by Linda Winter
How many birds and other wildlife do domestic cats kill in the US? At estimate, hundreds of millions of birds and more than a billion small mammals, such as rabbits, chipmunks, squirrels, and shrews, each year. Along with common small animals, cats kill rare and endangered species for which the loss of even one individual is significant. Naturalists and scientists are increasingly concerned about cat predation.
There are over 66 million pet cats in the United States. A recent poll shows approximately 35 percent never go outside. That leaves more than 40 million pet cats free to kill wildlife. Besides these, millions of strays and their feral descendants - 40 to 60 million in the US - lead short, miserable lives in cities, suburbs, farmlands and wild areas.
Loss and fragmentation of wildlife habitat is by far the leading cause of declining bird populations. Domestic cats are numerous, efficient, non-native predators who contribute to the decline. Habitat fragmentation provides cats easier access to wildlife. Rather than havens for wild creatures, these smaller tracts can be death traps.
Some presume that a cat's killing certain animals, such as field mice, is beneficial, but native small mammals matter to ecosystems. Mice and shrews are an important food source for birds such as the great horned owl, red-tailed hawk, and American kestrel.
Pet cats have huge advantages over native predators. They get protection from disease, predation, competition, and starvation, factors that control native predators such as owls, bobcats, and foxes. Unlike many natives, cats are not strictly territorial, and so can live at much higher densities. Unaltered cats are prolific breeders: up to three litters per year, with four to six kittens per litter.
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.
Extensive studies in Europe, North America, Australia, Africa, and at least 22 islands show that 60 to 70 percent of the wildlife cats kill is small mammals, 20 to 30 percent is birds, and up to 10 percent, amphibians, reptiles, and insects.
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. One regularly-fed cat that roamed a wildlife experiment station was recorded to have killed more than 1600 animals (mostly small mammals) over 18 months. 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.
Researchers at the University of Wisconsin in a four-year study calculated that rural free-roaming cats kill at least 7.8 million, perhaps as many as 217 million, birds a year in Wisconsin. 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. Island bird species now extinct primarily due to cat predation include the Stephen's Island wren (possibly the most infamous incident of this sort, committed entirely by a single cat), South Island thrush, Chatham Island rail, Stewart Island snipe, and the Auckland Island merganser. On Marion Island in the sub-Antarctic Indian Ocean, cats were estimated to kill about 450,000 seabirds annually, before cat eradication efforts.
Cats can have significant impacts on local wildlife populations, especially in habitat "islands" such as suburban and urban parks, and wildlife refuges. For birds, the loss of species from habitat islands is well documented, and nest predation is an important cause of the decline of neotropical migrants. Animals like the Point Arena mountain beaver, Stephen's kangaroo rat, and Pacific pocket mouse, all endangered and living on habitat "islands" in California, are susceptible to cats.
For more information, contact: Humane Society of the United States, 2100 L Street, NW, Washington DC. 20037, <www.hsus.org> or American Bird Conservancy, 1250 24th Street NW, Suite 220, Washington, DC 20037, or Cats Indoors!
Cats Indoors!