Q I am an avid bird watcher, and one of my greatest joys is watching the beautiful birds that flock to my feeders. But I'm horrified when my cat, Bruiser, leaves dead birds on the doorstep. Sometimes he also leaves dead mice or chipmunks. I know that he's only doing what his instincts tell him to do, but his behavior really upsets me, and I'm afraid he'll seriously reduce the population of the birds I love. What can I do?

A Members of the cat family are among nature's most successful predators. Predation was one of the traits (along with the purr, the snuggle, and the half-closed contented eyes) that made domestic cats such desirable companions during the earlier years of human existence. A good "mouser" was highly prized for its ability to reduce the rodent population and the terrible damage mice and rats inflicted on stored grain and other food supplies.

Taking the good with the bad
But feline traits that are "good" in some circumstances may be "bad" in others. In the right situation, a cat that hunts provides a valuable service. But what about the impact his hunting has on wildlife numbers? Without question, cats introduced onto small isolated islands can significantly diminish the numbers of native birds and small mammals, but the overall impact of feline predation on wildlife populations in North America and other large landmasses is less clear. Regardless of the global impact, it's heartbreaking to see a beloved cat destroy a beautiful bird that's been lured to your feeder, and the harm inflicted on the local bird population may be greater than many believe.

For whom the bell tolls
Aside from keeping Bruiser indoors (advisable for many reasons, including his own health), what can you do to give the unsuspecting birds a fighting chance? One approach is to attach a bell to Bruiser's breakaway collar. Theoretically, the audible alert will warn of a fast-approaching object, giving his prey a few extra moments to elude capture. This technique has been suggested for many years, but its success has been called into question. In fact, two studies performed during the last decade found that cats wearing bells were just as successful in their hunting attempts as were bell-less cats. But researchers at the University of Glasgow pointed out some shortcomings of these studies, and undertook a slightly different approach. Their study, "Bells Reduce Predation of Wildlife by Domestic Cats," appeared in the British Journal of Zoology. One question they sought to answer: Does wearing a bell reduce the amount of prey a cat captures?

Forty-one pet cats known to bring home prey were selected to take part in the study. The cats came from a variety of rural and urban environments, and were currently wearing collars without bells. The study period for each cat lasted for two continuous months, and each cat wore the bell half the time. When wearing the bells, the 41 cats delivered a total of 82 mammals, 26 birds, and 10 amphibians; without the bells, they delivered 167 mammals, 48 birds, and 11 amphibians. These results were statistically significant, and at least during the timescale of the study, bell-equipped cats appeared to kill only half as many mammals and birds as they did when not wearing bells. There was no apparent impact on amphibian prey, though, presumably because the hapless frogs and toads either couldn't hear the high frequency bell sound, or they didn't associate the sound with impending doom.

So what about your buddy, Bruiser? Placing a bell on his collar might impair his hunting success, but the only sure way to keep him from killing birds at your feeder is to completely prevent his access to it. I suggest keeping him indoors.