Every cat owner knows that the family tabby will from time to time deposit on the doorstep as a small gift the badly savaged corpse of a mouse, chipmunk or vole.

But according to research from the University of Georgia, this is only a fraction of the carnage inflicted by house cats allowed to run free. The roaming cats kill an average of two creatures a week, bring home a fourth of what they kill, eat 30 percent and leave about half of their prey behind to rot.

"If we extrapolate the results of this study across the country and include feral cats, we find that cats are likely killing more than 4 billion animals per year, including at least 500 million birds. Cat predation is one of the reasons why one in three bird species are in decline," according to George Fenwick, president of the American Bird Conservancy.

The study was done in Athens, Ga., by attaching the National Geographic's miniature CritterCam to the collars of about 60 house cats that roamed free during the day and downloading the data each night.

USA Today breathlessly said the researchers found "a secret world of slaughter." The cats killed a wide range of creatures -- lizards, snakes, frogs, chipmunks, voles, insects and worms. Birds represented only 12 percent of their prey.

The country has growing colonies of feral cats. Programs to trap and neuter them seem to be expensive and not very efficient, and the neutered cats, who are hardwired in any case, go right back to stalking prey.

The American suburbs, with their lush plantings and loosely secured garbage, have become mini-Edens for wildlife -- deer, fox, coyotes, even bears.

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Americans are loath to manage these populations through controlled kills, so it might be left to Mother Nature to find a solution, perhaps predators large enough to feed on cats. Suburbanites are reporting hearing more and more coyotes and occasionally getting a rare look at the reclusive predators.

Dale McFeatters is a senior writer for the Scripps Howard News Service.