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Aggression in household cats

By Victoria L. Voith, DVM, PhD, and Peter L. Borchelt, PhD

Myth: Aggressive behavior between household cats requires finding another home for one of them.

Miss Smith has two castrated male cats that are 5 and 6 years of age. They had always gotten along well until a few weeks ago, when they suddenly began fighting. Now, every time they see each other they hiss, attack each other and then run away. There is no indication that their behavior is getting better.

The Joneses have two 3-year-old spayed female cats, Precious and Sweeny, that are littermates. Until recently, the cats have always gotten along. Several months ago, Precious started growling at Sweeny and eventually began to swat at and chase her: Precious now sits and waits until she sees Sweetie and then attacks her: Sweeny hides and tries to avoid Precious. The problem is getting progressively worse.

The Browns have a 1-year-old cat and are thinking of getting another cat but have heard that cats sometimes do not get along with one another. They are concerned about how they should introduce another cat.

The Social System of the Cat

To understand what is happening with the cats described above, it is helpful to understand the social system of cats. A social system is the group living arrangement that has evolved to ensure optimum survival of the members of a species. Cats seem to have a flexible social system.

When food and shelter is abundant, they may live in large groups. When food or shelter becomes scarce, they divide into smaller groups or become solitary individuals.

The domesticated cat that survives off the land without help from people generally lives by itself except during courtship and when a mother is rearing her offspring. Kittens stay with their mother until they are 6 to 12 months of age and then disperse to establish their own hunting areas. When food and shelter are abundant, as on farms or in households, females and neutered cats may live in groups quite amicably.

A group of unneutered farm cats generally consists of related females and their kittens. Female social groups maintain territories separate from those of other female groups. The adult male or tomcat may have a very large territory that encompasses several female territories. When the male kittens reach approximately l year of age, the tomcat that periodically patrols the area will begin harassing the young males until they leave the family group. Most of the female kittens remain, but occasionally some may emigrate as well.

Kittens usually get along very well together. Through the process of domestication, we have probably selected for amicability among cats and kitten-like behaviors, which allows keeping multiple cats in our households. Despite this selection, some cats still become territorial and many retain the ability to switch to a solitary lifestyle.

Cats reach puberty or sexual maturity at approximately 6 to 9 months of age. They do not become full-grown adults, however, until they are 2 to 4 years of age. At maturity, some cats, even in a well-provisioned household, will become territorial and attempt to expel other cats that have been living with them. This behavior occurs most often between two intact members of the same sex and sometimes between neutered animals, either males or females.

Common Aggressive Behavior in Household Cats

1. Inter-male Aggression. As males reach adulthood they may begin challenging one another. Roaming intact tomcats frequently engage in ritualistic threats as well as actual fights. The cats sit or stand very stiffly and stare at each other. They tilt their heads slowly to a 45° angle and turn their ears so that the backs of the ears face forward. This posturing is accompanied by prowls and very loud howling. Cat owners and their neighbors often hear these vocalization duels at night. Then, one cat may leave very slowly or one or both cats may attack. Sometimes an attack will result in only one bite. Because cat bites frequently become infected, however, a single bite can be very serious and can even lead to death.

Castration usually prevents or stops inter-male fighting, particularly if both males are neutered. The effectiveness of castration does not seem to be related to the age of the cat or how long it has been fighting. A small percentage of castrated males continue to fight with other males. Some drugs may suppress a cat's motivation to engage in inter-male aggression; however, when the drug is withdrawn, the cat may become aggressive again. The advantages and disadvantages of drug therapy should be discussed with a veterinarian.

2. Territorial Aggression. Territorial aggression between cats in a household usually develops slowly and gradually. One cat is usually the aggressor and the other the "victim." The encounters begin with hissing and growling and progress to swatting, chasing, relentless pursuit, and finally attacking and fighting. The victim may become progressively more afraid of the aggressor and become defensive. It may hide on shelves or bookcases or in closets and come out only when the aggressor cat is not present. Occasionally, litter box problems occur because the fearful cat is too afraid to move from its hiding place.

We do not know what factors determine which cats will become territorial and will try to exclude other cats from the home. If territorial aggression develops, it usually does not start until one or both cats are between 1 and 3 years of age. A territorial cat can be aggressive toward one cat in the household yet get along well with other cats in the home. The aggressor is not necessarily always the first cat that was introduced into the household nor the eldest.

Territorial aggression is rarely treated successfully. Although new behavioral procedures are constantly being tried and new drug therapies explored, sometimes the best solution for this problem is to find one of the cats another home. Just because the cat is aggressive toward another cat does not mean that it is aggressive toward people. Territorially aggressive cats can be wonderful pets in a home without other cats.

Another method to manage the problem is to keep the cats in separate areas of the household or yard to avoid encounters. Sometimes providing a larger living area by moving from a small apartment to a large house or giving one of the cats access to the outdoors will help the problem.

People living with cats that are aggressive toward other cats must be careful. Owners that interfere with a cat that is either aggressive or frightened may be bitten. A territorially aggressive cat may even attack an owner who has recently handled another cat.

3. Fear-Induced Aggression. When two amicable cats in a household suddenly become aggressive toward each other, the cause is generally fear related. The cats do not seek each other out, but if they run into each other, both are startled and will attack.

Usually this problem begins "by mistake" or by accident. For example, Cat A may be sitting in a window as an outdoor cat walks by. Cat B. which is territorially aggressive toward outdoor cats, is in the middle of the room. Cat B sees the outdoor cat and rushes toward the window to attack it. Unfortunately, Cat A happens to be in the way and sees Cat B aggressively charging toward it. Cat A puffs up and hisses. Cat B turns its attention to Cat A and puffs up and hisses. Then the cats attack each other. Each acts as if the other started the fight.

Occasionally, two friendly cats may be resting when a frightening incident occurs, such as a bookshelf falling over. Both cats become startled, puff up, and assume defensive postures. When they see each other in a defensive posture, they respond as if the other is about to attack. Consequently, each reacts defensively, a fight ensues, and thereafter they are aggressive whenever they see each other. This type of aggressive behavior usually is treated successfully. Basically, the cats must become accustomed to each other again without either cat becoming afraid or aggressive. To implement this process, the cats first should be separated so that they cannot see each other except during treatment procedures. One way to reintroduce the cats is when they are hungry. The cats can be positioned at opposite ends of the room several times a day and fed small amounts of food. If both cats are hungry and occupied with eating they will see each other in an unaggressive state. The food dishes are brought closer together gradually over several days or weeks. Eventually after eating, the cats can spend some time with each other if they are kept apart on leashes at a safe distance. The owners can pet or play with the cats to keep them relaxed and in a good mood while the other cat is in the vicinity. This technique is more likely to work if the level of aggression is relatively low. If the cat's behavior does not improve, or even gets worse, using this method, the following technique can be tried.

Another way to reintroduce cats is to expose them to each other for prolonged periods without letting them come in direct contact. They might be kept in large cages at opposite ends of the room, where they can see each other but cannot escape. Alternatively. the cats could be kept on leashes or in harnesses and separated— but within sight of each other. After several hours, they might be brought closer together. After many such sessions, it should be possible for them to be close to each other, whereby they might groom or play together as they did before. Then they could be let loose.

Sometimes, however, a cat's defensive behavior is so intense that even the very sight of the other cat will lead to an aggressive fear response. In such cases, it may be necessary to gradually bring the cats into view of each other. For example, cats could be allowed to see each other through the crack of a fastened door (opened about an inch) or through the gap below the door. Such limited visual presentations can reduce the fear sufficiently so that subsequent progress can be made. The door can be gradually opened wider, perhaps as the cats are fed, played with or petted, or kept at a distance on leashes or in wire cages.

In some cases, the cats can be separated by a screen door, with the lower screen covered completely with a large piece of cardboard. First, the cats should be allowed to approach the screen door and encouraged to play with each other's paws at the under the door. Then, a very small gap or slit can be made in the cardboard so that they can barely see each other. The play under the door should be allowed for several days. Very gradually (every few days or so, the opening in the cardboard should be widened so that the cats can see more of each other. By the time they can see each other completely and still play (several weeks at least and maybe even several months), it is safe to let them play with the screen door removed.

4. Redirected Aggression. When a cat is highly aroused and in an aggressive state (e.g., by the sight of an outdoor cat or after being chased by a dog), it may redirect its aggression to a person or another animal within reach. Redirected aggression can occur whether the motive for the aggression is inter-male, territorial, fear-induced, or defensive in nature. Generally, cats do not redirect aggression unless they are touched or closely approached by another animal or person.

If a cat is in an aggressive state or mood, it is dangerous for an owner to approach it, touch it. or try to pick it Up. Cat bites are very serious to people, as well as to other cats. One should not pick up or approach a cat that is highly aroused and aggressive. People should wait until after the cat has groomed itself, played. or eaten. Then, it usually is safe to approach the cat. In an emergency, during which an aroused aggressive cat must be moved, a very thick blanket might be used to catch the cat and then pick it up.

In some communities, local humane officers, using special equipment, will help owners catch their cats.

Introducing New Cats or Reintroducing Cats to Each Other. Kittens usually adjust to one another quickly, but older cats take longer. When brought into a household, a new cat should be separated from the resident cat(s) for a few days to reduce the possibility of an aggressive encounter. The cats should be alternated in the rooms, allowing them to become more familiar with one another by odor. This procedure allows the new cat to acquaint itself with the environment, particularly with potential escape routes and hiding places. The cats can be exposed to each other gradually, using the techniques described above to reintroduce two fear-induced aggressive cats. Care must be taken not to introduce the cats too rapidly or they may attack each other. An introduction procedure usually takes only 2 or 3 days, particularly if the cats are young. Occasionally, however, it may take weeks.