The mammalian toll is even higher, concluded researchers from the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service, ranging from 6.9 billion to 20.7 billion annually.
The analysis, published Tuesday in the journal Nature Communications, suggests that feral and owned cats pose a far greater threat than previously thought. One study in 2011 estimated that cats in the United States kill roughly half a billion birds annually.
Peter P. Marra, the paper’s senior author and a research scientist at the Smithsonian institute, said he and his colleagues “pulled together all the best estimates” from 90 studies to reach their estimate, taking into account the difference in behavior between owned and unowned cats.
“I don’t think there’s ever been an attempt like this,” Marra said in a telephone interview, adding that the new estimate is “conservative.”