Inter-Cat Territorial Aggression

Posted by & filed under Dr. Nick, Pet Care Advice.

by Dr. Nicholas Dodman

Dr NIcholas Dodman

Aggression is one of the most common feline behavior problems reported to behaviorists. Cats may exhibit several different types of aggression including territorial aggression, non-recognition aggression, status-related aggression, fear aggression, redirected aggression and medically-induced aggression. Here I will address territorial aggression – one of the most common expressions of feline aggression.


Cats are, by nature, solitary hunters and have strong territorial instincts. Feral cats mark their territory with urine, feces, and certain natural odors secreted by scent glands. Scent marking serves to indicate that the territory is occupied and serves to reduce antagonistic encounters between cats. When food is plentiful, as it is in our homes, groups of cats can and often do live harmoniously. Groups of cats may even develop something of a social structure and seem to have a mutual understanding of their own house rules. These house rules may include time-sharing arrangements. It could be, for example, that one cat gets the prized window seat in the morning when the sunlight streams through while it is another’s turn later in the day. Even some well-fed cats who live harmoniously retain their natural instinct to defend their territory against unwelcome feline intruders. Problems of a territorial nature arise when owners decide to add a new cat into the mix — assuming everyone will automatically “get on.” That certainly is not always the case and some incompatible cats will begin to “duke it out” right from the get-go. Feuding cats have little chance to avoid each other within the four walls of the home and battles that would naturally end with one or other cat running away can never reach that conclusion. With this problem, clashes are usually ongoing with one cat the perpetrator of the attacks and the other simply trying to keep out of its way.

The best way to attempt to avoid this problem is to gradually introduce a new cat using the technique described below, though peace and harmony cannot be guaranteed using any approach. Gradual introduction of a new cat to a household may take 2-3 weeks, or more. If initial animosities are mild, they typically resolve spontaneously over a period of about four months but serious aggression at the time of introduction of a new cat is tough to resolve. Either it becomes the victim of territorial pursuit and skirmishes or, in some cases, the new cat claims territorial rights and becomes the antagonist. Most often territorial aggression is expressed between only two cats, even in a multi-cat home.

Treatment of Territorial Aggression

Systematic desensitization and counterconditioning is the behavioral technique of choice to reintegrate feuding cats. Systematic desensitization involves separating and then gradually (and systematically) increasing the two cats’ exposure to each other. Counterconditioning teaches the cats that good things happen when they are close together. These techniques work together to make a formerly antagonistic experience pleasant and rewarding. Patience on the part of an owner is key. Desensitization can’t be hurried and it may take months to get cats to tolerate each other.

Ideally, neither cat should show anxiety or aggression during the introduction or reintroduction process. If they do, the owner must arrange for them to go back to a previous peaceful level of exposure before attempting to advance in the program once more. Signs of ongoing anxiety caused by unease at another cat’s close proximity include not eating, leaving the scene, hiding and even trembling. Warning signs of impending aggression on the part of the territorially aggressive cat include staring, tail switching, flattening of the ears, growling, and hissing. Chasing, clawing and biting can occur if the cats are allowed together too soon. Below is what I call my 7STEP program for re-introducing feuding cat. A scaled down, more rapid version of the program can be employed when introducing a new cat to a cat-containing household.

STEP 1 (of the Desensitization Program)

Completely separate the feuding cats in 2 separate environments within the house. Perhaps one cat might be confined in the kitchen/hallway, nominally environment A, while the other cat is confined in an adjacent family room, so-called environment B. A solid door should separate the two areas so that they can neither see nor get at each other. Water and litterboxes should be accessible to both cats at all times. The tendency for them to develop territoriality in the environments is avoided by switching environments daily if possible.

An alternative strategy is to isolate the aggressive cat in a specific room and allow the other cat to have free range of the house. Relocate the aggressive cat to a different room each day, leaving the door to the vacated room open. The cat with the run of the house will investigate the recently occupied room and will be able to detect the scent of the adversarial housemate. Likewise, when the aggressor is returned to the room, at a future environmental switch, it will be able to detect the odor of its free-ranging companion’s scent. The exchange of scents maintains cat-to-cat familiarity in a non-threatening way and prevents territorial protectiveness of a particular environment from developing.


Now begins the process of desensitization and counterconditioning. If owners are accustomed to feeding their cats “free-choice,” they will have to forsake this practice and substitute a more controlled feeding schedule. All cats should be fed meals morning and evening to make them hungry enough to be drawn to participate in across-the-closed-door socialization at mealtimes (a family that eats together … and all that jazz). Alternatively, if time permits, the cats can be fed small amounts of food across the closed door at various times throughout the day providing numerous socialization opportunities during the day. This way the cats will be able to hear and smell each other on either side of the closed door at mealtimes so that hopefully they get used to each other’s presence. The food used should be highly palatable; perhaps offering them their preferred canned food. You may also choose to feed small tidbits of tuna, chicken, and other delectable treats. But it’s not just food that is used in the counterconditioning enterprise: Petting and playing with the cats when they are on opposite sides of the door can also be employed to reinforce the concept that pleasurable events occur only when they are in close proximity. Owners engaging in this program should limit the provision of all food, games and petting to these training sessions so the cats learn to associate each other’s presence with good things happening. Once the cats are feeding in a relaxed and happy manner on either side of the closed door for at least 1 week, it is now time proceed to the next phase of reintroduction.


The door should be cracked open 1-2 inches and secured with a doorstop or hook and eye. Now the cats have limited visual access to each other as they are getting occasional glimpses of each other through the eyeball-width crack in the door.


Only when peace prevails at the Step 2 level of exposure, he opening should be widened to a 4-6 inches. A newspaper-covered screen with a four-inch wide strip torn off provides even greater visual access but also a physical barrier to prevent actual direct contact between the cats. The opening can gradually be enlarged to afford the cats progressively more visual access – as long as peace reigns – until eventually the whole screen is free of newspaper but the barrier to physical interaction is still in place.


Once the cats are able to eat and play close to each other across the screen, the next step is to reintroduce them to each other for a short time in the same room. Initially they should be restrained on harnesses or be confined in separate cat carriers. They should at first be restrained on opposite sides of the same room for up to fifteen minutes as long as they remain relaxed. During this time, they should be fed a meal and/or given treats, attention, or toys to make the experience an enjoyable. Each day, assuming things remain peaceful, they should be brought a little closer to each other and the time that they are together can be extended. The goal is to have them eating side by side and ignoring each other’s presence while in the same room.


Once the cats are eating peacefully side-by-side on harnesses or in their carriers, the next stage is to free the more passive cat from the harness or carrier. If all goes well, the more aggressive cat can be released during the next feeding while the more passive cat remains confined in its carrier. If no signs of trouble are seen when each cat is freed individually, the next step is to try releasing both cats at the same time for side-by-side feeding. Once this is achieved they can be left together for progressively increasing periods of time. One feeding station and one litterbox should be available for each cat and should be located in open areas so the cats can always see each other and therefore not be surprised by each others’ approach.


Once the cats can be together peacefully for extended periods of time, the owner should make sure to praise them and/or give them food treats whenever they are seen together. If the more timid cat begins to avoid the other one or if the aggressor starts intimidating the pariah and attempting to control its movements or access to resources, it’s time to return to an earlier phase of the reintroduction program.


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 as that will only exacerbate the problem. You may wish to keep an “aggression diary” to help you document trends over time regarding the effectiveness of the therapeutic measures that you try.

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. Leading separate lives is often more problematic for the owner than it is for the cats. Sometimes the only recourse is to place one of the cats, usually the aggressor, in a new home.

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