August 2019

Audience: Foster Caregivers, Public, Shelter/Rescue Staff & Volunteers

Aggression between unfamiliar cats most frequently occurs when introducing new cats in a home, or if unfamiliar cats appear outside your home. These situations can lead to fights and potentially result in serious injuries. Stress from the conflict between your cats can also cause other signs such as not eating, not using the litter box appropriately, hiding, or over-grooming. If these subtle symptoms are exhibited and you only have one cat, observe carefully to see if unfamiliar outside cats are visible and causing this stress.

Even mild forms of aggression, when not properly addressed, can evolve into more serious problems. This is why it is important to address any change in your cat's behavior right away. Work with a professional who can look at the context in which aggression happens. Never use punishment as a training technique as it does not work, and only hurts your relationship with your cat. Aggressive behavior between unfamiliar cats can occur in cats of any breed, size, age, or sex, and it can have many different causes. The most common causes of aggression include:

Pay attention to your cat's body language. Signs of stress that may lead to aggression are dilated pupils, ears turning back, a twitching tail, growling, hissing, swatting, and biting. You may also see increased fearful behavior such as a low body posture with their tail wrapped around their body. A fearful cat may exhibit an increased startle response and be more prone to running and hiding. A more aggressive cat may have her ears back and her pupils may be very constricted, the tail can be up or down with fur standing on end.

Always separate fighting cats to prevent injuries. If the unfamiliar cat is an outdoor cat, then windows should be blocked so that your indoor cat cannot see out. Another option for keeping outdoor cats away is using motion-activated sprinklers.

Don't rush introductions. If you are introducing an unfamiliar cat as a new pet in the family, keep your new cat and resident cats in separate rooms at first. You are working towards a strong and friendly long-term relationship - being patient will pay off! Most cats will adjust to living within a multi-cat household. For more information, check out introducing cats and aggression between familiar cats.

This document created by the San Francisco SPCA with a grant from Maddie's Fund®.