Wild Side : Pet cats can skew the Martha's Vineyard ecosystem
Photo courtesy of University of Georgia
Among the vogue of automated trail camera photos and bird-nest video feeds currently revealing the secret lives of wild animals, one recent project in particular has caught the eye of conservationists. A collaboration between University of Georgia researchers and National Geographic's Remote Imaging Department, the so-called "Kittycam" study equipped 60 free-roaming house cats with tiny video cameras mounted on collars. Recording roughly what the cats saw during their outdoor excursions, the cameras gave researchers an intimate look at how kitties spend their outdoor time.
Cats, of course, are resolutely tight-lipped about their sojourns, though the occasional sparrow or vole deposited on a doorstep sometimes hints at what they've been up to. But the predatory proclivity of both house cats and feral ones has long been of concern to wildlife managers, who point out that domestic cats can live and hunt at densities many times higher than any natural predator would ever reach.
The result is carnage, in terms of direct mortality of small animals as well as the loss of prey items that would otherwise be available to native predators like hawks and owls. A summary on the American Bird Conservancy (ABC) website, abcbirds.org, pegs the number of small animals killed annually by cats in the U.S. at between 500 million and a billion. (With about 52 million roaming pet cats in the U.S., and as many as 100 million feral kitties, those numbers seem more than plausible.) Various studies differ in what they imply about the efficiency of hunting cats and their prey preferences: one especially talented feline was documented killing 1,600 animals over an 18-month period! Small mammals are generally the favorite prey, with birds in second place; the Kittycam cats, being down south, showed a fondness for killing lizards.
Most assessments of cat predation tally what the cats bring home, extrapolating from cat population figures to produce kill estimates for a particular area or time period. Hence the impact of the Kittycam, which made it possible to see what, exactly, hunting cats do in the field. Kittycams revealed that, within the study population, only about a third of the cats successfully killed prey (most previous studies indicated much higher rates of hunting success). But the cats that did kill did so on a daily basis, and moreover, the project's cats ate or simply left behind more than three-quarters of what they killed. While it is risky to put too much emphasis on such a small study, the implication is that previous estimates of the impact of hunting cats, based on prey brought home, may need to be multiplied by as much four in order to be accurate. In short, the Kittycam project launched outdoor cats several notches up the short list of threats to wildlife.
Kittycam, in conjunction with previous studies of cat predation, puts on ethical twist on the question of whether to allow your cat to roam. Though some outdoor cats are too lazy, good-natured, or inept to hunt successfully, killing smaller animals is natural behavior for these highly evolved predators, almost unchanged in the millennia. But there is nothing natural about stocking the landscape with carnivores that are heavily subsidized with food, shelter, and medical care; or with feral cats, their population constantly augmented by lost or dumped house pets as well as by reproduction. Keeping a cat and letting it roam may seem "natural," but it isn't, and it carries a price, in terms of dead wildlife, that many cat owners never consider.
A cat-lover from way back, I've made past and current felines 100 percent indoor cats. Keeping them from preying on the birds I love was an important reason, though I also know that indoor cats are less vulnerable to disease, getting lost or injured, or getting mashed by cars. For me, the decision of how (and even whether) to keep a cat was an ethically complex one: knowing that I have committed Pitzi to a life that is very different from what her species evolved for, I take very seriously my responsibility to provide her with as much comfort, variety, and stimulation as I can. She seems happy, and I know that her impact on the local ecosystem is minimal.
Ultimately, we can't really know what constitutes quality of life for a cat. We simply do the best we can to balance their apparent preferences with what we decide is best. Kittycam usefully reminds us that even if we don't know what cats are doing outdoors, they're still doing it. The Wild Side perspective is that responsible people should consider not just owner convenience or the cat's apparent preference, but the interaction between a cat and the natural world, when deciding whether or how to keep a kitty.
A brochure produced by the Kittycam research team summarizes the project at kittycams.uga.edu/other/kittycamsbrochure.pdf. The American Bird Conservancy's summary of the project can be found at abcbirds.org/newsandreports/releases/120806.html. A link at the bottom of that page takes you to actual Kittycam photos and videos, some of which make for pretty interesting viewing.