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D.C. Camera Data Shows Wildlife Encounters Slash Biodiversity, Risk Cat and Human Health
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Think your outside cat’s an outsize hero, prowling the fearsome urban landscape during its daily adventures to rid the neighborhood of vermin?
It’s time to shut the door on that misconception, say University of Maryland researchers, whose new study of cats in Washington, D.C., establishes the risks of letting your feline friend step out into the wild. These include catching and transmitting diseases and damaging native populations and biodiversity, thanks to cats’ uncontrollable hunting instinct.
“Many people falsely think that cats are hunting non-native populations like rats, when in fact they prefer hunting small native species,” said Daniel Herrera, lead author of the study and Ph.D. student in the Department of Environmental Science and Technology (ENST).
Published last week in Frontiers in Ecology and Evolution, the study concludes that humans are responsible for cats’ effect on ecosystems, and can significantly reduce a range of risks by keeping cats indoors.
The analysis used three years of data from the D.C. Cat Count, a Washington, D.C. survey that deployed 60 motion-activated wildlife cameras spread across 1,500 sampling locations. From 2018-20, the cameras recorded what cats preyed on and demonstrated how they overlapped with native wildlife, which helped researchers understand why cats and other wildlife are present in some areas, but absent from others. The resulting exposure to diseases like toxoplasmosis have potential to cat health, as well as humans in their households.
“We discovered that the average domestic cat in D.C. has a 61% probability of being found in the same space as racoons—America’s most prolific rabies vector—61% spatial overlap with red foxes, and 56% overlap with Virginia opossums, both of which can also spread rabies,” Herrera said.
The D.C. Cat Count survey demonstrated that cats that are allowed to roam outside also share spaces with—and actively hunt—native wildlife like gray squirrels, chipmunks, cottontail rabbits, groundhogs and white-footed mice. By killing these animals, cats can reduce biodiversity and degrade ecosystem health.
Cats’ observed outdoor lives run counter to arguments that free-roaming cats are simply stepping into a natural role in the ecosystem by hunting wildlife, the study found. Effectively mitigating the risks means restricting wandering cats from areas where they’re most likely to encounter wildlife, according to the study.
“These habitat relationships suggest that the distribution of cats is largely driven by humans, rather than natural factors,” said Travis Gallo, assistant professor in ENST and adviser to Herrera. “Since humans largely influence where cats are on the landscape, humans also dictate the degree of risk these cats encounter and the amount of harm they cause to local wildlife.”
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