In the wild
In the wild the Brown Rat lives in groups, developing strong relationships with others in the group.
They live mainly in burrows or sewers and sleep during the day, waking only for short periods. They are nocturnal and awake at dusk, being active at night.
In captivity the Rat is a sociable pet and will live with another of its own kind if they are introduced when young. However, an older rat (particularly males) may resent the addition of another rat of the same sex and a fierce fight can occur.
Rats establish an order of hierarchy and so one rat will be dominant over another.