What effects do domestic cats have on wildlife?
Although rural free-ranging cats have greater access to wild animals and undoubtedly take the greatest toll, even
urban house pets take live prey when allowed outside. Extensive studies of the feeding habits of free-ranging
domestic cats over 50 years and four continents indicate that small mammals make up approximately 70% of
these cats' prey while birds make up about 20%. The remaining 10% is a variety of other animals. The diets of free-ranging cat populations, however, reflect the food locally available. Observation of free-ranging domestic cats shows that some individuals can kill over 1000 wild animals per year, although smaller numbers are more typical. Some of the data on kills suggest that free-ranging cats living in small towns kill an average of 14 wild animals each per year. Rural cats kill many more wild animals than do urban, or suburban cats. Several studies found that up to 90% of free-ranging rural cats' diet was wild animals, and less than 10% of rural cats killed no wild animals. Recent research suggests that rural free-ranging domestic cats in Wisconsin may be killing between 8 and 217 million birds each year. The most reasonable estimates indicate that 39 million birds are killed in the state each year. Nationwide, rural cats probably kill over a billion small mammals and hundreds of millions of birds each year. Urban and suburban cats add to this toll. 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. In Florida, marsh rabbits in Key West have been threatened by predation from domestic cats. Cats introduced by people living on the barrier islands of Florida's coast have depleted several unique species of mice and wood rats to near extinction.
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. When present in large numbers, cats can reduce the availability of prey for native predators, such as hawks and weasels.
Free-ranging domestic cats may also transmit new diseases to wild animals. Domestic cats have spread feline leukemia virus to mountain lions and may have recently infected the endangered Florida Panther with feline panleukopenia (feline distemper) and an immune deficiency disease. These diseases may pose a serious threat to this rare species. Some free-ranging domestic cats also carry several diseases that are easily transmitted to humans, including rabies and toxoplasmosis.
Domestic cats vs. native predators
Although cats make affectionate pets, many domestic cats hunt as effectively as wild predators. However, they differ from wild predators in three important ways: 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. Whereas populations of native predators will decline when prey becomes scarce, cats receiving food subsidies from people remain abundant and continue to hunt even rare species. Third, unlike many native predators, cat densities are either poorly limited or not limited by territoriality. These three factors allow domestic cats to exist at much higher densities than native predators. In some parts of rural Wisconsin, densities of free-ranging cats reach 114 cats per square mile. In these areas, cats are several times more abundant than all mid-sized native predators (such as foxes, raccoons, skunks) combined. With abundant food, densities can reach over 9 per acre, and cats often form large feeding and breeding "colonies" (81 cats were recorded in one colony, and colonies of over 20 are not uncommon). Unlike some predators, a cat's desire to hunt is not suppressed by adequate supplemental food. Even when fed regularly by people, a cat's motivation to hunt remains strong, so it continues hunting.
In summary
Free-ranging cats are abundant and widespread predators. They often exist at much higher densities than native predators. They prey on large numbers of wild animals, some of which are rare or endangered. They compete with native predators, and they harbor a variety of diseases. Yet, cats are popular pets. In order to have and care for our pets--and still protect our native wildlife--we must make an effort to limit in a humane manner the adverse effects free-ranging cats can have on wildlife.
What you can do:
Keep only as many pet cats as you can feed and care for. Controlling reproduction and humanely euthanizing unwanted cats will keep cat populations from growing beyond the size that can be adequately cared for. On farms, keep only the minimum number of free-ranging cats needed to control rodents. Well-fed, neutered females will stay closest to farm buildings and do most of their killing where rodent control is needed most. Traps and rodenticides, as well as rodent-proof storage and construction, will usually contribute more to effective rodent control than cats.
If at all possible, for the sake of your cat and local wildlife, keep your cat indoors. Confinement will eliminate unwanted reproduction, predation on wild animals, and the spread of disease. Bells are mostly ineffective in preventing predation because, even if the bell rings, it's usually too late for the prey being stalked. Declawing may reduce hunting success, but many declawed cats are still effective predators. Keeping your cats indoors helps protect the wildlife around your yard and prevents your cat from picking up diseases from strays or getting injured. The two most common causes of death for rural cats in south central Wisconsin are disease and being struck by automobiles. If cats must be allowed outdoors, consider using a fenced enclosure or runway.
Neuter your cats or prevent them from breeding, and encourage others to do so. Support or initiate efforts to require licensing and neutering of pets. In areas where such laws already exist, insist that they be enforced. For information on local licensing and neutering laws, contact your local health department or humane society.
Locate bird feeders in sites that do not provide cover for cats to wait in ambush for birds. Cats are a significant source of mortality among birds that come to feeders. To prevent cats from climbing to bird nests, put animal guards around any trees in your yard that may have nesting birds.
Don't dispose of unwanted cats by releasing them in rural areas. This practice enlarges rural cat populations and is an inhumane way of dealing with unwanted cats. Cats suffer in an unfamiliar setting, even if they are good predators. Contact your local animal welfare organization for help.
Eliminate sources of food, such as garbage or outdoor pet food dishes, that attract stray cats.
