Summer 2013

Backyard Hunters

A recent report says our feline friends are killing wildlife at an alarming rate, but the issue is much more complex

By Genevieve Rajewski

TVM_SU13_backyard_hunter_embeddedScientists from the Smithsonian Conservation Biology Institute and the U.S. Fish and Wildlife Service recently released a report in the journal Nature Communications that sought to estimate the number of wildlife killed by cats in the United States. The mainstream media seized on the study, which used older, small studies to conclude that cats are killing billions of birds and mammals each year. Within days, the story generated significant outcry from cat lovers and others who questioned the accuracy of the research.

Two experts from the Center for Animals and Public Policy at the Cummings School—Emily McCobb, V00, M.S.02, the center’s assistant director, and ASPCA senior director of veterinary epidemiology Margaret Slater, who teaches a class on free-roaming cats—told Tufts Veterinary Medicine that the issue is way more complex than stalk, kill and devour.

Tufts Veterinary Medicine: How accurate are these new prey estimates?

Margaret Slater: There is no way to know the truth about cats’ effect on wildlife. There’s just not enough data available. The study in question is a meta-analysis of existing published research. While I haven’t recently reviewed each paper individually, I am familiar with them. They use a number of methodologies to determine the quantity and type of cats’ prey—including owners counting the number of dead animals their cats bring home and scat and stomach-content analyses—and each has its limitations.

For example, it’s pretty common in Australia to find sheep in cats’ stomach contents. It’s not because herds of cats are pulling down sheep, but because cats scavenge sheep carcasses by the side of the road. So when you are looking at what a cat has eaten, you don’t know how it got into the cat’s mouth in the first place, or what was going on with that particular animal at the time the cat found and ate it. Cats are specialists in catching rodents, but they are very flexible in terms of what else they’ll eat. And some data suggest that cats only catch birds that aren’t healthy to begin with.

Emily McCobb: Another issue with the study is that you can trace the research back through several publications, only to discover it’s based on one guy’s experiences with his cat in his backyard or that a widely cited study on predation is based on just three pet cats. Using those papers as a basis to extrapolate data for a state or country—or even incorporating them into a series of extrapolations—is problematic.

Are cats the invasive species suggested in this report?

McCobb: It is true that cats are excellent predators and that they were brought to this continent by human settlers. But how much effect cats have on wildlife really depends on the ecosystem where the cats are living. In Worcester, Mass., where the Cummings School works with the Spay Worcester program to manage feral cat colonies, I don’t think they are having much effect. Cats in urban environments are living off garbage as well as rodents that we consider to be pests. But there are other regions, such as protected shoreline, that are not appropriate locations for free-roaming cats, whether they are feral cats or pet cats that owners allow outdoors.

What can cat owners do to protect their pets and wildlife?

McCobb: A pet cat should be kept in-doors or safely confined on a leash or in a fenced backyard. All cats should wear identification on a collar. They also should get spayed or neutered and be vaccinated, which keeps them from contributing to the population of outdoor cats and decreases their risk of catching a disease if they do get outside.

Slater: Most animal-welfare and rescue organizations try to get people to keep their cats indoors—the American Bird Conservancy and the Humane Society of the United States had widely publicized programs with that goal—but I’m not aware that any of these educational efforts has been evaluated to determine how well they worked. That would be a great thing to do, because if we knew there were successful ways to get people to change their behaviors about their own pets, we could concentrate on those.

In a recent predation study involving 55 cats, researchers at the University of Georgia attached video cameras to the cats’ collars. Some of the cats in the study hunted (24 of the 55), although relatively few actually caught anything—only 16 cats did.

What was really eye-opening is all the risky things cats are doing. They encounter dogs, get into fights with other cats, dart across busy roads, drink and eat stuff of unknown origin and teeter along rooftops. This might be more compelling to people in terms of understanding why it’s imperative to keep their cats indoors. Everybody thinks, ‘My cat doesn’t go anywhere.’ But these videos show that’s not true. Ordinary house cats get into an amazing amount of mischief.

Editor’s Note: To read more about this issue, see “A Cat-Eat-Bird World.”

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