"Even feral cats were always within range of a building," she said. "That shows that even though they're feral, they still have a level of dependency on us."
One feral cat chased another out of a dairy barn. Another feral cat waited for a pet cat to emerge each morning and tried to chase it out of its own backyard, Horn said.
The overlap of feral and pet cat territories outdoors spells trouble for the environment, the cats and potentially also for the cat owners, the researchers said.
In an earlier study, co-author Richard Warner, an emeritus professor of natural resources and environmental sciences at Illinois, followed the cats of about two-dozen rural residences over several years.
"Two of the leading causes of cat deaths in that study were other cats and disease," Warner said. "And both of these leading causes of death are sitting here waiting for these owned cats outdoors."
Cats also get diseases from wildlife or other cats, Mateus-Pinilla said, and can bring them home and infect their owners and other pets.
"For example, Toxoplasma gondii, a parasite spread primarily by cats, may cause neurological, reproductive and even respiratory problems in humans, cats and wildlife, depending on the species affected," she said. Rabies, cat scratch fever, feline leukemia and feline immunodeficiency virus are also of concern to pet owners whose cats encounter other cats outdoors, she said. Vaccination of pet cats will reduce but not eliminate the threat of disease transmission, she said.
Even though pet cats have relatively small ranges and are active only in short bursts, Warner said, their impact on wildlife in the immediate vicinity of their homes is likely much more intense than that of a feral cat that wanders over a larger territory.
Unlike other feline predators, such as bobcats, that are native to the Midwest, domestic cats
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University of Illinois at Urbana-Champaign