Is There a Killer in Your House

Cats may kill 19 million songbirds in Wisconsin alone each year; are our beloved pets a serious danger to wildlife?

• George H. Harrison
• Oct 01, 1992

Say it ain't so! That adorable little ball of fluff snoozing on the sofa is a killer--one of the major predators of wildlife in the United States?

"Not my cat," is the usual retort. "She gets all the food she can eat at home." Yet recent studies in the United States and Great Britain confirm dramatically that house cats, including those well fed at home, kill millions of small birds and mammals every year, a death toll that may be contributing to declines in some rare species.

"It's shocking," says Stanley Temple, professor of wildlife ecology and conservation at the University of Wisconsin, Madison. Temple and colleague John Coleman have just completed a four-year study of the impact of free-ranging domestic cats on rural wildlife. By radio collaring about 30 farm cats for various periods of time, the researchers estimated that in Wisconsin alone, cats may kill 19 million songbirds and 140,000 game birds in a single year.

"Cats may be a major threat to some bird populations," Temple says, "especially ground-nesting birds living near farms." He suspects cats may have contributed to the significant declines in Midwestern grassland birds such as grasshopper sparrows and Le Conte's sparrows. "Western meadowlarks are particularly hard-hit by cats and are declining in Wisconsin at an annual rate of 8 percent," he says.

One reason cats are doing so much damage is that there are so many of them. Temple found that 78 percent of the residents in rural Wisconsin had more than four free-roaming cats each, giving some counties in that state a density of 57 cats per square mile. (Studies of city cats show that population densities in urban areas are even higher: 344 cats per square mile in Warsaw, Poland; 1,295 per square mile in Madison, Wisconsin).

The Wisconsin findings confirm a 1987 British study that shocked cat lovers around the world. The project sounded simple at first: Researchers Peter Church and John Lawton chronicled the predatory habits of 78 house cats living in Church's home village in Bedfordshire, England.

The scientists knew that house cats typically bring home about 50 percent of the prey; they kill and present their "trophies" to their owners (documented in a 1974 study of well-fed house cats in Illinois). So Church persuaded 77 of the 78 cat owners in his village to gather their cats' offerings in polybags and save them for science.

In a full year of collecting and identifying the carcasses, Church and Lawton accumulated 1,094 prey, 64 percent of which were small mammals, mostly wood mice, field voles and common shrews, plus the occasional rabbit, weasel and bat. The remaining 36 percent of the animals were birds, mostly house sparrows, song thrushes, blackbirds and robins.

Based on the astonishing volume of bones, feathers and fur collected in just one village, Church and Lawton estimated that Britain's 5 million house cats account for an annual toll of some 70 million animals, 20 million of which are birds.

The study probed deeper into cats' impact on house sparrows, which accounted for 16 percent of the Bedfordshire total. Cats, according to Church and Lawton calculations, are probably responsible for as much as a third to half of all the sparrow deaths in England.

These findings disturb most cat owners, who do not want to feel responsible for the demise of neighborhood wildlife. The Wisconsin study found that 94 percent of cat owners wanted songbirds on their property and 83 percent wanted game birds, yet only 42 percent were willing to reduce the number of cats to benefit these wild species.

"Cat owners demonstrate a lot of denial about the hunting achievements of their cats," Temple says. "In fact, they seem to have a certain pride in their cat's prowess and believe it to be 'neat' that their kitty cats can kill wildlife. Yet, they are convinced that their cats are harmless."

When the proposal for Temple's study became public in 1987, it caused an explosion outrage. "I was totally unprepared for the public reaction to this study," he remembers. "I gave a paper at a Wildlife Society meeting where a state senator happened to be in the audience. What we were proposing to do got to the media through the senator and then it really snowballed. People started calling, including the governor's office. I got hate mail from cat lovers and cat haters, including a shooting target with a cat's face painted on it and another letter that said, `If you want to study cats, we have a pile of dead ones for you.' "

Prior to the study, Stan Temple was a dog person. Though he had never kept a cat, he decided to take one on as a part of the study and to allow it to come and go through a cat flap in one of the doors of his rural south-central Wisconsin house. I've changed my mind about cats," he admits now. "They are really interesting animals."

But why do these interesting, usually demure lap pets turn into killers? It's the natural result of an ancient arrangement, according to animal-behavior expert Desmond Morris, former curator of mammals at the London Zoo and author of Catwatching. "Before the cat became elevated to the level of a companion and pet for friendly humans," he says, "the contact between man and cat was based on the animal's ability to destroy pests. From the time mankind first started to keep grain in storage, the cat had a role to play and carried out its side of the bargain with great success." (The Wisconsin study showed that the primary reason there are so many cats on farms today is precisely the same: people say they want rodent control.)

In a tempting misconception, farmers often believe that keeping their cats hungry is the best way to get them to scour barns for mice. Wrong, says Morris. Hungry cats range so far from home that they kill fewer of the pests on the farm. Well-fed cats, however, stay closer to home and end up catching more rodents in the barn.

"The fact that they had been fed already and were not particularly hungry made no difference to the number of prey they killed each day," explains Morris, "because the urge to hunt is independent of the urge to eat. Cats hunt for the sake of hunting." (In the Wisconsin study, 82 percent of cat owners fed their pets daily.)

Why cats bring their trophies home to their masters and mistresses the world over is another mystery. Morris thinks it's because "they consider their owners such hopeless hunters." House cats often treat their humans as pseudo-parents, but when it comes to hunting, the owners are "kittens." And "if kittens do not know how to catch and eat mice and small birds, then the cat must demonstrate to them," Morris explains. Temple, however, points out that wild cats cache leftover prey after eating their fill. The trophies of pet cats, he thinks, come from the same urge to store extra food.

All these natural urges can add up to significant destruction of wildlife unless cat owners step in. Yet putting a bell around a cat's neck or declawing the animal won't save birds, according to Temple. "Wildlife does not associate the ringing of a bell with a predator," he says. "Besides, when cats stalk their prey, their stealth makes them nearly motionless. The bell doesn't ring. Declawed cats don't stop hunting, either. Without claws, they simply bat down their prey."

The best solution is to confine the cats. But many cat owners aren't convinced. "Oh, I couldn't keep my cat inside all the time. I have to let her out, at least for a little while, or she would go crazy," is a common remark.

"That's not only unfair to wildlife, that's unfair to cats," says Rachel Lamb, program coordinator for companion animals at the Humane Society of the United States in Washington, D.C. The society has found that free-roaming pets live an average of 3 to 5 years, while it's "very common" for indoor cats to reach 17 years or more. Indoor pets avoid exposure to feline leukemia and rabies, which is rising among cats despite the existence of a vaccine. The greatest dangers outdoors, however, are cars, which kill 1.5 million cats a year. "Besides," says Lamb, "who's to say that the pleasure of our cats is more important than the lives of birds?"

A cat curfew is the solution adopted by the Sherbrooke Shire Council, near Melbourne, Australia. The council was horrified by cats stalking rare superb lyrebirds in a nearby forest, and now Sherbrooke residents must keep their pets indoors at night. If a cat breaks the curfew, the owner can be fined $100.

Yet to keep farm cats in a house their entire lives prevents rat catching, their reason for being on the farm to begin with. "Therefore, the solution on farms is to reduce the number of cats or control their rate of reproduction," Temple says.

"Farmers say that they are willing to reduce cat numbers if they could save wildlife, but the problem is how," says Temple. No one particularly wants to shoot, drown or otherwise kill their pet cats. "Neutering or spaying is the only acceptable way to reduce their numbers, but most farmers are not willing to spend the money to have it done."

Neutering and spaying are "just essential," pleads Lamb. "We have a severe pet overpopulation problem in this country." More than 8 million dogs and cats are euthanized in the United States every year because no one wants them. The future does not look better: Lamb says more than 35,000 kittens are born in this country every day (compared with 10,000 humans). One female and her offspring, according to the society's calculations, can produce a staggering 420,000 cats in just seven years.

This population problem has wildlife managers scratching their heads. "Federal and state wildlife agencies spend a great deal of money on incentives for farmers to provide habitat for wildlife," Temple explains, "but that may be a waste of money if the habitat is overrun with cats."

Field Editor George Harrison says that his cat stays indoors but has become an avid bird-watcher.