Inflated cat stats panic birders

From ANIMAL PEOPLE,  March 2013:

WASHINGTON D.C.––Inflating the U.S. pet cat population by ten million,  the outdoor pet cat population by closer to 50 million,  and the best documented estimates of the feral cat population by up to 64 million,  Smithsonian Conservation Biology Institute ornithologists Scott Loss and Peter Marra and U.S. Fish and Wildlife Service biologist Tom Will on January 29,  2013 alleged in the journal Nature Communications that domestic cats in the U.S. kill up to 3.7 billion birds and as many as 20.7 billion mice,  voles,  and other small mammals. Based on a review of previously published papers,  the findings were trumpeted by mass media with scant notice that the projected cat numbers appear to be more than four times the most plausible figures that could be drawn from actual cat population surveys. The projected estimate of cat predation was therefore magnitudes of order higher than the estimate of 100 to 125 million birds killed by cats per year issued by Albert Manville of the U.S. Fish & Wildlife Service in 2002. The U.S. pet cat population is down 18% from the 2007 peak of nearly 90 million,  and is now 74 million and still falling,  according to the 2012 edition of the American Veterinary Medical Association Pet Ownership & Demographics Sourcebook. Pet keeper surveys have shown since 1990 that more than two-thirds of U.S. pet cats are kept indoors. Loss,  Marra,  and Will guesstimated that there are between 30 and 80 million “unowned” cats in the U.S.,  but in the past 20 years no survey of animal control data,  roadkill counts,  or nationally representative sampling of feral cat habitat has shown any likelihood that the feral cat population exceeds 16 million. ANIMAL PEOPLE has estimated since 2003,   from the combination of available data sources,  that the annual midsummer peak of the feral cat population is steady at less than 13 million,  the winter low is just over six million,  and the year-round average is about nine million. Tufts University School of Veterinary Medicine graduate student Anne Fleming, at a December 2012 conference on outdoor cats hosted in Los Angeles by the Humane Society of the U.S.,   presented data from surveying 263 feral cat colonies in Rhode Island which projects a national feral cat population of 8.8 million. “This [Smithsonian] literature review was a thinly veiled attempt to promote an anti-cat agenda,”  charged Alley Cat Allies.  “The authors’ findings were based on extreme extrapolations made from miniscule studies;  their margin of error was in the billions;  and they included studies from decades ago.”  “If the real number for cat predation is even one tenth or one one-hundredth of the numbers invoked by the authors of this study,”  commented HSUS president Wayne Pacelle,   “it warrants serious attention from the animal protection movement and from everyone else concerned about cats and about wildlife.” But Pacelle admitted to skepticism.  “Loss,  Will,  and Marra have thrown out provocative numbers for cat predation, and their piece has been published in a highly credible publication,”  Pacelle continued,  “but they admit the study has many deficiencies.  Their work is derivative of what others have done on the topic,  and they have essentially rolled up what they could find in the literature and done their best to attach some numbers.”

Vox Felina responds

The most thorough critique came,  in several installments during the next two weeks,  from Vox Felina blogger Peter Wolf. Recounted Wolf,  “On May 25,  2011,  J. Scott Robinson,  director of the Office of Sponsored Projects for the Smithsonian Institute,  sent a three-page proposal to Randy Dettmers,  a biologist in the Division of Migratory Birds for the U.S. Fish and Wildlife Service,  outlining the scope and budget for a project called ‘Effects of subsidized predators on bird populations in an urban matrix.’  The work was to begin in just one week and continue through the end of September, conducted by Smithsonian Conservation Biology Institute researchers Peter Marra and Nico Dauphiné.  Two weeks earlier, on May 11,  2011,  Dauphiné had been arrested,  charged with attempted animal cruelty for trying to poison neighborhood cats.” Convicted in District of Columbia Superior Court of misdemeanor attempted cruelty to animals on October 31, Dauphine was on December 14, 2011 sentenced to do 120 hours of community service,  spend a year on probation,  and pay a fine of $100,  with 180 days in jail suspended. “Fast-forward a year and a half,”  Wolf continued,  “to the recent publication of the Smithsonian’s ‘killer cat study.’ If,  as [bird population researchers] T.W. Arnold and R.M. Zink have suggested,  the breeding population of North American landbirds is 4.9 billion,  then the 1.4 to 3.7 billion mortalities reported by Loss et al represent an astonishing 28.5–75.5% of the total population.  That’s on top of the 21% that Arnold and Zink attribute to collisions with towers and windows.  While some species are,  unquestionably,  on the verge of extinction,  the entire population of North American landbirds most certainly is not.” Further,  Wolf wrote,  “Loss et al fail to acknowledge that predation—even at very high levels—does not necessarily lead to population-level impacts.  Like all predators,  cats tend to prey on the young,  the old,  the weak,  or unhealthy. As the British Royal Society for the Protection of Birds notes:  ‘Despite the large numbers of birds killed, there is no scientific evidence that predation by cats in gardens is having any impact on bird populations United Kingdom-wide…It is likely that most of the birds killed by cats would have died anyway from other causes before the next breeding season,  so cats are unlikely to have a major impact on populations.’” Loss,  Marra,  and Will noted that cats have been found to prey upon at least 58 U.S. native bird species.  Observed Wolf,  “57 of the 58 species have been given a ‘Least Concern’ conservation status by the International Union for Conservation of Nature.” Wolf also obtained a brief critique of the Loss,  Marra,  and Will paper from Dennis Turner,  editor of The Domestic Cat:  The Biology of its Behaviour. “Such extrapolations of how many birds or rodents or reptiles and amphibians cats kill each year are absolutely meaningless on the species level if not put into context with the annual production of that species,”  said Turner.  “Any claim that cats are a much ‘more significant anthropogenic threat’ than other factors (e.g., construction with loss of habitat,  pollution,  road traffic kills,  etc.) are even more ridiculous,  in that there are rarely estimates (good or poor) of deaths of birds/mammals/amphibians to such factors to compare with.” Ironically,  Loss,  Marra and Will recently reached a similar conclusion,  Wolf recalled,  in a 2012 paper published in the journal Frontiers in Ecology and the Environment.   There,  Loss,  Marra,  and Will acknowledged,  “Quantification of direct anthropogenic mortality,  although critical for conservation efforts,  remains imprecise.  National mortality estimates are often based on extrapolation from a limited sample of small-scale studies,  and estimates of uncertainty are ignored or only superficially assessed.”

Historical context

While Loss,  Marra and Will argued that the U.S. outdoor cat population is increasing,  a variety of studies done since 1908 suggest that the combined totals of outdoor pet cats and feral cats have actually been quite consistent.  Frank M. Chapman of the American Museum of Natural History produced the first estimate,  putting the outdoor cat population at circa 25 million.  National Family Opinion founders Howard and Clara Trumbull did surveys in 1927,  1937,  and 1947-1950 that showed the outdoor cat population gradually rising from about 30 million to 35 million. ANIMAL PEOPLE found in surveys done in 1992 and 1996 that the combined outdoor pet and feral cat population had probably peaked circa 1991 at about 46 million,  and was in rapid decline.  Shelter admissions of cats dropped by about 75% during the 1990s,  after the introduction of neuter/return to the U.S.,  before leveling off at about four million per year during the past decade.

Oldest colony is zeroed out

Loss,  Marra and Will contended that neuter/return has not reduced feral cat numbers just five weeks after Inayat Singh of Canadian Press reported that neuter/return has eliminated possibly the oldest feral cat colony in North America. Living behind Parliament Hall in Ottawa,  above the Rideau Canal,  the cats were reputedly descended from cats brought by British engineer John By,  who built the canal in 1826-1832.  Ottawa was originally called Bytown in honor of By.  From completion of the first Parliament building in 1866 until 1955 the cats wandered the halls of Parliament as quasi-official mousers. After eviction,  the cats persisted on Parliament Hill,  fed by volunteers coordinated by Irene Desormeaux,  who died in 1987.  Neuter/return was begun by her successor,  Rene Chartrand.  About 30 cats were sterilized.  Chartrand retired for health reasons in 2008,  replaced by former civil servant Brian Caines and half a dozen volunteers.  The last kittens in the colony were born “probably 10 to 15 years ago,” Caines told Singh of Canadian Press. With just four cats left,  Caines found adoptive homes for three,  and adopted the last cat himself.   ––Merritt Clifton

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