Steps for a proper introduction
Quarantine your new kitten away from your other pets for a period of at least 7-10 days. This is to ensure that your new kitten gets enough time to destress from the travel and to begin adjusting to the new home slowly before adding the additional stress of meeting the other family pets. Also in case your new kitten were to come down with a stress related illness at that time everyone will stay safe.
After the 7 day quarantine period, your next step is to begin slow introductions. The best way to do this is to either set up a large crate or use a travel carrier. A large crate is the best option, I advise asking friends and family or checking at your local vet’s office or animal shelter and ask to borrow a crate, because you will only need it for a short period of time. Set the crate up in the common area of your home, your living room is a good option, and includes a littler pan, bed, toys, food and water, and a heat source for your cat.
Your new kitten will stay in the crate while introductions are made, and during this time, it is critical to monitor for signs of aggression. It is completely normal and acceptable behavior for the resident cats to approach the crate and sniff and even hiss a few times. Exhibiting some warning hisses and growls are okay and they should be left to express themselves. However, if they continue to hiss and growl/howl for than more than a minute straight, this is excessive, and the cat should be removed to try again later. If an aggressive cat is allowed to continually hiss and growl at the kitten even through the safety of the crate, this can leave a permanent fear in the kitten and ruin the chances of the cats forming a good relationship. Therefore, be very diligent to keep close watch and if aggressive behavior continues for more than one minute, take the cat away for one hour. Try again after an hour and continue to remove the cat again until any aggressive behaviors are kept under one minute in length.
There are several great tricks you can use to help speed up the process of introducing your new kitten to your existing cats/pets.
Giving the pets treats together is one of the best ways to socialize them to one another. To accomplish this, you will give treats to the kitten while they remain in the crate and give treats to the resident pet immediately outside of the crate at the same time. This trick allows the kitten and the resident pet to associate each other with a positive award when they are around each other.
Play with the pets with toys together; this works best when socializing two cats together; again, keeping the kitten in the crate and the resident cat outside of the crate. Great toys for socializing include treat toys, puzzle games, wand toys for catch and chase and laser pointers.
Rotate the pets by allowing the new kitten to be free to roam the house and put the resident cat into the crate or into a room. This is very important to allow the new kitten to explore their new surroundings in peace without the additional tension of the resident cat(s) other pets being present. Be certain to first show the new kitten the location of the litter pans in the home prior to setting them loose.
Another critical step in helping to ensure a happy transition for your new kitten and resident cat(s) is to be sure to add one additional litter pan into the home. Even if you already have multiple litter pans in your home; the rule is to have one more litter pan than you do cats. For example, if you already have two resident cats you should have three litter pans; and with the addition of the new kitten, your home should now have four litter pans.
It is also very important to be sure to provide your new kitten with the proper litter pan and litter.
Feeding time is another hugely beneficial opportunity for proper socialization and introductions. The best way to utilize feeding time as a socialization technique is to feed one cat inside the crate and one cat outside of the crate simultaneously. Placing the outside food dish 2-3 feet outside of the crate on the first feeding, and if all goes well, gradually move the dish closer and closer to the crate with each feeding time. Use this technique only with wet food, you do not want to use dry food and leave it down, as the continual presence of food can create aggression and negate your socialization attempt.