The Environmental Danger of Outdoor Cats

Free-ranging domestic cats are an environmental disaster. They may be the most destructive invasive species, the “single greatest source of anthropogenic mortality for U.S. birds and mammals” according to a study (pdf) co-authored by scientists at the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service. These authors found that domestic cats annually kill from 1.4-3.7 billion birds and 6.9-20.7 billion mammals in the U.S. “Unowned” or feral cats, as opposed to owned pets, cause the majority of this damage.

The literature on the subject of feral cats is substantial, and ranges from the modest to the encompassing. A. Whilde details the toll taken by two rural cats over three years, measured by corpses bought to his home. William G. George, writing in the middle 1970s, when the estimated U.S. cat population was a third of what it is now, detailed how cats compete with raptors for small mammal prey in winter. Coleman and Temple surveyed rural residents of Wisconsin on their attitudes to free-ranging cats and numbers thereof; they estimated 44 cats per square kilometer in their subject county.

Another problem is cross-breeding between domestic cats and wild cats and the corresponding loss of genetic singularity in the wild cats. In Europe, Africa, and Asia, populations of wild cats are threatened by hybridization with, as the four authors of this study in the Iberian Peninsula put it, “anthropogenically mediated dispersion of free-ranging domestic cats.” What’s at stake is the genetic uniqueness of the wild cats. In Europe, Felis silvestris silvestris is larger, longer-legged, and bushier than the domestic cat.

One solution might be convincing people to keep their cats indoors (though most of the problem is created by feral cats, with no homes to be kept in). Another solution might be found in coyotes, the natural predator of outdoor cats.


JSTOR Citations

The Prey of Two Rural Domestic Cats

By: A. Whilde

The Irish Naturalists' Journal, Vol. 24, No. 4 (Oct., 1992) , pp. 173-174

Irish Naturalists' Journal Ltd.

Domestic Cats as Predators and Factors in Winter Shortages of Raptor Prey

By: William G. George

The Wilson Bulletin, Vol. 86, No. 4 (Dec., 1974) , pp. 384-396

Wilson Ornithological Society

Rural Residents' Free-Ranging Domestic Cats: A Survey

By: John S. Coleman and Stanley A. Temple

Wildlife Society Bulletin, Vol. 21, No. 4 (Winter, 1993) , pp. 381-390


Hybridization versus Conservation: Are Domestic Cats Threatening the Genetic Integrity of Wildcats (Felis silvestris silvestris) in Iberian Peninsula?

By: Rita Oliveira, Raquel Godinho, Ettore Randi and Paulo C. Alves

Philosophical Transactions: Biological Sciences, Vol. 363, No. 1505, Hybridization in Animals: Extent, Processes and Evolutionary Impact (Sep. 12, 2008) , pp. 2953-2961

The Royal Society

Observations of Coyote-Cat Interactions

By: Shannon E. Grubbs and Paul R. Krausman

The Journal of Wildlife Management, Vol. 73, No. 5 (Jul., 2009) , pp. 683-685


Matthew Wills

Matthew Wills has advanced degrees in library science and film studies and is lapsed in both fields. He has published in Poetry, Huffington Post, and Nature Conservancy Magazine, among other places, and blogs regularly about urban natural history at

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