Taming Territorial Aggression In Cats

While it is not strictly true that cats belong to places and not to people, they are, by nature, a highly territorial species.

While it is not strictly true that cats belong to places and not to people, they are, by nature, a highly territorial species. They also have personality traits that make them more or less accepting of other cats within the social space called home.

But even if a cat is relatively mellow and socially accepting, peace is not guaranteed when a new cat is introduced to the home because there is the personality of the newcomer to consider as well.

Friends and Enemies

Cats that have lived in peace for some time usually have come to some arrangements about the allocation of space and privilege along the lines of timesharing. However, a newcomer can shake up a stable arrangement. On the one hand, the newcomer may begin to throw his weight around and incur the wrath of an incumbent. Alternatively, the incumbent may simply not like him and attempt to expel him from the group.

Cats have preferred associates (friends) and others who they conscientiously avoid, so likes and dislikes come into the equation, too. In nature, in a communal setting, preferred associates hang out and outsiders may have to go their own way. However, in a domestic situation, cohabitation within the four walls of a home is imposed upon them and some may rebel.

When a new cat is introduced into a home, its arrival is not always welcomed and infighting in the form of pursuit and aggression by one cat directed toward another may result. This level of non-acceptance is not always the case, however, because sometimes cats get along well even when newly introduced, and other times an initial mild hissing and apprehension are replaced by acceptance or even friendship over a period of about four months.

For unlucky owners, however, the introduction of a new cat can be the worst move they ever made in their lives, both for them and for the unfortunate victim cat.

Thinking of Solutions

When I first took a serious interest in animal behavior 25 years ago, a fellow behaviorist told me that territorial aggression between cats was particularly refractory and that she often advised finding a home for one or the other cat as the only solution.

She was, and is, not alone in this sentiment. More recently, I have heard it suggested by fellow veterinary behaviorists that it is often necessary to simply keep two cats in separate regions of the house permanently to avoid infighting. While these are solutions, they are not the most acceptable ones to most clients and other veterinary behaviorists, and I often struggle to resolve such inter-cat disputes without resorting to such measures.

The result we are trying to achieve is not mutual bonding of former adversaries but merely tolerance of two cats for each other within the home. The strategy is systematic desensitization along with counterconditioning in the form of a gradual reintroduction program. A successful outcome of such a program was reported a few years back in the Animal Behavior Case of the Month feature in the Journal of the American Veterinary Medical Association but the program takes a lot of time and patience on the part of the owner and the supervising behaviorist, and a successful outcome is not always guaranteed.

When attempting to rehabilitate feuding cats, the first step is to separate them into two parts of the house. Let’s call them environments A and B. These two environments preferably are separated by a solid door on either side of which the cats are fed simultaneously twice daily at mealtimes.

If two persons can be present to supervise the feeding, they can follow this up with a few games and food treats for both cats on either side of the door to amplify the positive experience. Note that the cats will be able to appreciate each other’s presence by sound and smell but will not be able to see each other so, hopefully, no conflagration will occur.

Once the cats are eating peacefully, the environments are switched—the cat in environment A is switched to environment B, and vice versa—so that neither cat builds up territoriality. This switching should occur every day or so throughout the program. Assuming all goes well at the closed-door stage, the door can be cracked an inch and properly secured with a weight or hook and eye so that the cats can catch sneak peeks of each other without the possibility of physical interaction.

Moving Forward

Once peace reigns at the 1-inch gap stage, the aperture through which the cats can see each other can be widened to 4 inches—the width of a cat’s head. This is somewhat tricky but can be facilitated by a screen with some material attached to it, paper or cloth, leaving a 4-inch opening to one side.

Next, allow the cats to see each other across a full screen, again continuing the simultaneous feeding and playing routine at set times of the day. The big jump comes when finally the cats are allowed in the same room together. At first this should be closely supervised with either both cats in carriers or wearing harnesses while they are indulged in the same aforementioned pleasures. The time period for the first introduction in the same room may be no more than 15 minutes.

It's not just new cats that can cause issues. Cats that have lived together peacefully can take a turn for the worse after one cat returns from the vet. Read about this in Dr. Dodman's column on Feline Non-recognition Aggression.

Next, allow one or the other cat free so it may explore and come closer to its former adversary. The roles can be reversed at the next meeting. Over time the two cats can be allowed increasing freedom to approach each other so that eventually they are both off leash and out of crates in the same environment, but being entertained as before for windows of time. Ultimately, the time they spend together is increased until it is all the time and the mission has been accomplished.

Although this sounds easy, it is not. It does take time, often several months, and setbacks can occur. I liken this desensitization process to the game of Chutes and Ladders, where you may take a couple of steps forward followed by one back and then, hopefully, to maintain some forward progress on average.

I have had some clients reach a near endpoint of this study and then decide to just throw the cats together. The results of a very limited number of cases have been successful. It seems that when you have taken eight steps of a 10-step ladder it is sometimes possible to achieve the last two rungs in a single leap of faith.


While this program can be achieved without medication, medication is often a helpful adjunct to facilitate more rapid reunion. Sometimes it is only necessary to medicate one cat, usually the aggressor, and fluoxetine (Reconcile) is often the best choice. Sometimes it is also helpful to medicate the other cat, especially if it has been intimidated for a long period of time and is basically living in fear of its former aggressor. In this case, buspirone (BuSpar) can alleviate the cat’s anxiety and seemingly will build its confidence.

Occasionally, I have used alprazolam (Xanax) to treat either the aggressor or the aggressee or both, but I prefer to avoid long-term treatment with this medication as it is addictive. Although paradoxical increases in aggression are theoretically possible with alprazolam, I have yet to see them materialize in this context.

Diazepam (Valium)—a prototypical benzodiazepine—should not be used in cats because of its potential for producing fulminating hepatic failure.

Using some or all of the above measures, it is often, but not always, possible to reintegrate two cats feuding as a result of territorial aggression. I have to say that despite all modern advances and enhanced knowledge about effective medications, territorial aggression in cats is still a behavioral condition we face with a guarded or uncertain prognosis.

We always hope for a peaceful solution but sometimes, it seems, two cats with contrasting personalities are something of oil and water. To paraphrase Helen Keller, we veterinarians do not need the peace that passeth understanding, but rather the understanding that bringeth (at least an element of) peace. 

An author and researcher, Dr. Dodman is a professor at Cummings School of Veterinary Medicine at Tufts University and founder of Tufts’ Animal Behavior Clinic.

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