Study: Cats linked to killing surprising number of birds, small mammals

Photo courtesy Wikimedia Commons.
Photo courtesy Wikimedia Commons.

Though few college students have the pleasure of sharing a house with a cat, surely many Calvin students grew up with feline housemates. And we, like many Americans, find our house cats so adorable that we’re willing to let them get away with murder — literally.

A study published on Jan. 29 in the journal “Nature Communications” reveals new estimates of the true harm inflicted by the average American cat. Peter Marra, animal ecologist with the Smithsonian Conservation Biology Institute, co-authored the study. His findings indicate that the United States houses 84 million owned cats and 30 million to 80 million feral, unowned felines, all bent on destruction.

Perhaps the old wives’ tales about cats killing babies deserve a second look; our feline friends certainly don’t shy away from murdering other small, relatively helpless creatures. An analysis of past studies led Marra and his co-authors to the conclusion that each American house cat probably slays between 4 and 18 birds per year. That’s on top of the 8 to 21 small mammals that also make the annual hit list.

Extrapolate this to the entire American cat population and the numbers get staggering. The study suggests that roaming cats kill between 1.4 and 3.7 billion birds and 6.9 to 20.7 billion small mammals every year. Before you call home and tell your parents to board up the kitty door, be aware that most of the killing is done by unowned cats, the ones who spend all of their time outdoors and who must hunt to survive. These cats are responsible for between 23 and 46 bird and 129 to 338 small mammal deaths every year.

Marra and his colleagues drew much of their data from a host of smaller-scale studies focused on feline activities. One such study was executed by Kerrie Anne Loyd of the University of Georgia. From Nov. 2010 to Oct. 2011, Loyd supplied the owners of 60 Athens, Georgia, house cats with lightweight critter-cams. The cameras, designed by “National Geographic” and equipped with LED lights and radio transmitters, accompanied the cats on their daily wanderings. At night, the owners could download the footage — 2,000 hours in all.

Loyd used the footage to catalog the activities of the roaming house cats: 85 percent risked their lives by crossing streets or poking into tight spaces, and 44 percent — nearly half — killed or attempted to kill other animals.

Numbers like these should not be taken lightly. Marra supposes that the billions of slain birds may account for 15 percent of the total U.S. bird population, making cats a serious threat to bird diversity in some regions. The study claims that “free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for U.S. birds and mammals.”

These findings imply a knee-jerk response: limit cats’ opportunities to kill other creatures. Perhaps greater emphasis should be placed on keeping cats indoors or removing their front claws to make them less effective hunters. But what if cats have become integral parts of urban and rural ecosystems, and what if limiting their access to the food chain initiates negative changes we can’t fully predict?

Cat lovers: when next you go home, give your cat a hug. But watch your back. The cat knows where you sleep.

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