Frequently cited estimates for birds killed by cats in the U.S. actually exceed the number of birds estimated to be in the country. Documents obtained via Freedom of Information Act raise as many questions as they answer.
As I pointed out recently, the annual mortality estimates proposed in the 2013 paper, “The impact of free-ranging domestic cats on wildlife of the United States,” don’t add up. Or, to be more precise, they do add up—and up and up. Indeed, the authors’ “conservative” estimate of birds killed by outdoor cats appear to exceed the total number of land birds estimated to be in the country.
According to the Partners In Flight Population Estimates Database—which, given its intended use for “bird-conservation planning,” would seem to be the go-to source for the best estimates available—that total is 3.2 billion. That’s only 33 percent greater than the median estimate (2.4 billion) developed by Scott Loss, Tom Will, and Peter Marra—leaving very little room for the many other sources of mortality,  including the 365–988 million birds they’ve estimated are killed annually as a result of building collisions. 
And the high-end of their “conservative” estimate of annual cat-caused mortalities (4.0 billion) actually exceeds the PIF estimate by a significant margin—raising serious questions about the validity of the work portrayed by Marra, in Cat Wars, as the culmination of a century’s worth of evidence implicating cats in the decline of birds and other wildlife. 
As documents obtained via Freedom of Information Act reveal, though, this isn’t the weirdest part of the story. Read more