AILSA CHANG, HOST:
Ever wonder what outdoor cats do all day? Well, it turns out they may be having a big impact on the local ecosystem. NPR's Lauren Sommer has more on a new study.
LAUREN SOMMER, BYLINE: In research studies, scientists are supposed to disclose any conflicts of interest. So are you a cat person or a dog person?
ROLAND KAYS: I'm actually more of a ferret person. I love the weasels, so we're just like those independent weirdos off on the side.
SOMMER: Right, so Roland Kays doesn't have a dog in this fight, and he's a scientist at North Carolina State University. He wanted to know what kind of harm outdoor house cats are doing to birds. So with some colleagues, he put GPS trackers on almost a thousand cats in six countries to see where they go all day.
KAYS: These cats are moving around their own backyard and a couple of their neighbor's backyards, but most of them are not ranging very much further. So initially, I thought, oh, this is good news. They're not going out into the nature preserves.
SOMMER: But then Kays factored in how much cats kill in that small area. Some cats in the study were bringing home 10 or 11 dead birds, rodents or lizards a month. And that doesn't include what they didn't bring home.
KAYS: That actually ends up being a really intense rate of predation on any unfortunate prey species that's going to live near that cat's house.
SOMMER: Kays reports in the journal Animal Conservation that compared to wild predators, house cats have four to 10 times the impact on local wildlife.
KAYS: The simplest thing to do is to keep your cat indoors.
SOMMER: But some people don't, like Susan Willson. She's an associate professor at St. Lawrence University. Her rescue cat known as the Gorilla was killing a lot of birds.
SUSAN WILLSON: I'm a biologist. You know, I'm a bird biologist, so that's just horrifying. And I...
SOMMER: So she found a special brightly colored collar.
WILLSON: It looks kind of like an Elizabethan collar/scrunchie around the cat's neck.
SOMMER: So birds can see the cat before it pounces. She tested it on her cat and dozens of others. It dramatically reduced the number of birds the cats brought home. Small rodents weren't so lucky.
WILLSON: Which isn't surprising because mammals see in black and white. You know, they're not as visual as a bird.
SOMMER: So as for Willson's cat...
WILLSON: Gorilla is now a happy indoor cat loving his life.
SOMMER: Lauren Sommer, NPR News.
(SOUNDBITE OF AL STEWART SONG, "YEAR OF THE CAT") Transcript provided by NPR, Copyright NPR.