A cat and a raccoon cross paths at night in Washington, D.C.

Outdoor D.C. cats put themselves and others in danger

Image: A cat and a raccoon cross paths at night in Washington, D.C. Credit: D.C. Cat Count, Humane Rescue Alliance

Letting pet cats spend time outdoors can put them at risk for contracting diseases, while simultaneously causing harm to wildlife and the ecosystem.

This finding came out of a larger effort to count all of the indoor, outdoor and shelter cats (Felis catus) in Washington, D.C., called the D.C. Cat Count.

“It’s well-known when cats go outdoors, they pose risks to the natural environment, and vice versa. There’s a risk for outdoor cats as well,” said Daniel Herrera, a graduate student at the University of Maryland. “All species encounter new risks whenever a cat steps outside.”

Herrera led a study published in Frontiers in Ecology and Evolution using camera traps and statistical modeling to determine how cats in D.C. may be affected by diseases and how they prey on other wildlife. Researchers specifically looked at how cats overlapped with wildlife to determine these risks.

“The project was massive,” Herrera said. “It took three years of a very collaborative team effort with camera traps all across D.C.” In total, they reviewed images from camera traps at 1,500 locations in the city. They reviewed each photo twice and noted which species was present, where and when. Then, the team used the data to run occupancy models to understand which species would have showed up in areas they missed.

When it came to disease transmission to cats, the team looked at three different vector species that pose the risk of spreading diseases like toxoplasmosis and rabies: raccoons (Procyon lotor), red foxes (Vulpes vulpes) and Virginia opossums (Didelphis virginiana). For diseases like toxoplasmosis, only spatial overlap is necessary, since cats can leave fecal matter that can infect another species despite the animals never having come in contact. Other diseases, like rabies, require spatial and temporal overlap between species.

They found that in time, all of these species overlapped with cats, since cats can be active at any hour of the day. With space, they found 61% overlap with raccoons, 61% with red foxes and 56% with Virginia opossums. That means that there are relatively high chances of cats contracting diseases from wildlife.

Then, they looked at overlap between cats and prey species—white-footed mice (Peromyscus leucopus), eastern gray squirrels (Sciurus carolinensis), groundhogs (Marmota monax) and eastern cottontails (Sylvilagus floridanus).

These species actually had a pretty low overlap of habitats with cats. The prey species tended to stick to the forest, which Herrera said is driven by a positive association with canopy cover. Cats seemed to stay away from these areas.

But that doesn’t mean cats don’t have the potential to consume these prey species. Herrera conducted previous research that showed cats prey on native species at a high rate within 425 meters of the forest. “Obviously, animals aren’t confined to the forest,” he said. “They will come out and go into yards and such, leaving their safe haven.”

The study shows multiple reasons why cat owners should keep their cat indoors. But not all of these cats are housecats on the prowl. Some are feral.

“The implications of this study are really calling for location-based management practices,” Herrera said. He suggests focusing management action specifically in forested areas. That could mean removing or relocating cats in some areas, or where it’s legal in some states, lethally removing them.

“When a cat goes outdoors, it’s welfare is threatened,” Herrera said. “Our angle is, we are caring for all animals best when cats are kept indoors.”

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