Free-Roaming Cats Are Top Bird-Killers, Researchers Say

Free-roaming cats, including domestic pets allowed out of the house, kill as many as 3.7 billion birds in the U.S. each year, far more than previous estimates, according to a report from wildlife researchers.

Feral cats and their prowling domestic cousins also dispatched as many as 20.7 billion small mammals such as rabbits and squirrels, making them more deadly to wildlife than cars, buildings, windmills or other objects, wrote Scott R. Loss, a scientist at the Smithsonian Conservation Biology Institute in Washington and an author of the report.

The findings suggest that free-ranging cats are “likely the single greatest source” of so-called anthropogenic mortality for U.S. birds and mammals, Loss wrote in the study conducted with colleagues at the Smithsonian and the U.S. Fish and Wildlife Service and published yesterday in the journal Nature Communications.

“Our estimates should alert policy makers and the general public about the large magnitude of wildlife mortality caused by free-ranging cats,” the authors wrote.

The report estimates that cats kill 1.4 billion to 3.7 billion birds annually and 6.9 billion to 20.7 billion mammals, including mice, shrews, voles, squirrels and rabbits. Previous research estimated bird deaths from cats in the “hundreds of millions” and “no large-scale mortality estimates exist for mammals,” the authors wrote.

The scientists derived their estimates using a mathematical model after analyzing previous research including small local studies of cat-wildlife contacts and various figures for the owned and wild cat population in the U.S.

“No precise estimate of the un-owned cat population exists in the U.S. because obtaining such an estimate is cost-prohibitive and feral, un-owned cats are wary of humans and tend to be solitary outside of urban area,” according to the report.

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