Housecats are the domestic animal most frequently reported rabid to the US Centers for Disease Control and Prevention. Cats are also suspected of spreading feline leukemia virus to a mountain lion in California and infecting the endangered Florida panther with feline distemper. Feline infectious peritonitis has been diagnosed in mountain lion and lynx, and feline immunodeficiency virus, in Florida panther and bobcat. The number and types of animals killed by cats vary greatly, depending on the individual cat, time of year, and availability of prey. Some free-roaming pet cats kill more than 100 animals each year.
Rural cats take more prey than suburban or urban cats.
Birds that nest or feed on the ground, nestlings, and fledglings are most susceptible to cat predation. They estimated that in some parts of the state, free-roaming cats outnumber all natural predators, at 114 cats per square mile. A study of 5,500 homes with bird feeders in winter 1989-90 showed that the domestic cat was a significant predator at feeders. A new predator introduced to an island can eliminate entire bird populations. Domestic cats are considered primarily responsible for the extinction of eight island bird species, and the eradication of over 40 bird species from New Zealand islands alone.