The second in a series of posts that breaks down my critique of the essay “Critical Assessment of Claims Regarding Management of Feral Cats by Trap-Neuter-Return” (Conservation Biology, Volume 23, No. 4, 887–894) by Travis Longcore, Catherine Rich, and Lauren M. Sullivan.
Like so many others interested in blaming cats for declining bird populations, Longcore et al. refer to a 1996 article in Wisconsin Natural Resources magazine , in which the authors estimate that 8–219 million birds are killed annually by “free-ranging rural cats” in the state. More than any other work, the “Wisconsin Study” (which is actually a series of articles, the first being published in 1993 ) has been used as “evidence” against advocates for free-roaming cats in general, and TNR in particular.
In my previous post, I referred only briefly to Coleman and Temple’s work; in fact, careful scrutiny is in order. Among the study’s more notable flaws:
- Its “estimate that 23 percent of [cats’] diet consists of birds” is well above the 7–10.5% figure suggested by Fitzgerald,  one of the world’s foremost experts on the subject (for a detailed account, see Ellen Perry Berkeley’s 2004 book, TNR Past present and future: A history of the trap-neuter-return movement ). In fact, Coleman and Temple cite Fitzgerald’s work, making the error all the more egregious.
- Coleman and Temple assume that all cats hunt; in fact, it has been suggested that only 35–56% of cats are hunters. [5,6]
- Their figures for cat density, too, have been challenged. 
Now 14 years old, the Wisconsin Study has achieved mythical status—but not in a good way. I suppose it’s because the numbers are so impressive. Forget the fact that they’re essentially fictitious—they’re simply too tempting for people who see cats as the primary reason for declining bird populations. James Tantillo, a Lecturer in the Department of Natural Resources at Cornell University’s College of Agriculture and Life Sciences, is right on the money when he refers to Coleman and Temple’s estimate as an example of a “‘mutant statistic’ whose origins and genesis have been greatly lost to the people who cite it.” 
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Among those who cite it are, of course, Longcore et al. But they failed to cite an important follow-up comment by one of the authors of the Wisconsin Study. In a 1994 interview, an “exasperated” Temple told The Sonoma County Independent:
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. 
More than the media, however, it’s been the wildlife conservationists and bird advocates who have had a field day with the Wisconsin Study. Here are just a few examples:
- The American Bird Conservancy refers to the study in its brochure Domestic Cat Predation on Birds and Other Wildlife. But 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.” 
- The U.S. Fish and Wildlife Service cites the study’s “intermediate” estimate of 39 million birds in its Migratory Bird Mortality Fact Sheet.
- A recent article in Audubon Magazine suggests “cats were annually knocking off somewhere in the neighborhood of 8 million birds just in rural Wisconsin.”  To the magazine’s credit, they used Coleman and Temple’s low estimate (a surprise given the overall tone of the piece). Still, none of the numbers from the Wisconsin Study are scientifically sound (indeed, one can make a strong argument that none of the work constitutes actual research).
For Longcore et al. to cite the Wisconsin Study without even a mention of its numerous flaws, or the rather public admission by one of its authors that their estimates “aren’t actual data,” casts serious doubt on the entire paper. Either they didn’t know how flimsy Coleman and Temple’s work was, or they knew and ignored the facts. Neither approach makes for good science, of course.
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Estimating the number of birds killed by cats is difficult enough; demonstrating that their predation is the cause of declining bird populations is an even greater challenge. Nevertheless, Longcore et al. suggest the evidence is both plentiful and compelling. I’ll lay out an argument to the contrary in my next post…
1. Coleman, J. S., & Temple, S. A. (1996). On the Prowl. Wisconsin Natural Resources, 20, 4–8. http://www.dnr.state.wi.us/wnrmag/html/stories/1996/dec96/cats.htm
2. Coleman, J. S., & Temple, S. A. (1993). Rural Residents’ Free-Ranging Domestic Cats: A Survey. Wildlife Society Bulletin, 21(4), 381–390.
3. Fitzgerald, B. M. (1988). Diet of domestic cats and their impact on prey populations. In D. C. Turner & P. P. G. Bateson (Eds.), The Domestic cat: The biology of its behaviour (1st ed., pp. 123–147). Cambridge; New York: Cambridge University Press.
4. Berkeley, E. P. (2004). TNR Past present and future: A history of the trap-neuter-return movement. Bethesda, MD: Alley Cat Allies.
5. Baker, P. J., Molony, S. E., Stone, E., Cuthill, I. C., & Harris, S. (2008). Cats about town: is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis, 150, 86-99.
6. Goldstein, L. D., O’Keefe, C. L., & Bickel, H. L. (2003). Addressing “The Wisconsin Study.” http://www.straypetadvocacy.org/html/wisconsin_study.html
7. Clifton, M. (2003). Where cats belong—and where they don’t. Animal People http://www.animalpeoplenews.org/03/6/wherecatsBelong6.03.html
8. Tantillo, J. A. (2006). Killing Cats and Killing Birds: Philosophical issues pertaining to feral cats. In J. R. August (Ed.), Consultations in Feline Internal Medicine Volume 5 (5th ed., pp. 701–708). St. Louis, MO: Elsevier Saunders.
9. Elliott, J. (1994, March 3–16). The Accused. The Sonoma County Independent, pp. 1, 10.
10. American Bird Conservancy (undated). Domestic Cat Predation on Birds and Other Wildlife. The Plains, VA. www.abcbirds.org/abcprograms/policy/cats/materials/predation.pdf
11. Williams, T. (2009). Felines Fatale. Audubon Magazine. http://www.audubonmagazine.org/incite/incite0909.html