Frequent grooming is another natural behavior of the cat. The feline tongue's prickly surface acts as a brush to remove loose hairs, parasites, and other foreign material from the coat. The saliva a cat transfers from its mouth to its coat contains proteins that may play a role in conditioning the hair.

Unfortunately, the saliva also contains a protein that causes an allergic reaction in some people. Allergists have recently learned that most of the nearly 10 per cent of people in the United States who are allergic to cats are sensitive to this protein in cat saliva. When these people are exposed to loose cat hairs in a room, they may come in contact with the protein and suffer an allergic reaction, such as sneezing, runny nose, or difficult breathing.

In some ways, the cat's natural behavior matches the life style of many families. The home is empty for much of the day, and that suits the cat because it has the genetic makeup and behavioral instincts to be a loner. But living with a pet cat may also bring us into confrontation with some behaviors that are normal for the wild cat, but which can be quite undesirable in our homes. For example, scratching one or two tree trunks outdoors is perfectly normal behavior for a wild cat. One function of scratching is to remove the worn outer layer of the claw, exposing a new claw underneath. This behavior also enables cats in the wild to mark their territories. A cat will scratch one or more trees or other prominent areas, and in the process of scratching, rub secretions from its feet onto the tree trunk. This gives the scratched area a distinct odor that other cats in the territory recognize. To maintain its territorial marker, the cat repeatedly scratches and freshens the visual and chemical marks.

Pet cats have the same instinctual response to mark a territory. Just as an outdoor cat chooses a prominent tree, an indoor cat chooses a prominent object, such as a couch or chair. The domestic cat also freshens its marker by repeatedly scratching it. But, a domestic cat that scratches furniture or drapes can prove costly to the cat's owner.

Pet owners are often disappointed that their cats do not read the label designating a carpet-covered post as a scratching post and that they continue to scratch a couch or chair. Training a cat to stop scratching furniture may mean removing or covering the mutilated furniture and replacing it with an alternative object, such as a scratching post, in the same prominent place.

Cats like to take long vertical strokes when scratching, so they prefer posts covered with a material that has vertically oriented threads. Cats also will use redwood or pine posts, if the posts are roughed up first with a wire brush. Because cats like to stay with a territorial marker once they have started scratching it, owners find that once a cat starts scratching a post, they can move the post to a less prominent place.

Urine spraying is another normal territorial behavior of cats in the wild that can become a major frustration for domestic cat owners. In the wild, this behavior familiarizes the cat with its territory and home range. The urine odor probably makes it feel self assured and comfortable and signals its presence to other cats in surrounding areas.

Veterinary behaviorist Leslie Cooper of the University of California, Davis, and I found in 1984 that 5 per cent of female domestic cats and 10 per cent of neutered male domestic cats become problem sprayers. The cat sniffs a target area a foot or so above the floor, and then turns and directs a stream of urine toward the target. Males and females spray using basically the same posture, but the behavior is most common in males. Neutering male cats markedly reduces the occurrence of this behavior, but even the neutered males and females may ruin household furniture or stereo speakers by their spraying behavior.

Frequently, a pet cat begins spraying after the introduction of a new adult cat or kitten into the household. A cat owner may have mistakenly believed that a cat needed company and brought home another cat, only to find that the resident pet is not at all thrilled with the newcomer. In this situation, the original cat begins to spray because it is anxious or otherwise threatened by the invasion of its territory.

Until 1991, the most common veterinary treatment to stop a cat from spraying was to administer a drug that mimics the female hormone progesterone. This treatment proved effective in controlling spraying behavior in about 50 per cent of neutered male cats but was much less effective in female cats. In 1991, Amy Marder, a veterinary behaviorist in Boston, introduced the notion of treating spraying cats with the human tranquilizer diazepam, also known as Valium. In a clinical study reported in March 1992, Cooper and I found that diazepam controlled spraying in 55 per cent of male and female cats.

Diazepam has side effects in cats, however, just as it does in people. The drug often causes excessive drowsiness and a temporary lack of coordination. Diazepam also produces physiological and behavioral dependency. In 1992, I —working with Robert Eckstein and Karen Powell at the University of California, Davis, and Nicholas Dodman of Tufts University in Medford, Mass—found that the tranquilizer buspirone, another drug gaining some popularity for the treatment of anxiety in people, is at least as effective as diazepam in controlling spraying behavior without producing the side effects of diazepam.

The need for drug treatments shows that as we remove cats from their natural environment, the expression of their normal behaviors may conflict with our human-oriented environment. Veterinary behaviorists may have to use ingenuity, and sometimes borrow from the area of human drug therapy, to help felines adjust to our environment.

We will also need ingenuity to solve problems stemming from the cat's natural hunting behavior. Much of what we understand about the predatory behavior of cats is the work of Paul Leyhausen, a German animal behaviorist, who spent the 1950's through the 1970's studying domestic cats and related felines.

Leyhausen believed that rodents are a cat's natural prey. Being naturally solitary creatures, Felis libica could successfully hunt rats and mice alone, whereas to hunt larger prey, two or more predators had to cooperate. Usually, the cat waits in front of a rodent's burrow until the rodent strays from its shelter. Then the cat stalks after it, slinking along a trail or ditch and pausing to wait for the opportune moment to pounce on the prey. Actually, the odds generally favor the prey. From his observations, Leyhausen estimated that a cat makes about three attempts before it catches one mouse.

Most cat owners have seen cats play with mice before killing them. The cat tosses the mouse in the air, bats it, rolls it over, clasps it, and kicks at it using its hind claws. The reasons cats play with their prey is not clear. Leyhausen favored the explanation that this play represents the release of pent-up energy associated with predatory behavior and is not necessarily done for pleasure.

A disturbing picture of feline backyard predatory behavior emerged in a 1989 study by biologist Peter Churcher of Bedford School in Bedfordshire, England, and ecologist John Lawton of the University of London. These investigators recorded the number and kind of prey brought home by 77 normal pet cats living in a village in Bedfordshire. They found that in a year's time almost 1,100 prey were claimed by the cats. About 64 per cent of the kill were small mammals, and 36 per cent were birds, including song thrushes, blackbirds, and robins. When they used these figures to calculate the impact of the entire population of 5 million house cats throughout Great Britain, they estimated the pet cats kill at least 20 million birds a year.

The larger number of cats in the United States probably prey on rodents and birds in much greater numbers. In fact, ecologists say that the British study no doubt underestimated the number of birds cats kill, because house cats bring home only about half their victims. In January 1992, California scientists said that cats have all but eliminated the wild bird population in San Francisco's Golden Gate Park.

Making sure that a pet cat is well fed may combat this carnage. But the hunting will probably continue because of the cat's strong predatory instincts. Still, in 1980, the work of animal behaviorist Tim Caro of the University of California, Davis, showed that many cats require experience with a particular type of prey in order to hunt it successfully. Cats exposed to mice as kittens gain efficiency killing rodents, but their success does not carry over very well to killing birds. Thus, one way of improving the odds of having a pet cat that will not hunt birds may be to adopt a kitten that has never been exposed to that prey.

The cats' increasing presence in human society suggests a growing interest in this most recently domesticated mammal. Many scientists share this interest and are pursuing research into just what it means to be a cat in a human world.