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Domestic Cat Predation on Birds and Other Wildlife
American Bird Conservancy, Cats Indoors! Campaign for Safer Birds and Cats, click here for a printer friendly version
How many birds and other wildlife do domestic cats kill each year in the U.S.?
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No one knows, although reasonable extrapolations from scientific data can be made. Nationwide, cats are estimated to kill hundreds of millions of birds and more than a billion small mammals, such as rabbits, chipmunks, squirrels, and shrews each year. Cats kill not only plentiful animals, but rare and endangered species for which the loss of even one animal is significant. The scientific community is increasingly concerned about cat predation.
There are over 66 million pet cats in the United States. A recent poll show approximately 35 percent are kept exclusively indoors, leaving more than 40 million owned cats free to kill birds and other wildlife, all or part of the time. In addition, millions of stray and feral cats roam our cities, suburbs, farmlands and natural areas. Abandoned by their owners or lost (stray), or descendants of strays and shunning all human contact (feral), these cats are victims of human irresponsibility through owner abandonment and the failure to spay or neuter pets. No one knows how many homeless cats there are in the U.S., but estimates range from 60 to 100 million. These creatures lead short, miserable lives.
Loss and fragmentation of wildlife habitat, resulting from development, road construction, intensive agriculture, and other land uses, are by far the leading causes of declining bird populations. Domestic cats are numerous, efficient, non-native predators who contribute to the decline. For example, habitat fragmentation provides cats easier access to wildlife forced to live on smaller tracts of land. Rather than providing havens for wild creatures, these small tracts can be death traps instead.
Cats are Not a Natural Part of Ecosystems
The domestic cat, Felis catus, is a descendant of the wild cats of Africa and extreme southwestern Asia, Felis silvestris libyca. Domesticated in Egypt approximately 4,000 years ago, cats were introduced to Europe around 2,000 years ago. Cats were introduced to North America when Europeans arrived on this continent, but were brought in large numbers during the latter part of the nineteenth century in an attempt to control burgeoning rodent populations associated with the spread of agriculture. Some people presume that a cat killing certain animals, such as field mice, is beneficial, but native small mammals are important to maintain biologically diverse ecosystems. For example, mice and shrews are an important food source for birds such as the Great Horned Owl, Red-tailed Hawk, and American Kestrel.
Cats Complete with Native Predators
Owned cats have huge advantages over native predators. They may be afforded some protection from disease, predation, competition, and starvation, factors which control native predators such as owls, bobcats, and foxes. Cats with dependable food supplies are not as vulnerable to changes in prey populations. Unlike many native predators, cats are not strictly territorial, keeping members of their own species out of a given area. As a result, cats can exist at much higher densities and may out-compete native predators for food. In addition, unaltered cats are prolific breeders. A female cat can have up to three litters per year, with four to six kittens per litter.
Cats Transmit Disease to Wildlife
Unvaccinated cats can transmit rabies and cats are the domestic animal most frequently reported rabid to the Centers for Disease Control and Prevention. Cats are also suspected of spreading feline leukemia virus to a mountain lion in California and may have infected the endangered Florida panther with feline distemper. Feline infectious peritonitis has been diagnosed in mountain lion and lynx, and feline immunodeficiency virus has been found in Florida panther and bobcat.
Studies of Cat Predation
Extensive studies of the feeding habits of domestic free-roaming cats have been conducted over the last 50 years in Europe, North America, Australia, Africa, and on at least 22 islands. These studies show that approximately 60 to 70 percent of the wildlife cats kill are small mammals, 20 to 30 percent are birds, and up to 10 percent are amphibians, reptiles, and insects.
Scientists have found that 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 domestic cats kill more than 100 animals each year. Some cats specialize in killing birds while others take mainly small mammals. 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 are the most susceptible to cat predation, as are nestlings and fledglings of many other bird species. Following are summaries of specific studies:
Wisconsin Study: Researchers at the University of Wisconsin coupled their four-year cat predation study with data from other studies, and predicted a range of values for the number of birds killed each year in the state. By estimating the number of free-ranging cats in rural areas, the number of kills per cat, and the proportion of birds killed, the researchers calculated that rural free-roaming cats kill at least 7.8 million and perhaps as many as 217 million birds a year in Wisconsin. They estimated that in some parts of the state, free-roaming cat densities reach 114 cats per square mile, outnumbering all similar-sized native predators. (Coleman, J.S. and S.A. Temple. 1995. How many birds do cats kill? Wildlife Control Technology:44.)
Virginia Study: Virginia researchers compared free-roaming domestic pet cats in a rural setting and a more urban one. A total of 27 native species (eight birds, two amphibians, nine reptiles, and eight mammals, including the star-nosed mole, a species of special concern) were captured by a single rural cat. Four urban cats captured 21 native species (six birds, seven reptiles, and eight mammals). Between January and November 1990 each cat caught, on average, 26 native individuals in the urban area, and 83 in the rural area. The study did not count prey killed and completely consumed, prey killed and left elsewhere, or non-native prey. (Mitchell, J. and R.A. Beck. 1992. Free-ranging domestic cat predation on native vertebrates in rural and urban Virginia. Virginia Journal of Science 43:197-206.)
Cats at Bird Feeder Study: A continent-wide survey of 5,500 homes with bird feeders during the winter of 1989-90 showed that the domestic cat was a significant predator of birds at feeders. Species killed by cats at bird feeders included Dark-eyed Junco, Pine Siskin, Northern Cardinal, and American Goldfinch. (Dunn, E.H. and D.L. Tessaglia. 1994. Predation of birds at feeders in winter. Journal of Field Ornithology 65:8-16.)
Cats on Islands
Because some island bird populations evolved in the absence of mammalian predators, they have no defense mechanisms against them. When an efficient predator such as the domestic cat is introduced or abandoned on an island, elimination of entire bird populations can result. 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 birds species that are now extinct primarily due to cat predation include the following: Stephen’s Island Wren, 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 prior to cat eradication efforts.
Cat Predation of Wildlife in Habitat Reduced to Islands
Cats can have highly significant impacts on local wildlife populations, especially in habitat “islands” such as suburban and urban parks, wildlife refuges, and other habitats that are surrounded by human development. 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. The Point Arena mountain beaver, Stephen’s kangaroo rat, and Pacific pocket mouse, protected under the Federal Endangered Species Act, now live on habitat islands created by destruction and fragmentation of their habitat in California. Domestic cat predation by pet and feral cats on these species is a serious threat to their future existence on the habitat that is left.
Cat Predation of Federally-Protected Wildlife
The Migratory Bird Treaty Act (MBTA) prohibits the hunting, taking, capturing, or killing of any migratory bird. However, owners of free-roaming domestic cats permit their pets to kill birds protected by the MBTA in seeming violation of this landmark law. Domestic cats are also killing birds and other wildlife protected under the Endangered Species Act.
Through the Endangered Species Act, the federal government protects and restores wildlife at risk of extinction. Habitat loss is the most significant cause of species declines, and predation, including killing by cats, ranks second. Although cats may not be responsible for the perilous status of endangered wildlife, the loss of even a single animal can be a setback to the survival of the species. It is not possible to document fully the predation of protected species by cats, but the following is a list of protected species for which there is at least one documented case of cat predation in the U.S.
Documented Cat Predation of Birds Protected by the Endangered Species Act
Light-footed Clapper Rail, Rallus longirostris levipes
California Clapper rail, Rallus longirostris obsoletus
California Least Tern, Sterna antillarum browni
Western Snowy Plover, Charadrius alexandrinus nivosus
California Brown Pelican, Pelecanus occidentalis californicus
California Gnatcatcher, Polioptila californica
Piping Plover, Charadrius melodus
San Clemente Loggerhead Shrike, Lanius ludovicianus mearnsi
Palila, Loxioides bailleui
Florida Scrub-jay, Aphelocoma coerulescens
Documented Cat Predation of Mammals Protected by the Endangered Species Act
Pacific Pocket Mouse, Perognathus longimembris pacificus
Stephens’ Kangaroo Rat, Dipodomys stephensi
Morro Bay Kangaroo Rat, Dipodomys heermanni morroensis
Point Arena Mountain Beaver, Aplodontia rufa nigra
Florida Beach Mouse, Peromyscus polionotus
Santa Rosa Beach Mouse, Peromyscus polionotus leucocephalus
Key Largo Woodrat, Neotoma floridana smalli
Key Largo Cotton Mouse, Peromyscus gossypinus allopaticola
Documented Cat Predation of Reptiles Protected by the Endangered Species Act
Island Night Lizard, Xantusia riversiana
Alameda Whipsnake, Masticophis lateralis euryxanthus
Correcting Four Myths about Cat Predation of Birds and Other Wildlife
Some people mistakenly believe:
(1) Well-fed cats are not a danger to wildlife;
(2) Putting a bell on a cat is an effective way to deter predation;
(3) Interrupting an attack by a cat allows the prey to escape and live;
(4) Stray cat colonies present no danger to wildlife.
Well-fed Cats Do Kill Birds: Well-fed cats kill birds and other wildlife because the hunting instinct is independent of the urge to eat. In one study, six cats were presented with a live small rat while eating their preferred food. All six cats stopped eating the food, killed the rat, and then resumed eating the food.
Cats With Bells on Their Collars Do Kill Birds: Studies have shown that bells on collars are not effective in preventing cats from killing birds or other wildlife. Birds do not necessarily associate the sound of a bell with danger, and cast with bells can learn to silently stalk their prey. Even if the bell on the collar rings, it may ring too late, and bells offer no protection for helpless nestlings and fledglings.
Birds That Seem to Escape Don’t Get Away Unscathed: Contrary to popular belief that birds and other small animals can be rescued from a cat attack and get away unharmed, wildlife rehabilitation centers report that most small animals injured by cats die. Cats carry many types of bacteria and viruses in their mouths, some of which can be transmitted to their victims. Even if treatment is administered immediately, only about 20 percent of these patients survive the ordeal. A victim that looks perfectly healthy may die from internal hemorrhaging or injury to vital organs.
Wildlife rehabilitation centers also report that a large percentage of their patients are cat attack victims and animals orphaned by cats. At Wildlife Rescue, Inc. in Pal Alto, California, approximately 25 percent of their patients during May and June 1994 were native cat-caught birds and 20 percent of mammals in the care of the Lindsay Wildlife Museum in California were caught by cats. Cat predation of wildlife is especially frustrating to wildlife rehabilitators. These losses are totally unnecessary because unlike other predators, pet cats don’t need these animals to survive.
Cat Colonies Are a Problem for Birds and Other Wildlife: Domestic cats are solitary animals, but clusters often form around an artificial feeding source, such as garbage dumps or food left out for them. These populations can grow very quickly, can have significant impacts on wildlife populations, and can cause significant health risks to other cats, wildlife, and humans. Feeding these cats does not prevent the predation of birds and other wildlife. For example, a famous heron and egret rookery of several thousand birds reportedly has been decimated, and songbird populations have plummeted, in Greynolds Park in Dade County, Florida where the numbers of cats and raccoons fed by humans have exploded.
Conclusion: Cats are not ultimately responsible for killing our native wildlife—people are. The only way to prevent domestic cat predation on wildlife is for owners to keep their cats indoors.
For more information, contact: American Bird Conservancy, Cats Indoors! Campaign for Safer Birds and Cats, 1834 Jefferson Place, NW, Washington, DC 20036. Web site: www.abcbirds.org
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