Some of these kills are house mice, rats and other species considered pests, but many are native songbirds and mammals whose populations are already stressed by other factors, such as habitat destruction and pesticide pollution. Despite the difficulties in showing the effect most predators have on their prey, cats are known to have serious impacts on small mammals and birds. Worldwide, cats may have been involved in the extinction of more bird species than any other cause, except habitat destruction. Cats are contributing to the endangerment of populations of birds such as Least Terns, Piping Plovers and Loggerhead Shrikes. Not only do cats prey on many small mammals and birds, but they can outnumber and compete with native predators.
Domestic cats eat many of the same animals that native predators do.
Free-ranging domestic cats may also transmit new diseases to wild animals. These diseases may pose a serious threat to this rare species. Although cats make affectionate pets, many domestic cats hunt as effectively as wild predators. First, people protect cats from disease, predation and competition, factors that can control numbers of wild predators, such as bobcats, foxes, or coyotes. Second, they often have a dependable supply of supplemental food provided by humans and are, therefore, not influenced by changes in populations of prey.