It is impossible to determine how well a pair or group of cats will get along. Some cats are really territorial and may never adjust to sharing the house and would do best in a one-cat family. Cats with aggression problems might never be the best of friends, but they can learn to mutually tolerate each other with a minimum of conflict. Working with aggression problems between cats will take time and commitment.

Common Types of Aggressive Behaviour between Cats

Territorial Aggression

Cats are very territorial animals (more than dogs). This type of aggression occurs when a cat feels their territory is invaded by an intruder. In some cases, cats may view the whole neighbourhood as their territory. Female cats can be just as territorial as males.

The behaviour patterns for this type of aggression include chasing and ambushing the intruder and hissing and swatting when contact occurs. These behaviours can often occur when a new cat is brought into the household, when a kitten reaches maturity or when a cat encounters neighbourhood cats outside. Cats can be aggressive towards one cat in a family and friendly and tolerant towards another.

Inter-male Aggression

This type of aggression occurs when an adult male threatens and fights with another adult male cat. This can be for sexual challenges over a female or to achieve a high position in a cat’s loosely organized social dominance hierarchy.

The behaviour patterns of inter-male aggression include ritualized body posturing, stalking, staring, yowling and howling. Attacks can be avoided if one cat “backs down” and walks away. If an attack does happen, the attacker will jump forward and direct a bite to the nape of the neck, while the opponent falls to the ground on their back and attempts to bite and scratch the attacker’s belly with his hind legs. The cats may roll around biting and screaming, stop suddenly, and then resume posturing, and will either fight or walk away.

Most cats do not usually severely injure one another, but you should check for puncture wounds to ensure infection does not set in. Intact males are more likely to fight this way than neutered males.

Defensive Aggression

Defensive aggression will occur when a cat attempts to protect herself from an attack she cannot escape. She will attack because of punishment or the threat of punishment from a person, an attack or attempted attack from another cat or anytime she feels threatened or afraid.

Defensive postures include crouching with the legs pulled in under the body, laying the ears back, tucking the tail and rolling slightly to the side. These are not the same as a dog’s submissive postures because they are not intended to “turn off” an attack from another cat. Approaching a cat in this posture will cause an attack.

Redirected Aggression

This is aggression that has been redirected toward an animal that did not initially provoke the behaviour. For example, a household cat sitting in the window may see an outdoor cat walk across the front yard.  The cat cannot attack the outdoor cat so he turns and attacks the other family cat sitting next to him in the window. Redirected aggression can be offensive or defensive in nature.

What Can You Do?

• If your cat’s behaviour changes suddenly, contact your veterinarian. Cats will hide symptoms of illness until they are seriously ill. A change in behaviour could signal a medical issue.

• Spay or neuter your pets. The behaviour of one intact animal can affect the behaviour of all other animals in the household.

• Start the slow introduction process over from the beginning (see handout on Introducing a Second Cat into Your Home). You may need to elicit help from professionals.

• Consult your veterinarian regarding the possibility of medicating your cats while using a behavior modification program. Never give your cats any over-the-counter or prescription medications without first talking with your veterinarian. Animals do not respond to medications the way humans do and medications that are safe for us are often fatal for cats. Medications are not meant to be a permanent solution and should only be used with behaviour modification techniques.

What NOT to Do

• If your cats are fighting, do not allow the fight to continue. Cats will not be able to “work things out” because of their territorial nature and inflexible hierarchies. The more they are allowed to fight, the worse the situation will get. To stop a fight in progress, make a loud noise, such as blowing a whistle, squirt cats with water or throw something soft at them. Do not try to pull them apart.

• Prevent future fights. This might mean keeping your cats completely separated from each other while working on the problem or preventing contact between them in situations likely to cause a fight.

• Do not try to punish the cats involved. This will likely cause further aggression and fearful responses that will make the problem worse. If you attempt to punish the fighting cats, you may become the target of redirected or defensive aggression.

Due to their inflexible social organization, cats can be tolerant of sharing their house and territory with multiple cats. They may tolerate some cats, but not get along with others in the house. The more cats sharing the same territory, the more likely they will fight with one another.

When introducing cats to each other, they may send play signals that can be misinterpreted by another cat. If the signals are interpreted as aggression by one of the cats, handle the situation as aggressive.

It is not certain what factors determine how well cats get along with each other. Cats that are well socialized and have had pleasant experiences with other cats as kittens are likely to be more sociable than those who have not been around other cats. “Street cats” that are accustomed to fighting with other cats to defend territory and food resources, may not do well in multi-cat homes. Genetic factors may also influence a cat’s temperament, so friendly parents are more likely to produce friendly offspring.