Again, some hissing when they see each other is normal so don't be alarmed. Some light swatting is also common. Separate them if the hissing doesn't die down after 1 or 2 minutes or if there is any sign of threat (swatting with force, chasing, screaming, ears flattened, etc.).
The introduction must be gradual. Following the initial introduction, it can take a very long time for a relationship to grow. It takes most cats eight to 12 months to develop a friendship with a new cat. Although some cats certainly become close friends, others never do.
Sometimes cats hiss at other adult cats to show dominance. Cats are territorial and may have specific spaces in your home marked as "theirs." When another cat encroaches on that space, hissing might occur to re-establish the hierarchy in your home until they learn to get along again.
Don't be alarmed; it's normal for cats to hiss at something new or something they don't understand. Hissing is a distance-increasing behavior. Simply put, it's a warning saying, “Please back off, and do not come any closer.”
Our pets like to be in control, so it may take some time for resident cats to adjust to new kittens, cat hissing at new cat is there way to communicate discomfort. It's possible that your kitties will hit it off from the start - you might notice them playing, sneaking around, and snoozing together.
When you introduce them to each other in the same room, a bit of growling and hissing is to be expected. Although the two cats may be used to each other's scent; your first cat will still feel a bit awkward with your new cat being in his territory.
Introducing too quickly with little preparation will often lead to cats feeling threatened and scared, which increases the chance of aggressive behaviour being shown. Once cats feel this way about each other, it can be extremely difficult to change their minds.
If one or both of the cats are intent on chasing and can't be redirected into another activity, it's time to take a step back. Work your way back through the introduction steps, really focusing on building a relationship through food and mutual play at the door of the new cat or kitten's acclimation room.
Cats with a strong link will frequently show clear indicators that they regard themselves to be members of the same social group. Grooming each other, sleeping, or lying next to each other are examples of these indicators. They may regularly greet each other by touching noses or making a little meow as they pass.
Each day, have the cats switch rooms so that they both experience some variation and get access to each other's scents. You may need an assistant to do this safely. After several days, if both of your cats appear relaxed, crack the door open one inch. If they remain calm, open the door a bit more, then a bit more.
Your older cat may have a period of time when it tries to establish boundaries with the new kitten. Your older cat may hiss and swat at the kitten when the newcomer does something unfavorable. This is completely normal and as long as it is just hissing and swatting, do your best to not interfere.
Introductions, when done properly, can take more time than expected. Introductions and building a relationship for some cats may take a few hours or up to a few months. Your cats may play and groom each other or just sit and watch each other. Don't force them to be what you think best buddies act like.
In general, cats that are play fighting will not make much noise. If they do make any noises, you are more likely to hear a meow than a hiss or growl. If you hear an unending succession of growling or hissing, then your cats may be fighting.
Over time, they'll likely start getting along again. Just remember, this process can sometimes take weeks, and that's okay. Give your cats the time and space they need. If you're wondering if your cats will ever get along again, the answer is they likely will.
Fortunately, neutered and spayed cats are much more likely to get on well together than intact adult cats. Generally, female cats tend to be more accepting of new cats into their home. They are more likely to accept another female cat than a male cat.
Cats that have set up separate territories in the house and don't really get along will: Chase or run away from one another and avoid contact. You may notice that one cat consistently leaves the room when one enters. Watch each other intently and may hiss or spit when they meet.
Can Cats Get Jealous of Other Cats? Jealousy over the presence of another cat is very common. All cats have different personalities, and some will be made insecure and display jealousy more easily than others. It is important to watch your cat and observe their cues and triggers.
Like many animals, cats are territorial. That means, when they feel someone or something has invaded their territory, they may act aggressively. They may hiss at the "intruder" or even try to attack them. It could be another cat, a new baby in the household, or a guest they haven't met before.
Keep Them Separated.
It is best to immediately place the newcomer in the separate space and then direct your attention back to your senior. Spend most of your time with your older cat. She may go over to the door and hiss at the new intruder but just ignore this behavior and act like nothing has changed.
Even in the absence of physical aggression, introductions can provoke anxiety that leads to inappropriate elimination, decreased appetite, or other signs of stress in one or both cats. Fortunately, you can increase the likelihood of a successful introduction by introducing two adult cats slowly and gradually.
You can test this by following a simple 3 second rule: If you pause after 3 seconds of stroking your cat, do they try to reinitiate contact (i.e. rub against you)? If not, your cat has probably had enough for now!
The younger they are when introduced, the greater the chances of their getting on amicably most of the time. After about two years of age, acceptance of another cat can be a bit random, but they will very rarely totally reject another cat in the long-term.
Don't interfere in their interaction unless necessary—Some hissing and growling are normal and will stop as the older cat gets used to the kitten. Step in and separate the cats only when the situation escalates.