Discover Life | All Living Things | IDnature guides | Mammalia | Muridae | Rattus | norvegicus

Species Description

• Adult total length: 12 1/2 - 18 1/2 in. (325 - 475 mm)

• Tail: 5 3/4 - 8 1/2 in. (150 - 215 mm)

• Hind foot: 1 1/2 - 1 3/4 in. (39 - 43 mm)

• Weight: 10 - 11 3/4 oz. (280 - 335 g)

• Physical Characteristics: The Norway rat is a moderately large, robust, grayish or brownish rodent with coarse fur and a long, sparsely haired, scaly tail. The tail is shorter than the combined length (approximately 80 percent) of the head and body. This feature serves as a key identification character in differentiating this species from the black rat. The underparts and feet are grayish to whitish.

left lateral view of skull and mandible	dorsal view of skull	ventral view of skull

The Norway rat is a non-native (exotic) species that is thought to have arrived in North America on ships about 1775 and has since spread over most of the continent (Silver, 1927). It is native to Japan and possibly the eastern mainland of Asia. Norway rats are found nearly everywhere humans have settled.

• Range Maps

  Great Smokies

• Great Smoky Mountains National Park: The Komareks recorded Norway rats commonly around buildings and occasionally in rock fences bordering corn fields. One individual, however, was recorded by the Komareks five miles from the nearest habitation along Eagle Rocks Creek (3,800 feet) (Komarek and Komarek, 1938). Due to a more limited food supply than in pre-park days, this non-native species has become less abundant in the park.
  • Sevier Co.: Greenbrier Cove (1,750 feet ); Elkmont (2,500 feet); Eagle Rocks Creek (3,800 feet).

  • Haywood Co.: Big Creek (1,700 feet).

  • Swain Co.: Clingmans Dome Road (6,000 feet).

Index

Natural History

• Reproduction
  Norway rats are among the most prolific of all mammals. If food and shelter are abundant, Norway rats may breed all year. Litters range in size from 6 to 22 young, but usually average 7 to 9. A single female may give birth to as many as 12 litters in a year.

  Nests consisting of rags, paper, and other debris may be located in a burrow, a trash pile, under a building or woodpile, in a haystack, or in some other similarly protected place. Newborn rats are blind, naked, and helpless. They grow rapidly, with the eyes opening between 14 and 17 days of age. The young are weaned when approximately three weeks old. A half-grown individual was taken along Clingmans Dome Road in July (Linzey, 1995b). Most rats breed for the first time when between three and four months old.

• Longevity
  Although Hamilton (1943) noted that the normal life span of a wild Noway rat was thought to be about three years, Davis (1948) reported that only 5 percent of the rats remained alive for 12 months on a Maryland farm.

• Terrestrial Ecology
  These rodents are mainly nocturnal and are active throughout the year. They commonly occur in colonies. Signs of their presence include gnawings, feces, and despoiled food. They are aggressive and often drive out native rats and mice. The Norway rat is more of a burrower and a less agile climber than the black rat.

  Because Norway rats travel along narrow runways, it is difficult to measure the area of the home range. Movements depend mainly on the availability of food and the density of the population. Jackson (1982) reported an average home range radius of 30 to 50 m. Stroud (1982) recorded an average home range of 0.24 ha.

  Norway rats are omnivorous and feed on grain, green vegetation, meat, eggs, nestl ing birds, insects, fruit, and garbage. A rat will eat a third of its weight in food in 24 hours and apparently prefers to feed shortly after dark and again in the early morning (Linzey, 1998).

  Perhaps the only redeeming feature of this species is that the common laboratory rat or white rat is an albino strain of this species, and it has proved extremely valuable in many fields of biological and medical research, including genetics, physiology, immunology, epidemiology, and pathology.

• Predators and Defense
  Snakes, hawks, owls, mink, weasels, cats, foxes and other carnivores prey on these rodents.

• Parasites
  None recorded from the park.

• University of Michigan, Museum of Zoology
• eNature

Index

Acknowledgements

• Text
  • Dr. Donald W. Linzey, Wytheville Community College - wclinzd@wcc.vccs.edu
  • Christy Brecht, Wytheville Community College - wcbrecc@wcc.vccs.edu

• Photographs
  • Roger Barbour

• Map development
  • Richard Schulz, Great Smoky Mountains National Park - richard_schulz@nps.gov

• Web page design & coding
  • Denise Lim, University of Georgia, Athens
  • John Pickering, University of Georgia, Athens

• Davis, D. E. 1948. The survival of wild brown rats on a Maryland farm. Ecology 29: 437-448.

• Hamilton, W. J., Jr. 1943. The Mammals of Eastern United States. Ithaca, New York: Comstock Publishing Company.

• Jackson, W. B. 1982. Norway rat and allies. Pages 1077-1088. In: J.A. Chapman and G.A. Feldhamer (eds.). Wild Mammals of North America. Baltimore: The Johns Hopkins University Press.

• Komarek, E.V. and R. Komarek. 1938. Mammals of the Great Smoky Mountains. Bulletin of the Chicago Academy of Sciences 5 (6): 137-162.

• Linzey, D. W. 1995a. Mammals of Great Smoky Mountains National Park. Blacksburg, Virginia: The McDonald & Woodward Publishing Company, Inc.

• Linzey, D. W. 1995b. Mammals of Great Smoky Mountains National Park-1995 Update. Journal of the Elisha Mitchell Scientific Society 111(1):1-81.

• Linzey, D.W. 1998. The Mammals of Virginia. Blacksburg, Virginia: The McDonald & Woodward Publishing Company, Inc.

• Silver, J. 1927. The introduction and spread of house rats in the United States. Journal of Mammalogy 8 (1): 58-60.

• Stroud, D.C. 1982. Population dynamics of Rattus rattus and R. norvegicus in a riparian habitat. Journal of Mammalogy 63 (1): 151-154.