Every cat may secretly (or openly) wish to be an only pet, getting all the treats and attention you can dole out. But two cats can learn to cohabit, if you provide the right environment for your resident cat to accept a roommate. While cats' preferences are highly individual, some breeds, such as Persians, Maine Coons, ragdolls and Birmans tend to be more easygoing, adaptable and gentle, and may more readily accept a feline friend. To safeguard the health of both cats, have the new cat examined and vaccinated by a vet, particularly if he is a stray, to ensure he has no parasites, upper respiratory infections or other health issues. With the right precautions in place, all you have to do now is persuade the kitties that life is better with two.
How age (or gender) can be a factor
In an ideal new cat/old cat matchup, the newcomer would be a younger and smaller cat that is fixed and of the opposite gender. If you're going for the same sex, two female cats will pair up better than two males, whose instincts may prompt aggression. The resident cat's disposition should be compatible with the newcomer's and they should share similar energy levels. An older cat that's been the only pet for his entire life will adapt more slowly to another cat's presence, and may especially resent a bouncy kitten. On the other hand, a kitten just separated from his littermates may be grateful for companionship. If one cat is or was a rescued kitten, his life has already been filled with stress, and he may be fearful about living with another cat.
How cats respond to newcomers
Bringing a new cat into your home, even with careful preparation, can still be a stressful experience for your cats. Their first and subsequent early encounters may be marked by hissing or growling, which are feline warnings of unhappiness. Never simply place a new cat in your home and hope the cats will work things out for themselves. More likely, without patient human intervention, the two will fight, or the resident cat will express displeasure by marking your floors or walls.
Secure the two cats in separate rooms; mingle both cats' scents on a sock or washcloth (by rubbing the cloth on their fur) and place the objects next to their feeding areas. Supervise their initial encounters to help the relationship progress smoothly.
Remember the territorial rights
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.
Bringing both cats together
With both cats sniffing the other's scent on those cloth items you've offered, they'll be familiar with each other even before they meet face-to-face. Let the resident cat see the new one through the partially opened door of his safe room, and once you've repeated this for a few days or a week, allow them to meet, with your supervision, in a neutral room. They'll sniff at each other, and may posture with tails up or just stare. Offer a toy they can share to encourage them to play. If one or both cats seem stressed, keep the encounter short, and then repeat for a longer period later. Gradually, they will accept each other. Coping with aggression If either cat flattens his ears, growls or spits, you can clap or talk loudly to distract them from getting into a fight, but if their aggression ramps up, separate the cats for a day. Try another meeting after they have calmed down. Their 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 space on your couch. They may realize that your attention and affection is doubled, just for them.