Posts tagged with Nico Dauphiné

Inside Job II

22 Oct 2010

Another study demonstrates that the majority of pet cats spend their time indoors.

In my previous post on the subject, I somehow overlooked Linda Lord’s paper, “Attitudes toward and perceptions of free-roaming cats among individuals living in Ohio.” [1] In it, Lord, Assistant Professor in Ohio State University’s College of Veterinary Medicine, presents the results of an extensive 2007 telephone survey.

Fifty-nine percent of the 217 cat owners participating in the study reported that their cats were indoor-only. Nearly 20% more allowed their cats outdoors no more than three hours each day.

Linda Lord Indoor-Outdoor Data

Lord’s results are very much in line with findings from the three studies I cited previously. [2–4] All of which contradict the bogus claims made recently by Washington Post columnist Adrian Higgins, and last year by Nico Dauphiné and Robert J. Cooper (download their Partners in Flight conference paper here). [5]

These findings also raise questions about a comment made by Pete Marra in the Post story. Referring to his recent investigation into the mortality of catbird fledglings, Marra suggests that the culprits “aren’t feral cats; they’re domestic cats allowed to go outside.” I’ll take a closer look at Marra’s study in my next post…

Literature Cited
1. 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.

2. 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.

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

4. APPA, 2009–2010 APPA National Pet Owners Survey. 2009, American Pet Products Association: Greenwich, CT.

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

Inside Job

26 Sep 2010

Results from the American Pet Products Association’s 2009­­–2010 National Pet Owners Survey suggest that cats in this country are spending more time indoors than ever before. Although the proportion of owners keeping their cats inside at night has remained relatively steady since 1998 (at approximately 66%), their has been a 14% increase in daytime confinement (from 56% to 64%) over the same period. [1]

Indoor&Outdoor Access-APPA

It must be noted that owners were asked where they usually kept their cat(s), thereby raising some doubts about the accuracy of their responses. (There are actually two issues here: first is the level of truthfulness—did owners, intentionally or not, provide accurate information? But there is also the obvious ambiguity surrounding the term usually.) Nevertheless, these results correspond reasonably well with those of two earlier surveys: one commissioned by the American Bird Conservancy (ABC) in 1997, [2] the other conducted by Clancy et al. in 2001 [3] (the only other surveys I’ve found that investigated this issue specifically).

The ABC’s study (in which 250 cat owners participated in a telephone survey) indicated that “35% keep their cats indoors all of the time,” while “31% keep them indoors mostly with some outside access.” [2]

The 2001 survey included 168 cat owners, each of whom was part of the Feline Health Study, conducted at the Foster Hospital for Small Animals, Cummings School of Veterinary Medicine, Tufts University. Sixty percent of these cats were “strictly indoor cats,” while 40% “had some level of outdoor access.” [3] Probing further, Clancy et al. discovered that nearly half of the cats with outdoor access were outside for two or fewer hours a day. And 29% of them were outdoors for less than an hour each day. [3]

Considering the differences in sampling (most notably the fact that participants in the 2001 survey were all clients of a veterinary hospital, whereas APPA survey results for 2000 indicate that 27% of cat owners did not visit the vet in the previous 12 months), and the inherent uncertainty surrounding the terms mostly, usually, and some, the results of these three surveys are remarkably similar.

Counting Cats
Such findings are critical for developing accurate estimates of the number of birds killed by cats (assuming a reasonable level of accuracy is achievable, given the complexity of the issue). Simply put, cats that don’t go outside can’t kill birds.

Recognizing this, some researchers have inflated their figures for cats allowed outdoors. [4–6]

Dauphiné and Cooper, [6] for instance, cite the APPA’s 2007–2008 survey when referring to the number of owned cats in the U.S., but either ignored or overlooked its findings about confinement: 63% of owners reported that they kept their cat(s) indoors during the day, 70% during the night. (It’s also possible that the authors consulted only the APPA’s online summary, which probably didn’t include this information.)

By contrast, Dauphiné and Cooper claim that 65% of pet cats “are free-ranging outdoor cats for at least some portion of the day,” [6] citing not the APPA survey, but Linda Winter’s 2004 paper, “Trap-neuter-release programs: the reality and the impacts” (which can be downloaded here). Indeed, Winter, the former director of the ABC’s Cats Indoors! campaign, had suggested as much—misrepresenting the findings of a study commissioned by her own organization:

“A 1997 nationwide random telephone survey indicated that 66% of cat owners let their cats outdoors some or all of the time.” [7]

Double the proportion of cats allowed outdoors, and—just like that—the number of birds killed by pet cats doubles too. (Dauphiné and Cooper actually go much further, employing some grossly inflated predation rates as well.)

Counting Birds
Of course, such estimates do not necessarily relate directly to population impacts. The predation may be largely compensatory, for example; and there are source-sink dynamics to be considered as well.

Nevertheless, researchers persist—more often, it seems, in pursuit of staggering, media-friendly figures than a better understanding of what’s actually going on (e.g., Dauphiné and Cooper’s bumper-sticker-worthy “one billion birds”). As a result, the scientific literature is plagued with some rather spectacular failures where predation numbers are concerned (e.g., The Wisconsin Study, Christopher Lepczyk’s dissertation, Carol Fiore’s thesis, etc.).

*     *     *

The surprising level of agreement among the three “outdoor access” studies provides researchers a rare opportunity to agree among themselves. Which, in turn, could move us closer to an honest debate of the larger issues—arguing about which action is most appropriate, for instance, rather than about whose numbers are most valid.

Despite how results of these surveys have been—as recently as last year—overlooked, ignored, and misrepresented, I remain cautiously optimistic. As Patronek has suggested, “predation of songbirds tends to be noticed because it takes place during the day.” [8] It’s time predation research received the same kind of visibility. Sunlight, after all, is said to be the best of disinfectants.

Note: There is a an amendment to this post here.

Literature Cited
1. APPA, 2009–2010 APPA National Pet Owners Survey. 2009, American Pet Products Association: Greenwich, CT.

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

3. 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.

4. 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

5. 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.

6. 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.

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. 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.

False Confessions

12 Aug 2010

Whether the latest iteration of reality TV— Animal Planet’s Confessions: Animal Hoarding—is more education, entertainment, or exploitation is a matter of debate. But it’s a safe bet that by streaming “an unflinchingly honest look at a human condition that affects people and animals” into living rooms across the country, a problem too rarely acknowledged (not to mention taken seriously) is now receiving unprecedented attention.

Even if I were a cable subscriber, though, I don’t think I’d be tuning in. Although I was nowhere near the “front lines” of the Great Kitty Rescue, I’ve seen and heard plenty where animal hoarding is concerned. But in reading about Confessions, I was reminded of some remarks included in a comment published earlier this year in Conservation Biology. There, Christopher 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 compared TNR to animal hoarding:

“The animal welfare community opposes ‘cat hoarding,’ whereby people care for more pets than they can adequately support, because it is considered inhumane. Trap-neuter-return is essentially cat hoarding without walls. Considering that most communities have laws banning animal hoarding, we should consider the same standard for outdoor cats as those that are in a person’s home.” [1]

This strikes me as almost desperate—the latest volley in the kitchen-sink/something-for-everybody approach taken by some TNR opponents. Nevertheless, the analogy—however incongruous—is not new. In 2004, David Jessup made essentially the same comparison:

“Some people are compelled to own and care for excessive numbers of cats. This psychological illness is referred to as ‘collectors psychosis.’ How is the person who must save 25 to 30 cats in their home different from the person who sees themselves [sic] as the savior of 25 to 30 cats in a park? Some ‘cat people’ may be ‘collectors,’ and it is possible that TNR is enabling and supporting some people who need psychologic counseling and assistance.” [2]

Jessup doesn’t burden himself or his audience with even the slightest support for his assertions; his claims are as much conjecture as anything else, his question largely rhetorical. Five years later, Dauphiné and Cooper revisited Jessup’s query, but—despite a handful of references—do no better in terms of its resolution:

“In many cases, the characteristics and behavior of people involved in TNR are suggestive of the psychiatric disorders described in problematic animal hoarding [3]. When presented with alternatives to TNR, such as enclosed sanctuaries, no-kill shelters, and traditional animal control, many such people can be “fiercely protective, retaliatory, and uncooperative,” [4] and will subject public officials and other citizens opposing TNR to harassment and threats [5, 6].” [7]

Animal Hoarding
Dauphiné and Cooper’s argument presupposes that enough is known both about “people involved in TNR” and “the psychiatric disorders described in problematic animal hoarding” for a valid comparison to be made. In fact, very little is known about either one. Randy Frost, whose 2000 article the authors cite, begins by noting, “almost no psychiatric literature exists on this topic.” [3] A year earlier, Gary Patronek (a collaborator of Frost’s, whose work Frost cites throughout his paper) observed: “Unlike the hoarding of inanimate objects, which may be linked with a variety of psychiatric conditions, animal hoarding has not yet been linked with any specific disorder.” [8]

Nevertheless, both Patronek and Frost describe—based on some of the earliest research on the subject—some common characteristics of, and explanatory models for animal hoarding. And provide this definition:

“someone who accumulates a large number of animals; fails to provide minimal standards of nutrition, sanitation and veterinary care; and fails to act on the deteriorating condition of the animals (including disease, starvation and even death) or the environment (severe overcrowding, extremely unsanitary conditions), or the negative effect of the collection on their own health and well-being and on that of other household members.” [8]

This seems to have been the framework for the definition adopted by the Hoarding of Animals Research Consortium (with which Patronek and Frost were involved), which places greater emphasis on two key elements: denial, and accumulation and control:

  • Having more than the typical number of companion animals;
  • Failing to provide even minimal standards of nutrition, sanitation, shelter, and veterinary care, with this neglect often resulting in illness and death from starvation, spread of infectious disease, and untreated injury or medical condition;
  • Denial of the inability to provide this minimum care and the impact of that failure on the animals, the household, and human occupants of the dwelling;
  • Persistence, despite this failure, in accumulating and controlling animals.

“Saving” 25 or 30 cats, then—whether in one’s home or in the park—does not constitute animal hoarding. As Patronek pointed out during a recent interview on NPR’s Radio Times, “numbers alone don’t define hoarding… you’ve got to have these functional deficits and denial, in combination with the numbers.”

Opponents of TNR (and of free-roaming cats in general) will likely seize upon that second point, arguing that feral cat colonies—by definition—lack adequate care. But the very fact that these cats are part of a TNR program means they’ve been evaluated by veterinary professionals, requiring a concerted effort—sometimes bordering on the heroic—on the part of the trappers and caregivers involved. Some programs perform vaccinations (that this is not standard practice, is, admittedly, a controversial issue); at a minimum, cats deemed too sick to be returned are euthanized.

A 1999 survey of survey of “101 individuals or couples who cared for 132 colonies of free-roaming cats in north central Florida” illustrates the importance caregivers place on health:

“More than a third of the caretakers reported that they had provided some kind of veterinary care (not including being neutered at the TNR clinic) for the cats in the past or would provide veterinary care if it was necessary in the future. This type of care included booster vaccinations, parasite control, antibiotic treatment, ear medication, veterinary examinations, and emergency treatment.” [9]

In addition, 96% provided food, and 75% provided shelter. It’s important to note, too, that these numbers are conservative relative to the care received by the cats, in that (1) some caregivers were responsible for multiple cats, and (2) respondents to the survey were not necessarily the individuals who provided food, shelter, and so forth.

Such findings are certainly consistent with my own experience. The TNR networks I’m tapped into (mostly by way of e-mail or online bulletin boards) are typically buzzing with requests from, and recommendations to, caregivers committed to maintaining and improving the health of feral cat colonies.

On the other hand, it’s not clear from Dauphiné and Cooper’s paper that their reference to animal hoarding has anything to do with the behavior’s defining characteristics at all. More than anything else, the authors seem to be suggesting that resistance to TNR “alternatives” constitutes some psychiatric disorder—a possible reference to animal hoarders’ “reluctance to remove any animals, even when adequate homes were available.” [3]

Alternatives to TNR
Respectable sanctuaries, as I’ve already discussed, are few and far between, and typically at operating at capacity. In any case, such environments are not in the best interest of unsocialized cats. No-kill shelters, too, are scarce, and—recognizing realities Dauphiné and Cooper (and veterinarian Christine Storts, whose letter they cite) overlook or ignore—generally endorse TNR as their feral cat management approach. [10]

And as for “traditional animal control,” that’s nothing more than a rather cowardly euphemism for trap-and-kill.

What about the harassment and threats? Here, Dauphiné and Cooper cite Paul Barrows’ 2004 article “Professional, Ethical, and Legal Dilemmas of Trap-Neuter-Release,” and Pamela Jo Hatley’s 2004 paper, “Will Feral Cats Silence Spring in Your Town?” “During the past several years,” writes Barrows:

“as debate regarding abandoned and feral cats has become more heated, concerns have emerged regarding the extent to which some activists will go to promote their cause. Those supporting trap and removal of abandoned and feral cats, rather than TNR, have reported verbal abuse, personal threats, disruption of public forums, and interference with the conduction of their businesses.” [5]

Dauphiné and Cooper buy into Barrows’ account without bothering to check out his source (actually, these two make a shameful habit of such shortcuts throughout their paper, thereby raising questions about their numerous assertions, and, more problematically, their capabilities and integrity as researchers). In fact, Barrows cites a 2002 Wall Street Journal story in which exactly one of “those supporting trap and removal”—Frank Spiecker, of Garden State Pest Management—was interviewed:

“…property managers, fearing health complaints or lawsuits, hire Mr. Spiecker to trap and remove stray cats… Cat jobs have gotten him screamed at, threatened and jostled. His truck has been jumped on and pounded, his traps run over, and his trapped cats freed… To cat lovers, he abets feline mass murder, since most of the cats he traps end up dead.” [11]

All of which seems remarkably flimsy for describing and condemning—as Dauphiné and Cooper do—the behaviors of “many such people.” Until it’s compared to the even flimsier “evidence” provided by Hatley:

“Many citizens and public officials have voiced concerns about the public health issues and wildlife issues involved in hoarding large numbers of cats in the wild. Some who have resisted the extreme efforts by proponents of TNR and cat colonies have been subjected to verbal abuse and threats.” [6]

Dodgy research practices aside, the notion that one’s preference for TNR over “enclosed sanctuaries, no-kill shelters, and traditional animal control” is indicative of some psychiatric disorder remains a mighty hard sell. Dauphiné and Cooper’s so-called alternatives are simply not—in a very literal sense—viable options.

*     *     *

To compare TNR to animal hoarding betrays either a profound lack of knowledge about either one, or a desperate attempt to taint the former by association with the latter. I suspect that, like the most despicable political strategists, Jessup, Dauphiné and Cooper, and Lepczyk et al., threw it out there just to see if it would stick—the connection they’re attempting to make certainly has nothing to do with science.

I’ve a friend who jokes that the only thing feral cats aren’t being blamed for these days is climate change. Well, not yet, anyhow.

Literature Cited
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. Jessup, D.A., “The welfare of feral cats and wildlife.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1377-1383.

3. Frost, R., “People Who Hoard Animals.” Psychiatric Times. 2000. 17(4).

4. Storts, C.M., “Discussion on TNR programs continue (letter).” Journal of the American Veterinary Medical Association. 2003. 222: p. 711–712.

5. Barrows, P.L., “Professional, ethical, and legal dilemmas of trap-neuter-release.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1365-1369.

6. Hatley, P.J. (2004) Will Feral Cats Silence Spring in Your Town? www.pamelajohatley.com/Articles/ABA.pdf Accessed August 8, 2010.

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. 2009. p. 205–219.

8. Patronek, G.J., “Hoarding of animals: An under-recognized public health problem in a difficult-to-study population.” Public Health Reports. 1999. 114(1): p. 81–87.

9. Centonze, L.A. and Levy, J.K., “Characteristics of free-roaming cats and their caretakers.” Journal of the American Veterinary Medical Association. 2002. 220(11): p. 1627-1633.

10. Winograd, N.J., Redemption: The myth of pet overpopulation and the no kill revolution in America. 2007: Almaden Books.

11. Sterba, J.P., Tooth and Claw: Kill Kitty?, in Wall Street Journal. 2002: New York. p. A.1

Repeat After Me

3 Aug 2010

Listening to NPR’s On the Media this weekend, I was struck by a story (first broadcast in 2006) about how certain “sticky” numbers—however dubious—find their way into the media landscape and beyond, as On the Media co-host Brooke Gladstone noted:

“Four years ago, we delved into the mysterious number, said to be 50,000, of child predators online at any given time. It was cited by the NBC Dateline program “To Catch a Predator” and also by then Attorney General Alberto Gonzales.

But spokespersons for the FBI, the National Center for Missing and Exploited Children, and the Crimes against Children Research Center said it was not based on any research they were aware of. The A.G.’s office at the time, well, they said it came from Dateline.”

Wall Street Journal columnist Carl Bialik, who spoke to Gladstone for the story, described the process whereby such slippery figures gain traction:

“An interesting phenomenon of these numbers is that they’ll often be cited to an agency or some government body, and then a study will pick it up, and then the press will repeat it from that study. And then once it appears in the press, public officials will repeat it again, and now it’s become an official number.”

All of which sounds very familiar—Bialik could easily be describing the “official numbers” put out by so many TNR opponents. Among those that have gained the most currency are the predation estimates from the Wisconsin Study, the American Bird Conservancy’s figure for the proportion of birds in the diets of free-roaming cats, and Dauphiné and Cooper’s estimate of free-roaming cats in the U.S.

The Wisconsin Study
Despite its having been discredited long ago (see, for example, “Addressing the Wisconsin Study”), the Wisconsin Study continues to be cited as if its estimate of 8–219 million birds killed by the state’s rural cats [1] was credible. As recently as last year, Longcore et al. cited the work in their essay “Critical Assessment of Claims Regarding Management of Feral Cats by Trap–Neuter–Return.” [2]

This, despite the fact that—15 years earlier—co-author Stanley Temple told the press:

“The media has had a field day with this since we started. Those figures were from our proposal. They aren’t actual data; that was just our projection to show how bad it might be.” [3]

It’s true: the media has had a field day. Among the major newspapers to cite the Wisconsin Study are the Wall Street Journal [4], the New York Times [5], and the Los Angeles Times [6]. However, as I’ve described previously, it’s been the wildlife conservationists and bird advocates who’ve really had a field day with the Wisconsin Study:

  • The American Bird Conservancy (ABC) refers to the study, in its brochure Domestic Cat Predation on Birds and Other Wildlife. And the ABC goes one step further, pointing out that Coleman and Temple’s estimate was for rural cats, and that “suburban and urban cats add to that toll.” [7]
  • A 2009 article in Audubon Magazine suggests “cats were annually knocking off somewhere in the neighborhood of 8 million birds just in rural Wisconsin.” [9] To the magazine’s credit, they used Coleman and Temple’s low estimate—but none of the numbers from the Wisconsin Study are scientifically sound.

Birds Represent 20–30% of the Diet of Free-roaming Cats
According to an ABC report (downloadable from their website), “extensive studies of the feeding habits of domestic, free-roaming cats… show that approximately… 20 to 30 percent [of their diet] are birds.”

This, apparently, is the same report that Ellen Perry Berkeley debunked in her book, TNR Past Present and Future: A history of the trap-neuter-return movement, noting that the ABC’s 20–30% figure was not based on “extensive studies” at all. [10] In fact, just three sources were used: the now-classic “English Village” study by Churcher and Lawton [11], the Wisconsin Study (described above), and Mike Fitzgerald’s contribution to “The Domestic Cat: The Biology of Its Behaviour.” [12]

This gets a little complicated, so bear with me.

When Churcher and Lawton reported, “overall, birds comprised 35% of the total catch,” [11] they were referring to prey tallies recorded by study participants—not to the overall diets of the cats involved. Figures obtained through similar methods for the Wisconsin Study were 20–23%, [1, 13, 14] which the authors suggest—citing Fitzgerald’s comprehensive review of predation and dietary studies—are in line with other work:

“Extensive studies of the feeding habits of free-ranging domestic cats over 50 years and four continents [12] indicate that small mammals make up approximately 70% of these cats’ prey while birds make up about 20%.” [14]

But they’re comparing apples and oranges. Both the English Village and Wisconsin Studies report the percentage of birds returned as a portion of the “total catch,” whereas Fitzgerald reports percentage by frequency (i.e., the occurrence of birds in the stomach contents or scats of free-roaming cats), a point apparently lost on Coleman and Craven. The 21% figure [12] they refer to, then, is simply not comparable to their own (or that of the English Village study, a fact Churcher and Lawton acknowledge in their paper). As Berkeley notes, “this 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!”

To put all of this into more familiar terms, it’s a bit like saying that coffee makes up 20–30% of the American diet versus saying that 20–30% of Americans drink coffee each day.

Nevertheless, 13 years after the ABC first published its report, the myth persists. The report—including the mistaken dietary figures—is still available. And the National Audubon Society has helped perpetuate the error, noting in its Resolution Regarding Control and Management of Feral and Free-Ranging Domestic Cats:

“…it has been estimated that birds represent 20–30% of the prey of feral and free-ranging domestic cats.”

Estimates of Free-roaming Cats
In January, Steve Holmer, the ABC’s Senior Policy Advisor, told the Los Angeles Times, “The latest estimates are that there are about . . . 160 million feral cats [nationwide].” Sounds like an awful lot of cats—nearly one for every two humans in the country. So where does this figure come from?

The source is a paper by Nico Dauphiné and Robert Cooper (which can be downloaded via the ABC website), presented at the Fourth International Partners in Flight conference. In it, Dauphiné and Cooper use some remarkably creative accounting, beginning with an unsubstantiated estimate of unowned cats, to which they add an inflated number of owned cats that spend time outdoors. In the end, they conclude that there are “117–157 million free-ranging cats in the United States.” [15] (For a more thorough explanation, see my previous post on the subject.)

Estimating the number of free-roaming cats wasn’t even the point of their paper. As the title—“Impacts of Free-ranging Domestic Cats (Felis catus) On Birds In the United States: A Review of Recent Research with Conservation and Management Recommendations”—suggests, the primary purpose was to describe the cats’ impact on birds. The authors’ exaggerated figure was merely a convenient route to their estimate of birds killed annually by cats: “a minimum of one billion birds” [15] (which, it should be clear, has the potential to become a very sticky number).

Holmer goes a step further, using only the upper limit of the range published by Dauphiné and Cooper, and making the subtle—but important—shift from free-ranging to feral cats.

When I asked him about this, he explained that those figures were “based on an earlier version of Nico’s latest paper and are now being updated in our materials.” I don’t know that any such changes were made; and in any event, the bogus estimate has already been published in the L.A. Times—as if it were true.

*     *     *

TNR opponents will often point to the vast collection of research studies, government reports, news accounts, and the like, that support their assertions. Drill down a bit into that collection, though, and they all start to look alike: the same familiar sources, the same flawed studies—and the same bogus figures. These figures have become the kind of “official numbers” Bialik refers to: quantitative poseurs owing their popularity to tireless—and irresponsible—repetition more than anything else.

Literature Cited
1. 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

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

4. Sterba, J.P., Tooth and Claw: Kill Kitty?, in Wall Street Journal. 2002: New York. p. A.1

5. Barcott, B., Kill the Cat That Kills the Bird?, in New York Times. 2007: New York. http://www.nytimes.com/2007/12/02/magazine/02cats-v–birds-t.html

6. Kennedy, J.M., Killer Among Us, in Los Angeles Times. 2003: Los Angeles. http://articles.latimes.com/2003/dec/23/news/os-cat23

7. 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

8. FWS, Migratory Bird Mortality. 2002, U.S. Fish and Wildlife Service: Arlington, VA. www.fws.gov/birds/mortality-fact-sheet.pdf

9. Williams, T., Felines Fatale, in Audubon Magazine. 2009, National Audubon Society: New York, NY. http://www.audubonmagazine.org/incite/incite0909.html

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

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. 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. 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

14. 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

15. 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.

Out-Sciencing the Scientists

4 Jul 2010

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.

Learning Your ABC

18 Jun 2010

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

14 Jun 2010

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

11 Jun 2010

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

4 Jun 2010

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?

31 May 2010

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

27 May 2010

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

24 May 2010

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 survey—commissioned 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.

Hold Your Applause

20 May 2010

Three months after my letter to Conservation Biology was rejected, it’s become apparent what they were really looking for: applause, not criticism.

Of course it probably doesn’t help that I’m not a member of the club; I don’t even know the secret handshake. (Michael Hutchins, writing for the Wildlife Society Blog, “Making Tracks,” has accused me—an outsider—of trying to “out-science the scientists.”)

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. 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.

The reasons behind this lack of opposition are unclear, but 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. Or, they simply do not want to devote time and energy to the issue and are unaware of policy actions.

I’d like to offer an alternative explanation. Yes, the work speaks for itself, but there are plenty of observers—surely, there are conservation biologists and wildlife ecologists among them—who don’t particularly like what it’s saying.

For the next few posts, then, I’m going to present a sampling of the more serious flaws—including exaggerated and misleading claims, botched analyses, questionable research and review methods, and widespread bias—all too common in the feral cat/TNR literature. Let’s see what Lepczyk at al. are cheering about…

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.

The Things People Say (or Don’t)—Part 3

30 Apr 2010

The American Bird Conservancy (ABC) is among the most visible organizations to oppose TNR—and put PR ahead of the relevant science (which ABC has been doing for years now).

ABC was one (along with the L.A. Audubon Society and Urban Wildlands Group) of several petitioners in the case that eventually led to an injunction against publicly supported TNR in Los Angeles. Following the court’s decision, ABC’s Senior Policy Advisor, Steve 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.

Days later, I sent Holmer an e-mail, asking for details about his figure of 160 million feral cats (the number of birds killed could, I assumed, be addressed later). To his credit—and unlike the people I tried to contact at the Urban Wildlands Group and L.A. Audubon Society—Holmer actually replied, leading to a cordial but brief correspondence in which he directed me to the work of Nico Dauphiné and Robert J. Cooper.

Sure enough, just two pages into Dauphiné and Cooper’s article [1] (available for download via the ABC website):

There is therefore an estimated total of 117–157 million free-ranging cats in the United States.

But there are a number of significant problems with their estimate—which is calculated by combining an estimated number of feral cats with an estimated number of owned cats having outdoor access. Here, in a nutshell, is a breakdown of their calculation:

Dauphiné and Cooper start with 60–100 million “stray and feral (unsocialized) cats, nearly all of which range freely outdoors” a figure taken from a 2004 paper by David Jessup [2]. But, because Jessup didn’t cite his source(s), this is actually no estimate at all. At best, it’s a guess—and one intended to paint as stark a picture as possible.

Then, citing a 2004 paper (which in turn cites a study commissioned by ABC—the results of which are summarized here) by ABC’s Linda Winter [3], Dauphiné and Cooper suggest that “approximately 65%” of pet cats “are free-ranging outdoor cats for at least some portion of the day.” Taking 65% of 88 million—the number of pets cats estimated by the American Pet Products Association’s 2008 National Pet Owners Survey—the authors arrive at 57 million pet cats with outdoor access.

But what does that mean, to be free-ranging for at least some part of the day?

A 2003 survey conducted by Clancy, Moore, and Bertone [4] suggested 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. And a closer look at the study commissioned by ABC  indicates similar behavior: “35% keep their cats indoors all of the time” and “31% keep them indoors mostly with some outside access.” [5]

For Dauphiné and Cooper, though, these cats are no different from feral cats. For them to simply add the number of “part-time” outdoor cats to the population of “free-ranging outdoor cats” is highly misleading! The authors have no idea what impact these cats might have on bird populations—which is the stated purpose of their paper.

Note: For a closer look at the flaws in Dauphiné and Cooper’s paper, download “One Million Birds,” by Laurie D. Goldstein.

*     *     *

OK, back to Steve Holmer and the L.A. Times…

Holmer’s estimate of 160 million is not a range, but the high limit of a seriously-flawed estimate (which is itself based on little more than wild guesses). And he refers specifically to feral cats—an error even Jessup, Dauphiné, and Cooper (none of whom, it seems, is likely to give feral cats even the slightest benefit of the doubt) don’t make.

Given the context of the discussion—TNR in Los Angeles—such an error was likely (perhaps intended?) to have serious consequences. To suggest that there are 160 million feral cats in this country—approximately one feral cat for every two human inhabitants—is irresponsible and manipulative. And it raises doubts about the integrity of ABC and its representatives. All of which I told Holmer. His reply read, in part:

We are doing are [sic] best to convey the facts as they become available. The 160 million figure was based on an earlier version of Nico’s latest paper and are now being updated in our materials which 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 haven’t checked the ABC website to verify Holmer’s claim. In any event, the damage was already done; ABC and the other petitioners had put a stop to publicly supported TNR in Los Angeles. And, from what I’ve seen (I’ve yet to wade through the thousands of pages of discovery documents in the case), they’d done so by selectively overlooking, ignoring, and misrepresenting the scientific research. Or, in the case of Holmer’s comment to the Times, simply “inventing” it.

By the way, I asked Holmer about his revised figure of “more than one million birds each day” killed by cats. He’s stopped replying to my e-mail.

References
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. 2010. p. 205–219

2. Jessup, D. A. (2004). The welfare of feral cats and wildlife. Journal of the American Veterinary Medical Association, 225(9), 1377-1383.

3. Winter, L., “Trap-neuter-release programs: the reality and the impacts.” Journal of the American Veterinary Medical Association. 2004. 225(9): p. 1369-1376.

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

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