Brown rats have been bred for research and the pet trade. They spread across Britain via the shipping traffic from foreign countries in the 18th Century, largely replacing the black rat. Along with house mice, they are considered to be the most widespread terrestrial mammal.

Life span
Typically up to 18 months in the wild, but domestic rats live for an average of three years.

Statistics
Head and body length: 18cm, Weight: 200-400g.

Physical description
Brown rats have coarse brown (occasionally black) fur, with a pale underside. They have a long tail, which is sparsely haired.

Distribution
Although originally native to east Asia and Japan, brown rats are now distributed world-wide. They are found all over Britain except for exposed mountain regions and some small offshore islands.

Habitat
Brown rats are highly adaptable and can be found in a variety of habitats, typically near human habituation.

Diet
Brown rats are omnivorous but prefer starch and protein-rich foods, such as cereals. Their diet includes meat, fish, vegetables, weeds, earthworms, crustaceans, nuts and fruit. They sometimes cache food to return to later.

Behaviour
They are typically nocturnal, although they will sometimes forage for food during the day.

They live in loose colonies, made up of aggregations of clans - usually consisting of a mated pair, or a male and a harem of females.Clans will defend their territory from other rats, and there is a dominance hierarchy whereby the biggest rats are dominant over their smaller counterparts.

Home ranges are generally 50 metres in diameter. In areas of high population, fights will often break out, involving a vigorous scuffle leading to the loser being chased off and bitten on the rump.

Brown rats swim well and are sometimes mistaken for water voles. Rats have well-developed senses of hearing and smell.

Reproduction
Brown rats breed throughout the year and can produce five litters a year. Females give birth to an average of eight young, after a gestation of 22-24 days. These are weaned after 3-4 weeks.

Conservation status
Brown rats are common. They are subject to persistent pest control due to the damage they cause and the numerous diseases they spread.