Thom Smith | Naturewatch: Free-roaming cats kill billions of animals, birds annually

Before I continue, this column is in answer to Linda, who reads us in The Bennington Banner, and writes, "Please write a column about the statistics of bird deaths caused by house cats. It must rate [them] up there with glass fatalities."

Let me say that I have nothing against cats as pets, and as Pete Marra (I will quote him later) says, "I love cats. And perhaps I'm being overly generous to myself, but they have a strange affection for me, too." Just keep them in the house. And never release a litter of kittens to fend for themselves, or when moving, leave the cat behind (unless at an animal shelter, etc.) Contrary to popular belief, domestic cats do not automatically fend for themselves except to rely on their predator instincts, and mostly spend the rest of their days hungry."

A 2012 study of house cats allowed to roam outdoors finds that nearly one-third succeeded in capturing and killing animals. The cats, which wore special video cameras around their necks that recorded their outdoor activities, killed an average of 2.1 animals every week they were outside, but brought less than one of every four of their kills home. Of particular interest, bird kills constituted about 13 percent of the total wildlife kills. Based on these results, American Bird Conservancy and The Wildlife Society estimate that house cats kill far more than the previous estimate of a billion birds and other animals.

Ornithologist Pete Marra, the director of the Smithsonian Migratory Bird Center, and his colleagues at the Smithsonian published a study about such free-range cats. Marra called outdoor cats "as invasive and disruptive to native ecosystems as gypsy moths or West Nile Virus" in a Washington Post op-ed ( March 18, 2011). "We estimate that free-ranging domestic cats kill 1.3 to 4 billion birds and 6.3 to 22.3 billion mammals annually," states the Smithsonian report. "Domestic cats have been listed among the 100 worst non-native invasive species in the world. Free-ranging cats on islands have caused or contributed to 33 (14 percent) of the modern bird, mammal and reptile extinctions recorded by the International Union for Conservation of Nature (IUCN) Red List," the study reveals. "The free-ranging domestic cat, both pet and feral, has become by far the most abundant mammalian predator on Earth, numbering 80 million to 120 million in the United States alone."

It is also important that we understand when a house cat is allowed (on demand) to roam free, or is lost or abandoned and becomes a stray, most, if not all, will kill songbirds. A difference between stray and feral, is stray cats are accustomed to contact with people and are often tame while the feral cat is the "wild" offspring of domestic cats or other feral cats. Feral cats are wild animals and do their very best to stay away from people.     

And whether pet or feral, a cat on its own isn't a carefree kitty. The American Veterinary Medical Association estimates "that free-ranging cats have half the life expectancy of indoor cats. Causes of cat death can be gruesome — getting hit by cars, being mauled by dogs or becoming a meal for foxes and coyotes. Life outdoors also means greater exposure to diseases, such as toxoplasmosis and feline leukemia. Cats are now the most common domesticated animal to carry and transmit rabies to humans and other wildlife."

Feral cats often live in colonies. Marra says, " The cats in these colonies, although fed, not only suffer the same fates as those described above for free-ranging ferals, but the places in which they live can become devoid of most wildlife. Worse, these colonies encourage the dumping of unwanted cats. While neutering can slow a colony's growth, it is rarely fully effective because more than 70 percent of the cats must be sterilized. New cats arrive, and many go unneutered and unvaccinated. The result is reproductively active colonies that continue to devastate wildlife.


Earlier this May:

"The numbers are horrifying: 90 Nashville Warblers, 60 Blackburnian Warblers, 42 Chestnut-sided Warblers, 41 Ovenbirds — and that's just four of the 25 dead species collected from the American National Building in Galveston, Texas, on Thursday morning. In total, 395 small feathered bodies were found, and they were all victims of glass collisions.

"Josh Henderson, the head of Animal Services for the Galveston Police Department, was called to the scene at 7:20 a.m. He was able to rescue three of the stunned birds, which were then taken to a wildlife triage center. But the sheer number of casualties shocked him. 'This is the largest event like this I have ever been a part of in over 10 years,' " Henderson said in a press release.

"After sorting and [identifying] the bodies, Henderson's final list also included: 29 Yellow Warblers, 26 Black-and-white Warblers, 24 Magnolia Warblers, 21 American Redstarts, 15 Indigo Buntings, 8 Black-throated Green Warblers, 5 Kentucky Warblers, 4 Eastern Wood-Peewees, 3 Golden-winged Warblers, 2 Painted Buntings, 2 Orchard Orioles, plus a Hooded Warbler, Gray Catbird, Blue Grosbeak, Rose-breasted Grosbeak, Orange-crowned Warbler, Summer Tanager, Worm-eating Warbler, Red-eyed Vireo, and Cerulean Warbler."

Thom Smith welcomes your questions and comments. Email him at or write him care of The Berkshire Eagle, 75 S.

Church St., Pittsfield, MA 01201


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