Scientists looked into the mysterious lives of outdoor cats. They learned kitties don't go far, but they kill a lot of wildlife.

With much of the human population staying home because of the coronavirus pandemic, some pet owners may have started to wonder where their pets cats go and what they do all day.

A study published in the peer-reviewed journal Animal Conservation last month offers insight into the mysterious lives of outdoor cats.

Researchers and citizen scientists tracked the movements and behavior of 925 outdoor cats for a week in six countries by fitting them with GPS devices  and found that while they don't venture far, the cats can do a lot of ecological damage.

"There was a big knowledge gap about knowing where cats go. We have a pretty good idea about how many animals they kill," Roland Kays, lead study author and zoologist at the North Carolina Museum of Natural Sciences, told USA TODAY. "But we didn’t know where they did that killing."

No matter where they lived, most the cats had remarkably small home ranges, with only three cats venturing farther than 1 square kilometer, or less than half a square mile, the study found. Of the three, two cats were in New Zealand, where cats have no natural predators, and one was in England, and it traveled back and forth between two villages. 

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The cats roamed mostly in habitats disturbed by humans, such as housing developments. Surprisingly, there was no relationship between the presence of natural predators like coyotes and the size of the cats' home range.

Owners reported their pets killed an average of 3.5 prey a day. Accounting for the prey that cats don't bring home, that adds up to an average of 14.2 to 38.9 prey per 100 acres per year. Kays said the ecological impact was amplified because of the high density of cats in neighborhoods and because their impact is concentrated within about 110 yards of their homes.

Kays was surprised to learn that house cats' effect on native species could be two to 10 times bigger than that of natural predators.

"The good news is it’s mostly focused around near people’s houses," Kays said. "That helps us focus our attention on where cats are likely to be the biggest problem: where rare or endangered species are living close to people."

For example, Kays noted areas in Southern California where shorebirds nest on beaches near homes. He and other researchers are working on a high-resolution GPS tracker to help better understand where cats are hunting and how successful they are.

What's the lesson that Kays wants pet owners to take away from his research?

"They should keep their cats indoors."

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