Brown rat (Rattus norvegicus)
|Also known as:||common rat, house rat, Norway rat, sewer rat, water rat, wharf rat|
|Synonyms:||Epimys norvegicus, Epimys rattus norvegicus, Mus decumanus, Mus hibernicus, Mus norvegicus, Rattus caraco, Rattus caspius, Rattus decimallus, Rattus decumanus|
|Size||Total length: 31.5 - 48 cm (2)|
Head-body length: up to 28 cm (3)
Tail length: 12.2 - 21.9 cm (2)
|Weight||150 - 500 g (4)|
- The brown rat is one of the most abundant and widespread of all mammals, but is also one of the world’s most serious mammalian pests.
- Originally native to parts of China, Siberia and Japan, the brown rat is now found virtually worldwide.
- The brown rat is a sociable species and usually lives in groups which have a dominance hierarchy and defend a territory.
- The brown rat commonly lives close to humans, often occupying buildings, farmland, sewers and rubbish tips.
The brown rat is classified as Least Concern (LC) on the IUCN Red List (1).
One of the most abundant and widespread of all mammals (3), the brown rat (Rattus norvegicus) is a highly successful and adaptable rodent that has colonised nearly every part of the world. A relatively large and stocky species, the brown rat has a long, scaly, almost naked tail which is slightly shorter than the head and body (2) (3) (4) (5). This species’ snout is pointed (3), while its ears are relatively short (4) and have thin fur on the back (2).
As its common name suggests, the brown rat typically has brown to brownish-grey fur (3), but it can vary in colour from white to pale reddish-brown or almost black (2). The fur on the underside of the body and on the feet is slightly paler, and the tail is also lighter below than above (2). In captivity, albino versions of the brown rat have been used in laboratories for research, and various colour varieties have been bred as pets (2) (3).
The male brown rat is usually slightly larger and heavier than the female (2). This species can be confused with the closely related black rat (Rattus rattus), but differs in its larger size, shorter ears, smaller eyes and proportionately shorter tail (2) (3) (4) (5).
The brown rat produces a variety of sounds, including squeals, whistles, shrieks, soft chirps, hisses, and teeth chattering or grinding (2) (6). This species is also able to hear ultrasonic sounds, above the range of human hearing, and uses a number of ultrasonic calls. Pet rats have even been recorded producing a particular ultrasonic call known as ‘rat laughter’ when playing and being tickled (2).
Thought to originally have been native to north-eastern China, south-eastern Siberia and Japan (1) (2) (4), the brown rat has spread around the globe and now occurs almost worldwide (1) (2) (3) (5) (6). This species is only absent from Antarctica, northernmost parts of the northern hemisphere, and some tropical and subtropical areas (2) (3) (5).
The brown rat is believed to have spread into Europe from Central Asia by natural dispersal, made possible by this rodent’s association with human settlements (2) (5). It has also spread around the world as a stowaway on ships, arriving in Britain in the 1700s (3) (5) and later reaching North America (2) (6). At one time, the brown rat was thought to have arrived in Britain on ships from Norway, leading to the species’ scientific name, norvegicus, and its alternative common name of ‘Norway rat’ (3).
The brown rat is a highly adaptable species and can inhabit a wide range of environments, particularly in association with humans (1) (5). However, brown rats tend to be more common in cooler climates, and in tropical regions are usually restricted to human-modified environments such as buildings and ports (1). This species is only really absent from deserts and polar regions (3).
In its native range, the brown rat may have originally inhabited stream banks, later spreading rapidly as canals were built and rice fields developed (6), and it is still often found along water courses and in wetlands, as well as in woodland and coastal areas (3) (4) (5). However, this rodent is now also commonly found living alongside humans, on farmland, in buildings, and even in sewers and rubbish tips (3) (5) (6).
Unlike the black rat (R. rattus), which commonly climbs, the brown rat is largely a ground-dwelling species (1) (4) (6) and is a strong swimmer (2) (3) (5) (6), capable of crossing quite large stretches of open water (2) (4). This species is mainly nocturnal and has quite poor vision, but it makes up for this with its acute senses of smell, touch, taste and hearing (2).
The brown rat typically lives in underground burrows that have one or more exits and rooms for nesting and for food storage (2) (4) (6). There is usually a well-travelled system of pathways around the burrow, along which the rats regularly forage and which they can use to escape danger. These pathways are scent-marked with urine (2) (3).
The brown rat has a varied and opportunistic diet, feeding on almost anything edible. As well as grains, seeds, nuts, fruits and other plant material, this species also eats insects and other invertebrates, birds and their eggs, fish, and other small animals such as mice and young rabbits (2) (3) (4) (6). The brown rat has been known to attack larger animals such as poultry and young lambs (2) (3) (6), and will also eat carrion (2) and even substances such as soap, paper and beeswax (6). Food is sometimes carried back to the burrow to be stored (4) (6).
A sociable species, the brown rat tends to live in social groups which occupy a territory and can be aggressive to individuals outside of the group (2) (3) (6). The group has a dominance hierarchy, with dominant males typically occupying the prime areas in the territory and mating with several females. Females within the group often collectively nurse their young, although individuals may maintain their own nesting burrows (2) (6).
The brown rat is a prolific breeder and is capable of breeding year-round in some areas (2) (3) (5) (6), although there are usually peaks at certain times of year (2) (6). The female brown rat builds a nest in which to give birth (3), and usually has about 6 to 9 young per litter (2), although litters of up to 22 have been recorded (2) (6). The young rats are born after a gestation period of 21 to 24 days (2) (3) (4) and are naked and blind at birth, developing fur at about 1 week old and opening their eyes after around 2 weeks (2) (6). Young brown rats are weaned and leave the nest at about a month old (2) (4).
Female brown rats can become pregnant again soon after giving birth, and can raise as many as 12 or 13 litters a year (2) (5) (6). The brown rat can reach sexual maturity at just two to three months old, further contributing to this species’ rapid reproductive rate (2) (3) (5) (6). When the brown rat population becomes particularly high, large migrations of individuals away from an area may occur (3) (4) (6).
Young brown rats face a wide variety of predators, including owls, foxes, weasels, stoats, and domestic cats and dogs (2) (3) (4) (5), and most do not live for more than a year (2) (3). Many rats are also deliberately killed by humans (2). However, healthy, full-grown brown rats are less vulnerable to predators as they are relatively large and aggressive (3) (5). In captivity, this species can potentially live for up to five years (2) (3).
The brown rat is a common species and does not currently face any major threats (1). This rodent is considered to be one of the world’s most serious pest species, consuming or fouling vast quantities of human food, damaging property, and causing electrical hazards by chewing through cables. It is also a carrier of disease, and has caused or contributed to declines in many native plants and animals through predation or competition (2) (3) (4) (5) (6).
A highly adaptable species, the brown rat easily invades new areas (2). This species has already devastated native wildlife on many oceanic islands (6), and there is an ongoing risk of it reaching other islands where it could do further damage (2).
There are no conservation actions currently in place or needed for this successful mammal (1). Various control measures, including poisoning and trapping, are used to control brown rat populations and limit the damage they can do. To prevent the brown rat from becoming established on islands, measures to stop the species from arriving in the first place are usually more effective than any subsequent eradication attempts (4).
Although it can be a serious pest, the brown rat has played an important role as a laboratory animal in biological and medical research (6). This species is also kept as a pet (2) (3).
Find out more about the brown rat:
BBC Nature - Brown rat:
More information about the brown rat as an invasive species:
GB Non-native Species Secretariat (NNSS): Factsheet - Brown rat:
Invasive Species Compendium: Datasheets - Rattus norvegicus (brown rat):
This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
- Carrion: the flesh of a dead animal.
- Gestation: the state of being pregnant; the period from conception to birth.
- Invertebrates: animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones) and echinoderms.
- Nocturnal: active at night.
- Territory: an area occupied and defended by an animal, a pair of animals or a colony.
IUCN Red List (October, 2013)
- Naughton, D. (2012) The Natural History of Canadian Mammals. University of Toronto Press, Toronto.
- Burton, M. and Burton, R. (2002) International Wildlife Encyclopedia. Third Edition. Marshall Cavendish, New York.
Invasive Species Compendium: Datasheets - Rattus norvegicus (brown rat) (October, 2013)
GB Non-native Species Secretariat (NNSS): Factsheet - Brown rat (October, 2013)
- Nowak, R.M. (1991) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore and London.