Introduction to Domestic Cats
Have you ever wondered why falling cats always seem to land on their feet? Or why cats are compelled to hunt birds and rodents no matter how well the pets are fed? Like cat owners, many scientists are intrigued by the cat's behavior and physical features. Ecologists say that the sheer number of cats kept as pets—about 67 million in the United States alone—means that the animals have a significant influence on the ecology of urban areas. And studies of the domestic cat's physical makeup and behavior not only add to our knowledge of all members of the cat family, but also provide practical benefits for millions of pet owners.
Much of the current scientific interest in cats stems from their changing relationship with human beings. For years, most cats in the United States lived in wild or semiwild states in cities, on farms, or in the countryside. They reproduced and flourished because people brought them food or because stored food attracted rodents, which the cats preyed upon. Today, although there are still many feral (wild) cats, millions of others have achieved the status of family members and live in a human-dominated environment. And, after long being neglected as subjects for scientific inquiry, the cat has caught the interest of biologists.
Cats and Their Nearest Wild Relatives
Domestic cats belong to the Felidae family of the animal kingdom, which also includes such large cats as the lion, tiger, cheetah, and leopard. The wild ancestor of the domestic cat is Felis libica, commonly called the African wild cat. This species still exists in Africa, but because it is most active at night, it is rarely seen and therefore difficult to study.
Scientists have learned, however, that the African wild cat lives a solitary life on a well-marked territory. Male and female adults interact very little other than during mating. Later, females interact with their own kittens.
The Cat Is the Newest Domesticated Animal
The cat is the most recently domesticated mammal. Domestication in its broadest sense refers to a process in which an animal species becomes tame and unafraid of people. But for biologists, domestication also means that a species has been genetically altered to produce traits desirable to people. In contrast to dogs, cattle, and other domestic animals, the domestic cat is the least altered anatomically and behaviorally from its wild ancestor. This is partly because people have lacked a reason to breed specific traits in cats as they have with cows, for example, to produce more milk.
Fascinating Feline Physiology
Like their wild ancestor, domestic cats are physically adapted for hunting small prey. Although their vision is not especially keen, they see well in dim light and readily perceive motion. Their padded feet and flexible muscles allow them to silently stalk prey or give chase by running about 48 kilometers (30 miles) per hour.
Researchers studying the cat still have much to learn about the animal and its relatives. A wide range of felines, for example, exhibit unusually playful or sexual behavior when they smell the catnip plant. No other animal responds to the plant in this way. Although research has shown that the catnip response occurs in about 50 per cent of all cats and appears to be an inherited trait, exactly how the odor affects the cat brain is still unknown.
Purring
Biologists have been a little more successful in understanding how cats purr. In February 1991, physiologists Dawn Frazer and David A. Rice of Tulane University in New Orleans, La., and G. Peters of the Alexander Koenig Museum in Germany reported that purring consists of low frequency sound produced by vibrations of the cat's larynx (voice box) during inhaling and exhaling. These researchers recorded the sounds through instruments that they placed on various parts of the cat's body. They found that the sounds were not linked to the sounds of the cat's breathing pattern, which is why purring is continuous. Purring may in fact occur simultaneously with other vocalizations.
Scientists do not know the purpose of purring, however, especially as it might have served the cat's wild ancestor. Purring appears to be a sign of contentment, yet even cats that are ill and in discomfort may purr. Cat owners recognize that purring occurs when cats are around people, but the presence of people is not essential for purring. Cats may purr during mating —and kittens, while nursing. But cats of any age do not purr while they are sleeping.
How Cats Survive Falls
Perhaps more intriguing than purring is the cat's ability to survive falls. The research of veterinarians Wayne Whitney and Cheryl Mehlhaff at the Animal Medical Center in New York City shed light on this ability in 1987. The cat's habit of falling out of open windows provided the researchers with an opportunity to study 115 cats that had fallen from high-rise apartments in New York City. The average fall was 5.5 stories. Of the 115 cats studied, 90 per cent survived, including one cat that fell 32 stories onto a sidewalk and suffered only a mild chest injury and a chipped tooth. Interestingly, cats that fell from 9 or more stories suffered fewer injuries than those falling from lower heights. Among cats that fell from 9 to 32 stories, only 5 per cent suffered fatal injuries, but 10 per cent of those that fell from 7 or fewer stories died.
How do cats manage to take falling so easily? For one thing, in comparison to human beings, a cat is much smaller and lighter. Also, a cat has more body surface area in proportion to its weight than a human being has. This increase in surface area results in greater air resistance, which slows the fall. The important thing, however, is that a falling cat apparently positions itself to form a sort of parachute. Less than one second after it starts to fall, a cat quickly rights itself in midair with all four legs pointing downward. The cat's inner ears act like an internal gyroscope, telling the cat which direction it is falling. With the legs pointed downward, the cat then spreads its legs so that its body forms a sort of parachute that increases air resistance. With its limbs flexed, the cat also cushions the force of impact by landing on all four legs. The force of the impact is distributed through the muscles and joints.
Whitney and Mehlhaff believe that the parachute effect comes into play mainly above four stories, at the point where the cat has reached its greatest rate of descent. Of the 115 cats the researchers studied, only 1 of 13 cats that fell nine or more stories sustained a bone fracture, whereas most of the cats that fell from lower stories suffered some type of broken bone.
Researching Feline Disease
Cats may be able to escape injuries from falls, but many suffer from serious diseases, such as feline leukemia; infectious peritonitis, an inflammation of the membrane that lines the walls of the abdomen; and panleukopenia (cat distemper). Since the mid-1980's, veterinary researchers have made great strides in understanding two other major diseases: a type of heart disease called dilated cardiomyopathy and a type of AIDS that strikes only cats.
For years, dilated cardiomyopathy was recognized as a significant cause of death of pet cats in the United States. This disease is characterized by enlargement and weakening of the heart to the point where it is incapable of pumping blood. Until 1987, the cause of the disease was unknown, and veterinarians could offer no cure. In 1987, veterinarians Paul Pion and Mark Kittleson and their colleagues at the University of California, Davis, School of Veterinary Medicine reported that cats suffering from dilated cardiomyopathy had a deficiency of an amino acid called taurine. (Amino acids are the building blocks of protein.) Giving the cats taurine supplements reversed the disease and led to a full recovery.
Before the California study, cat specialists had thought that taurine deficiencies occurred only in cats fed commercial dog food or home-cooked food that was nutritionally unbalanced. But the California veterinarians discovered that cats fed exclusively with some types of commercial cat food could develop the heart disease. Since the 1987 study, manufacturers of the cat foods have added more taurine to their products, and there has been a dramatic decrease in the number of cases of the disease.
Feline AIDS
Another important discovery was the recognition of feline AIDS in 1988 by veterinarian Neils Pedersen and his colleagues at the University of California, Davis. The disease is caused by a virus called the feline immunodeficiency virus (FIV). FIV is usually transmitted during a fight through the saliva of an infected cat that bites another cat, puncturing the skin. Because cat fights generally occur outdoors, feline AIDS is found mainly in cats that are allowed to roam freely or in multiple-cat households that adopt wild or homeless cats. In many areas of the United States where there is a large population of freely roaming cats, about 5 per cent of the feline population is infected. Since the disease was first diagnosed in 1988, veterinarians have found feline AIDS in cats throughout the United States, Canada, South Africa, Australia, New Zealand, and Japan.
The virus and the disease pattern are similar to that of human AIDS, but cats do not get the human virus, and people are not susceptible to the cat virus. Veterinarians had observed the symptoms of FIV infection for many years, but investigators did not recognize the disorder as a type of AIDS until the symptoms of human AIDS were recognized as a disease.
Like human AIDS, feline AIDS attacks the body's disease-fighting immune system. The feline disorder has two stages. The first stage begins when a cat is infected through a bite. About four weeks after the initial infection, the cat becomes ill with a fever but usually recovers. The second stage begins about two to four years after infection and is marked by the appearance of infections in the mouth and respiratory system and on the skin. These infections are called opportunistic because they afflict only cats whose immune systems are too weak to fight off the infection-causing microbes. Death from these AIDS-related infections is inevitable.
According to veterinarians, cat owners can best protect their cats from FIV infection by not allowing the cats to run free. If a cat is kept indoors even with an infected animal, the likelihood of transmission is small because indoor cats rarely bite each other.
Focusing On Cat Behavior
Another major focus of research is cat behavior. Many people think of cat behavior merely as grooming, scratching, and sleeping. However, just because cats are not often seen performing tricks does not mean that cats do not easily learn.
Animal behaviorists say the intelligence or learning ability of cats is no greater or less than that of dogs. But comparing different species is difficult, because tests of their learning abilities must take into account differences in the animals' sensory and motor capabilities and in their inherited behavioral predispositions. For example, cats being tested for learning ability will not respond to the reward of petting as consistently as dogs will.
How Smart Are Cats?
Nevertheless, as early as the 1920's, researchers found that cats can learn complex tasks, especially if the reward is food. And in highly structured tests of learning ability, cats often outperformed dogs in the ability to master conceptual problems. In the 1950's, animal behaviorist J. M. Warren at Pennsylvania State University at University Park described the cat's ability to master "oddity learning" in which the animal is shown three objects and is rewarded for selecting the one that is most unlike the other two. In the test, cats learned to paw a square block rather than two round blocks presented at the same time, because food was hidden beneath the square block. In similar tests, the cat chose the different object when presented with one round block and two squares.
Such tests require the ability to understand concepts, in this case, that of similarity and dissimilarity. Researchers have found that some cats do as well with this type of conceptual learning as monkeys. And, aside from monkeys and other primates, cats are among the most adept at learning by observing the successes and failures of other animals attempting to complete tasks to obtain a reward.
Grooming Behavior
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.
Collisions Between Feline and Human Worlds
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.
Training Pet Cats Not to Scratch Furniture
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.
Problem Sprayers
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.
Anti-spraying Drugs
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.
Cats As Backyard Predators
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.
Cats and Bird Kills
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.
Keeping Cats Well-fed and Content
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.