One of the most abundant and widespread of all mammals, 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. This species’ snout is pointed, while its ears are relatively short and have thin fur on the back.
As its common name suggests, the brown rat typically has brown to brownish-grey fur, but it can vary in colour from white to pale reddish-brown or almost black. The fur on the underside of the body and on the feet is slightly paler, and the tail is also lighter below than above. In captivity, albino versions of the brown rat have been used in laboratories for research, and various colour varieties have been bred as pets.
The male brown rat is usually slightly larger and heavier than the female. 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.
The brown rat produces a variety of sounds, including squeals, whistles, shrieks, soft chirps, hisses, and teeth chattering or grinding. 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.
Thought to originally have been native to north-eastern China, south-eastern Siberia and Japan, the brown rat has spread around the globe and now occurs almost worldwide. This brown rat is only absent from Antarctica, northernmost parts of the northern hemisphere, and some tropical and subtropical areas.
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. It has also spread around the world as a stowaway on ships, arriving in Britain in the 1700s and later reaching North America. 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’.