It is impossible to estimate how well any particular pair or group of cats will ultimately tolerate each other. Some cats are unusually territorial, and may never adjust to sharing their house, doing best in a one-cat family; while other cats can live well together in a multi-cat family. If aggression does occur however, it is important to know that most aggressive problems between cats can be successfully resolved. You may need help from both your veterinarian and from an animal behavior specialist who is knowledgeable in cat behavior. Cats with aggression problems may never be best friends, but can often learn to mutually tolerate each other with minimal conflict. Working with aggression problems between family cats will take time and commitment from you. Don’t give up without consulting the appropriate experts.
Territorial Aggression: Cats are very territorial, by nature. Territorial aggression occurs when a cat feels that his territory/survival is threatened. Depending on where your cat spends his time, he may view your whole neighborhood as his territory. The behavior patterns in this type of aggression include chasing and ambushing the intruder, as well as hissing and swatting when contact occurs. Territorial problems often occur when a new cat is brought into a household, when a young kitten reaches maturity, or when a cat encounters neighborhood cats outside. It’s not uncommon for a cat to be territorially aggressive toward one cat in a family, and friendly and tolerant to another.
Intermale Aggression: Intact adult male cats tend to threaten, and sometimes fight with other males. These behaviors can occur as sexual challenges over a female. This type of aggression involves ritualized body posturing, stalking, staring, yowling, and howling. Attacks are usually avoided if one cat “backs down” and walks away. If an attack occurs, the attacker will usually jump forward, directing a bite to the nape of the neck, while the opponent falls to the ground on his back and attempts to bite and scratch the attacker’s belly with his hind legs. The cats may roll around biting and screaming, suddenly stop, resume posturing, fight again or walk away. Cats don’t usually severely injure one another this way, but you should always check for puncture wounds which are prone to infection.
Defensive Aggression: Defensive aggression occurs when a cat is attempting to protect himself from an attack he believes he cannot escape. This can occur in response to punishment or the threat of punishment from a person, an attack or attempted attack from another cat, or anytime he feels threatened or afraid. Defensive postures include crouching with the legs pulled in under the body, laying the ears back, tucking the tail, and possibly rolling slightly to the side. Continuing to approach a cat that’s in this posture is likely to precipitate an attack.
Redirected Aggression: This type of aggression is directed toward another animal that didn’t initially provoke the behavior. For example, a household cat sitting in the window may see or be threatened by an outdoor cat. Because he can’t respond respectively to the outdoor cat, he may instead turn and attack the other family cat that’s sitting next to him in the window. Redirected aggression can be either offensive or defensive in nature and can occur up to 24 hours after the initial sighting or incident with the outdoor cat.