Cats aren't naturally inclined to live with other cats, so you may need to introduce a second cat carefully and slowly to help them get along and feel that they are part of the same social group.
While many cats love the company of other cats, this is not natural cat behaviour. In the wild, cats usually live solitary existences, guarding their territory against other cats so that they always have enough food and water. By understanding your cat's ancestry as a wild, solitary hunter, you can better understand their needs in your home.
It's not always obvious when cats are at war. They may be involved in a 'cold war' that does not include obvious signs of conflict like fighting and hissing. Some cats will block access to food, water and litter trays. This can be done subtly so the owners are unaware, but this can be very stressful for the affected cat and can even lead to behavioural problems.
This is why it's important to monitor your cats' behaviour carefully to make sure they are getting on well.
Cats can live well together if:
In some multi-cat households, resources are sometimes shared throughout the day. One cat may use a space in the morning and then swap in the afternoon. In other cases, cats will live separately in a particular part of the house, and rarely interact with the other cats. Some cats never become friends or share the same social group, no matter how carefully they are introduced.
Remember, you have a legal duty of care to provide for your cat's needs, which includes their need to be housed with or apart from other animals.
You can tell if cats are in the same social group because they will sleep touching each other and spend time rubbing and grooming each other, sharing and reinforcing their common scent.
If you have more than two cats, you may find you have more than two social groups. In fact, it is possible to have six cats and five or six social groups within them.
This is more likely to happen if your cats were introduced as adults, forced to interact too quickly or given insufficient resources. Even sibling cats may not necessarily remain in the same social group and may drift apart as they reach social maturity, between 18 months and four years of age.
The locations of key resources like food, water and litter trays is often a source of conflict for cats. Ideally, each cat should have their own food, water and litter tray in a separate location - even if the cats are in the same social group. Keeping resources apart can help prevent relationship breakdown.
Cats can feel vulnerable when they're eating and drinking. By placing food and water bowls away from walls your cat can sit with their back to the wall so they can watch the room while eating and drinking.
Think carefully before getting another cat, because while you may have the time for another cat, you need to consider the impact on the cats you already have. Many cats prefer the single life, and adding another cat can create additional competition for resources such as food, hiding places, litter trays - and your attention.
Cats are all unique and have different characters. Even if your cat has lived with another cat in the past, they may not tolerate a new cat immediately - or at all.
If a cat's companion cat has recently died, don't rush to get a replacement 'friend'. At least allow some time for your cat to adjust to the loss. In some cases, cats actually seem to blossom once they are on their own and prefer to remain in a one-cat household. This can be difficult to understand because we are sociable beings. Thinking from a cat's perspective may help you to understand their feelings.
Cats that have been in contact with unrelated and non-aggressive cats when they were kittens - less than seven weeks of age - sometimes cope better with the presence of other cats when they are adults.
The key to successfully introducing cats is to take your time and make sure that both cats have easy access to food, water and a litter tray.
If you rush the process and the cats don't get along, you may need to separate the cats and reattempt the introduction process, so it's worth taking your time so the cats start their relationship positively.
See also - Introducing cats to other cats
If your cats are apart for any reason, such as a stay at the vets, then their scent may be affected and they may not be recognised as part of their social group when they return. The longer a cat is away, the harder it can be to reintegrate.
Try keeping the returning cat apart so they can pick up the smells of home and then gradually reintroduce them.