|Rattus norvegicus (Berkenhout)|
Don Linzey & Christy Brecht
Wytheville Community College
Wytheville, Virginia 24382
Last updated: 26 November, 2005
- Adult total length:
12 1/2 - 18 1/2 in. (325 - 475 mm)
5 3/4 - 8 1/2 in. (150 - 215 mm)
- Hind foot:
1 1/2 - 1 3/4 in. (39 - 43 mm)
10 - 11 3/4 oz. (280 - 335 g)
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.
||Mice, Rats, etc.
||Murid Rats and Mice
Norway rats are found wherever food and shelter are abundant. They are aggressive and extremely
adaptable to a wide range of conditions. They are found in towns, cities, and rural areas. They
may be found in barns, fields, ditches, corn cribs, and dumps. Unlike the black rat, they often
burrow in the ground beneath protective cover.
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).
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.
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.
None recorded from the park.
Links to Other Sites
- Special Protection Status
- In Park:
All plants and animals are protected within Great
Smoky Mountains National Park. Collection requires
a permit which is usually granted only for research
or educational purposes.
- Map development
- 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.
Last modified: 10 April, 2002