “is due almost exclusively to the destruction of its prairie habitat through plowing and over-grazing.”)

BBS Data: Three Raptors across MinnesotaBBS Data: Three raptor species across Minnesota (adapted from North American Breeding Bird Survey website)

Raptors Across the Country
Of course, isolating the relationship between the population of a predator and that of its preferred prey species is incredibly difficult; there are simply too many additional—often interdependent—factors that must be considered. Zooming out for a big-picture view of population dynamics across the U.S. only blurs such relationships, thereby complicating any subsequent analysis.

Nevertheless, I think it’s worth a look. George claimed (unfortunately, without referring to a specific source, and without specifying whether he was referring only to owned/pet cats) that there were 31 million cats in the U.S. at the time of his study. [1] Today, according to the American Pet Products Association’s 2009–2010 National Pet Owners Survey, there are 93.6 million.

Direct comparisons over this 40-year time frame are difficult for a number of reasons (e.g., lack of reliable data, the increasing proportion of indoor-only cats in recent years, etc.). But if, as some suggest, cats are having an negative impact on raptor populations—and there are now three times as many of them (not accounting for feral cats, whose numbers have also likely increased)—well, one might expect find these birds in dire straights by now.

Hawk Mountain Sanctuary
To see for myself, I turned to Hawk Mountain Sanctuary’s Conservation Status Reports. Located in east-central Pennsylvania, Hawk Mountain Sanctuary is, according to its website, “the world’s first refuge for birds of prey.”

The outlook for the Northern Harrier and Red-tailed Hawk is mostly good. “The Northern Harrier is considered secure in most of North America,” notes its 2007 conservation report, “but it is a species of concern regionally in many of the [Bird Conservation Regions] west of the Mississippi River.”

The Red-tailed Hawk, too, “is considered secure throughout most of its range in North America.

“Migration counts have declined in eastern North America since 1995, but concurrent increases in [Breeding Bird Surveys] and [Christmas Bird Counts] suggest that these migration trends may be the result of changes in migration geography or behavior. Elsewhere in North America, population monitoring generally indicates increasing or stable populations of this common raptor.”

American Kestrels, on the other hand, seem to be in trouble: “Overall, the data suggest substantial declines in populations… across much of North America, and consequently strong cause for conservation concern.” The factors affecting these declines are unknown and, the report notes, “warrant further investigation.” However, some patterns have been observed—“factors exerting negative influences on populations are strongest along the Atlantic coast,” for example. Also: “More recent declines in western North America… appear to have occurred in concert with a prolonged drought.”

The Cornell Lab of Ornithology’s website paints a rather different picture, noting that the population of American Kestrels “increased greatly with historical deforestation of North America. No significant trend across North America, but some local increases and decreases.”

*     *     *

All of which adds up to… what? Like the BBS data, the Hawk Mountain Sanctuary Conservation Status Reports reveal population trends perhaps best described as “mixed.” Nowhere is there any indication that declining raptor numbers can be linked to the success of competing predators—including cats.

For George, the idea was nothing more than a hypothesis anyhow. But rather than put it to the test (ostensibly the role of scientists), Longcore, Dauphiné, Jessup, and the rest, have instead tried to elevate its status through nothing more than repetition—thereby betraying an agenda that has little to do with science at all.

Literature Cited
1. George, W., “Domestic cats as predators and factors in winter shortages of raptor prey.” The Wilson Bulletin. 1974. 86(4): p. 384–396. elibrary.unm.edu/sora/Wilson/v086n04/p0384-p0396.pdf

2. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

3. Guttilla, D.A. and Stapp, P., “Effects of sterilization on movements of feral cats at a wildland-urban interface.” Journal of Mammalogy. 2010. 91(2): p. 482-489. http://dx.doi.org/10.1644/09-MAMM-A-111.1

4. Loyd, K.A.T. and DeVore, J.L., “An Evaluation of Feral Cat Management Options Using a Decision Analysis Network.” Ecology and Society. 2010. 15(4). http://www.ecologyandsociety.org/vol15/iss4/art10/

5. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2009. p. 205–219. www.pwrc.usgs.gov/pif/pubs/McAllenProc/articles/PIF09_Anthropogenic%20Impacts/Dauphine_1_PIF09.pdf

6. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201. http://www.sciencedirect.com/science/article/B6V5X-48D39DN-5/2/d27bfff8454a44161f8dc1ad7cc585ea

7. Mosher, J.A., Accipiters, in Northeast Raptor Management Symposium and Workshop, B.A.G. Pendleton, Editor. 1989, National Wildlife Federation Scientific and Technical Series No. 13.: Syracuse, NY. p. 47–52.

8. Mosher, J.A., “Breeding Biology of Raptors in the Central Appalachians.” Raptor Research. 1982. 16(1): p. 18–24.

9. Jessup, D.A., “The welfare of feral cats and wildlife.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1377-1383. http://avmajournals.avma.org/doi/abs/10.2460/javma.2004.225.1377

The Scat Hits the Fan

Relative to other studies of the domestic cat’s predatory habits, Carol Fiore’s 2000 thesis work is cited only occasionally in the literature. [1, 2] Indeed, it might easily go unnoticed were it not for its inclusion in the American Bird Conservancy’s brochure Domestic Cat Predation on Birds and Other Wildlife, and the fact that Fiore posted a summary of the study on her website—making much of its content available to anybody interested in the topic.

Fiore’s “primary goal,” she writes, “was to estimate the number of cats in Wichita, the average number of birds killed per cat and the total number of birds killed by cats each year.” [3] In fact, there was more to it than that.

Fiore was also trying to quantify the number of birds killed by cats without their owners’ knowledge, thereby addressing a concern frequently expressed by researchers whose predation estimates rely on prey records kept by cat owners. [4–7] In other words, how many birds were being killed by cats, really?

Fiore’s thesis project was an ambitious undertaking—perhaps too ambitious. Although her goal was admirable, her small sample size, flawed analytical methods, and various confounding factors cast considerable doubt over her findings. In addition, Fiore’s thesis document is peppered with evidence of bias. Indeed, she raises questions about her motivation for the project (and underlying assumptions) when, early on, she refers uncritically to the ABC’s Cats Indoors! campaign and the Wisconsin Study, and mischaracterizes the work of William George (see Note 1).

I’m afraid that, in the end, Fiore’s work does little to enhance our understanding of the domestic cat’s hunting behavior. In fact, because her conclusions tend to misrepresent the study’s findings, Fiore actually does more to perpetuate the mythology surrounding predation than the science.

The Study
Fiore’s research incorporated several methods, each intended to provide a key piece of the predation puzzle:

  1. Twenty-eight Wichita, Kansas cat owners were recruited and asked to record the number and, when possible, also the species, of birds killed by their 41 cats over the period of approximately one year.
  2. Some of these same participants were asked to collect scat samples, which were then analyzed for feathers. Detection of feathers was used to account for kills not reported by cat owners.
  3. The behavior of eight participating cats was observed with the help of radio collars.
  4. Cat density in the area was estimated by combining telephone survey results (regarding the proportion of area cats that received the rabies vaccine) with information from local veterinarians (regarding the yearly total of rabies vaccines administered to cats).
  5. Using Christmas Bird Count data, the density of Northern Cardinals in the Wichita area was estimated.
  6. The impact of free-roaming cats on the population of cardinals was then estimated by combining findings from each of the investigations described above (with the exception of the radio collar monitoring).
  7. A second telephone survey was conducted, this time to learn about residents’ attitudes concerning possible cat regulations (e.g., leash laws, licensing, etc.).

Birds Brought Home by Cats
Twenty-nine (71%) of the cats were reported to have killed birds during the study period, while 12 (29%) were credited with no kills. (These figures would later be adjusted based on the results of the scat analysis, as described below.) However, multi-cat households posed a particular problem. “For owners with more than one cat,” writes Fiore, “kills were alternated between cats if the owner was unsure of the cat responsible.” [3]

As a result of her “alternating attribution” (my term, not Fiore’s) method, it’s possible that five cats were incorrectly included among the hunters (see Note 2 for details). If so, the proportion of hunters was not 71%, but 61%.

Other Studies
Either way, Fiore’s findings correspond reasonably well with those of a five-month survey of 618 British households, in which 986 cats brought home 14,370 prey items. This research revealed that, although 91% of cats returned at least one item, “approximately 20–30% of cats brought home either no birds or no mammals.” [5] Her results also seem to be in line with those published by Churcher and Lawton, whose yearlong “English Village” study (involving approximately 70 cats and 1,090 documented prey items) found that that 8.6% of cats brought home no prey [4] (though the authors don’t specify the percentage of cats that returned no birds).

On the other hand, it is not uncommon for such studies to find that more than half of the study cats returned no prey. In their pilot study of cat predation in Bristol (UK), for example, Baker et al. reported that 77 cats returned a total of 212 prey items to 52 participating households, but that “in each sampling period, the majority of cats (51–74%) failed to return any prey.” [6] Their subsequent 12-month study (this time involving 186 Bristol households, 275 cats, and 495 prey items) found a similar level of apparent non-hunters: roughly 61%. [7]

Any number of factors might contribute to these apparent differences, perhaps the most likely “culprits” being environmental (e.g., density of both birds and cats, habitat type and size, etc.) and sampling bias (as Baker et al. put it, “cat owners whose pets were killing lots of birds may have wished to hide the fact; alternatively, they may have been keen to show off their cat’s prowess.” [7])

Add It Up
Fiore began to quantify predation by calculating, based on the number of birds brought home by study cats, an average number of birds killed each year per cat. But, as I’ve discussed previously, using the average to describe predation rates (the distribution of which is highly skewed) overestimates the impact of cats on wildlife. Barratt offers a useful rule-of-thumb method (one echoed by Fitzgerald and Turner [8]) as an alternative:

“…median numbers of prey estimated or observed to be caught per year are approximately half the mean values, and are a better representation of the average predation by house cats based on these data.” [9]

Using the median—1.91 birds/cat/year—instead of the mean, cuts Fiore’s estimated predation rate of 3.44 nearly in half. (Among the more puzzling items I uncovered while reviewing Fiore’s thesis was her apparent miscalculation of the average predation rate—where Fiore comes up with 3.44 birds/cat/year, I get only 2.79. See Note 3 for a detailed explanation.)

In any case, what’s far more interesting is how Fiore adjusts her estimate based on the results of feathers discovered in scat.

Scat Analysis
Three of Fiore’s participants (who, together, owned six of the study cats) collected and bagged their cats’ scat for five consecutive days on a monthly basis. A fourth owner participated in this part of the study for just one month, and collected scat for three days.

Additional scat data was acquired via “litter box cleanups,” in which “a few volunteers were convinced to bag the entire contents of the litter box when it was cleaned.” [3] The results, according to Fiore, were rather dramatic:

“Out of 215 separate scat analyses, each of which could have composed several beakers of fecal material, feathers were found a total of 28 times. In only one instance, however, did the owner know that a bird had been killed and/or consumed.” [10]

Equally dramatic were the mathematical and statistical gymnastics Fiore employed to arrive at her conclusions. Her figure of 21%, for example, as “a mean value of the percentage of time a cat could be expected to ingest a bird with no owner knowledge,” [10] remains a mystery to me. Despite numerous attempts, I have been unable to sort out exactly how Fiore arrived at this figure.

Dividing 27 occurrences of “unexpected” feathers by 214 total analyses (subtracting in each case for the one instance of “expected” feathers) ought to get us close, it seems—but falls well short (12.6%).

Litter Box Cleanups
Of the 215 analyses, 24 were litter box cleanups, a data collection method plagued with problems. To begin with, only 11 owners (representing 19 cats) participated. Fiore acknowledges the limitations associated with this small sample size, but overlooks a thornier issue.

Fiore considered each cleanup—regardless of how many cats were using the litter box, or for how many days—a single data sample. If a feather was found during analysis (the details of which are described on Fiore’s website), then one additional kill was attributed to a single cat (again, alternating among cats in multi-cat households). While this is a conservative approach in one respect—no more than one bird could be recorded for any positive result—it fails to adequately account for the high number of negative results. A litter box containing the waste of three cats, accumulated over a period of five or more days (six of the 24 cleanups were of this type, and in only one case were feathers found), was treated no differently from one containing a single day’s waste from one cat.

This per-household approach allows a negative result in the first case to be offset by a positive result in the second—despite their very different implications.

On the other hand, at least two volunteers involved in the litter box cleanups also owned indoor cats, and it was impossible to determine whether it was their indoor or indoor/outdoor cats that were “contributing” to the study. This may have resulted in some false negatives.

Given all the uncertainty involved with Fiore’s litter box cleanups, it’s difficult to see how this aspect of her study contributes in any meaningful way to the overall findings. Better, I would say, not to include these results in any calculations—and perhaps disregard them entirely.

Monthly Collections
Fiore’s primary method (making up 191 of the 215 analyses) for scat analysis proved less problematic than the litter box cleanups—but was not without its own shortcomings.

Again, the sample size was quite small—only four participants in all (representing seven cats). And, once again, owners of multiple cats (two of the three long-term participants) were treated—from a statistical point of view—as if they each owned just one cat. A negative result in a three-cat household was weighted the same as an instance of feathers found in a single-cat household.

Worse, by alternating attributions of kills that could not linked to a specific cat in a multi-cat household, Fiore effectively makes hunters out of non-hunters (see Note 2 for a detailed explanation). In fact, given enough of these attributions—and it wouldn’t take many—all of the study cats would be categorized as killers.

Taking into account the number of cats in each household that participated in monthly collections (see Note 4), the number of scat analyses rises dramatically, from 215 to 354—and the average occurrence of feathers drops to just 7.6%.

Lucky 13
In the case of Cat 13—the study cat with the most “scat kills” (instances of feathers detected in scat when no birds were returned home) by far—feathers were found in 14 of 80 (17.5%) daily samples collected, prompting this reaction from Fiore:

“It is interesting to speculate as to the outcome of this study if all the volunteer owners had been as conscientious as this particular owner in collecting scat every month. Additionally this owner, who is retired, is very mindful of her cat’s whereabouts but still failed to find many kills.” [3]

But even Cat 13’s apparent penchant for secretive hunting yielded a frequency of found feathers well below Fiore’s suggested overall rate of 21%. And what about the other two long-term participants, whose 23 monthly samples (108 days’ worth—collected from five cats, not one, don’t forget) revealed just eight occurrences of feathers? Their frequency of secretive hunting was 7.4%—before accounting for the multiple cats involved (as described in Note 4), which would drop the rate to just 3%.

Was the owner of Cat 13 any more conscientious than the other two? Perhaps. Fiore notes that this woman, “appeared to be very serious about the study and never failed to turn in scat on a monthly basis; reminders were never required.” [3] Still, the other owners were hardly sitting on the sidelines—they turned in 108 samples between them. And it’s not clear what detrimental effect requiring a reminder might have had on the results; on the contrary, Fiore writes: “It is believed that scat volunteers conducted their collection correctly.” [3]

It’s difficult not to detect bias in Fiore’s praise for the diligence demonstrated by Cat 13’s owner—or, more to the point, her appreciation for the cat’s performance. Although this cat’s behavior is—as illustrated by Fiore’s own data—exceptional, Fiore seems to suggest that it’s the norm.

Corroboration and Disclaimers
Fiore is quick to point out various factors that would have allowed kills to go undetected by scat analysis. The condition of the birds recovered, for example, suggests that some cats don’t eat their prey, in which case scat would not have contained feathers. Nestlings, because they lack feathers, also would go undetected.

And even adult birds, suggests Fiore, may not have feathers to be discovered later. “Generally,” she writes, “cats pluck the feathers before consuming the bird.” [3] Although Fiore cites the work of other researchers on this point (work I’ve yet to chase down), her own findings seem to contradict this claim; plenty of feathers were found in scat. (Fiore’s claim also begs the question: If cats are expected to strip the feathers from the birds they kill, why use feathers found in scat as a measure of predation?)

Fiore is doubtful that “one of the study cats ate a bird it did not kill and that in turn feathers were detected in the scat,” [3] but Fitzgerald and Turner have suggested otherwise:

“Carrion is eaten, but is difficult to distinguish from animals killed by cats, unless it is from a large animal that a cat could not kill (e.g., sheep or kangaroo). Even the presence of maggots with the food is not a certain indicator, because cats may return later to prey they have killed and cached.” [8]

Although Fiore acknowledges the challenges inherent in her analysis method, she argues that they are outweighed by the benefits:

“Scat analysis is probably the most reliable estimate of bird kills, although it is a very conservative one. The results are hard to refute. When a feather is found it is proof that a kill was made or a carcass consumed… scat analysis is important because often cats do not bring their kills to the owner, and frequently the owner is not home to accept a kill should one be presented. Many of the owner volunteers reported not seeing their cat(s) for many days in a row (one owner did not see her cat for several months during the study). Collected kills were very conservative, and seemed to be based in part on the relationship of the owner with their cat(s). Unfortunately, absentee owners were the ones most unwilling to provide scat.” [3]

It seems Fiore wants to have it both ways: When it comes to defending the value of scat analysis, she’s quick to point out how much predatory activity the owners might be missing. When she’s emphasizing the conservative nature of prey tallies, though, Fiore cites a number of detailed firsthand accounts from cat owners—painting a rather different picture of owner involvement:

  • “There were numerous calls during the course of data collection about missing remains, cats seen eating birds but no remains could be found, cat running off with prey…”
  • “The wife of one of the volunteers admitted to seeing her cat drag a cardinal under the porch, but she would not retrieve it…”
  • “The owner of Cat 30 reported that she had seen… her cat eat an entire bird (even the head) and that there was no evidence left to give us.”

Her inconsistency raises questions not only about her findings, but also—far more unsettling ones—about her objectivity as a researcher.

Found Feathers
Despite results that are—at best—mixed, Fiore’s conclusions are imbued with certainty and drama. They also tend to misrepresent her research. Fiore’s claim that “scat analysis may indicate, as in this study, that a far greater number of birds are consumed than was previously thought” [3] is based on her misuse of means to characterize predation levels. Using medians instead, it becomes clear that—in terms of the distributions’ central tendency—there is no difference between her original data set and the one that includes scat kills.

More problematic, though, are Fiore’s claims about the secretive hunting habits of cats:

“Probably the most important information which can be gained from the scat analysis (coupled with owner bird collection) is that most cats do kill birds. And in all cases but one, when feathers were found in scat, the owner was unaware that the cat had eaten a bird. This and other data from this study would seem to refute Dr. Patronek’s claim that ‘cats tend to bring prey home.’” [3] (See Note 5 for details regarding Fiore’s apparent dispute with Patronek.)

Actually, Fiore’s own data indicate that cats do, in fact, “tend to bring prey home”—nearly four in five, if her mysterious 21% figure is to be believed. And her assertion about the surprising nature of kills revealed through scat analysis is—although technically true—highly misleading. She seems to be suggesting that scat collection was done randomly, in which case we would expect some collections to correspond with documented kills. Fiore’s reporting, however, indicates no such randomness. In fact, it’s entirely likely that participants (thinking such activity would at least be redundant, or worse, detrimental to the study) would have collected scat only when they were unaware of their cat(s) having killed a bird.

By framing her findings this way, Fiore effectively dismisses the vast majority of analyses (187 of 215, or 87%, using her analysis method; 326 of 354, or 92%, accounting for multi-cat households) in which no feathers were found.

When the ABC summarizes Fiore’s work in their brochure Domestic Cat Predation on Birds and Other Wildlife, they only make matters worse by conflating different aspects of her research:

“In a study of cat predation in an urban area, 83% of the 41 study cats killed birds. In all but one case, when feathers were found in scat, the owner was unaware that their cat had ingested a bird. In fact, the majority of cat owners reported their cats did not bring prey to them. Instead, the owners observed the cats with the bird or found remains in the house or in other locations.” [11]

Reading the ABC’s version, one might easily get the impression that all 41 cats were involved in the scat analysis, or that the scat collections were done randomly. (Or that cats, in order to be considered cooperative participants in predation studies, are expected to deposit their prey in the laps of their owners, or some other pre-determined location.)

Connecting the Dots
Let’s set aside my (numerous) complaints regarding Fiore’s scat analysis, and my claim that she both miscalculated and misused the average predation rate. Assuming both figures are valid, Fiore’s use of that 21% figure to adjust the predation rate upward, from 3.44 to 4.2 birds/cat/year is also a problem. The scat analysis should (again, assuming it was done properly, included sufficient sample sizes, etc.) reveal something about the secretive hunting behavior of the study cats—in terms of (1) its frequency, and (2) its extent. Fiore’s misstep is in linking the frequency directly to predation levels.

Properly adjusting the estimated predation level would involve, first, correcting the proportion of cats that hunt to account for the frequency of secretive hunters. Using Fiore’s data to illustrate:

71% + [(100%-71%) x 21%] = 77%

Once we adjust for those cats that don’t bring prey home, we can multiply this figure by the number of outdoor cats (see Note 6). Again, using Fiore’s data (described in the Cat Density section below):

40,836 pet cats x 43% allowed outdoors = 17,559 hunting cats

Multiplying this result by the median predation rate (1.91), we get a total of 33,538 birds/year killed by pet cats in Wichita—less than half Fiore’s estimate of 73,750. (This figure might be refined further by considering separate predation levels: one for the secretive hunters, and another for those cats known to bring prey home. Unfortunately, Fiore’s sample size is too small to make such a comparison, but it’s not difficult to imagine different hunting behaviors resulting in different success rates.)

To reiterate, I’m using Fiore’s numbers here only to illustrate how I would connect the dots between scat analysis results and predation levels.

Two Key Points
Fiore’s goal of obtaining a more accurate tally of birds killed by cats was (and is) admirable. However, her use of scat analysis was largely unsuccessful in achieving that goal. In fact, Fiore’s analysis method actually added to the uncertainty in two important ways:

  1. By alternating attributions of kills that can’t be linked to any one cat in a multi-cat household, Fiore essentially categorizes each one of them as a hunter.
  2. By weighting multi-cat households no differently from single-cat households, Fiore ignores a great deal of evidence suggesting that most cats are not, in fact, hunting without their owners’ knowledge. Although the number of “scat kills” is conservative as a result, her analysis method gives greater importance to what is unknown than to what is known.

Radio Tracking
Among the many challenges Fiore ran into while trying to track study cats were owner objections, physical barriers (e.g., fences), and radio signal strength/continuity in an urban setting. As a result, she was able to study only eight cats for a total of 57 hours (almost all during daylight hours).

Given the limited value of Fiore’s tracking activities—and my focus on the aspects of her thesis that pertain more directly to predation—I’ll move on to her estimate for the number of cats in Wichita.

Cat Density
Fiore used two different methods to estimate the number of cats in Wichita. The first, which is rather clever, involved combining the results of two telephone surveys: the Pet Ownership Survey was used to (among other things) poll respondents about whether or not they had vaccinated their cat(s) against rabies; a survey of local veterinarians was used to estimate the annual total of such vaccinations in Wichita. “If 500 cats received vaccinations,” writes Fiore, “and respondents indicated that 50% of pet cats had been vaccinated, 1000 cats would be the expected density.” [10]

For the second method, Fiore multiplied the number of Wichita households by the estimated number of cats per household (1.52), as determined through a random telephone survey.

Results of the first method yielded an estimate of 35,737 pet cats in Wichita, whereas the second method produced an estimate of 40,836 pet cats. (The skewed nature of the cats/household distribution (many owners having one or two cats, and a few having many cats) will tend to push such estimates upward.)

In addition, Fiore estimates (in her original thesis document, but not in the summarized version that appears on her website) the number of stray and feral cats in the city, ultimately arriving at a figure of 124,537. Deriving such estimates is always dodgy work, as so little trustworthy information is available. Additional caution is in order when these figures are used to project predation levels of stray and feral cats, as Fiore has done (as described in the Christmas Bird Count section, below).

For one thing, there are some questionable assumptions wrapped up in her estimates—not the least of which is that the predation rates and patterns of stray and feral cats are similar to those of pet cats. Clifton has suggested that they are not:

“The feral cat toll on birds is unlikely to be more than half as high as the pet cat toll. First, there may be twice as many free-roaming pet cats as ferals old enough to hunt for a living. Second, ferals who hunt for a living tend to hunt mice by night, not birds, who are mostly not out at night. Third, feral cats appear to hunt no more, and perhaps less, than free-roaming pet cats. This is because, like other wild predators, they hunt not for sport but for food, and hunting more prey than they can eat is a pointless waste of energy… Finally, relatively few cats are even capable of successfully hunting birds.” [2]

Christmas Bird Count
Fiore used data from the Wichita Audubon Society’s “first area-wide bird count of Northern Cardinals,” [3] an event coinciding with the National Audubon Society’s 99th annual Christmas Bird Count. Combining this data with the number of households in the city, she estimated that there were 316,477–424,922 cardinals in Wichita at the time.

It’s important to remember, as is made clear on the North American Breeding Bird Survey website, that such surveys provide “an index of relative abundance, rather than a complete count of breeding bird populations.” Fiore admits, “a census of a single bird species effected [sic] by urban cats in Wichita is an estimate of population density within an accuracy of one order of magnitude,” [3] but persisted.

As a result, Fiore was able to compare estimates of the overall cardinal population with estimates of those killed by cats. However, her “accounting practices” suggest that she’s not exactly impartial on the subject of predation. Fiore states unequivocally, for example, “the mean of 2.98… cardinals seen per residence is high as very few surveys were returned by people who saw no cardinals.” [3] Sure that “people only reported when they saw cardinals, thus skewing the data towards high values,” Fiore discards the mean and uses frequency quantiles instead.

Among the possible sources of participant bias Fiore cites:

“…adding counts together rather than reporting total numbers seen at one time, counting birds on someone else’s property, estimating numbers by song alone, or sending in the forms with numbers that did not exist on December 19 but that the resident had seen on some previous occasion.” [3]

Perhaps she was correct in her assessment, but it’s peculiar that Fiore never expressed a similar concern for her obviously skewed distribution of birds killed by cats—and as a result, overestimated predation levels. In short, she seems determined to lower the estimate of birds in the area while at the same time raising the estimate of birds thought to be killed by Wichita’s cats. (In fact, her thesis is littered with such maneuvering; Fiore uses nearly every instance of uncertainty to imply an impact on wildlife greater than her research actually suggests.)

Fiore’s bird collection data indicated that 7% of the birds taken were Northern Cardinals. Combining this figure with her estimates of the populations of all outdoor cats and cardinals in Wichita, she concludes, “there are at least 43,035–50,285 Northern Cardinal deaths per year due to cat predation.” [3] This corresponds to roughly 15% of her estimated cardinal population—a figure Fiore describes as “extremely conservative.”

Impact of Free-roaming Cats
Considering the numerous limitations of her study (many of which she acknowledges), Fiore seems quite comfortable extrapolating her results—arguing, for example, that “over half a million birds meet their death each year in the city of Wichita because of a cat.” [3] Of course, this figure relies on dubious estimates of the number of outdoor cats, an exaggerated predation estimate, and other factors that cast serious doubt on its accuracy.

Fiore’s confidence may come, in part, from the fact that other researchers have reported similar findings. But, as I have gone to great lengths to emphasize over the past few months, such findings rarely hold up to careful scrutiny. And sometimes, results are simply misunderstood—as when Fiore misinterprets Fitzgerald’s work:

“…several studies have been done to access [sic] the importance of birds as a percentage of total diet, as in Fitzgerald [12] who estimates birds represented 21% of cat diets.” [3]

In fact, Fitzgerald was referring not to the percentage of dietary intake, but of how often birds were found in scat or stomach contents (a distinction I explain in detail here):

“On all continents, birds are usually much less important than mammals; birds were present on average at 21 per cent frequency of occurrence, and mammals at 68 per cent. Many species are represented by just one or two individuals.” [12]

Something else Fiore overlooks is that the type of predation observed by her participants may have been largely compensatory; that is, the birds killed were of sufficiently poor health that they were unlikely to survive anyhow. Two studies have reported such findings. [7, 13] If this were the case, even her inflated estimates—however dramatic sounding—would actually have little impact on the population of Wichita’s birds.

In any case, the cardinals in the area seem to be doing fine. Between 1970 and 2000, Wichita’s human population increased 24.5%, from 276,554 to 344,284. Such an increase—accompanied by various related development activities—is generally associated with habitat loss, fragmentation, pollution, and any number of other factors that adversely affect bird populations. Including more cats. Nevertheless, data from the North American Breeding Bird Survey suggests that the number of Northern Cardinals in the area was on the increase over this period.

Wichita Cardinals Over Time
Caption: BBS Data: Northern Cardinals for Three Wichita-area Survey Routes (adapted from North American Breeding Bird Survey website)

Cat Regulations
Fiore used a telephone survey of Wichita residents to inquire about a range of pet ownership issues, as well attitudes concerning possible regulations affecting cats/cat owners. Among the questions Fiore posed to Wichita pet owners:

“At the present time dogs have to be licensed and kept on leashes. How do you feel about having cats regulated so that they would have to be licensed and confined to the owner’s property?”

Thirty-one percent of cat owners were completely opposed, while 44% said they were at least somewhat in favor—“a surprisingly high figure,” as Fiore notes. Pet owners were then asked a follow-up question:

“If it were found that unregulated cats are killing too much wildlife, would you change your opinion?”

Survey results are always tricky to interpret, and two people can often draw very different conclusions from them. Rather than focus on the responses, then, I’d like to take just a moment to focus on the question—starting with the term unregulated. Is that even necessary? How about simply cats? And what do me mean by wildlife here? And how much is too much?

Nearly half of respondents said that they would not change their minds, and Fiore sounds downright exasperated with their explanations:

“Cat owners are in denial about what their cats are doing. They seem sad over the death of a cardinal, but they refuse to take responsibility for the cat by stating ‘There is nothing I can do’ or ‘…but that’s what cats do.’ The owner of study cat 14 wrote ‘Cats are part of nature same as birds. Species come and go. I don’t think nature should be artificially regulated.’” [3]

Fiore clearly disagrees. Indeed, she tipped her hand much earlier, when, in Chapter 1, she wrote:

“If a human killed any of these birds or was caught in possession of them without a valid permit, he or she would face penalties including fines, and depending on the severity and species, possible jail time. Cats across America and their owners face no punishment.”

*     *     *

A story in the April 18, 1998 edition of The Wichita Eagle explained Fiore’s proposed project this way:

“Fiore, a graduate student at Wichita State University, will spend a year counting Wichita cats and their feathered victims for her master’s thesis. As bird populations decline, Fiore thinks it’s important to know how far cats are sinking their teeth into the feathered world… She points out that even the cutest kitty can be a remarkable hunter, although skill varies from cat to cat. But Fiore doesn’t want people to think she’s anti-cat. ‘I’m out to study the problem.’” [14]

In the same piece, Fiore brings up the Wisconsin Study (referring to its “intermediate value” of 39 million birds), and it’s revealed that she’s the vice president of the Wichita Audubon Society. Nevertheless, Fiore assures readers of her objectivity: “We’re just scientists who want to see if there’s a problem.”

Fiore’s thesis dedication, too, suggests an air of integrity and goodwill:

“This thesis is dedicated to my cat owner volunteers who made this study possible and to cat lovers and bird lovers around the world in the hopes that we can all work together to preserve native wildlife.” [3]

Having spent weeks reviewing Fiore’s work, though, I’m not buying it. In fact, I can’t help but read in her dedication an inside joke of sorts: her invitation is to preserve native wildlife; domestic cats, as she makes clear elsewhere, are not native.

In a follow-up story for The Wichita Eagle, Fiore reported her results: Wichita cats kill anywhere from 542,000 to 645,000 each year. But, according to the Eagle’s Roy Wenzl, it wasn’t the results that got some residents worked up. “Fiore’s study upset people. Not what she found. But what she did, in raising the question.” [15]

“‘I didn’t understand that,’ said Bob Gress, a cat owner, a naturalist and the director of the Great Plains Nature Center, who helped her with her study. ‘All she was doing was collecting information. I don’t think any of us should ever be afraid of the truth,’ Gress said. ‘But some people saw this as an assault on cats. Even some veterinarians seemed to resent what she was doing.’” [15]

Gress’ comment got me thinking not just about Fiore’s thesis, but also about how it’s been used—primarily by the ABC. As much as we might like to believe otherwise, scientific inquiry doesn’t happen in a vacuum; there is always a context to consider. It’s clear from her document that Fiore was well aware of the debate surrounding free-roaming cats at the time—and must have a good idea, too, of the possible implications of her work (e.g., ammunition for those who oppose free-roaming cats and TNR, the possible wholesale extermination of stray and feral cats, etc.).

And then there’s the matter of just how much truth there is in Fiore’s findings—plagued as they are by her flawed analysis and obvious bias.

Which is not to say that she (or anybody else) should be discouraged from studying such complex, controversial issues. But there is a great responsibility that comes with such endeavors. Fiore, in her thesis work, simply didn’t live up to that responsibility.

Notes
1. Fiore writes: “A researcher in southern Illinois estimated that his three house cats, which he followed for 6 years, only brought home about 50% of killed prey.” [16] As I’ve pointed out previously, this is a surprisingly common misunderstanding of George’s work. In fact, George was merely adjusting predation levels based on the fact that the “delivery area” was not always monitored: “…the study registered 50 percent of the cats’ captures—a percentage roughly corresponding to: 1, the average amount of total time the delivery area was under observation for recording prey; and 2, the number of prey items logged in the same year when the delivery area was under continuous day-and-night scrutiny, compared to the number logged (during equivalent seasonal and hourly periods) when continuously scrutinized for lesser amounts of time.” [16]

2. Fiore provides little detail regarding the application of her alternating attribution method, requiring some speculation on my part. An example, however, may prove illustrative. Consider Cats 17 and 18, which lived in the same home. During the bird collection phase of the study, Cat 17 was credited with just two kills. Cat 18, on the other hand, brought home 17 birds—clearly the more successful hunter. The question is: Did Cat 17 really kill those two birds, or are these simply the result of kills that could not be attributed to either cat?

At any time during the yearlong study, kills that could not be connected directly to a particular cat were, as Fiore explains, “alternated between cats.” Imagine if, at the time Cat 17 had 15 known kills, another kill was discovered—but this time, it was unclear which cat was responsible. That kill, then, would be attributed to Cat 17, bringing its total to 16. The next such kill would be attributed to Cat 18—effectively shifting its status from non-hunter to hunter. Two more such instances would yield the results described by Fiore: two kills for Cat 17 and 17 for Cat 18—though it should be clear that just two “mystery kills” would, using Fiore’s analysis method, create the impression that both cats are hunters. (In fact, were it not for their random numbering—Cat 17 being credited with the first “mystery kill” only because of its lower ID number—such an impression would result from just one such kill.)

To be clear: the scenario described above is speculative. But, given the impact of Fiore’s alternating attributions—increasing rather dramatically the proportion of apparent hunters—careful scrutiny is warranted.

3. Calculating the mean should be quite straightforward, of course. Fiore first calculated a daily rate for each cat by dividing that cat’s catch by the number of days in which its owner participated in the study. She then averages that rate over all 41 cats (coming up with 0.0094, compare to my 0.0076), and multiplies the result by 365 days/year.

4. Using this analysis method, a five-day collection from a three-cat household would constitute not five, but 15 analyses. Now, there’s no way of knowing that all three cats contributed to the scat collection; conversely, there’s no reason to think that just one cat contributed, as Fiore assumes.

5. At times, Fiore’s thesis reads as if it was a rebuttal to Gary Patronek’s article, Free-roaming and feral cats—their impact on wildlife and human beings, which was published around the time Fiore was conducting her research. Interestingly, had Fiore read Patronek’s paper more closely, she might not have used the mean to estimate predation rates. “The small proportion of cats with a large number of kills,” writes Patronek, “indicate that the number of animals killed per cat has a skewed distribution, which would tend to bias the mean upward.” [17]

6. Fiore is skeptical of her Pet Ownership Survey results, which indicate that 43% of cat owners keep their cats indoors (“People who interpreted this question to mean that because the cat was inside ‘most of the time’ it was an indoor cat, would be incorrect for purposes of this study.” [10]). However, as Merritt Clifton points out, it’s likely that she actually overestimates the number of outdoor cats when she “decided, based on a survey of Wichita residents, that about half of all cat-keepers allow their cats to roam, and presumed that could be extrapolated to mean that half of all pet cats roam.” This, writes Clifton, contradicts Animal People findings “that cat-keepers whose cats do not roam have, on average, from two to three times more cats than those whose cats can roam.”  [2] Further support comes from a 2003 survey that found 60% of cats were kept strictly indoors, and nearly half of those allowed outdoors were out for less than two hours each day. [18]

Literature Cited
1. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2009. p. 205–219.

2. Clifton, M. Where cats belong—and where they don’t. Animal People 2003 [cited 2009 December 24].  http://www.animalpeoplenews.org/03/6/wherecatsBelong6.03.html.

3. Fiore, C.A., The Ecological Implications of Urban Domestic Cat (Felis catus) Predation on Birds In the City of Wichita, Kansas, in College of Liberal Arts and Sciences. 2000, Wichita State University: Wichita, Kansas

4. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455.

5. Woods, M., McDonald, R.A., and Harris, S., “Predation of wildlife by domestic cats Felis catus in Great Britain.” Mammal Review. 2003. 33(2): p. 174-188.

6. Baker, P.J., et al., “Impact of predation by domestic cats Felis catus in an urban area.” Mammal Review. 2005. 35(3/4): p. 302-312.

7. Baker, P.J., et al., “Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86-99.

8. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

9. Barratt, D.G., “Predation by house cats, Felis catus (L.), in Canberra, Australia. II. Factors affecting the amount of prey caught and estimates of the impact on wildlife.” Wildlife Research. 1998. 25(5): p. 475–487.

10. Fiore, C.A. and Sullivan, K.B. (2000) Domestic Cats (Felis catus) Predation of Birds in an Urban Environmenthttp://www.carolfiore.com/Article.html Accessed July 27, 2010.

11. ABC, Domestic Cat Predation on Birds and Other Wildlife. n.d., American Bird Conservancy: The Plains, VA. www.abcbirds.org/abcprograms/policy/cats/materials/predation.pdf

12. Fitzgerald, B.M., Diet of domestic cats and their impact on prey populations, in The Domestic cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 1988, Cambridge University Press: Cambridge; New York. p. 123–147.

13. Møller, A.P. and Erritzøe, J., “Predation against birds with low immunocompetence.” Oecologia. 2000. 122(4): p. 500-504.

14. Potter, T., Counting Cats and Their Winged Prey, in Wichita Eagle, The (KS). 1998. p. 9A

15. Wenzl, R., Are You Harboring a Killer on Your Couch?, in Wichita Eagle, The (KS). 1999. p. 9A

16. George, W., “Domestic cats as predators and factors in winter shortages of raptor prey.” The Wilson Bulletin. 1974. 86(4): p. 384–396.

17. Patronek, G.J., “Free-roaming and feral cats—their impact on wildlife and human beings.” Journal of the American Veterinary Medical Association. 1998. 212(2): p. 218–226.

18. Clancy, E.A., Moore, A.S., and Bertone, E.R., “Evaluation of cat and owner characteristics and their relationships to outdoor access of owned cats.” Journal of the American Veterinary Medical Association. 2003. 222(11): p. 1541-1545.

Red Herrings, White Lies, and Blue Birds

A pair of Eastern Bluebirds in Michigan, USA. Photo courtesy Wikimedia Commons and Sandysphotos2009

As I sift through my growing collection of studies, news stories, press releases, and anything else relevant to the free-roaming cats/TNR debate, it’s not unusual for me to be diverted by a seemingly minor item—a claim, interpretation, or reference that simply doesn’t sit right with me. (The subsequent investigation of which helps explains the almost alarming rate at which the collection continues to grow.) Sometimes these diversions snowball, taking on a momentum all their own and, ultimately, evolve into their own blog post(s). Others remain largely in the background—overshadowed by more pressing issues—but are too compelling to be ignored for long.

This was the case with some comments Lepczyk et al. made about “two species of conservation concern” in their 2003 paper “Landowners and Cat Predation Across Rural-to-Urban Landscapes,” [1] which I discussed some time ago. The study, in which surveys were distributed across three southeastern Michigan landscapes (rural, suburban, and urban) corresponding to established breeding bird survey (BBS) routes, asked respondents to recall the number of birds their cat(s) brought home April through August 2000. Among the authors’ conclusions:

“The fact that both Eastern Bluebirds and Ruby-throated Hummingbirds were listed [among those killed by cats] indicates that some species of concern are being captured.” [1]

Eastern Bluebirds
Of the 137 birds (representing an estimated 23 species) identified by landowners (approximately one-third were not identified), six (4.4%) were Eastern Bluebirds. What piqued my curiosity was not the tally itself, but the authors’ subsequent comment that “the location of the three landscapes represents an area of Michigan where the species is rarest and not always identified on bird atlas survey routes.” [1]

Wait a minute. The people conducting bird counts along these routes rarely, if ever, locate Eastern Bluebirds—but the cats that live nearby managed to find at least six of them over the course of just five months? Where Lepczyk et al. see reason for concern, I see reason for (cautious) optimism: There are, as the cats demonstrated, more Eastern Bluebirds than we thought!

Just to be clear: I don’t mean to dismiss conservation concerns for uncommon or rare species. Nor am I criticizing the efforts of the many dedicated professionals and volunteers responsible for bird counts. But in trying to reconcile these seemingly contradictory findings, one can’t help but wonder: How many birds are there, really?

To find out, I began by consulting The Atlas of Breeding Birds of Michigan, the very source Lepczyk et al. cite, where, sure enough, a map indicates that no more than two Eastern Bluebirds are typically found along survey routes in the southeastern part of the state. Indeed, even in the most abundant parts of Michigan, no more than four of this species are reported. [2] But this atlas was published in 1991, more than 10 years prior to Lepczyk’s dissertation research.

To look at more recent data—and long-term trends—I referred to the website for the North American Breeding Bird Survey, where the survey is explained this way:

“The BBS is a large-scale survey of North American birds. It is a roadside survey, primarily covering the continental United States and southern Canada, although survey routes have recently been initiated in Alaska and northern Mexico. The BBS was started in 1966, and the over 3,500 routes are surveyed in June by experienced birders.”

The BBS site allows visitors to investigate trends (spanning roughly 40 years) by species, region, and survey route. What I found for Eastern Bluebirds along the three routes employed by Lepczyk et al. (49053, 49167, and 49168) was rather surprising. In all three cases, the abundance of Eastern Bluebirds trends upward—in some cases dramatically.

Eastern Bluebird BBS Data
BBS Data: Eastern Bluebirds for Three Michigan Routes (adapted from North American Breeding Bird Survey website)

Route 49053 is of particular interest for a couple reasons. First of all, it is the only one of the three for which data going back to the BBS’s inception is available, allowing the best long-term perspective. Secondly, the increase in Eastern Bluebird abundance corresponds almost perfectly to publication of The Atlas of Breeding Birds of Michigan. Between 1991 and 2000 (the year Lepczyk was conducting his research), the picture changed considerably.

The other two routes—to a lesser degree, certainly—also exhibit notable increases. Why Lepczyk referred to the Atlas rather than to this more recent data is unclear.

Bird Counts
It’s important to recognize that bird counts are not intended to quantify, in any absolute sense, the number of birds in a particular area, a point made clear on the BBS website:

“The survey produces an index of relative abundance rather than a complete count of breeding bird populations.”

In addition, the use of roadside surveys has been criticized for its potential biases. Roadside habitats may not reflect—and/or may change at rates different from—an area’s overall habitat, for example. [3] Also, a number of factors affect an observer’s ability to detect or identify a particular species. Some—sight, hearing, and training, and even clothing color, for example—are associated with the surveyors, while others (e.g., plumage, body size, coloration, and density) have to do with the birds being surveyed. [4] Rosenstock et al. suggest that such impediments raise serious questions about index counts in general:

“Measures of relative abundance derived from index counts… represent an uncertain, confounded combination of detectability and density. Given these weaknesses, index counts should not be expected to provide reliable information or a valid basis for inference.” [4]

All of which makes weighing the six Eastern Bluebirds in Lepczyk’s study against those detected along the survey routes a dodgy proposition. (Dodgier still is the more expansive claim made by Longcore et al. that Lepczyk’s work is “evidence indicat[ing] that cats can play an important role in fluctuations of bird populations.” [5])

House Sparrows
To reiterate, I’m not discounting conservation concerns for rare or protected species (the Eastern Bluebird, it should be noted—and Lepczyk et al. acknowledge—is neither “extremely rare” nor a “species of state or national concern.” [1]) I’m merely pointing out some of the complexities involved in trying to connect predation levels of one species to population levels of another.

Which brings me back to The Atlas of Breeding Birds of Michigan, where I discovered an interesting twist in this story. The Eastern Bluebird, it seems, probably peaked in Michigan during the late 1800s.

“A gradual decline occurred in the early 1900s as the House Sparrow advanced, and favorite nesting places such as wooden fenceposts and old apple orchards were eliminated.” [2]

As it turns out, House Sparrows were at the top of the list in Lepczyk’s study, making up 38% of the identified species of birds taken by cats.

“Although the species group of Sparrows could not be broken down into species, it is very likely that the dominant species observed was the House Sparrow (Passer domesitcus). Sparrows were also the most commonly observed depredated species found in England and Australia [6, 7].” [1]

While I’m not prepared to suggest that the cats’ heavy predation of House Sparrows is responsible for the increasing numbers of Eastern Bluebirds, perhaps it’s not as far-fetched as it sounds. Similar assertions have been made regarding the role of cats in the larger ecosystem (though such claims are rarely in defense of the cats).

Nature’s interconnectedness rarely makes for punchy sound bites or bumper sticker aphorisms. Then, too, such complex relationships are often overlooked, ignored, or dismissed simply because they don’t fit cleanly into one’s argument.

Literature Cited
1. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201.

2. Brewer, R., McPeek, G.A., and Adams, R.J., The atlas of breeding birds of Michigan. 1991, East Lansing, MI: Michigan State University Press.

3. Keller, C.M.E. and Scallan, J.T., “Potential Roadside Biases Due to Habitat Changes along Breeding Bird Survey Routes.” The Condor. 1999. 101(1): p. 50-57.

4. Rosenstock, S.S., et al., “Landbird Counting Techniques: Current Practices and an Alternative.” The Auk. 2002. 119(1): p. 46-53.

5. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

6. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455.

7. Barratt, D.G., “Predation by House Cats, Felis catus (L.), in Canberra, Australia. I. Prey Composition and Preference.” Wildlife Research. 1997. 24(3): p. 263–277.

Out-Sciencing the Scientists

Although it’s taken me two months to respond, it took less than two weeks for Vox Felina to come under attack by feral cat/TNR opponent Michael Hutchins, CEO and Executive Director of The Wildlife Society. In his post, Hutchins accuses me of trying to “out-science the scientists,” and refers to my critique of the essay “Critical Assessment of Claims Regarding Management of Feral Cats by Trap-Neuter-Return” as “a flawed analysis, which could have been written by a high school biology student, and not a very good one at that.”

Hutchins goes on to write:

“Unless the author, who is obviously not a trained scientist himself, can publish a strong and verifiable critique of the Longcore et al. paper in the peer-reviewed wildlife biology/ecology literature, all of his arguments must be taken with a gigantic grain of salt.”

In the weeks since Hutchins’ post, I’ve gone to some length to point out some of the more blatant instances of errors, misrepresentations, and bias in the wildlife biology/ecology literature he defends. As this seven-part series, called “The Work Speaks,” (beginning with this post) makes clear, Hutchins’ had better have plenty more salt on hand as he reviews the work of his colleagues.

In the interest of transparency, then, here is my response—as an open letter—to Hutchins’ May 3rd post:

Dear Michael,

Let me begin by introducing myself. My name is Peter J. Wolf, and I’m the writer behind the Vox Felina blog. I’d like to address some of the points you made in your May 3rd critique of my work. (In the interest of transparency, this letter will be posted in its entirety on my blog.)

By way of clarification, you referred to me in your post as “the author, who is obviously not a trained scientist himself.” In fact, my training is in mechanical engineering and qualitative research methods. That said, does it require a trained scientist to point out the numerous flaws in the anti-feral cat/TNR literature—to, if I might borrow from the title of your post, out-science the scientists? I don’t think so. Indeed, some of your colleagues—including those you defend—have set an astonishingly low bar. Consider, for example, some of the issues I’ve addressed in my recent posts:

  • When did it become acceptable to cite work one hasn’t actually read? As I pointed out in “Lost in Translation,” this seems to be surprisingly common. Nico Dauphiné and Robert Cooper, for example, are just the latest to get William George’s classic 1974 study [1] wrong. George never “found that only about half of animals killed by cats were provided to their owners,” [2] as these two authors suggest. This is an error—and an all-too-tempting-shortcut to the doubling of predation rates—that, as Fitzgerald noted 10 years ago, “has been reported widely, though it is unfounded.” [3] (Of course, if Dauphiné and Cooper aren’t reading George’s work—which they cite—I don’t imagine they’d bother with Fitzgerald’s—which they don’t even mention.)
  • Are scientists no longer expected to recognize and deal appropriately with non-normal data sets, such as the positively skewed distributions that describe prey catches, cat ownership, time spent outdoors by pet cats, and more? As I describe in “Mean Spirited,” this seems to be the exception, not the rule. Using simple averages overestimates the factor in question, and in turn, the impact of free-roaming cats on wildlife. Such errors increase rapidly when one is multiplied by another, as Christopher Lepczyk demonstrated in his PhD work. [4]
  • While we’re on the subject of statistics, what about appropriate sample sizes? This was the focus of my 27-May post, “Sample-Minded Research.” Among the examples I discussed was Kays and DeWan’s misguided conclusion that the actual “kill rate” of pet cats allowed access to the outdoors is “3.3 times greater than the rate estimated from prey brought home.” [5] This “correction” factor has been used by many [2, 6–8] as another easy multiplier, despite the fact that it’s based on the behavior of just 24 cats—12 that returned prey home, and another 12 that were observed hunting for a total of 181 hours.Even setting aside the size of the samples, their dissimilarities are striking: the cat observed the most (46.5 hours) was only a year old—the youngest of the 12 observed, and therefore likely to be the most active hunter. In addition, larger, more comparable samples would probably have revealed a profile of time spent outdoors more similar to those found in other studies [9] and [10] (thereby reducing the magnitude of Kays and DeWan’s error).
  • And finally, there’s the issue of how some of these studies are designed. Take Cole Hawkins’ PhD work, for example. Hawkins compares rodent and bird numbers between two areas, and draws conclusions—infers important causal relationships—without (1) taking into account various factors (e.g., the many differences between the two study areas) that likely affected the differences he observed, and (2) any evidence of what “pre-treatment” conditions were like. Although he concludes, “the differences observed in this study were the results of the cat’s predatory behavior,” [11] he offers no explanation for the numerous exceptions—for example, the five (of nine) species of ground-feeding birds that showed no preference for the “no-cat area” over the area with cats. Lepcyzk, too, started off his PhD work on shaky ground, asking owners of cats to recall the number and species of birds killed or injured by their cats over the previous six-month period. Five years earlier, David Barratt demonstrated that such guesswork tends to overestimate predation rates—perhaps by a factor of two or more. [12]

In your post, you write:

“One goal of the peer review process is to assess an author’s command of the existing literature and whether or not it is being cited selectively to support the author’s views, without critical evaluation of contradictory evidence.”

But the essay you defend is plagued by such “selective support.” For example, Longcore et al. trot out figures from the long-discredited (and non-peer-reviewed, by the way) Wisconsin Study. In 1994, co-author Stanley Temple told the press that their estimates “aren’t actual data; that was just our projection to show how bad it might be.” [13] But 16 years later, Longcore et al. seem to be suggesting otherwise—that these figures are actual data. By publishing these deeply flawed estimates, the authors—and, by extension, Conservation Biology—give them undeserved credibility.

Longcore et al. also give too much weight to the claim made by Baker et al. that cat predation may produce a habitat sink, [6] ignoring strong evidence that the predation observed was compensatory rather than additive [7, 14] (as well as the significant flaws in their estimates of predation rates/levels). In this case, the contradictory evidence you refer to was provided by the authors of the original study, and still, Longcore et al. fail to acknowledge it—never mind offer any critical evaluation. Indeed, they fail to acknowledge any distinction between the two types of predation—a critical point in the discussion of cat predation and its impact on wildlife.

And what about the authors’ reference to the 2003 paper by Lepczyk et al. as evidence that “cats can play an important role in fluctuations of bird populations”? [15] One might get that impression from the paper’s abstract. However, the study’s focus was—as Lepczyk et al. note themselves—on cat predation, not bird populations:

“Although our research highlights a number of important findings regarding outdoor cats, there remains many aspects that are in need of further research… conservation biologists lack data on how specific levels of cat predation depress wildlife populations and if there are thresholds at which cat densities become a biologically significant source of mortality.” [4]

Somehow, all of this (and much more) survived the peer-review process you so revere—a system whose failures have been made quite public over the past eight months or so, first, when climate scientists’ e-mail messages were hacked at a British university, and later, when the Lancet retracted a 1998 paper incorrectly linking vaccinations to autism in children.

Obviously, these are spectacular cases. But if such high-profile work can be published and circulated widely, then how much easier is it for other papers—facing far less scrutiny—to do so as well?

Scientific Publications and the Peer-Review Process
I find your criticism ironic—even hypocritical—in light of the Scientific Societies’ Statement on the Endangered Species Act you co-authored in 2006. There, you acknowledged the value of the peer-review process, but also cautioned that “proposed limitations on the use of non-peer-reviewed technical reports and other studies will weaken, not strengthen, the science employed in endangered species decisions by limiting the data available to scientists and decision-makers.” Can we not make a similar argument for critiques and reviews such as those I’ve carefully composed and compiled via Vox Felina?

It’s curious that neither you nor the editors at Conservation Biology actually dispute any of the claims I’ve made regarding the flaws in “Critical Assessment.” Instead, you call my work “vaguely scientific” and “editorializing,” ultimately dismissing it because of its lowly status as a blog (“clearly not the place that the debate should occur”).

This is quite a departure from the position you took just four years ago. Rather than advocating for rigorous scientific discourse—regardless of a particular work’s origin—you’re now putting publication above all else. Would you suggest, for example, that using means to describe highly skewed populations—because such practice has been published in peer-reviewed journals—is appropriate and acceptable? And, further, that my calling these researchers on the carpet for it—because I’ve done it via a blog—is somehow invalid? Or that the predation rates proposed in the Wisconsin Study have merit?

The same can be said for the numerous issues I’ve covered in the past several weeks (many of which I’ve outlined above): if I’m right, then I’m right; if I’m wrong, then I’m wrong. In the end, it shouldn’t matter whether these critiques are published in a peer-reviewed journal, posted at Vox Felina, or scribbled on the back of a cocktail napkin. What matters is simply whether the points I’ve made are valid or not.

It’s difficult not to see a certain irony in your immediate and wholesale dismissal of my work—based only on the first of a four-part series (and clearly “advertised” as such). You’re quick to criticize, for example, my apparent failure to “address any of the more recent work that Longcore et al. relied on, or that have subsequently been published.” I wonder: did you bother to read any of my subsequent posts, in which I addressed these points at some length? As a trained scientist, wouldn’t you want to see all the “data” before drawing your conclusions? Your post has done far more to highlight the need for Vox Felina than to discredit it.

Don’t get me wrong—I’ve nothing against criticism; indeed, that’s the very premise of Vox Felina. But, before rendering judgment, you owe it to your readers, your colleagues, and yourself to at least have all the relevant information in front of you. This, it seems to me, is a necessary first step not only for scientific discourse, but for any civil discourse.

Los Angeles Court Case
With regard to the injunction against publicly supported TNR in Los Angeles, you’re correct in noting that the case was not about the efficacy of TNR. However, there’s far more science in the administrative record than you suggest. Though the majority of the record is made up of e-mail communications, trapping permits, and the like, it is peppered throughout with various papers, reports, and numerous references to scientific literature.

To take just one example, there’s this excerpt from a letter dated March 27, 2006 by Babak Naficy, the attorney representing the Urban Wildlands Group and the American Bird Conservancy:

“A decision by the Commission to implement the TNR policy will likely result in an increase in the population of feral cats in the City by returning feral cats to the environment that otherwise would be taken into shelters, and by issuing permits to maintain feral cat colonies. Notwithstanding the goal of the project to reduce feral cat numbers, TNR programs are less effective than removal in controlling feral cat populations, [16] and consequently this shift in policy would increase the number of feral cats in the environment. As has been communicated to the Commission by my clients in the past, it is well settled that feral and domestic cats adversely affect the population of songbirds and other small animals, such as small mammals and lizards. [11] Furthermore, the scientific literature shows that TNR is not effective in decreasing the number of feral cats on a regional basis. [17] An intensive TNR program combined with cat adoption at a Florida university took 11 years to reduce a county by two-thirds (6% per year), and even then animals continued to be abandoned and added to the colony.” [18]

“Additionally, City-endorsed feral cat colonies present a severe public health risk, [19] especially to vulnerable human populations such as the homeless. Maternal exposure to toxoplasmosis, often carried by feral cats, increases risk of schizophrenia in humans. [20] Therefore, any decision that mandates return of unowned cats to the environment may increase the number of free-roaming cats in the City and will likely result in a concomitant adverse impact on the environment.”

That said, perhaps I was not clear in my post. I was not implying any direct connection between the Longcore et al. paper and the Los Angeles TNR case (e.g., that the paper itself was part of the administrative record). The point I was trying to make was that the Urban Wildlands Group—lead petitioner in the case—was not a disinterested party concerned with science for its own sake. Longcore et al. were key stakeholders—focused, it seems, more on their “message” (the timing of which was itself uncanny) than the validity of any scientific claims.

And in any event, I don’t see how the case can be so easily divorced from science. This is not about property rights or tax code. Its status as a California Environmental Quality Act (CEQA) case presupposes the possibility of “either a direct physical change in the environment or a reasonably foreseeable indirect change in the environment.” The evidence of such changes, of course, would rely on scientific research. As I say, the administrative record contains numerous claims regarding potential impacts and the studies supporting or refuting them. Whether the judge in the case allowed this material to influence his eventual decision is unknown; but it’s clear from court transcripts that he considered it quite relevant:

“Look, you put feral cats in the wild, they endanger wildlife. That is an environmental concern…”

“It doesn’t affect birds? It doesn’t affect other wildlife? A fair argument has been made that it does. A fair argument… a fair argument has been made that when you take them out of the wild—not all of them are taken out of wild—but you take 50,000 cats out of the wild and do not consider other alternatives such as euthanizing them and return them back to the wild, I would be embarrassed to stand there and argue that there is no environmental effect… so you bring them in, you neuter the them and you put them out, and they endanger other wildlife and perhaps health and a lot of other issues that come to bear, and that’s the only consideration made and that’s not a project. Please, spare me.”

“And who is to go out and if the feral cats are running wild, does the Animal Services have a program to round up a herd of cats, if that’s possible—that’s an old expression—and bring them in a neuter them and let these little kitties out to kill birds and other wildlife?”

Whether or not Los Angeles had an official TNR program in place may have been at the center of the case, but it was certainly not the whole case.

Compromise, Courage, and Leadership
As I’ve noted on Vox Felina’s About page, there are legitimate issues to be debated regarding the efficacy, environmental impact, and morality of TNR. But attempts at an honest, productive debate are hampered—if not derailed entirely—by the dubious claims so often put forward by TNR opponents. Exactly the sort of claims I’ve attempted to untangle over the past several weeks.

But from what I’ve read of your work, you don’t seem interested in such a debate, and even less interested in finding common ground:

“Cooperation and compromise, no matter what the cost, is not courageous leadership.” [21]

Perhaps it’s impressive as rhetoric, but your comments strike me as somewhat hypocritical (your attempt to make a virtue of the same ideological inflexibility you dismiss in the animal rights community), misguided, and, in the end, simply unhelpful. More worrisome, however, is your willingness to let your ideology blind you to the numerous errors in the work you so vigorously defend.

Michael, how can you expect so much courage and leadership from your colleagues when you demand so little honesty and integrity?

Peter J. Wolf
www.voxfelina.com

Literature Cited
1. George, W., “Domestic cats as predators and factors in winter shortages of raptor prey.” The Wilson Bulletin. 1974. 86(4): p. 384–396.

2. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2009. p. 205–219.

3. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

4. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201.

5. Kays, R.W. and DeWan, A.A., “Ecological impact of inside/outside house cats around a suburban nature preserve.” Animal Conservation. 2004. 7(3): p. 273-283.

6. Baker, P.J., et al., “Impact of predation by domestic cats Felis catus in an urban area.” Mammal Review. 2005. 35(3/4): p. 302-312.

7. Baker, P.J., et al., “Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86-99.

8. van Heezik, Y., et al., “Do domestic cats impose an unsustainable harvest on urban bird populations? Biological Conservation. 143(1): p. 121-130.

9. ABC, Human Attitudes and Behavior Regarding Cats. 1997, American Bird Conservancy: Washington, DC. http://www.abcbirds.org/abcprograms/policy/cats/materials/attitude.pdf

10. Clancy, E.A., Moore, A.S., and Bertone, E.R., “Evaluation of cat and owner characteristics and their relationships to outdoor access of owned cats.” Journal of the American Veterinary Medical Association. 2003. 222(11): p. 1541-1545.

11. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. 1998, Texas A&M University

12. Barratt, D.G., “Predation by house cats, Felis catus (L.), in Canberra, Australia. II. Factors affecting the amount of prey caught and estimates of the impact on wildlife.” Wildlife Research. 1998. 25(5): p. 475–487.

13. Elliott, J., The Accused, in The Sonoma County Independent. 1994. p. 1, 10

14. Møller, A.P. and Erritzøe, J., “Predation against birds with low immunocompetence.” Oecologia. 2000. 122(4): p. 500-504.

15. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

16. Andersen, M.C., Martin, B.J., and Roemer, G.W., “Use of matrix population models to estimate the efficacy of euthanasia versus trap-neuter-return for management of free-roaming cats.” Journal of the American Veterinary Medical Association. 2004. 225(12): p. 1871-1876.

17. Foley, P., et al., “Analysis of the impact of trap-neuter-return programs on populations of feral cats.” Journal of the American Veterinary Medical Association. 2005. 227(11): p. 1775-1781.

18. Levy, J.K., Gale, D.W., and Gale, L.A., “Evaluation of the effect of a long-term trap-neuter-return and adoption program on a free-roaming cat population.” Journal of the American Veterinary Medical Association. 2003. 222(1): p. 42-46.

19. Patronek, G.J., “Free-roaming and feral cats—their impact on wildlife and human beings.” Journal of the American Veterinary Medical Association. 1998. 212(2): p. 218–226.

20. Brown, A.S., et al., “Maternal Exposure to Toxoplasmosis and Risk of Schizophrenia in Adult Offspring.” Am J Psychiatry. 2005. 162(4): p. 767-773.

21. Hutchins, M., “Animal Rights and Conservation.” Conservation Biology. 2008. 22(4): p. 815–816.

The Work Speaks—Part 7: Leaky Sink

In April, Conservation Biology published a comment authored by Christopher A. Lepczyk, Nico Dauphiné, David M. Bird, Sheila Conant, Robert J. Cooper, David C. Duffy, Pamela Jo Hatley, Peter P. Marra, Elizabeth Stone, and Stanley A. Temple. In it, the authors “applaud the recent essay by Longcore et al. (2009) in raising the awareness about trap-neuter-return (TNR) to the conservation community,” [1] and puzzle at the lack of TNR opposition among the larger scientific community:

“…it may be that conservation biologists and wildlife ecologists believe the issue of feral cats has already been studied enough and that the work speaks for itself, suggesting that no further research is needed.”

In fact, “the work”—taken as a whole—is neither as rigorous nor as conclusive as Lepczyk et al. suggest. And far too much of it is plagued by exaggeration, misrepresentations, errors, and obvious bias. In Part 6 of this series, I critiqued Christopher Lepczyk’s paper Landowners and cat predation across rural-to-urban landscapes, published in 2003. Here, I’m going to examine two studies conducted by Philip J. Baker and various collaborators.

The Studies
In the first study, Baker et al. distributed questionnaires to 3,494 households across a 4.2 km2 area of northwest Bristol (UK), and used responses to estimate cat ownership and predation levels (via prey returned home). [2] This work served as a pilot study for the subsequent study.

The second study, conducted August 2005–July 2006, was also conducted in Bristol. Added to the original 4.2 km2 site were nine 1 km2 sites. The researchers used very similar sampling methods, but, based on results of their pilot study, had somewhat more specific objectives:

  1. To quantify cat density
  2. To quantify the various species of birds killed by cats.
  3. To estimate the impact of cat predation by species and site.
  4. To determine whether the predation observed was compensatory or additive. [3]

Sources and Sinks
Among the authors’ conclusions from the pilot study was that, at least for three of the ten bird species surveyed:

“…it is possible that cat predation was significantly affecting levels of recruitment and creating a dispersal sink for more productive neighboring areas.” [2]

Dispersal sinks or habitat sinks, are patches of low-quality habitat that are unable to sustain a population of a particular species were it not for immigration from higher quality habitat patches—called sources—nearby. So, what Baker et al. are suggesting is that predation by cats may be extensive enough to deplete populations of certain bird species at their study site, such that at least some of the birds observed there were immigrants from nearby habitat.

But the authors also point out that, “despite occurring at very high densities, the summed effects on prey populations appeared unlikely to affect population size for the majority of prey species.” [2] And even for House sparrows, which were among the three species of concern (and, apparently, in decline throughout the UK’s urban areas), Baker et al. note that their “numbers appear to be stable in Bristol as a whole.”

So, is the area a habitat sink or not?

A cursory look at the theory and empirical measurement of source-sink dynamics reveals great complexity. Variations across time and geography must be taken into account—the ebb and flow of local populations might easily be overlooked or misunderstood by applying a short time horizon (i.e., 12 months) and arbitrary boundaries (i.e., those that define the study site). Annual rainfall, for example, can dramatically influence yearly population levels on a local scale. And it’s been shown that source-sink dynamics can occur over distances of 60–80 km. [4] In fact, the determination of sinks and sources in the field can be problematic enough that sources sometimes appear to be sinks and vice-versa. [5]

Given the complex nature of source-sink dynamics, the suggestion by Baker et al. that cat predation may be creating a habitat sink seems rather premature. Such assertions—despite the requisite disclaimers (the authors note only that “it is possible”)—tend to attract attention and gain traction. Longcore et al., for example, cited the pilot study in their 2009 essay, “Critical Assessment of Claims Regarding Management of Feral Cats by Trap-Neuter-Return.” [6]

Of greater interest to me, though, are the assumptions Baker et al. used to estimate the impact of cat predation.

Counting Cats and Counting Birds
In both studies, the authors quantified the impact of cat predation on bird populations by comparing different levels of predation with different bird densities. Their maximum impacts, for example, assumed that all cats were hunters—despite the fact that 51–74% of the cats included in the two studies brought home no prey at all—and that bird productivity was zero (i.e., no young birds survive to adulthood). As the authors admit:

“This was clearly not realistic, as the estimated maximum numbers of birds killed typically exceeded breeding density and productivity combined, such that the prey populations studied would probably have gone extinct rapidly at a local level or acted as a major sink for birds immigrating from neighbouring areas.” [3]

But how realistic are their other estimates?

A detailed examination of a single species at a one site (taken from the second study, for which such information is available) illustrates some flaws. I looked at House sparrows for the 1 km2 site designated as ST5277. Here, 18 participants reported that their 22 cats returned a total of 30 prey items, nine of which were birds (two of them “unidentified”). Of the birds returned home, two were House sparrows.

When it comes to estimating impacts, though, Baker et al. use figures of 332–1,245 House sparrows killed by the cats of ST5277. The maximum, we already know, is “not realistic,” but even the minimum seems awfully high. So, where are these birds coming from?

To start with, two adjustments have to be made to the original predation figure. First, the two unidentified birds are “distributed” across the categories of bird species that were identified. Then, we have to account for participant drop-out; not all of the 22 cats were surveyed for the entire year of the study. Now we’re up to an average of 8.7 House sparrows brought home annually by the cats at this site.

But of course there are more than 22 cats at ST5277. Baker et al. estimate that there are 314 of them (although we know very little about the factors that affect their hunting ability and success—for example, their access to the outdoors, age, etc.). We also know that only seven of the 22 cats included in the study brought home prey. In other words, 32% of the cats surveyed were documented hunters. Based on these numbers, then, we can estimate the yearly predation rate of House sparrows at ST5277 to be roughly 125—well short of the minimum proposed by Baker et al. (and just a quarter of their intermediate rate).

There are some minor differences between their method for estimating predation rates and mine. For the most part, though, the “missing” sparrows can be found in the authors’ use of a correction factor (3.3) proposed by Kays and DeWan to account for prey killed but not returned home. [7] Undoubtedly, cats fail to bring home all the prey they catch (though they also undoubtedly bring home prey they didn’t kill), but there is good reason to doubt Kays and DeWan’s “correction.” Among the flaws in their analysis were small, dissimilar samples of cats, and a failure to account for highly skewed data sets.

So, even setting aside the complexities of source-sink dynamics, these inflated predation rates, combined with the fact that “the estimates of breeding density presented in this manuscript should be regarded as minima,” [3] raise serious doubts about whether the site is in fact a habitat sink (or, if so, to what extent).

Compensatory and Additive Predation
As I’ve discussed previously, even accurately predicted levels of predation can be deceptive. There’s compensatory predation (in which prey would have died even in the absence of a particular predator, due to illness, starvation, other predators, etc.) and additive predation (in which healthy prey are killed). It’s the difference between, as Beckerman et al. put it, the “doomed surplus hypothesis” and the “hapless survivor hypothesis.” [8]

When it comes to relating predation to population levels, it’s critical to understand the difference, and know the extent to which each type is occurring.

To get at this critical issue, Baker et al. compared the physical attributes (e.g., muscle mass score, mean fat score, etc.) of 86 birds killed by collisions (e.g., with cars, windows, etc.) to those of 48 birds killed by cats. Although the authors point out, “the relationship between body mass and quality (i.e., likelihood of long-term survival and therefore reproductive potential) in passerines is complex,” they nevertheless conclude that the birds killed by cats “were likely to have had poor long-term survival prospects.” [3] (An earlier study comparing spleen mass arrived at essentially the same conclusion: that birds killed by cats “often have a poor health status.” [9])

Still, Baker et al. express caution about their findings:

“The distinction between compensatory and additive mortality does, however, become increasingly redundant as the number of birds killed in a given area increases: where large numbers of prey are killed, predators would probably be killing a combination of individuals with poor and good long-term survival chances. The predation rates estimated in this study would suggest that this was likely to have been the case for some species on some sites.”

But their inflated predation rates and low estimates of breeding density combine to diminish the apparent level of compensatory predation. Were these estimates adjusted to better reflect the conditions at the site, the “redundancy” the authors refer to would be reduced considerably.

*     *     *

It’s not clear why Longcore et al. cited the pilot study their essay, but left out any mention of the much larger subsequent study. Perhaps it was just a matter of timing—“Cats About Town” was published in August of 2008, while “Critical Assessment” was published in August of 2009. A year is not much time in the world of scientific journals, and it’s possible that the two manuscripts more or less crossed in the mail. On the other hand, the pilot study fits more neatly into the argument put forward by Longcore et al.—an argument that doesn’t even recognize the distinction between compensatory and additive predation.

Of course, Baker et al. did themselves no favors, either. By using inflated predation rates—the result of some peculiar, unjustified assumptions—they virtually buried the most important findings of their study.

References
1. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201.

2. Baker, P.J., et al., “Impact of predation by domestic cats Felis catus in an urban area.” Mammal Review. 2005. 35(3/4): p. 302-312.

3. Baker, P.J., et al., “Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86-99.

4. Tittler, R., Fahrig, L., and Villard, M.-A., “Evidence of Large-Scale Source-Sink Dynamics and Long-Distance Dispersal among Wood Thrush Populations.” Ecology. 2006. 87(12): p. 3029-3036.

5. Runge, J.P., Runge, M.C., and Nichols, J.D., “The Role of Local Populations within a Landscape Context: Defining and Classifying Sources and Sinks.” The American Naturalist. 2006. 167(6): p. 925-938.

6. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

7. Kays, R.W. and DeWan, A.A., “Ecological impact of inside/outside house cats around a suburban nature preserve.” Animal Conservation. 2004. 7(3): p. 273-283.

8. Beckerman, A.P., Boots, M., and Gaston, K.J., “Urban bird declines and the fear of cats.” Animal Conservation. 2007. 10(3): p. 320-325.

9. Møller, A.P. and Erritzøe, J., “Predation against birds with low immunocompetence.” Oecologia. 2000. 122(4): p. 500-504.

Learning Your ABC

According to an AP story posted on MSNBC, city officials in Barre, VT, are considering a leash law for cats—effectively prohibiting them from roaming. Such stories tend to vary only in their specifics; quotes from embattled citizens, and feline references that are more dismissive than clever (e.g., in Barre, the debate “sparked a hissing match”) are pretty much a given. And, more often than not, there’s a statement from the American Bird Conservancy (ABC) about the threat free-roaming cats pose to wildlife. This story was no exception:

“Scientists estimate that free-roaming cats kill hundreds of millions of birds, small mammals, reptiles and amphibians each year,” the Virginia-based American Bird Conservancy, which runs a “Cats Indoors!” campaign, says on its website. “Cat predation is an added stress to wildlife populations already struggling to survive habitat loss, pollution, pesticides, and other human impacts.”

Although I don’t know anybody who would argue with ABC’s second point, that first one bears closer inspection.

I discussed a similar claim by ABC’s Senior Policy Advisor, Steve Holmer, in one of my first Vox Felina posts. In January, Holmer told the Los Angeles Times:

“The latest estimates are that there are about . . . 160 million feral cats [nationwide] . . .  It’s conservatively estimated that they kill about 500 million birds a year.”

Late last year, an article in Audubon Magazine had published nearly identical figures, citing ABC as its source. [1]

The feral cat estimate comes from a conference paper written by Nico Dauphiné and Robert J. Cooper, available for download via the ABC website. When I pressed Holmer about the authors’ “creative accounting,” he backed off, assuring me that ABC’s materials “should now say”:

There are currently 88 million pet cats in the U.S. according to a pet trade association, and that number is growing. In addition, it is estimated that there may be 60–100 million free-ranging feral cats in the U.S., and that these cats may collectively kill more than one million birds each day. Reducing this mortality even a small amount could potentially save millions of birds each year.

I never received a reply, though, to my inquiries about that “more than one million birds each day” claim. Such incidents are, unfortunately, not uncommon; when it comes to assertions about cat predation and its impact on wildlife, ABC has a rich—and rather shameful—history.

Cats Indoors!
Holmer’s comment to the L.A. Times is just one example of ABC’s concerted effort to use the (largely unquestioning) media in getting their message out. Last year, at a news conference about the “The U.S. State of the Birds” report, ABC’s Darin Schroeder told the press, “education is urgently needed to make the public aware of the toll of pet cats.” Which is precisely what ABC’s Cats Indoors! campaign—launched in 1997—aims to do.

The question is, what kind of education is the public getting from ABC?

  • A 1997 report by ABC claimed, “extensive studies of the feeding habits of domestic, free-roaming cats… show that approximately… 20 to 30 percent [of their diet] are birds.” [cited in 2] In fact, as Ellen Perry Berkeley points out in her book, TNR Past Present and Future: A history of the trap-neuter-return movement, the 20–30% figure was not based on “extensive studies” at all. [2]ABC’s Linda Winter, writing to Berkeley, cited just three sources. Two of them—the now-classic “English village” study by Peter Churcher and John Lawton, and the “Wisconsin Study” by John Coleman and Stanley Temple—have been widely discredited. [3–5] And the third, Mike Fitzgerald’s contribution to “Diet of domestic cats and their impact on prey populations,” [6] was misinterpreted and/or misrepresented by ABC. (As Berkeley notes, Fitzgerald’s data “would put birds, as a portion of the diet of cats, at roughly 7 to 10.5 percent—nowhere near the ‘20 to 30 percent’ figures unleashed on the unscientific public by ABC!” [2])
  • Winter, director of Cats Indoors! (assuming she’s still at ABC; their website does not list her among the staff), and ABC president George Fenwick were among those thanked “for helpful and constructive reviews” in the Acknowledgements section of Christopher Lepczyk’s 2003 paper, “Landowners and cat predation across rural-to-urban landscapes.” As I detailed in my previous post, Lepczyk’s study is flawed both in terms of its method and analysis, and his predation estimates are highly inflated as a result. The fact that Winter and Fenwick were involved in such as study—at any level—raises questions about ABC’s credibility (and its possible influence on research outcomes).
  • In 2004, Winter misrepresented the results of a survey commissioned by ABC. In “Trap-neuter-release programs: The reality and the impacts,” published in the Journal of the American Veterinary Medical Association, she suggested, “66% of cat owners let their cats outdoors some or all of the time.” [7]In fact, the survey indicated that “35% keep their cats indoors all of the time” and “31% keep them indoors mostly with some outside access.” [9] While Winter’s claim isn’t exactly untrue, it certainly paints a very different picture: rather than one-third, two-thirds of cats are free-roaming. Which, apparently, is exactly how Dauphiné and Cooper read it, combining this with an inflated figure for the number of feral cats to come up with their estimate of “117–157 million free-ranging cats in the United States.” [8] (It’s difficult not to see a certain coziness here: Dauphiné and Cooper citing Winter’s “interpretation” of her own survey results, and Holmer’s reliance on Dauphiné and Cooper’s conference paper.
  • To this day, ABC refers to the highly-criticized Wisconsin Study in its brochure Domestic Cat Predation on Birds and Other Wildlife: “Researchers… estimated that rural free-roaming cats kill at least 7.8 million and perhaps as many as 217 million birds a year in Wisconsin. Suburban and urban cats add to that toll.” [9]And, despite Berkeley’s efforts to untangle their erroneous dietary figures, ABC has backed off only slightly: “In an ongoing, but unpublished, study of cat prey items including stomach contents, scat analysis, observations of kills, and prey remains, birds were 19.6% of 1,976 prey captured by 78 outdoor cats (Temple, S.A, Univ. of WI, personal communication, 1/22/04).”

    [Note: Download Laurie D. Goldstein’s Addressing the Wisconsin Study for a comprehensive critique of this work.]

*     *     *

Don’t get me wrong; I’m all for keeping cats indoors. But what about the feral and stray cats out there—what happens to them? Here, ABC doesn’t seem to have a lot of answers. At least not any they’re willing to be up-front about.

In fact, by disseminating information that is at best misleading—and often, just plain wrong—ABC is doing whatever it can to shape policy in such a way that many of these cats will, one way or another, be killed. Intentional or not, Cats Indoors! has become a kind of Trojan horse for those determined to eliminate all free-roaming cats. Attention can very quickly shift from the impact of a proposed leash law, for example, to the “cat problem” in general.

Although it’s packaged as sound advice for cat owners, the Cats Indoors! campaign has probably had a far greater (deadly) impact on unowned cats than on pet cats.

References
1. Williams, T., Felines Fatale, in Audubon Magazine. 2009, National Audubon Society: New York, NY. http://www.audubonmagazine.org/incite/incite0909.html

2. Berkeley, E.P., TNR Past present and future: A history of the trap-neuter-return movement. 2004, Bethesda, MD: Alley Cat Allies.

3. Goldstein, L.D., O’Keefe, C.L., and Bickel, H.L. Addressing “The Wisconsin Study”. 2003.  http://www.straypetadvocacy.org/html/wisconsin_study.html.

4. Clifton, M. Where cats belong—and where they don’t. Animal People 2003. http://www.animalpeoplenews.org/03/6/wherecatsBelong6.03.html.

5. Patronek, G.J., “Free-roaming and feral cats—their impact on wildlife and human beings.” Journal of the American Veterinary Medical Association. 1998. 212(2): p. 218–226.

6. Fitzgerald, B.M., Diet of domestic cats and their impact on prey populations, in The Domestic cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 1988, Cambridge University Press. p. 123–147.

7. Winter, L., “Trap-neuter-release programs: the reality and the impacts.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1369-1376.

8. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2009. p. 205–219.

9. ABC, Domestic Cat Predation on Birds and Other Wildlife. n.d., American Bird Conservancy: The Plains, VA. www.abcbirds.org/abcprograms/policy/cats/materials/predation.pdf

The Work Speaks—Part 6: Pain by Numbers

In April, Conservation Biology published a comment authored by Christopher A. Lepczyk, Nico Dauphiné, David M. Bird, Sheila Conant, Robert J. Cooper, David C. Duffy, Pamela Jo Hatley, Peter P. Marra, Elizabeth Stone, and Stanley A. Temple. In it, the authors “applaud the recent essay by Longcore et al. (2009) in raising the awareness about trap-neuter-return (TNR) to the conservation community,” [1] and puzzle at the lack of TNR opposition among the larger scientific community:

“…it may be that conservation biologists and wildlife ecologists believe the issue of feral cats has already been studied enough and that the work speaks for itself, suggesting that no further research is needed.”

In fact, “the work”—taken as a whole—is neither as rigorous nor as conclusive as Lepczyk et al. suggest. And far too much of it is plagued by exaggeration, misrepresentations, errors, and obvious bias. In Part 5 of this series, I critiqued Cole Hawkins’ 1998 PhD dissertation. Here, I’m going to untangle some of Lepczyk’s own PhD work: Landowners and cat predation across rural-to-urban landscapes, published in 2003.

The Study
In this study, surveys were distributed across three southeastern Michigan landscapes (rural, suburban, and urban) corresponding to established breeding bird survey (BBS) routes. [2] Among the survey questions:

“If you or members of your household own cats that are allowed access to the outside, approximately how many dead or injured birds a week do all the cats bring in during the spring and summer months (April through August) (0, 1, 2–3, 4–5, 6–7, 8–9, 10–15, 16–20, more than 20)?”

Based on 968 surveys returned from 1654 private landowners (a decent response rate of 58.5%), Lepczyk et al. conclude:

“Across the three landscapes there were ~800 to ~3100 cats, which kill between ~16,000 and ~47,000 birds during the breeding season, resulting in a minimum of ~1 bird killed/km/day.”

Increasing Uncertainty
How do Lepczyk and his collaborators arrive at these figures? It’s not entirely clear, actually. Despite numerous attempts, I’ve been unable to follow all of their calculations. However, using their data, I developed my own estimate: 1,119 outdoor cats, 511 of which were reported to be successful hunters.

Using this figure, I then summed across all three landscapes the birds killed or injured, plus those killed or injured by non-respondents’ hunting cats (based on the ratio of hunters to outdoor cats owned by respondents, or about 50%). The resulting estimate is 15,856 birds killed over the 22-week breeding season—close to the low estimate suggested by Lepczyk et al., but just a third of their maximum.

So, why the discrepancy?

One reason is that, at least for some of their estimates, Lepczyk et al. assumed that every landowner who didn’t respond to the survey owned outdoor cats. This, despite their survey results, which indicated that only about one-third of landowners fell into this category.

But the authors go further, generating predation estimates based on pure speculation, specifically that “non-respondents have 150% the number of outdoor cats as respondents.” [2] It should be noted that Lepczyk et al. also ran another scenario in which non-respondents had half the outdoor cats as did respondents—but, again, in both cases they assume that every non-respondent owned outdoor cats.

As a result of this approach, the authors end up in some strange territory: the estimated number of cats owned by non-respondents (based on the assumptions described above) far exceeds the number owned by respondents—by more than a two-to-one margin, in some cases. If the greatest impacts are going to be attributable to non-respondents, then what’s the point of doing the survey in the first place? There are accepted methods by which one can manage uncertainty—statistical analysis, confidence intervals, and the like. What Lepczyk et al. have done serves just one purpose: to inflate apparent predation rates.

Skewed Distributions
In addition to the flaws described above, there are some fundamental errors in the way the authors handle their data. Like so many others, Lepczyk et al. ignore the fact that their data is not normally distributed:

  1. Lepczyk et al. use the average number of birds killed/cat to calculate the total number of bids killed for each of the three landscapes. As I discussed previously), this is a highly positively skewed distribution—using a simple average, therefore, greatly overestimates the cats’ impact (by as much as a factor of two).
  2. A similar error is made when the authors use an average to describe the number of outdoor cats owned by each landowner. Again, because this is a skewed distribution, their use of a simple average exaggerates the extent of predation.
  3. The two inflated figures described in (1) and (2) are multiplied together, further inflating estimated predation rates.

Barratt has suggested that “median numbers of prey estimated or observed to be caught per year are approximately half the mean values, and are a better representation of the average predation by house cats based on these data.” [3] Accounting for the first point alone, then, my estimate is reduced to 8,000 birds killed over the 22-week breeding season.

Accounting for the second point is somewhat trickier. For one thing, we don’t know what constitutes an outdoor cat here—the survey simply asked respondents if they owned cats “that are allowed access to the outdoors.” [2] However, we do know the results of a 2003 survey, which indicated that nearly half of the cats with outdoor access were outside for two or fewer hours a day. And 29% were outdoors for less than an hour each day. [4] Although these figures almost certainly reflect owners in urban and suburban landscapes more than those in rural landscapes, it’s clear that a simple yes-or-no question on the subject is insufficient. Indeed, such a question will invariably overestimate the number of “outdoor cats”—which in turn overestimates predation rates.

This, coupled with the error inherent in using a simple average, pushes predation estimates lower. And the third point reduces those estimates further still. Taken together, these corrections could put my estimate closer to 4,000 birds. More important, the upper estimate proposed by Lepczyk et al.—47,000 birds—could easily be 10 times too high.

The Small Print
Despite their inflated figures, Lepczyk et al. suggest—rather absurdly, in light of the substantial flaws described above—that perhaps their estimates are actually too conservative:

“One caveat to our study is that landowners may have underestimated the number of cats they allow access to the outside. Such a result was found in a similar study of landowners in Wisconsin (Coleman and Temple, 1993).” [1] (Note: After reviewing “Rural Residents’ Free-Ranging Domestic Cats: A Survey,” [5] I’ve found no evidence of such a result.)

“… we found that a very common volunteered response among landowners that had no outdoor cats was that either their neighbors owned outdoor cats or that feral cats were present in the vicinity of their land… [suggesting] that at least some landowners under reported or chose not to report the number of outdoor cats they owned.”

But what about their reports of birds brought home killed or injured—how trustworthy were those? After all, the survey (mailed during the first week of October) asked respondents to recall the number of birds their cat(s) brought home April through August. Surely, there was a lot of guesswork involved. In fact, David Barratt found this kind of guesswork to overestimate predation rates. In a study published five years prior to “Landowners and Cat Predation,” Barratt concluded, “predicted rates of predation greater than about ten prey per year generally over-estimated predation observed.” [3]

The two studies cannot be compared directly for a number of reasons, but by way of comparison, the average predation rate used by Lepczyk et al. is approximately 31 birds/cat for the 22-week breeding season. Using Barratt’s work, in which the “heaviest” six continuous months correspond to about 58% of yearly prey totals, [6] I converted this to a yearly rate of 53 birds/cat/year. Barratt has shown that the actual predation rate, at this level, is less than half the rate predicted by cat owners. In other words, predictions of 50 birds/year generally correspond to catches closer to 25 birds/year.

While Lepczyk et al. emphasize the potential for under-estimating predation levels, they never consider the risk of over-estimating these levels—or their most obvious potential source of error: landowners’ recollections of birds killed. The authors question respondents’ reports of outdoor cats, but accept without question their reports of birds injured or killed over the previous six-month period. And, as Barratt indicated, such reports can be inflated by a factor of two or more!

Something else I find troubling comes, of all places, from the Acknowledgements section. Among those thanked “for helpful and constructive reviews” are American Bird Conservancy (ABC) president George Fenwick and Linda Winter, director of ABC’s Cats Indoors! campaign. It’s not clear how Fenwick and Winter contributed to the final paper, but their involvement on any level raises questions about possible bias. Certainly, Winter has credibility issues when it comes to “research” about the impact of free-roaming cats on birds, as I’ve already described (see also pp. 18–24 of TNR Past present and future: A history of the trap-neuter-return movement [7]).

*     *     *

The same year Lepczyk’s paper was published, the American Veterinary Medicine Association held an Animal Welfare Forum “devoted to the management of abandoned and feral cats.” [8] In attendance were more than 200 veterinarians, animal control officials, wildlife conservationists, and animal advocates—each with a different perspective on feral cats in general and TNR in particular.

In welcoming this diverse group, then-President-Elect Bonnie Beaver recognized the range of contentious issues before them:

“Feral cats evoke hot debates about ecological issues, individual cat welfare, human responsibilities, intercat disease transmission, humaneness, zoonosis control, and management and dissolution of unowned cats.” [8]

Amidst the “hot debate,” though, Beaver was optimistic:

“We will not always agree, but we will come away with increased knowledge and a renewed commitment to work for the welfare of all the animals with which we share the earth” [8]

While I tend to share Beaver’s optimism, I think the debate is hurt—if not derailed entirely—by the publication of research aimed not at increasing our collective knowledge, but rather at supporting a particular position. Like Cole Hawkins’ dissertation, “Landowners and Cat Predation” is, at best, an interesting pilot study for subsequent work. And yet, it’s widely—and uncritically—cited in the feral cat/TNR literature. Longcore et al., for example, refer to it as “evidence [indicating] that cats can play an important role in fluctuations of bird populations,” [9] despite the fact that Lepczyk et al. don’t actually address the issue of bird populations at all. More recently, Dauphiné and Cooper use the inflated predation rate suggested by Lepczyk et al. (along with rates proposed by other researchers) to arrive at their “billion birds” figure. [10]

The method employed in “Landowners and Cat Predation”—asking owners of cats to recall the number and species of birds over the previous six-month period—invites overestimation from the very outset. Lepczyk et al. then inflate these numbers through both careless (e.g., using averages to describe skewed data) and deliberate (e.g., assuming all non-respondents owned cats—perhaps 50% more than respondents did) means. Rather than getting us any closer to the truth about cat predation, this study only obscured it further.

Worse, it’s been packaged and sold—and subsequently “bought”—as rigorous science, thereby giving it an undeserved legitimacy. Such efforts are impediments to knowledge and understanding—and therefore, to progress.

References
1. Lepczyk, C.A., et al., “What Conservation Biologists Can Do to Counter Trap-Neuter-Return: Response to Longcore et al.” Conservation Biology. 2010. 24(2): p. 627-629.

2. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201.

3. Barratt, D.G., “Predation by house cats, Felis catus (L.), in Canberra, Australia. II. Factors affecting the amount of prey caught and estimates of the impact on wildlife.” Wildlife Research. 1998. 25(5): p. 475–487.

4. Clancy, E.A., Moore, A.S., and Bertone, E.R., “Evaluation of cat and owner characteristics and their relationships to outdoor access of owned cats.” Journal of the American Veterinary Medical Association. 2003. 222(11): p. 1541-1545.

5. Coleman, J.S. and Temple, S.A., “Rural Residents’ Free-Ranging Domestic Cats: A Survey.” Wildlife Society Bulletin. 1993. 21(4): p. 381–390.

6. Barratt, D.G., “Predation by House Cats, Felis catus (L.), in Canberra, Australia. I. Prey Composition and Preference.” Wildlife Research. 1997. 24(3): p. 263–277.

7. Berkeley, E.P., TNR Past present and future: A history of the trap-neuter-return movement. 2004, Bethesda, MD: Alley Cat Allies.

8. Kuehn, B.M. and Kahler, S.C. The Cat Debate. JAVMA Online 2004 November 27, 2009 [accessed 2009 December 24].  http://www.avma.org/onlnews/javma/jan04/040115a.asp.

9. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

10. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2010. p. 205–219.

The Work Speaks—Part 5: Jumping to Conclusions

In April, Conservation Biology published a comment authored by Christopher A. Lepczyk, Nico Dauphiné, David M. Bird, Sheila Conant, Robert J. Cooper, David C. Duffy, Pamela Jo Hatley, Peter P. Marra, Elizabeth Stone, and Stanley A. Temple. In it, the authors “applaud the recent essay by Longcore et al. (2009) in raising the awareness about trap-neuter-return (TNR) to the conservation community,” [1] and puzzle at the lack of TNR opposition among the larger scientific community:

“…it may be that conservation biologists and wildlife ecologists believe the issue of feral cats has already been studied enough and that the work speaks for itself, suggesting that no further research is needed.”

In fact, “the work”—taken as a whole—is neither as rigorous nor as conclusive as Lepczyk et al. suggest. And far too much of it is plagued by exaggeration, misrepresentations, errors, and obvious bias. In Part 4 of this series, I discussed how feral cat/TNR researchers often misuse averages to characterize skewed distributions, and how that error overestimates the impact of free-roaming cats on wildlife.

For the next few posts, I’m going to critique three of the studies most often cited by these researchers, starting with Cole Hawkins’ 1998 PhD dissertation, Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. I mentioned Hawkins’ dissertation previously, but only briefly. Here, I’ll take a closer look, paying particular attention to how he gets from his results to his rather dubious conclusions.

The Study
Hawkins’ two-year study was conducted in Alameda County, CA, spread across two adjacent parks. He started by designating a “cat area” (where, nearby, free-roaming cats were being fed) and a “no-cat area” (where no cats were being fed), and then designated “rodent grids” (nine locations used for trapping and counting rodents) and walking transects (from which bird surveys were conducted) in each area. Hawkins then compared the number of birds and rodents detected in the two areas.

Among Hawkins’ conclusions:

“The differences observed in this study were the results of the cat’s predatory behavior.” [2] (It should be noted that Hawkins tempered this assertion in his 1999 article summarizing the work: “The differences observed in this study may have been due to the cats’ predatory behavior.” [3] (italics mine))

And this:

“The presence of cats in this study area already has caused a shift in the composition of the rodent community; it is possible that a shift in the larger biotic community could follow.”

And, finally:

“It is not prudent to manage for wildlife and allow cat feeding in the same parks.”

Unfair Comparisons
But Hawkins’ findings are insufficient to supports such claims; indeed, his methodology doesn’t allow for them. Hawkins has no idea what the cat area was like prior to his arrival; he merely assumes the populations of birds and rodents would have been identical to those found at the no-cat area, and makes his comparisons accordingly. In fact, there are a number of factors that indicate that the two areas are not as comparable as Hawkins suggests:

  • The cat area was almost a peninsula, with a lake on one side and a residential area (within 0.5 km) on the other. The no-cat area, on the other hand, was located largely in the interior of the parks.
  • Hawkins notes that there were more people in the cat area (of­ten twice as many as were observed at the no-cat area), but dismisses the possibility that their presence may have influenced the numbers of birds and rodents he observed there.
  • The habitat along the 2.2 km transects from which bird counts were conducted varied considerably between the two areas. Compared to the no-cat area, the cat area had 31% less chaparral, 183% more trees, 52% less grass, and 240% more “modified” habitat (it’s not clear what Hawkins means by “modified,” but I assume it refers to habitat that reflects significant human impact).
  • Finally, the presence of pesticides may have played a role. According to a 2002 report (the earliest I was able to find) from the East Bay Regional Park District, “The focus of Lake Chabot’s weed control efforts are vegetation reduction within the two-acre overflow parking lot, picnic sites and firebreaks around park buildings, corp. yard, service yard, and the Lake Chabot classroom.” [4] And it’s clear from Hawkins’ 1999 article that the cat area did include picnic sites: “…over half of the cat scat in this study was collected under and around picnic tables.” [3] Now, Hawkins’ fieldwork was done in 1995 and 1996, but if there was any pesticide use during the study period, it may have affected the results—especially if the pesti­cide was distributed differently across the two areas.

Cats and Birds
“Almost twice as many birds were seen on the no-cat transect as on the cat transect,” writes Hawkins. But it’s not quite as simple as that—the details reveal a rather complex, often uneven count over the course of the study. Nevertheless—and despite the differences between the two areas—Hawkins’ only explanation is the cats. This is especially true for ground-feeders:

The preference of ground feeding birds for the no-cat treatment was striking; for ex­ample, California quail were seen almost daily in the no-cat area, whereas they were never seen in the cat area.

What’s more striking to me is the fact that five of the nine ground-feeding species included in the study showed no preference for either area. But Hawkins scarcely acknowledges the point, and doesn’t even hint at an explanation. “Birds that were known to nest on or near the ground or in shrubs and vines ≤ 1.5 m in height” also showed no preference between the two areas (though no nest counts were conducted).

The picture painted by Hawkins is that bird species absent from the cat area represent species killed off by the cats. But it’s generally accepted that cats are opportunistic hunters, catching whatever prey is readily available and easily caught. [5–8] Fitzgerald and Turner, for ex­ample, argue that “domestic cats (both house and feral ones) are best described as generalist resident preda­tors, exploiting a wide range of prey, and able to switch readily from one prey to another.” [9] So, how is it that some species were present at the cat site while others were not? Again, Hawkins offers no explanation.

In fact, it’s clear from Hawkins’ study that the cats aren’t much of threat at all to the birds—even vulnerable ground-feeding and ground-nesting species—in the cat area. Of the 120 scat samples found by searching the cat area, “65% were found to contain rodent hair and 4% feathers.” [2] This finding comes toward the end of the study, when the cat population was at its greatest—and still, only 4% contained feathers. And this could easily represent one cat and one bird.

One final point about the birds: Hawkins suggests (without explanation) that the olive-sided flycatcher, American robin, and Stellar’s jay—all of which showed no preference for either the no-cat area or the cat area—may have been responding to a “specialized habitat.” Could it be that the birds not seen in the cat area were also responding to a specialized habitat—by “migrating” to a place with less human activity (e.g., the no-cat area), for example? Once again, Hawkins has no comment.

Cats and Rodents
The fact that scats indicated rodents were predated to a greater extent than birds is hardly surprising [5, 6, 9, 10], but it should be noted the 65% figure represents the frequency of occurrence, and not a predation rate (a topic I address in greater detail here).

Hawkins’ analysis didn’t reveal whether the rodent hair was that of deer mice, harvest mice (both of which were found less often in the cat area than in the no-cat area), house mice (found more often in the cat area), or California voles (which showed no preference for either area). In any case, it’s not clear that the cats were responsible for the presence or absence of any of these rodent species. Again, the selective dietary habits suggested by Hawkins simply don’t fit with the domestic cat’s profile as a “generalist resident predator.”

Two additional points that might explain the differences Hawkins observed concern the habitat of the cat area. First, there’s the nearby lake and residences—potential sources of pollution that could affect nearby plant and animal life. Secondly, there’s the issue of possible pesticide use mentioned previously. As I say, it’s largely conjecture on my part; at the same time, though, it’s easy to imagine its potential impact on small mammals (and ground-feeding birds, for that matter).

Finally, Hawkins suggests that certain bird species were responding to specialized habitat—perhaps the rodents were simply doing the same.

Cats
Hawkins used track plates (baited devices that detect the presence of mammals by way of preserved “footprints”) for “estimating a relative cat presence index,” but found only one cat track in 200 track plate nights. And, “in 560 days of exposure, no scat was found in any of the sand boxes.” [2] Now, the cats were seen at feeding stations and on the rodent grids of the cat area—as many as 26 during a one-week period toward the end of the study. But clearly, they were not where Hawkins was expecting them to be. If, after two years at the study site, Hawkins was unable to get a better handle on the presence of the cats, how can he be so sure of their behavior when it comes to predation?

If, as Hawkins argues, the differences observed between the two areas are a result of the cats’ predatory behavior, then one would expect the number of birds and rodents to decrease as the number of cats increases. Yet, Hawkins’ findings don’t bear this out.

And then there are the unanswered questions about the cats—for example:

  • Where did these cats come from—were they illegally dumped, the result of nearby residents’ unsterilized cats breeding? Did they belong to the residents?
  • Were the cats sterilized? (Their increasing numbers would suggest that they weren’t.)
  • Were these cats part of a managed TNR colony? (Local newspaper reports indicate a long-standing battle between TNR advocates and opponents. [11–13])

Considering the central role these cats played in Hawkins’ two-year study, he knew surprisingly little about their behavior—including various factors that surely had an impact on his findings.

*     *     *

In their recent comment, Lepczyk et al. suggest that conservation biologists and wildlife ecologists “look to the evolutionary biology community” [1] for an example of how to influence policy. For feral cat/TNR opponents interested in shaping policy, it seems Hawkins’ study has become quite popular. [14–17] Actually, Nico Dauphiné and Robert J. Cooper take its already-tenuous claims one step further, citing Hawkins’ work (actually a 2004 conference paper that summarizes his dissertation [18]) as evidence that “the continuous predation pressure exerted by exotic predators in exponentially high densities can and has resulted in numerous local extinctions of continental land birds.” [8]

But is Hawkins’ methodology one that evolutionary biologists would advocate—or even recognize? Not likely.

Hawkins draws conclusions—infers important causal relationships—without any evidence of what “pre-treatment” conditions were like. And ignores entirely his own findings when they contradict his conclusions. Rather than beginning his inquiry with questions to answer, it seems Hawkins had his answer from the outset. At best, his work is an interesting pilot study—generating research questions for a more rigorous, less biased investigation.

References
1. Lepczyk, C.A., et al., “What Conservation Biologists Can Do to Counter Trap-Neuter-Return: Response to Longcore et al.” Conservation Biology. 2010. 24(2): p. 627-629.

2. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. 1998, Texas A&M University.

3. Hawkins, C.C., Grant, W.E., and Longnecker, M.T., “Effects of Subsidized House Cats on California Birds and Rodents.” Transactions of the Western Section of the Wildlife Society. 1999. 35: p. 29–33.

4. Brownfield, N.T., 2002 Annual Analysis of Pesticide Use East Bay Regional Park District. 2003, East Bay Regional Park District. www.ebparks.org/files/stew_pest_report_02.pdf

5. Barratt, D.G., “Predation by house cats, Felis catus (L.), in Canberra, Australia. II. Factors affecting the amount of prey caught and estimates of the impact on wildlife.” Wildlife Research. 1998. 25(5): p. 475–487.

6. Fitzgerald, B.M., Diet of domestic cats and their impact on prey populations, in The Domestic cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 1988, Cambridge University Press: Cambridge; New York. p. 123–147.

7. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201.

8. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2010. p. 205–219.

9. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

10. Woods, M., McDonald, R.A., and Harris, S., “Predation of wildlife by domestic cats Felis catus in Great Britain.” Mammal Review. 2003. 33(2): p. 174-188.

11. Chui, G., Stray Cats Live Harsh Lives in Area Parks, in San Jose Mercury News. 1985. p. 1

12. Bogue, G., Those Poor Cats Need a Human Assist, in Contra Costa Times. 1997: Walnut Creek, CA. p. A02

13. n.a., Spring controversy: What to do with feral cats?, in San Mateo Daily Journal, The (CA). 2001.

14. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

15. ABC, Domestic Cat Predation on Birds and Other Wildlife. n.d., American Bird Conservancy: The Plains, VA. www.abcbirds.org/abcprograms/policy/cats/materials/predation.pdf

16. Winter, L. and Wallace, G.E., Impacts of Feral and Free-Ranging Cats on Bird Species of Conservation Concern, G.E. Wallace, Editor. 2006, American Bird Conservancy. www.abcbirds.org/newsandreports/NFWF.pdf

17. Ash, S.J. and Adams, C.E., “Public Preferences for Free-Ranging Domestic Cat (Felis catus) Management Options.” Wildlife Society Bulletin. 2003. 31(2): p. 334–339.

18. Hawkins, C.C., Grant, W.E., and Longnecker, M.T. Effect of house cats, being fed in parks, on California birds and rodents. in Proceedings Of The 4th International Symposium On Urban Wildlife Conservation. 2004. Tucson, AZ: University of Arizona. http://cals.arizona.edu/pubs/adjunct/snr0704/snr07042l.pdf

The Work Speaks—Part 4: Mean Spirited

In April, Conservation Biology published a comment authored by Christopher A. Lepczyk, Nico Dauphiné, David M. Bird, Sheila Conant, Robert J. Cooper, David C. Duffy, Pamela Jo Hatley, Peter P. Marra, Elizabeth Stone, and Stanley A. Temple. In it, the authors “applaud the recent essay by Longcore et al. (2009) in raising the awareness about trap-neuter-return (TNR) to the conservation community,” [1] and puzzle at the lack of TNR opposition among the larger scientific community:

“…it may be that conservation biologists and wildlife ecologists believe the issue of feral cats has already been studied enough and that the work speaks for itself, suggesting that no further research is needed.”

In fact, “the work”—taken as a whole—is neither as rigorous nor as conclusive as Lepczyk et al. suggest. And far too much of it is plagued by exaggeration, misrepresentations, errors, and obvious bias. In Part 3 of this series, I discussed the distinction between compensatory and additive predation. Here, I’ll focus on how feral cat/TNR researchers often misuse averages to characterize skewed distributions, and how that error overestimates the impact of free-roaming cats on wildlife.

Something’s Askew
When a data set is skewed, it is inappropriate to use the mean, or average, as a measure of central tendency. The mean should be used only when the data set can be considered normal—the familiar bell curve. As Woods et al put it:

“the simple average number of animals brought home is not a useful measure of central tendency because of the skewed frequency distribution of the numbers of prey items brought home…” [2]

Studies of cat predation routinely reveal a positively skewed distribution; a few cats are responsible for many kills, while many of the cats kill few, if any, prey. So when researchers use the mean to calculate the total number of prey killed by cats in a particular area, they overestimate the cats’ impact.

How common is this? Very [see, for example, 3-9]. Of the many cat predation studies I’ve read, only a few [2, 10, 11] properly account for the skewed nature of this distribution. And others [12-17] often take these inflated figures at face value—as evidence of the impact cats have on wildlife. Published repeatedly, the erroneous estimates take on an undeserved legitimacy.

The proper method for handling skewed distributions involves data transformations, the details of which I won’t go into here. The important point is this: in the case of a positively skewed distribution, the back-transformed mean will always be less than the simple mean of the same data set.

Big Deal
Depending on the particular distribution, the difference between the simple mean and the back-transformed mean can be considerable. Let’s use the 2003 study by Woods et al. [2] to illustrate. In the case of mammals killed and returned home by pet cats, the back-transformed mean was 28.3% less than the simple mean. Or, put another way, the simple mean would have overestimated the number of mammals killed by 39.5%. Similarly, when all prey items were totaled (as depicted in the illustration above), the simple mean would have overestimated the total number off all prey (mammals, birds, herpetofauna, and “others”) by 46.9%.

On the other hand, the figures for birds appear to break the rule mentioned above. In this case, the back-transformed mean (4.1) is actually a bit higher than the simple mean (4.0). How can this be? In order to log-transform the data set, Woods et al. had to first eliminate all the instances where cats returned home no prey—you can’t take the logarithm of 0. So, they were actually working with two data sets. Now, the second data set—which includes only those cats that returned at least one prey item—is also highly positively skewed. As a point of reference, its simple mean was approximately 5.6 birds/cat, which, compared to the back-transformed mean, is an overestimation of 37.5%.

By now, it should be apparent that log-transformed means have another important advantage over simple means: because you have to eliminate those zeros from the data set, you are forced to focus only on the cats that returned prey home—which, of course, is the whole point of such studies! And in the case of this study, Woods et al. found that 20–30% of cats brought home either no birds or no mammals. And 8.6% of the cats brought home no prey at all over the course of the study.

Transforming a data set (and then back-transforming its mean) is simpler than it sounds, but Barratt offers a useful alternative, rule-of-thumb method (one echoed by Fitzgerald and Turner [18]):

“…median numbers of prey estimated or observed to be caught per year are approximately half the mean values, and are a better representation of the average predation by house cats based on these data.” [10]

So, whereas Dauphiné and Cooper (and others) suggest increasing such estimates by factors of two and three (“predation rates measured through prey returns may represent one half to less than one third of what pet cats actually kill…” [14]), they should, in fact, be reducing them by half.

Cat Ownership
There are other instances in which simple averages are used to describe similarly skewed distributions—with similar results. That is, they overestimate a particular characteristic—and not in the cats’ favor.

Cat ownership, for example, is not a normal distribution. Many people own one or two cats; a few people own many cats. This is precisely what Lepczyk et al. found in their 2003 study:

“The total number of free-ranging cats across all landscapes was 656, ranging from 1 to 30 per landowner…” [6]

In fact, about 113 (I’m estimating from the histogram printed in the report) of those landowners owned just one cat apiece. About 70 of them owned two cats. Only one—maybe two—owned 30 cats. And yet, Lepczyk et al. calculate an average of 2.59 cats/landowner (i.e., 656 cats/253 landowners who allow their cats outdoors), thereby substantially overestimating cat ownership—and, in turn, predation rates (which calculations are based upon the average number of cats/landowner).

Lepczyk et al. are not the only ones to make this mistake; several other researchers have done the same. [4, 5, 7-9]

Outdoor Access
The amount of time cats spend outdoors is also highly positively skewed, as is apparent from the 2003 survey conducted by Clancy, Moore, and Bertone. [19] Their work showed that nearly half of the cats with outdoor access were outside for two or fewer hours a day. And 29% were outdoors for less than an hour each day.

Among those researchers to overlook the skewed nature of this distribution are Kays and DeWan, who calculate an average of 8.35 hours/day. This greatly overestimates potential predation, and leads them to conclude—erroneously—that the actual number of prey killed by cats was “3.3 times greater than the rate estimated from prey brought home,” [9] as was discussed previously.

Compound Errors
Clearly, these errors are substantial—in some cases, doubling the apparent impact of cats on wildlife. Of course the errors are even more significant when one inflated figure is multiplied by another—as when Lepczyk et al. [6] multiply the average number of prey items returned by the average number of outdoor cats per owner. The resulting predation figures may well be four times greater than they should be! (Actually, there are additional problems with the authors’ predation estimates, which I’ll address in a future post).

*     *     *

The fact that such a fundamental mistake—one a student couldn’t get away with in a basic statistics course—is made so often is shocking. The fact that such errors slip past journal reviewers is inexcusable.

References
1. Lepczyk, C.A., et al., “What Conservation Biologists Can Do to Counter Trap-Neuter-Return: Response to Longcore et al.” Conservation Biology. 2010. 24(2): p. 627-629.

2. Woods, M., McDonald, R.A., and Harris, S., “Predation of wildlife by domestic cats Felis catus in Great Britain.” Mammal Review. 2003. 33(2): p. 174-188.

3. Coleman, J.S. and Temple, S.A., On the Prowl, in Wisconsin Natural Resources. 1996, Wisconsin Department of Natural Resources: Madison, WI. p. 4–8. http://dnr.wi.gov/wnrmag/html/stories/1996/dec96/cats.htm

4. Baker, P.J., et al., “Impact of predation by domestic cats Felis catus in an urban area.” Mammal Review. 2005. 35(3/4): p. 302-312.

5. Baker, P.J., et al., “Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86-99.

6. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201.

7. Crooks, K.R., et al., “Exploratory Use of Track and Camera Surveys of Mammalian Carnivores in the Peloncillo and Chiricahua Mountains of Southeastern Arizona.” The Southwestern Naturalist. 2009. 53(4): p. 510-517.

8. van Heezik, Y., et al., “Do domestic cats impose an unsustainable harvest on urban bird populations? Biological Conservation. 143(1): p. 121-130.

9. Kays, R.W. and DeWan, A.A., “Ecological impact of inside/outside house cats around a suburban nature preserve.” Animal Conservation. 2004. 7(3): p. 273-283.

10. Barratt, D.G., “Predation by house cats, Felis catus (L.), in Canberra, Australia. II. Factors affecting the amount of prey caught and estimates of the impact on wildlife.” Wildlife Research. 1998. 25(5): p. 475–487.

11. Barratt, D.G., “Predation by House Cats, Felis catus (L.), in Canberra, Australia. I. Prey Composition and Preference.” Wildlife Research. 1997. 24(3): p. 263–277.

12. May, R.M., “Control of feline delinquency.” Nature. 1988. 332(March): p. 392-393.

13. Jessup, D.A., “The welfare of feral cats and wildlife.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1377-1383.

14. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2010. p. 205–219

15. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

16. Winter, L., “Trap-neuter-release programs: the reality and the impacts.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1369-1376.

17. Clarke, A.L. and Pacin, T., “Domestic cat “colonies” in natural areas: a growing species threat.” Natural Areas Journal. 2002. 22: p. 154–159.

18. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.

19. Clancy, E.A., Moore, A.S., and Bertone, E.R., “Evaluation of cat and owner characteristics and their relationships to outdoor access of owned cats.” Journal of the American Veterinary Medical Association. 2003. 222(11): p. 1541-1545.

The Work Speaks—Part 3: Predatory Blending?

In April, Conservation Biology published a comment authored by Christopher A. Lepczyk, Nico Dauphiné, David M. Bird, Sheila Conant, Robert J. Cooper, David C. Duffy, Pamela Jo Hatley, Peter P. Marra, Elizabeth Stone, and Stanley A. Temple. In it, the authors “applaud the recent essay by Longcore et al. (2009) in raising the awareness about trap-neuter-return (TNR) to the conservation community,” [1] and puzzle at the lack of TNR opposition among the larger scientific community:

“…it may be that conservation biologists and wildlife ecologists believe the issue of feral cats has already been studied enough and that the work speaks for itself, suggesting that no further research is needed.”

In fact, “the work”—taken as a whole—is neither as rigorous nor as conclusive as Lepczyk et al. suggest. And far too much of it is plagued by exaggeration, misrepresentations, errors, and obvious bias. In a previous post, I presented examples of researchers drawing big conclusions from small sample sizes. Here, I’ll discuss the important distinction between compensatory and additive predation—a point too often left out of the feral cat/TNR discussion.

Sins of Omission
Focusing on the number of prey injured or killed by cats, without also recognizing that there are different types of predation, implies that each and every bird, mammal, reptile, etc. is destined to be part of its species’ breeding population. Of course, that’s not at all how things work out in the natural world—with or without predation by cats.

And yet, numerous studies [2-10], reviews [11], and other published papers [12-14] fail to acknowledge the critical difference between compensatory predation (in which prey would have died even in the absence of a particular predator, due to illness, starvation, other predators, etc.) and additive predation (in which healthy prey are killed). It’s the difference between, as Beckerman et al. put it, the “doomed surplus hypothesis” and the “hapless survivor hypothesis.” [15]

This is a critical point when it comes to connecting predation rates (from cats or any other predator) to population impacts. The more additive the predation, the greater the potential impact on population numbers. Purely compensatory predation, on the other hand, is less likely to affect overall populations. Of course, the connection is seldom so simple and direct, and a number of factors (e.g., habitat area and type, base population numbers, etc.) influence the ultimate outcome—making it quite difficult to tease out specific causal relationships. Nevertheless, if we want to better understand the impact of free-roaming cats on wildlife, we cannot ignore the distinction between—and inherent implications of—these two types of predation.

Honorable Mentions
Although Churcher and Lawton failed to mention the distinction between compensatory and additive predation in their now-classic “English village” study [4], Churcher later suggested that their findings were largely in the compensatory category: “If the cats weren’t there, something else would be killing the sparrows or otherwise preventing them from breeding.” [16]

Woods et al. don’t address the topic directly, but warn against drawing direct connections between predation numbers and potential effects on population dynamics:

“Our estimates of the total numbers of animals brought home by cats throughout Britain should be treated with requisite caution and these figures do not equate to an assessment of the impact of cats on wildlife populations.” [3]

Unfortunately, other researchers have used this study to make exactly that connection. In “Critical Assessment,” for example, Longcore et al. cite Woods et al. (along with Lepczyk et al. 2003, the subject of a future post) when they write, “evidence indicates that cats can play an important role in fluctuations of bird populations.” [11]

Under-Compensating?
In their 2008 study, Baker et al. found that “birds killed by cats in this study had significantly lower fat and pectoral muscle mass scores than those killed by collisions,” [17] suggesting that they may have been among the “doomed surplus” portion of the population. Similar results were reported eight years earlier by Møller and Erritzøe, who found that “small passerine birds falling prey to cats had spleens that were significantly smaller than those of conspecifics that died for other reasons,” concluding ultimately that the birds killed by cats “often have a poor health status.” [18]

But Baker et al. express caution about their findings:

“…the distinction between compensatory and additive mortality does… become increasingly redundant as the number of birds killed in a given area increases: where large numbers of prey are killed, predators would probably be killing a combination of individuals with poor and good long-term survival chances.”

Whatever their concerns, it must be noted that Baker et al. inflated their predation numbers by a factor of 3.3 on the basis of Kays and DeWan’s dubious conclusions [9] (which I discussed in some detail previously). Doing so raises considerable doubts about any level of “redundancy,” as well the authors’ suggestion that cat predation in the area might be “creating a dispersal sink for more productive neighboring areas.” [19] (Such “sinks” can occur when predation outstrips local prey populations, requiring that prey be “recruited” from surrounding areas.)

Implications
Given all the work that’s been done on cat predation, one might expect the subject of compensatory predation to be addressed more fully and more often. By omitting this important issue from the feral cat/TNR discussion, researchers portray a situation both simpler and harsher (in terms of what it implies about the impact of free-roaming cats) than reality suggests. Whether or not such omissions are intentional, I cannot say. I do, however, find it curious—what’s included compared to what’s left out, and by whom.

References
1. Lepczyk, C.A., et al., “What Conservation Biologists Can Do to Counter Trap-Neuter-Return: Response to Longcore et al.” Conservation Biology. 2010. 24(2): p. 627-629.

2. Coleman, J.S. and Temple, S.A., On the Prowl, in Wisconsin Natural Resources. 1996, Wisconsin Department of Natural Resources: Madison, WI. p. 4–8. http://dnr.wi.gov/wnrmag/html/stories/1996/dec96/cats.htm

3. Woods, M., McDonald, R.A., and Harris, S., “Predation of wildlife by domestic cats Felis catus in Great Britain.” Mammal Review. 2003. 33(2): p. 174-188.

4. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455.

5. Coleman, J.S. and Temple, S.A., “Rural Residents’ Free-Ranging Domestic Cats: A Survey.” Wildlife Society Bulletin. 1993. 21(4): p. 381–390.

6. Coleman, J.S. and Temple, S.A., Effects of Free-Ranging Cats on Wildlife: A Progress Report, in Fourth Eastern Wildlife Damaage Control Conference. 1989: University of Nebraska—Lincoln. p. 8–12. http://digitalcommons.unl.edu/ewdcc4/7

7. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. 1998. PhD Dissertation, Texas A&M University.

8. Hawkins, C.C., Grant, W.E., and Longnecker, M.T., “Effects of Subsidized House Cats on California Birds and Rodents.” Transactions of the Western Section of the Wildlife Society. 1999. 35: p. 29–33.

9. Kays, R.W. and DeWan, A.A., “Ecological impact of inside/outside house cats around a suburban nature preserve.” Animal Conservation. 2004. 7(3): p. 273-283.

10. Lepczyk, C.A., Mertig, A.G., and Liu, J., “Landowners and cat predation across rural-to-urban landscapes.” Biological Conservation. 2003. 115(2): p. 191-201.

11. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

12. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2010. p. 205–219

13. Coleman, J.S., Temple, S.A., and Craven, S.R., Cats and Wildlife: A Conservation Dilemma. 1997, University of Wisconsin, Wildlife Extension. http://forestandwildlifeecology.wisc.edu/wl_extension/catfly3.htm

14. Andersen, M.C., Martin, B.J., and Roemer, G.W., “Use of matrix population models to estimate the efficacy of euthanasia versus trap-neuter-return for management of free-roaming cats.” Journal of the American Veterinary Medical Association. 2004. 225(12): p. 1871-1876.

15. Beckerman, A.P., Boots, M., and Gaston, K.J., “Urban bird declines and the fear of cats.” Animal Conservation. 2007. 10(3): p. 320-325.

16. n.a., What the Cat Dragged In, in Catnip. 1995, Tufts University School of Veterinary Medicine: Boston, MA. p. 4–6

17. Baker, P.J., et al., “Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86-99.

18. Møller, A.P. and Erritzøe, J., “Predation against birds with low immunocompetence.” Oecologia. 2000. 122(4): p. 500-504.

The Work Speaks—Part 2: Sample-Minded Research

In April, Conservation Biology published a comment authored by Christopher A. Lepczyk, Nico Dauphiné, David M. Bird, Sheila Conant, Robert J. Cooper, David C. Duffy, Pamela Jo Hatley, Peter P. Marra, Elizabeth Stone, and Stanley A. Temple. In it, the authors “applaud the recent essay by Longcore et al. (2009) in raising the awareness about trap-neuter-return (TNR) to the conservation community,” [1] and puzzle at the lack of TNR opposition among the larger scientific community:

“…it may be that conservation biologists and wildlife ecologists believe the issue of feral cats has already been studied enough and that the work speaks for itself, suggesting that no further research is needed.”

In fact, “the work”—taken as a whole—is neither as rigorous nor as conclusive as Lepczyk et al. suggest. And far too much of it is plagued by exaggeration, misrepresentations, errors, and obvious bias. In my previous post, I presented examples of researchers “reinterpreting” the work of others to better fit their own arguments. For the next few posts, I’ll focus on some of the major flaws in the feral cat/TNR research itself—beginning with the reliance, by some, on small sample sizes.

Size Does Matter
There are all kinds of reasons for small sample sizes, perhaps the most common being limited resources (e.g., time, funding, etc.). And they are often a fact of life in real-world research, where investigators have less control over conditions than they might in a laboratory environment. Studies employing small sample sizes are not without value; indeed, they often serve as useful pilot studies for future, more comprehensive, work. They do become problematic, though, when broad conclusions are drawn from their results. Below are three (among many!) examples of such studies.

Impressive Estimates
In “Free-Ranging Domestic Cat Predation on Native Vertebrates in Rural and Urban Virginia,” [2] published in 1992, the authors estimated that the state’s 1,048,704 cats were killing between 3,146,112 and 26,217,600 songbirds each year. “This number,” they note, “is certainly inaccurate to some degree, although the estimates are impressive.” [2] Impressive? I suppose. Maybe incredible is more fitting—since the study from which they were derived included exactly five cats, four “urban” and one “rural.”

Mitchell and Beck acknowledged “the limitations of extrapolation to large areas from relatively small data sets such as ours,” suggesting that their work was intended to provoke future “careful and detailed studies that can reveal truer estimates of the impact of this introduced species.” Hawkins [3] and Dauphiné and Cooper [4], however, seem to take them at their word, regardless of any disclaimers.

Many Cats, Multiple Seasons
In a recent study on Catalina Island, the researchers “examined the home-range behavior and movements of sterilized and intact radiocollared feral cats living in the interior” [5] of the island. Although Guttilla and Stapp concede that “sample sizes, especially for males, were relatively low” despite having “tracked many cats across multiple seasons,” they nevertheless come to some rather dramatic conclusions. Among them: “sterilization likely would not reduce the impact of feral cats on native prey.” [5]

So what do the authors mean by many and multiple? Actually, there were just 27 cats in the study (of an estimated 614–732 on the island). “Four cats were tracked during all four seasons, 9 cats were tracked for three consecutive seasons, 4 cats were tracked for 2 consecutive seasons, and the remaining cats were tracked for 1 season.” [5] And these numbers were effectively cut in half, because the researchers were comparing sterilized and non-sterilized cats. At best, this is a pilot study—though it’s already morphed into something more substantial in the mainstream media.

Myth vs. Math
In their 2004 study, “Ecological Impact of Inside/Outside House Cats Around a Suburban Nature Preserve,” Kays and DeWan observed hunting cats, concluding that their kill rate (13%) is “3.3 times greater than the rate estimated from prey brought home.” [6] Not surprisingly, this figure has been used as an instant multiplier (much in the same way William George’s work has been misused) for researchers interested in “correcting” (inflating?) prey numbers. [4, 7-11]

But this ratio, 3.3, hinges on the hunting behaviors of just 24 cats—12 that returned prey home, and another 12 (11 pets and 1 feral) that were observed hunting for a total of 181 hours (anywhere from 4.8–46.5 hours per cat). It’s interesting to note that the cat observed the most (46.5 hours) was only a year old—the youngest of the 12 observed, and likely the most active hunter. This factor alone could have had a significant influence on the outcome of the study.

Also, as several studies have shown [7,8,12,13], the distribution of prey catches tends to be highly skewed (many cats catch few/no prey, while a few catch a lot). In other words, the distribution is not the familiar bell curve at all—making it inappropriate to use a simple average for calculating estimations (a topic I’ll address in detail later). What’s more, with only 12 cats being monitored, how can we be sure their behaviors accurately represent any real distribution at all?

But the key to their calculation is the average time spent outdoors. This, too, tends to be a highly skewed distribution [14, 15], although—curiously—Kays and DeWan’s data suggest otherwise. By way of example, a 2003 survey conducted by Clancy, Moore, and Bertone [15] revealed that nearly half of the cats with outdoor access were outside for two or fewer hours a day. And 29% were outdoors for less than an hour each day. A survey conducted by the American Bird Conservancy revealed similar behavior, reporting that “35% keep their cats indoors all of the time” and “31% keep them indoors mostly with some outside access.” [14]

Kays and DeWan’s average of 8.35 hours/day, then, seems rather out of line with other studies. This, in addition to a number of unknowns (e.g., influence of time of day/night on hunting success, actual time spent hunting by each cat, etc.) raises serious questions about their conclusions.

By way of comparison, using an average of 2.5 hours/day (which is not out of line with the surveys described above) would yield a ratio of 1:1. In other words, no difference between predation rates predicted by actual hunting observation and those predicted by way of prey returned home. Which is not to say that I agree with Kays and DeWan’s underlying methods—we don’t know the possible effects of seasonal variation, for example, or differences in habitat. I’m only pointing out how sensitive this one factor—with its enormous consequences—is to the amount of time cats actually spend outdoors (and, just to introduce one more complication: I’d be very surprised if the amount of outdoor time cats spend hunting is normally distributed; it, too, is probably skewed).

Ironically, while the authors express disappointment that “biologists have rarely sampled both cat and prey populations in such a way that direct effects on prey populations can be shown,” [6] they seem to have had no misgivings about how their work—suffering from its own sampling issues—might be used to misrepresent those same effects.

*     *     *

Next, I’ll discuss the difference between compensatory and additive predation, and how that affects predictions of feral cat impacts on wildlife.

References
1. Lepczyk, C.A., et al., “What Conservation Biologists Can Do to Counter Trap-Neuter-Return: Response to Longcore et al.” Conservation Biology. 2010. 24(2): p. 627-629.

2. Mitchell, J.C. and Beck, R.A., “Free-Ranging Domestic Cat Predation on Native Vertebrates in Rural and Urban Virginia.” Virginia Journal of Science. 1992. 43(1B): p. 197–207.

3. Hawkins, C.C., Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. 1998. PhD Dissertation, Texas A&M University.

4. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2010. p. 205–219

5. Guttilla, D.A. and Stapp, P., “Effects of sterilization on movements of feral cats at a wildland-urban interface.” Journal of Mammalogy. 2010. 91(2): p. 482-489.

6. Kays, R.W. and DeWan, A.A., “Ecological impact of inside/outside house cats around a suburban nature preserve.” Animal Conservation. 2004. 7(3): p. 273-283.

7. Baker, P.J., et al., “Impact of predation by domestic cats Felis catus in an urban area.” Mammal Review. 2005. 35(3/4): p. 302-312.

8. Baker, P.J., et al., “Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis. 2008. 150: p. 86-99.

9. van Heezik, Y., et al., “Do domestic cats impose an unsustainable harvest on urban bird populations? Biological Conservation. 143(1): p. 121-130.

10. Nelson, S.H., Evans, A.D., and Bradbury, R.B., “The efficacy of collar-mounted devices in reducing the rate of predation of wildlife by domestic cats.” Applied Animal Behaviour Science. 2005. 94(3-4): p. 273-285.

11. MacLean, M.M., et al., “The usefulness of sensitivity analysis for predicting the effects of cat predation on the population dynamics of their avian prey.” Ibis. 2008. 150(Suppl. 1): p. 100-113.

12. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455.

13. Woods, M., McDonald, R.A., and Harris, S., “Predation of wildlife by domestic cats Felis catus in Great Britain.” Mammal Review. 2003. 33(2): p. 174-188.

14.  ABC, Human Attitudes and Behavior Regarding Cats. 1997, American Bird Conservancy: Washington, DC. http://www.abcbirds.org/abcprograms/policy/cats/materials/attitude.pdf

15. Clancy, E.A., Moore, A.S., and Bertone, E.R., “Evaluation of cat and owner characteristics and their relationships to outdoor access of owned cats.” Journal of the American Veterinary Medical Association. 2003. 222(11): p. 1541-1545.

The Work Speaks—Part 1: Lost in Translation

In April, Conservation Biology published a comment authored by Christopher A. Lepczyk, Nico Dauphiné, David M. Bird, Sheila Conant, Robert J. Cooper, David C. Duffy, Pamela Jo Hatley, Peter P. Marra, Elizabeth Stone, and Stanley A. Temple. In it, the authors “applaud the recent essay by Longcore et al. (2009) in raising the awareness about trap-neuter-return (TNR) to the conservation community,” [1] and puzzle at the lack of TNR opposition among the larger scientific community:

“…it may be that conservation biologists and wildlife ecologists believe the issue of feral cats has already been studied enough and that the work speaks for itself, suggesting that no further research is needed.”

In fact, “the work”—taken as a whole—is neither as rigorous nor as conclusive as Lepczyk et al. suggest. And far too much of it is plagued by exaggerations, misrepresentations, errors, and obvious bias. For the next few posts, I’m going to present a sampling of its more serious flaws, beginning with how some researchers “reinterpret” work of others to suit their own purposes.

Tell It Like It Is
Studies of cat predation frequently cite the work of William G. George, who, in 1974, published a paper documenting his meticulous observations of the hunting behavior of three cats on his southern Illinois farm. “The results,” wrote George, “established a basis for examining the possibility that cat predation may result in depleted winter populations of microtine rodents and other prey of Red-tailed Hawks, Marsh Hawks, and American Kestrels.” [2]

Thirty years later, David A. Jessup interpreted things rather differently, giving George’s work an additional—and unwarranted—degree of certainty. Gone are the doubts that George expressed—first, regarding the impact of cat predation on rodent and other prey populations; second, regarding the relationship between these populations and the raptors that feed on them. For Jessup—who offers no additional evidence—it’s all very straightforward: “Feral cats also indirectly kill native predators by removing their food base.” [3]

More recently, Guttilla and Stapp seem to prefer Jessup’s take: “Human-subsidized cats… can spill over into less densely populated wildland areas where they reduce prey for native predators (George 1974).” [4]

If any additional work has been done on the subject (surely there are more cats in the area these days; how are the voles and raptors faring?), it seems to have gone unnoticed. Instead, Jessup, Guttilla, and Stapp (and others, too, no doubt) have simply rewritten George’s conclusion to suit their own purposes. Perhaps their version makes for a better story, but it’s rather poor science.

Credit Where Little/None Is Due
When the Lancet recently retracted a 1998 paper linking vaccinations to autism in children—“research” that sparked the ongoing backlash against vaccinations—it was headline news. The move prompted this criticism from one member of the British Parliament: “The Lancet article should never have been published, and its peer review system failed. The article should now be expunged from the academic record…”

At the risk of drawing too many parallels between the two papers, I think the same can be said for Coleman and Temple’s infamous “Wisconsin Study.” (On the other hand, it does serve a useful purpose as a red flag.) Actually, as Goldstein et al. point out, Coleman and Temple’s paper was never peer-reviewed (not necessarily a deal-breaker in my book, but such publications do warrant additional scrutiny), but achieved its mythical status by being cited ad nauseam in peer-reviewed journals, as well as the mainstream media.

Does anybody actually believe the numbers suggested by Coleman and Temple? Stanley Temple (one of the co-authors of the recent anti-feral cat/TNR comment in Conservation Biology) himself admitted their published figures “aren’t actual data; that was just our projection to show how bad it might be.” [5]

I don’t think Longcore et al. [6] or the editors at Conservation Biology put much stock in the Wisconsin Study—so why continue to publish “projections” that have been so thoroughly discredited? Because doing so strengthens their case, at least among those who don’t know any better—especially people outside the scientific community, including many journalists, policy makers, judges, and the general public.

In their recent comment, Lepczyk et al. suggest that conservation biologists and wildlife ecologists “look to the evolutionary biology community” [1] for an example of how to influence policy:

“When local policies or regulations are put forth that promote the teaching of creationism or intelligent design, the evolutionary biologists have responded in force from across the nation and world.” [1]

Let’s set aside for the moment all the baggage associated with their analogy. My question is this: Is the evolutionary biology community still publishing bogus “projections” from 13 years ago? I doubt it.

Check Your Premises
In their recent paper (available for download via the American Bird Conservancy (ABC) website), Dauphiné and Cooper arrive at their absurd figure of “117–157 million free-ranging cats in the United States,” [7] in part, by way of Jessup’s “estimated 60 to 100 million feral and abandoned cats in the United States.” [3]

So where does Jessup’s figure come from? We have no idea—there’s no citation. And Jessup is no authority on the subject—having conducted no studies or reviews of studies that quantify the feral cat population. What’s more, his “estimation” is among the highest figures published. Yet this is the shaky foundation upon which Dauphiné and Cooper attempt to build their subsequent argument.

The authors then add to the (dubious) number of feral cats the proportion of pet cats allowed outdoors. They refer to a 2004 paper by Linda Winter, director of ABC’s Cats Indoors! campaign, in which it was reported, “A 1997 nationwide random telephone survey indicated that 66% of cat owners let their cats outdoors some or all of the time.” [8]

That’s an interesting way to put it—Winter makes it sound like two-thirds of pet cats are essentially outdoor cats. But the surveycommissioned by ABC!—actually indicates that “35% keep their cats indoors all of the time” and “31% keep them indoors mostly with some outside access.” [9] The difference in wording is subtle, and hampered by imprecision—it all comes down to the meaning of some.

Winter’s 2004 paper implies that there are twice as many outdoor pet cats as was indicated in the original survey—an interpretation Dauphiné and Cooper seem to embrace. Had they looked further—and to a less biased source—they might have been able to get a better handle on the degree of outdoor access. For example: a 2003 survey conducted by Clancy, Moore, and Bertone [10] revealing that nearly half of the cats with outdoor access were outside for two or fewer hours a day. And 29% were outdoors for less than an hour each day.

Do these “part-timers” have the same impact on wildlife as feral cats? Dauphiné and Cooper would have us believe they do.

[Note: For a closer look at the flaws in Dauphiné and Cooper’s paper, download “One Billion Birds,” by Laurie D. Goldstein.]

The lesson? Credible research begins with a solid foundation; a weak foundation—one plagued with unsubstantiated claims—on the other hand, leads to pseudoscience.

Or worse. ABC’s Senior Policy Advisor, Steve Holmer, cited Dauphiné and Cooper’s bogus numbers when he spoke to the Los Angeles Times about his organization’s involvement with the legal battle against TNR. It’s like the Wisconsin Study all over again.

When All Else Fails, Look It Up
Though this would seem to be utterly obvious, it apparently bears repeating: Don’t cite work you haven’t actually read.

Isn’t this emphasized in all graduate (indeed, undergraduate, too) programs? What grad student isn’t, at one time or another, tempted to take the easy way out—ride the coattails of somebody else who’s (presumably) done the real work? In addition to the ethical implications, such shortcuts tend to invite more immediate troubles, too. Again, George’s work (described above) provides an excellent case study. Below are some examples of how his work has been referenced in the cat predation literature:

“It is very unlikely that cats bring home all of the prey that they capture. What proportion they bring home has been little studied. George (1974) on a farm in Illinois USA found that three house cats, all adequately fed, brought home about 50% of the prey that they killed.” [11]

“George found that about 50% of prey were indeed brought home, with the other 50% being eaten, scavenged by other animals or simply not found.” [12]

“These approximations are probably underestimates, assuming that cats do not bring back all the prey that they kill.” [13]

Trouble is, George never said these things; what he said was:

“… the cats never ate or deposited prey where caught but instead carried it into a ‘delivery area,’ consisting of the house and lawn. The exclusive use of this delivery area was verified in 18 to 70 mammal captures per cat, as witnessed between early 1967 and 1971.” [2]

In 2000, Fitzgerald and Turner pointed out the fact that George’s work was being misrepresented, noting that the erroneous 50% figure “has been reported widely, though it is unfounded.” [14] Nevertheless, the myth persists—even in 2010.

“In Illinois, George (1974) found that only about half of animals killed by cats were provided to their owners, and in upstate New York, Kays and DeWan (2004) found that observed cat predation rates were 3.3 times higher than predation rates measured through prey returns to owners. Thus, predation rates measured through prey returns may represent one half to less than one third of what pet cats actually kill…” [7]

As Dauphiné and Cooper demonstrate, the “reinterpreted” version of George’s work makes for a very convenient multiplier—suddenly, every kill reported is doubled (or tripled, if Kays and DeWan are to be believed—and they’re not, but that’s a topic for another post). Never mind the fact that it has no basis in actual fact.

Getting a copy of George’s study isn’t difficult, especially with the inter-library loan services available today. To reference it—to use George’s work so that your own appears more credible—without ever having actually read it, is simply inexcusable. But citing it blindly suggests more than laziness—it points to a certain coziness that has no place in scientific discourse. Too much Kool-Aid drinking, and not enough honest research.

*     *     *

Scientists can (and do) look at identical results and come to very different conclusions. But misinterpreting, misrepresenting, or dismissing the conclusions of others, is something else altogether. As the above examples (and there are many, many more!) illustrate, this happens far too often in the feral cat/TNR literature. And if we can’t believe what researchers are saying about the work of others, why would we believe what they say about their own work?

Next, I’ll focus on some of the major flaws in the feral cat/TNR literature—beginning with small sample sizes

References
1. Lepczyk, C.A., et al., “What Conservation Biologists Can Do to Counter Trap-Neuter-Return: Response to Longcore et al.” Conservation Biology. 2010. 24(2): p. 627-629.

2. George, W., “Domestic cats as predators and factors in winter shortages of raptor prey.” The Wilson Bulletin. 1974. 86(4): p. 384–396.

3. Jessup, D.A., “The welfare of feral cats and wildlife.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1377-1383.

4. Guttilla, D.A. and Stapp, P., “Effects of sterilization on movements of feral cats at a wildland-urban interface.” Journal of Mammalogy. 2010. 91(2): p. 482-489.

5. Elliott, J., The Accused, in The Sonoma County Independent. 1994. p. 1, 10

6. Longcore, T., Rich, C., and Sullivan, L.M., “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” Conservation Biology. 2009. 23(4): p. 887–894.

7. Dauphiné, N. and Cooper, R.J., Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, in Fourth International Partners in Flight Conference: Tundra to Tropics. 2010. p. 205–219

8. Winter, L., “Trap-neuter-release programs: the reality and the impacts.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1369-1376.

9. ABC, Human Attitudes and Behavior Regarding Cats. 1997, American Bird Conservancy: Washington, DC. http://www.abcbirds.org/abcprograms/policy/cats/materials/attitude.pdf

10. Clancy, E.A., Moore, A.S., and Bertone, E.R., “Evaluation of cat and owner characteristics and their relationships to outdoor access of owned cats.” Journal of the American Veterinary Medical Association. 2003. 222(11): p. 1541-1545.

11. Churcher, P.B. and Lawton, J.H., “Predation by domestic cats in an English village.” Journal of Zoology. 1987. 212(3): p. 439-455.

12. May, R.M., “Control of feline delinquency.” Nature. 1988. 332(March): p. 392-393.

13. Crooks, K.R. and Soule, M.E., “Mesopredator release and avifaunal extinctions in a fragmented system.” Nature. 1999. 400(6744): p. 563.

14. Fitzgerald, B.M. and Turner, D.C., Hunting Behaviour of domestic cats and their impact on prey populations, in The Domestic Cat: The biology of its behaviour, D.C. Turner and P.P.G. Bateson, Editors. 2000, Cambridge University Press: Cambridge, U.K.; New York. p. 151–175.