My cat is territorial with other cats. When should I intervene?

Most cats will settle down within a few weeks. Kittens do play rough and it can be hard to tell. If they willingly come together, play willingly and you don't see any bullying behavior (avoidance, hiding, arching the back and puffing up the tail) they are likely playing rough. If they play too rough they could injure each other by accident so continue to separate them when not supervised but most kittens will not require this. Giving each kitten one on one play time with you to burn energy, feeding out of a food puzzle and providing cats trees/other environmental stimulation can also help. Continue the current therapy as well. I hope this helps.

While it's fine that they growl and hiss at each other, as they are letting this new cat know they don't appreciate his presence on their territory, you don't want it to escalate into aggression and one of your cats get injured. I would keep an eye on their interactions as best you can, and step in if it appears that anyone is going to get aggressive.

Neutering will help him from running off and fighting. It will unlikely stop him from fighting to protect where he lives and his food. He should be tested for feline leukemia and aids though as this can be a fatal disease and he may continue to spread it if he keeps fighting. The other cat likely will need to be caught, neutered and released to minimize the behaviour

The next step is to rotate rooms daily for at least 2-3 days. This allows the new cat explore the rest of the house while the resident cat spends some time in the new cat's room. This will give your resident cats a chance to smell the new cat and rub their own scent on objects. The cats should be fed in each area with wet food twice daily, and it is also good to play with the cats in each area at least twice daily. The practice of setting up a schedule of feeding treats of wet food, as well as a playtime routine, minimizes anxiety and makes the cats feel more secure. Keep the cats in separate areas for as long as it takes to allow them the chance to become desensitized to the smells and sounds of the cats in the other area. When they all seem particularly relaxed with this process, begin to expose them to the sight of each other. A good way to accomplish this visual introduction is to bring the new cat(s) in a carrier to meet your cats and sniff each other through the carrier wire door. Place the carrier on the floor and allow them to meet this way several times a day for about an hour. Continue these meetings for several days or until they remain calm in each other's presence. If and when the cats are able to stay calm in each other's presence during these meetings, it is time to let the new cat out into the rest of the house for a few minutes. The length of the visits can be increased gradually each day. Depending on the personalities of the cats involved, this process may take a few days or a few months. If it appears that any fighting maybe be close to occurring while you are supervising, put the newcomer back in his/her room and proceed more slowly. If those supervised play times go well, you can begin to allow them to cohabitate in your home. If any aggressive behavior occurs at any time, begin the introduction process again. It is very important to understand that this process can take as little as a few days, to sometimes much longer. It is all dependent on the cats involved. If things don’t go well right away... One of the most important steps to dealing aggressive behavior between cats is to recognize the different types of aggression and understand their underlying causes. A short list and description of some commonly seen aggressive behaviors include: chasing; ambushing; hissing; swatting; and/or biting. If you see these behaviors, seek help from your veterinarian. Most cats get along fine if the introductory process is done correctly. Please seek help from your veterinarian if you feel that things are not progressing well, or if you have other questions.

This happens. Cats take time to get used to each other. It can take 6 months before they are either friends or tolerate each other. I have 5 cats, and two of them keep having tiffs when their paths cross, however, in general they get along by ignoring each other. Make sure your new kitty is checked for FIV and FeLV as these diseases are spread by saliva (deep bites when fighting) and also have the new cat vaccinated against rabies. Most cat fights are loud with lots of hissing, spitting and screaming but hardly any injuries....so they sound far more dramatic than they are. Give them time. Eventually peace will rule.

If you rescued Saoirse just a few months ago there is still hope that they will learn to at least tolerate each other. It can take cats several months to get used to a new being in the house. You could add an extra litter box if you have space - the recommendation is to have one more litter box than the number of cats in the house. If you are still having trouble in 3 months or so I’d recommend reaching out to your vet to see if there is a cat behaviorist in your area.

Cats are very sensitive to other cats in their territory. Unlike most dogs that will accept another dog into their house relatively easily, for cats it can be a different story. Your cat is upset by the presence of the strange cat in your house. Animals behave that way sometimes for reasons that are unclear, taking their anger out on you. She may smell the foster cat on you. I would definitely keep them separated from each other and give her some time and space to possibly accept the fosters presence. Don't get hurt! I wouldn't force your attention on her for now. Maybe in a few days she'll be easier to approach.