One cat just might be so overly territorial, or it just might be the wrong pairing for a variety of factors. Sometimes one cat will not abide a certain other cat at all, going to attack it at any chance, but, that same aggressive cat might accept a certain other cat. In that case, rehoming one of the cats or having the cats live in separate areas of the home might be the best thing to do. This is referring to aggressive behavior between the cats, not just that they ignore each other or hiss at each other once in a while. Take each step slowly, holding onto one step for as many days as it takes for the cats to be ok at that step before moving on to the next step. A few hisses are ok, but not prolonged hissing, growling or yowling, nor fights. Rushing things will not make the cats accept each other faster, but will likely wind up making them not get along.
Once things go badly between cats new to each other, it is difficult to get them to go well. If you thought it would be fine to move on to the next step, but the cats turned out not to be ready, simply back track to the previous step for a few more days. Click on the names for each step below to get more details about that step and the reasons for doing those steps. The new cat also needs time to calm down and get used to being in a strange place, as well as getting used to the new people, before he or she is in a good frame of mind to meet other cats. Scent familiarization with items, such as towels, rubbed on each cat, then left in the area of the other cat, while the cats are being kept separately. Petting one cat and then letting the other cat smell the scent on your hand is also helpful. This is done along with Scent Familiarization.
Switching the cats’ places for a while every day, with no physical contact between them. This is added to doing Scent Familiarization and Visual Familiarization. Start developing positive associations with no physical contact, such as by feeding the cats tastly canned food or treats on opposite sides of a door when cracked opened and even when it is shut. Continue with the above steps as well. Do not place the cats next to one another, but rather merely in the same room a somewhat far distance apart so they can freely, or not, approach one another. Do not allow any fights or one cat to chase the other. These short visits need to be kept positive in order for positive feelings to have a chance to develop between the cats.
Continue with Room Swapping, but Scent Familiarization and Visual Familiarization can be discontinued. Separate the cats at signs of hostilities, or great fear. Learn cat body language to tell when a problem is starting. Click on the name of this step to read about cat body language and to see some pictures. Mingling under very careful supervision for up to a few hours, before total separation again. When the above have gone well, free mingling except when the people are not home or asleep, so quick intervention can be done if needed. The cats are let together freely all the time when all the above steps have gone well.
Backtrack to the limited mingling if the cats weren’t quite ready to be together all the time. Stay on each step for as many days, weeks, or even months, as necessary for your particular combination of cats. Some cats take longer to adjust to a new cat than some other cats will. You may come across advice saying to ignore the new cat in the presence of the resident cat so that the resident cat doesn’t get upset. If you ignore a new cat in front of the resident cat, it can make the resident cat feel you don’t really care for or want the new cat there either. It also makes the new cat feel unwanted and uncared for. It is good to show some attention to the new cat in the presence of the resident cat, but don’t go overboard.
When you take in a new cat, you need to feel as much loyalty and concern for that cat, and worry just as much about how the new cat feels as you do your first cat. The whole of this article goes into more detail than many others do. And, simply, if you want all the nitty gritty details not usually included in articles on introducing cats. To start with, the new cat should be set up in a separate room, often referred to as a «safe room». No other animals should be allowed in that room at first. A cat carrier, with the door of it wedged open, or a small box on it’s side can be used as a «hidy spot».
A window view in the room is preferred, but only open it a crack as cats can push out or rip some types of window screens. If one has taken in a tame stray from the streets, the first day and night in the house can be a bathroom or other room with no carpet, so any spraying or urinating on the floor can be easily cleaned, and so that if the cat has fleas, there won’t be a problem with flea eggs being embedded in carpet. Once the cat is using the litterbox, and has had a flea treatment applied if necessary, a more suitable and comfortable room should be used for the «safe room». Note: If after a full 24 hours the cat has not urinated anywhere, take him or her to the vet as the cat might have a urinary blockage, which can kill the cat in as little as 24 hours from the time you realize something is wrong. Homeless cats who never used a litter box will hold it for a long time, not wanting to soil the area. It can take them up to 24 hours before they decide to use the litter box, which they were not sure was the correct place to eliminate. If the new cat has not yet been neutered, that should be done during the isolation period so that hormonal influences are out of the equation of the meeting of the cats. There are no cures for FIV or FeLV, so one really needs to know the status of all new cats before allowing any contact with other cats. However, cats testing positive for FIV and FeLV do not need to be euthanized if they are not suffering. Cats with FIV and FeLV can live symptom free for many years as only cats or with other cats who have the same condition. FIV and FeLV, an incubating illness would not be able to be diagnosed yet. The new cat should remain isolated for several days to allow you to notice any signs of a respiratory or other illness that might take a few days to manifest if the cat acquired it just before you took it in or adopted it from a shelter, or other person. The time spent in the safe room away from the other cats is important also to allow the new cat to settle down and start to relax.