Here’s an alarming but little-known figure—stray cats and pet cats allowed outdoors kill 3.6 million birds every day on average in the United States, for a total of at least 1.3 billion birds per year. That’s most likely a sizable chunk out of the U.S. land-bird population, which the Smithsonian Migratory Bird Center estimates is around 10-20 billion. While habitat loss and climate change pose long-term dangers to birds in this country, recent research shows that outdoor cats currently kill more of them than any other threat caused by humans.
It’s not just a problem in the U.S. A 2011 study found that domestic cats have directly contributed to extinctions of 22 bird species on islands around the world, and threatened dozens more. Researchers in the United Kingdom estimated that 55 million birds fall prey to domestic cats there each year; in Australia, threats to endangered species led government officials to announce plans for euthanizing 2 million feral cats.
Cat predation of wildlife, in other words, is a worldwide issue. But here’s something else that stretches across borders: People love cats. In the U.S., there are about 84 million pet cats, and around 46 million of them are allowed to roam outside. An estimated 30-80 million more live as strays. That’s a lot of cats, and many spend their days doing what they’ve done since the first cats were domesticated more than 9,000 years ago: hunting small animals. Humans originally used domesticated cats as efficient predators, protecting stores of food from vermin. But there’s little need for working cats anymore; these days, most people just think of them as gentle companions and Internet memes. But their instincts haven’t caught up to our evolving needs—cats are still highly effective stealth hunters. And our having them around in such numbers means trouble for birds.