Aggression in Cats: Other Household Cats

Why are my cats suddenly fighting with each other?

There are many possible causes of aggression between household cats. Most importantly, changes in health can affect behavior. If your cats have recently started fighting, both cats should be examined by your veterinarian.

Sometimes, a specific trigger can be identified. For example, a cat disturbed by a stray cat outside the window may suddenly hiss or lunge at a companion cat because they cannot reach the cat outside. This is called redirected aggression. Other leading causes of aggression between household cats include territorial behavior, fear-based behavior, and incompatible personalities. Multiple causes can occur at the same time.

Even a subtle environmental change, such as rearranging furniture, can change household dynamics. Initial aggressive communications between cats can be subtle. Though it may seem that your cats began fighting suddenly, aggression often develops gradually. Early signs of tension and threats are easily missed or misinterpreted. 

If you are concerned about tension or aggression between your cats, have your veterinarian examine them. Then consult a veterinary behaviorist for a thorough assessment of your cats’ personalities and interactions, as well as their physical environment. Once the underlying causes of tension have been determined, a treatment plan can be designed.

What is territorial aggression?

Territorial aggression is directed toward a cat, another pet, or a person that approaches an area the aggressor cat considers their territory. An indoor cat may behave aggressively when a new cat is introduced to the home. A cat may also claim a specific indoor space, posturing aggressively when another household cat approaches its boundary. Territorial behavior is more likely after cats mature socially, typically between two and three years of age.

What does territorial aggression look like?

Cats may initially use subtle communications to block other cats from accessing certain areas of the home. Sometimes, a simple stare effectively blocks other cats. More overt communications include growling, stalking, lunging, and chasing. Cats often use their position along a pathway to effectively block another cat’s access. They may sprawl across a doorway, for example. The posture of the territorially aggressive cat is usually upright, with ears forward.

Why does territorial aggression escalate?

Each cat’s personality can affect how territorial aggression progresses. When the cat receiving the aggression is calm, social, and able to recognize a subtle threat, such as a body block, they may quietly walk away rather than engage. In that case, the aggressor can relax and maintain their desired territory without physical conflict.

If the cat receiving the aggression hisses or runs away, perhaps due to fear, tension may escalate. The territorial cat may respond by chasing, creating a cycle: the fleeing cat becomes increasingly fearful and is more likely to run away quickly the next time they encounter the aggressor. The aggressor becomes increasingly aroused, ready to pursue. With emotions running high, the risk of physical injury increases.

Sometimes, the cats’ personalities also contribute to escalating aggression. For example, some cats do not use subtle postures. They quickly become frustrated and may impulsively lunge at or chase any cat that approaches, leaving no opportunity for a peaceful resolution.

How can territorial aggression be prevented?

The risk of tension and territorial aggression between resident cats may be reduced by providing an enriched environment with adequate resources spread throughout the living space.

• Place multiple litter boxes so that each cat can reach one easily. 
• Provide perches and cat beds in several desirable locations to reduce conflict over views and resting spots. 
• Set up multiple feeding stations so that each cat can easily reach food. 
• Provide plenty of toys in different areas and schedule regular play sessions. If the cats can share toys, create games that allow them to take turns batting at a shared toy.

To help prevent territorial aggression when a new cat joins the home, introduce the newcomer gradually. Pheromone diffusers such as Feliway MultiCat® (Feliway Friends® in Canada) and Feliway Optimum® can be placed in several locations to help reduce stress and tension.

What is fear-based aggression?

Fear-based aggression occurs in response to a perceived threat. A frightened cat may freeze, flee, or fight. Sometimes, the threat is genuine, such as when one cat approaches another aggressively. Some cats are innately fearful and show signs of fear in response to things that are not actually dangerous. An unusually fearful cat may initiate an aggressive response toward a friendly cat.

Initially, a fearful cat may avoid the other household cat. Their posture may be low, and their ears may be held back as they retreat. If the other cat is very social and continues to approach, the fearful cat may freeze and hiss or growl with their ears held back. However, if freezing does not give them relief, the fearful cat may, over time, put their ears forward and lunge.  Although this response looks aggressive, it is motivated by fear and so it is called fear-based aggression.

Why does fear-based aggression escalate?

Cats naturally chase things that move away. A cat that was initially friendly or neutral may pursue a fearful cat that flees and become aroused and aggressive in the process. This increases the fleeing cat’s fear and reinforces the chasing cat’s aggressive response.

How can fear-based aggression be prevented?

It is important to recognize subtle signs of fear. If you notice that one of your cats is spending more time alone or resting in unusual places, such as the top of the refrigerator or under a bed, look more closely at the interactions between your cats. Notice whether one of your cats is overly eager to play with or approach the fearful cat. If so, provide plenty of activities to keep the eager cat busy.

Providing an enriched environment with a wide range of toys and opportunities for social play is particularly important for social cats. Create multiple comfortable resting spots in the main living spaces, with easy access to all resources, so your fearful cat does not have to stay under a bed or alone on a high piece of furniture. Seek professional help early, as fear can increase over time.

Can aggression between cats be treated?

If your cats show signs of tension, particularly aggression toward each other, arrange an assessment with a professional such as a veterinary behaviorist. Once the motivation for the behavior is determined, a treatment program can be designed to improve the relationship between the cats. Behavior modification, and sometimes medication may be recommended to address underlying fear or frustration. A professional can also create an enrichment program to reduce stress.

Monitor your cats for signs of physical discomfort, such as hesitation to jump on or off furniture. Because cats routinely hide their discomfort, have your veterinarian examine both cats.

Until your cats can be evaluated, separate them if you are concerned for their safety. It is important to prevent staring, stalking, and chasing until they can be assessed. Give each cat a comfortable space with a litter box, food, water, toys, and, if possible, a seat with a view of the outdoors. When the cats are together, keep a heavy blanket handy to toss over one that might be about to pounce.