The Norway rat, a moderately large member of the rodent family, inhabits areas of the park wherever food and shelter are abundant. Interestly, Norway rats are among the most prolific of all mammals, are aggressive, and are extremely adaptable to a wide range of conditions. They often drive out native rats and mice. These rodents are mainly nocturnal, and are active throughout the year. They commonly occur in colonies.

Species Measurements:
- Adult Total Length: 325-475 mm (12?-18? in.)
- Tail: 150-215 mm (5?-8? in.)
- Hind Foot: 39-43 mm (1?-1? in.)
- Weight: 280-335 g (10-11? oz.)

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.

Habitat:
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.

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.

Feeding Habits:
Norway rats are omnivorous and feed on grain, green vegetation, meat, eggs, nestling 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).

Interesting Fact:
One of the redeeming features 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.

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.

In the Smokies, 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.

References:

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. The McDonald & Woodward Publishing Company, Inc., Blacksburg, Virginia.

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. The McDonald & Woodward Publishing Company, Inc., Blacksburg, Virginia.

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.