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Inter-Cat Aggression

Aggression is the number two feline behavior problem reported to behaviorists, second only to inappropriate elimination. Cats show several different types of aggression including status-related (dominance) aggression, fear aggression, territorial aggression, and redirected aggression.

Territorial Aggression

By nature, cats are solitary hunters, not pack animals. However, when food is plentiful, as it is in most of our homes, a group of cats can often live harmoniously, at least most of the time. But even well fed cats retain their instinct to define and defend a territory. Outdoor cats mark their territory with urine, feces, and various natural odors (so-called “pheromones“) from various scent glands. Scent marking serves to indicate that the territory is occupied and reduces encounters between cats.

In close quarters, though, cats often live by certain subtle territorial rules, respecting distinct territories within a single room, like access to a particular couch or favored window perch. Moreover, some feline housemates learn to “time share” these favored locations with one cat taking the front window in the morning and the other taking it over in the afternoon.

Unfortunately, anything that disturbs the established “rules” can lead to confrontation, and what starts as occasional minor spats of aggression may erupt into a full-blown feud unless precautions are taken. It is important to keep in mind that when cats are confined indoors they have little chance to avoid each other, and aggression, once it occurs, is often compounded.

Problems with territorial aggression are most common when a new cat is added to the household. If sudden introductions lead to aggression, this can set the stage for future battles and may not bode well for the future. The way to circumvent this problem is to gradually introduce unfamiliar cats to each other across a closed door. A gradual introduction of a new cat to the household may take two to three weeks. This said, if initial animosities are mild, they often resolve spontaneously over a period of four months, even without such precautionary measures.

Territorial aggression between cats in the same household tends to develop gradually. The more confident cat may begin to guard various resources and threaten its feline housemate over the slightest infraction. Gradually the threats may progress to attacks and the victim may become progressively more frightened. Depending on the victim’s temperament, he may choose to retaliate or hide, only making an appearance when the territorial cat is not around. Occasionally litter box problems may arise because the fearful cat is too afraid to leave his hiding place. Additional problems of spraying and other forms of marking may occur if both cats are of close to equal status.

Non-Recognition Aggression

This explosive type of aggression occurs between feline housemates that have previously had a reasonable relationship. It probably occurs through “failure of recognition.” Non-recognition is most often triggered when one cat in the family is brought back from the veterinarian’s office, or the groomer, and smells and behaves differently. If a fight ensues, it can damage irreparably the relationship between the cats and lead to the development of territorial aggression. It is best avoided by separating indoor cats after outside excursions until it can be established that they are friendly toward each other.

Redirected Aggression

Aggression intended for an outdoor intruder that is redirected onto a feline housemate can also severely damage the social bond between cats that have previously cohabited in harmony. A typical scenario is of one cat resting by a window when a second cat sees an intruder cat outside the window and rushes to attack it. A sudden conflagration ensues with both cats fighting with one another. Theories as to who first attacks whom vary. One theory is that the would-be attacker, behind the window, being unable to attack the unwelcome visitor on the other side of a window, turns and attacks the cat next to it instead. This is true “redirected aggression” and is analogous to an angry man who punches a wall.

A second possible scenario is that one of the inside cats becomes extremely frightened by its buddy’s aggressive display (intended for the cat outside) and adopts a defensive posture with its pupils dilated, claws unsheathed, crouched body posture, ears flattened, and perhaps hissing and swatting. The other cat observes this display, interprets that it is about to be attacked, and takes the offensive. A fight ensues.

A variation on the theme of redirected aggression occurs when two cats are resting in the same vicinity when a frightening incident occurs, such as an unusual and particularly loud noise. Both cats are startled and assume a defensive posture. When they see each other in this stance, they each assume the other is ready to launch an attack. Each cat responds defensively, a fight erupts, and they remain fearful and aggressive toward each other afterwards.

In cases of redirected aggression, the cats should be separated immediately. If this is done and they are given several hours, if not overnight, to cool off you may be able to reintroduce them the next day over a bowl of food.

General Recommendations

If cats end up in a fight, do not reach between them as you could be injured. Instead, separate them with a blanket, broom, or whatever is handy. Alternatively, make a loud noise to startle them by dropping a pan or book. Cats become extremely agitated after an aggressive event and respond best to isolation until they become calm. You should banish the aggressor to a less desirable area. Cats may need to be separated for as long as 12 hours before they calm down and it is safe to reintroduce them.

Counter-conditioning and Desensitization

A systematic desensitization and counter-conditioning program can reintroduce feuding cats. Systematic desensitization gradually accustoms a cat to something he fears or is uncertain about. Counter-conditioning rewards the cat when he is in the presence of his “enemy,” with something he needs or wants, such as food or attention. Over time, these techniques work together to make a formerly stressful experience pleasant and rewarding.

Time is the key word here. Desensitization can take months and will require considerable persistence and patience. Throughout the process, owners must be prepared to return to the previous stage at the first sign of hostile behavior before advancing to the next stage of exposure.

Neither cat should show anxiety or aggression during the reintroduction process. If they do, go back to a distance (or level of exposure) at which both cats are comfortable. Look for signs of anxiety from the victim and aggression by the aggressor. Signs of anxiety may include not finishing the food, eating quickly and leaving, avoiding eye contact, hiding, or trembling. Warning signs of impending aggression include staring, tail switching, flattening of the ears, growling, hissing, and stiff body posture. Banish the aggressor to another room if this behavior is observed.

Reward the cats for ignoring each other. If the aggressive cat averts his gaze, he should be rewarded immediately. If the cat that has been attacked makes direct eye contact with the aggressor, reward that response. Do not give food treats or praise to either cat for showing fear or aggression; Reward only positive interactions between the cats.

Steps to Follow

Step I

Step II

Now begins the process of desensitization and counter-conditioning. If you are accustomed to feeding your cats “free-choice,” you will have to abandon this practice for more controlled feeding practices. One approach is that during the retraining period, all cats should be “meal fed” in the morning and at night so they will be hungry enough to want to participate in across-the-door socialization at mealtimes. The one thing the cats shouldn’t be able to do is eat wherever and whenever they want.

Step III


The process described above is tedious and it may take several months to achieve acceptable results. However, no matter how frustrating it may be, do not rush the reintroduction process.

Be advised that the above techniques work well in some, but not all cases. Some cats will never be able to be left alone together but they may be perfectly happy living separately in the same household.