Do cats need to socialise with other cats in order to be happy and healthy? What the question is asking is whether a domestic cat needs to successfully live with another domestic cat in a good relationship in order to be happy and healthy. And the answer is no because there are many millions of happy and healthy individual cats in homes and the only companion that they have is their human caregiver. That’s almost the default form of cat ownership as cats a still essentially solitary by nature. But this does not mean that these cats might not be happier with a cat companion as well. It depends on their personality.

But the question is quite interesting in the way it has been phrased because a linked topic is the process of socialisation of domestic cats which takes place in the first seven weeks of life concerns the socialisation of cats to humans and perhaps dogs but not necessarily cats.
And that point being made, it is arguable that kittens whether they be the offspring of a feral cat or the offspring of a purebred cat in the home of a breeder, are automatically socialised to other cats because they have siblings with whom they share their mother’s milk and with whom they play while they develop. And of course, they are socialised to their mother.
So, cats are automatically socialised to other cats. But if, perhaps exceedingly rarely, there is one surviving offspring of a litter of cats and the mother dies, that cat would be unsocialised to other cats. It still wouldn’t matter as long as that individual kitten was adopted by a good caregiver who ensured that she was socialised to humans as part of their caregiving.
Here are some further points to be made on this topic. We know that cats are generally solitary by nature; a trait that they inherit from their wildcat ancestor. They therefore don’t need social interaction with other cats in order to be happy and healthy. However, it can be beneficial to certain individual cats. This will be about individual cat personalities and whether they feel more content interacting with another cat in the human home. Some cats are like that. And the domestic cat has shed some of that solitary cat nature over 10,000 years of domestication. Arguably they are social animals in 2023.
Cats have unique personalities which leads to different social needs. Some might enjoy the company of other cats while others are less interested. They may even prefer solitude. If they’ve been raised by a person from a tiny kitten then that person may be imprinted on the cat as their surrogate mother and they might not want any other cat interfering with their very close relationship.
It’s important for a caregiver to try and get into the mind of their cat to understand their preferences in this regard.
It is probably better, provided the cats get along that they do share their lives with another cat because it enriches their lives and it provides for mental stimulation. And it takes some responsibilities away from the caregiver to entertain and mentally stimulate as they can do this on their own without any input from their human caregiver.
It can help to alleviate boredom and provide opportunities to exercise and each cat to engage in allogrooming (social grooming, each one grooming the other). This can improve their contentment. Jackson Galaxy, the American cat behaviourist recommends the adoption of two cats from a shelter if they get along.
And it might be reasonable to suggest that when two kittens live together or a kitten lives with another adult cat who is not their mother, they can learn from the adult and indeed if two kittens live together, they might learn from each other especially if they are young and still developing their social skills.
There is also the benefit of stress reduction. Two cats living together can help reduce stress levels and minimise or even eliminate separation anxiety caused through separation from their human caregiver. This will particularly be the case when their owner has to be out of the home a lot.
But despite the fact that cats are automatically socialised to other cats as described above, they are essentially solitary with their own home range i.e. their own home territory and their natural personality trait will be to reject incoming cats onto that territory. This goes to that well-known problem of introducing new cats to a resident cat’s home. You have to do it carefully although rarely new cats can get on well with a resident cat from the get go.
There are two issues at play here: the solitary nature of the domestic cat which is still an inherent part of their personality to varying degrees depending upon the individual cat which can be set against the fact they are socialised to each other. Being socialised does not overcome this deeply embedded trait of the need to occupy their own home range i.e. their own space. This is seen in adult sibling cats that were friendly as kittens but become hostile with each other as adults.
In multi-cat homes or in homes where there are two cats, this desire to protect the home range can be loosened and each cat’s home range will overlap with the other and they may merge when they become very friendly.