"One cat just leads to another." said Ernest Hemingway, and was right.
It would seem once you've opened your heart to one Cat, more will surely follow...and who could possibly resist. All the Crazy cat Ladies with they 30+ cats surely agree :) Cat lovers raise next generations of Cat lovers. My father loved Cats, and even though we did not have much room in our apartment he would eventually,"unwillingly", give in to the pleads of his little girl whenever we came across hurt or lost kitten, or any animal for that matter. We usually had one resident Cat at home, but there were "patients" which we would nurse back to health and find them a home away from the city streets and traffic.
I am now in my 30's and have two Cats- one followed the other. One adopted and one rescued from the crowded parking lot.They are the best of friends. I have several times during my Cat owning career met with a challenge of introducing a new Cat or a kitten to a resident Cat. In my experience, even though these are animals led by their urges and their instinct, they are better in finding a common ground in agreeing and learning to live with each other than us ,"reasoning" ,humans.
Be that as it may, some supervised transition period is required and a bit of help from us if necessary. How will Cats react to their new roommate will depend on their personality, gender, age and you. My cats would usually get accustomed to each other in a couple of days and their relationship would evolve from casual acquaintances to best buds in less then a month. Truth be told they were all males (wonder if that's significant (wink :))
Regardless of the fact that most of the animals will learn to get along with each others just fine, much like humans, there are some who find change difficult, see it as invasion of their territory and need help as well as more time with accepting newcomers. Also there is a better chance your cats will get along if the newcomer is younger because then he/she won't pose a threat. Introducing two males at the same age, especially if they are not fixed could result in a lot of stress and fighting.
There are few things you can do to help both of your Kitties get through this transition as smooth as possible:
Provide New Kitty With A Safe Haven
This means you set up a space in your household so that your new Kitty can get accustomed to her new environment and which you can close off from the rest of the house. At this stage do not introduce your residential Cat to newcomer. Getting into new home is usually stress-full for Cats and they need to sniff everything out and map new area. Set her up with litter box, food, water and toys so she can relax and slowly develop trust.
The Game of Sock
Even though your old Cat did not yet see newcomer, she surely smelled him. Rub a piece of cloth or an old sock on new Kitties fur (preferably around the face where the pheromone glands are) and let residential Cat smell it and vice versa so they can get used to the new scent.
My Turf My Rules
Cats do not like change, and will notice even the addition of a new piece of furniture in their territories. So a cat's first reaction to a new feline arrival may be anxiety or confusion. Set up one litter box per cat, with one extra, in separate areas, and check to see that the resident cat is not displaying his unhappiness by eliminating outside of his box. The presence of another cat, even if unseen, presents an inconvenience to your existing cat, so to minimize this change in his household routine, offer him quality time and opportunities to play or simply sit on your lap if he wants to.
Let's Cat Together
As you've made all preparation and your Kitties have gotten to know each other before an actual encounter, slowly begin to show your residential Cat the newcomer by partially opening the "safe haven's" door. Repeat that for a few days and then allow them to meet under your supervision. They will sniff each other, maybe hiss or pose a defensive posture or as one of my Cats did, just stare for hours in disbelief :) Motivate them to play by introducing a toy, and distract them if they exhibit signs of agression. If either of them seems stressed keep these play dates short and repeat them daily-eventually they'll get used to each other.
It Doesn't Seem To Work Out?
Sometimes even with the best of efforts it seem that Kitties can't kick it off. Period of introduction and adjustment may take weeks or even months. Cats with aggressive temperaments will instinctively stalk or attack shyer cats that may retreat or hide. You'll need to offer a lot of reassurance and extra attention to each cat if aggression becomes a factor. If both the resident cat and the new one are aggressive, especially if both are males, your hopes for a happy feline home may decline into all-out war. But when cats do accept the reality of a multi-cat home, they can tolerate each other without fussing, or become devoted friends, sometimes grooming each other and sharing sp