Best Available Science?

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

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

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

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

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

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

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

In other words, consider the source.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

•     •     •

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

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

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

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

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

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

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

5. n.a., Multi-Species Recovery Plan for South Florida: Lower Keys Rabbit. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 151–171.

6. Jones, E. and Coman, B.J., ” Ecology of the feral cat, Felis catus (L.), in southeastern Australia.” Australian Wildlife Research. 1981. 8: p. 537–547.

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

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

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

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

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

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

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

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

15. Cruz, J.B. and Cruz, F., “Conservation of the dark-rumped petrel Pterodroma phaeopygia in the Galápagos Islands, Ecuador.” Biological Conservation. 1987. 42(4): p. 303-311.

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

17. Calver, M., et al., “Reducing the rate of predation on wildlife by pet cats: The efficacy and practicability of collar-mounted pounce protectors.” Biological Conservation. 2007. 137(3): p. 341-348.

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

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

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

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

22. Sax, D.F. and Gaines, S.D., Species invasions and extinction: The future of native biodiversity on islands, in In the Light of Evolution II: Biodiversity and Extinction,. 2008: Irvine, CA. p. 11490–11497.

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

24. Fitzgerald, B.M., Karl, B.J., and Veitch, C.R., “The diet of feral cat (Felis catus) on Raoul Island, Kermadec group.” New Zealand Journal of Ecology. 1991. 15(2): p. 123–129.

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

26. Courchamp, F., Langlais, M., and Sugihara, G., “Cats protecting birds: modelling the mesopredator release effect.” Journal of Animal Ecology. 1999. 68(2): p. 282–292.

27. Bergstrom, D.M., et al., “Indirect effects of invasive species removal devastate World Heritage Island.” Journal of Applied Ecology. 2009. 46(1): p. 73-81.

28. n.a., Key Largo Cotton Mouse (Peromyscus gossypinus allapaticola) 5-Year Review: Summary and Evaluation. 2009, U.S. Fish and Wildlife Service, Southeast Region, South Fiorida Ecological Services Office: Veero Beach, FL. p. 19.

29. n.a., Multi-Species Recovery Plan for South Florida: Key Largo Cotton Mouse. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 79–96.

30. n.a., Key Largo Woodrat (Neotomafloridana smalli) 5-Year Review: Summary and Evaluation. 2008, U.S. Fish and Wildlife Service, Southeast Region, South Fiorida Ecological Services Office: Vero Beach, FL.

31. n.a., Multi-Species Recovery Plan for South Florida: Key Largo Woodrat. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 195–216.

32. n.a., Multi-Species Recovery Plan for South Florida: Rice Rat. 1999, U.S. Fish and Wildlife Service: Atlanta, GA. p. 173–194.

33. n.a., Rice rat (Oryzomys palustris natator) 5-Year Review: Summary and Evaluation. 2008, U.S. Fish and Wildlife Service, Southeast Region, South Florida Ecological Services Office: Vero Beach, FL.

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

35. Nogales, M., et al., “A Review of Feral Cat Eradication on Islands.” Conservation Biology. 2004. 18(2): p. 310–319.

36. Veitch, C.R., “The eradication of feral cats (Felis catus) from Little Barrier Island, New Zealand.” New Zealand Journal of Zoology. 2001. 28: p. 1–12.

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