What’s Several Billion Birds, Among Friends?

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, [1] including the 365–988 million birds they’ve estimated are killed annually as a result of building collisions. [2]

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. [3]

As documents obtained via Freedom of Information Act reveal, though, this isn’t the weirdest part of the story. Read more

Appealing to Our Better Nature

It’s not every day that I hear from somebody whose work I’ve criticized. (In fact, I rarely receive a response from those I reach out to for comments or clarification.) Imagine my surprise, then, when I received an e-mail from somebody involved with Nature Canada’s “cats indoors” campaign who was interested in better understanding my objections. Even more surprising was my subsequent telephone conversation with Sarah Cooper: exactly the sort of thoughtful, open exchange I’d hoped for when I launched Vox Felina six years ago today.

It doesn’t hurt that Cooper, who’s largely responsible for Nature Canada’s communication strategy for the campaign, is curious, witty, and charming.

Over the course of our conversation (nearly two hours, if I recall correctly), she gave me plenty to think about. So, to mark Vox Felina’s six-year anniversary, I want to reflect on that previous post a little bit and ask readers to weigh in as well. Read more

O (Environment) Canada!

In “Estimated Number of Birds Killed by House Cats (Felis catus) in Canada,” published late last year in Avian Conservation and Ecology, Environment Canada research scientist Peter Blancher estimates that cats—owned and unowned—“kill between 100 and 350 million birds per year in Canada,” and suggests that this level of predation “is probably the largest human-related source of bird mortality in Canada.” [1]

I submitted the following comments to the journal in response to Blancher’s article, but retracted my submission upon learning that (1) the length is nearly twice as long as what is permitted, and (2) that I would be required to pay an “author fee” of about $340.

I’m not naïve enough to think that posting my comments here is comparable to having them published in ACE, but, given the considerable work involved—and, more important, the obvious policy implications of Blancher’s paper—I think it’s important that they be available. Read more