Why Rats need company

Pet rats are usually kept in groups of two or more animals of the same
sex. However, sometimes people keep rats as single pets. A
consideration of the social life and welfare needs of pet rats implies
that it is far better for them to be kept in pairs than as single
rats, and in this essay I shall argue that whilst there is no
compelling reason to keep a rat alone, there are many for keeping rats
in company. This is a topic which is only touched upon in the
literature available on pet rats; of the 3 or 4 books generally
available, most simply do not consider the social needs of the rat
itself - they cover only practical topics such as feeding and housing,
and the welfare needs of the animal are not discussed.

Social animals in general
-------------------------
Rats are social animals and it is very unnatural for them to live
alone - similar to keeping a human in solitary confinement. Unlike
Syrian hamsters, which are natural loners, rats live in large family
groups in the wild. In captivity, rats are fascinated by others of
their own kind and will rarely miss an opportunity to meet another rat
- even if it is just to sniff at each other and indulge in a
territorial dispute through the bars of a cage. Rats living together
play often (even very old rats enjoy playing occasionally at fighting,
wrestling and chasing other rats), groom each other (there are parts
of a rat's body which it cannot reach to groom itself, eg behind the
ears and the back of the neck), provide warmth and security for each
other at night, and communicate - sometimes by touch and smell, and
sometimes (probably) by sound at frequencies we can't hear.

That is not to say that rats kept in company don't fight; they
certainly do scrap occasionally, especially when the rats are
teenagers (3-6 months). However, this fighting is usually just
horseplay and it serves a useful function in providing the rats with
exercise and stimulation as they establish a social order in their
community; it is a valuable part of their lives. Animals which
naturally live in communities usually have established social
behaviour patterns which are part of their nature. They can only
express this part of their nature fully when with other animals of
their own kind which interpret their communications correctly and
respond in kind. One theory of social evolution claims that human
language evolved from grooming rituals which help social animals to
enjoy each others company and so functio as a harmonious society.

It is reasonable to assume that some such social rituals are
species-specific; just as we cannot expect a pet rat to respond to our
conversation in the same way another human would, no human can enjoy
and respond to a ratÕs social rituals as another rat could. Then
as a general principle it seems that whenever we keep any social
animal alone, we are depriving it of a whole range of experiences
which it has evolved to enjoy. No amount of human attention can make
up for the company of another rat - just as the company of a dog could
not, for most humans, make up for the fact that they never saw another
person.

...you feed one rat, it's just as easy to feed two rats...