Outdoor cats bring home few souvenirs from their daily treks into the wild—a dead bird here, a torn ear there. But even the most talkative cat can’t convey the tales of its adventures. So owners might wonder: where do their pets go all day? In a new study, researchers from the United States, United Kingdom, Australia and New Zealand put GPS trackers on nearly 1,000 outdoor cats and tracked their movements for about a week.
The results, published last week in Animal Conservation, give a detailed account of the travels and dangers encountered by outdoor cats. As pet cats, most of them had food at home and were neutered or spayed. The results showed that the majority of cats stayed in the area immediately around their home base, either a few city blocks or the surrounding neighborhood of a suburb. But the evidence also shows that by staying close to home, the cats have a concentrated effect on neighborhood wildlife.
“Without the motivations of food and sex, most cats seem content to be homebodies,” zoologist Roland Kays tells National Geographic’s Jonathan Losos. “I was surprised at how little these cats moved. Most of them spent all their time within 100 meters [330 feet] of their yard.”
The researchers compared the journeys of cats by age, sex, whether or not they were spayed or neutered, and home environment. Young, male, unaltered, rural cats tended to travel further than their counterparts. Three cats were especially intrepid travelers: Blue, a farm cat, had a large territory; Penny, a cat in New Zealand, traveled over three square miles in six days; and Max, a neutered tomcat in southwest England, took a mile-long walk to a neighboring village and then turned around and walked home.
Still, most cats didn’t wander far, whether or not they lived in a region with natural predators like coyotes. Roads in particular appeared to be a greater danger than previously thought.
“A lot of people, when they received the data on their cats, were more concerned about them crossing roads than their effect on wildlife,” Victoria University of Wellington urban ecologist Heidy Kikillus, co-author and leader of the New Zealand team, tells National Geographic. Cats crossed the road an average of 4.5 times during a week of tracking. When Kikillus checked back in with the owners months after tracking the cats, she learned that many of the pets were hit by cars.
The researchers also asked owners to count up how many gifts of prey their cats dropped at home, and learned it was about 42 dead animals per year. But because cats don’t share all of their kills, the researchers estimate that their real impact may have been up to three times the prey that the cats brought home, putting each cat’s kill count closer to 130 per year, per Gizmodo’s Ryan Mandelbaum.
That doesn’t sound like a lot, but with the GPS data showing that these cats are hunting in a concentrated area, they are actually killing at a higher rate than native predators, according to the paper. And about 25 to 33 percent of the U.S.’s 86 million pet cats are allowed outside, so their impact is huge, Rachel Gross reported for Smithsonian magazine in 2016. A cat named Tibbles was brought to an island south of New Zealand in 1984 and independently pushed the Stephens Island wren to extinction, according to Smithsonian migratory bird expert Pete Marra.
“Because the negative impact of cats is so local, we create a situation in which the positive aspects of wildlife, be they the songs of birds or the beneficial effects of lizards on pests, are least common where we would appreciate them most,” co-author North Carolina State ecologist Rob Dunn says in a statement.
The new study also doesn’t account for stray and feral cats, which can have triple the impact on wildlife that housecats do. Domestic cats’ impact also goes beyond the wildlife they hunt—they’re carriers for toxoplasmosis, a parasite that can kill endangered seals.
Kays and his colleagues are planning future work using higher-resolution GPS tracking combined with accelerometers, which could show where cats are pouncing on prey. But for now, the results are clear to Kays, who tells Gizmodo: “Keep your cats indoors.”