Field Guide/Mammals/Norway Rat

Rattus norvegicus (Norway Rat)

Family: Rodents (Muridae) Size: Total Length: 17.3 inches (440 mm.) Tail: 8 inches (205 mm.) Weight: 14-17.6 oz. (400-500 g.) Description: Large and robust. Belly is mostly gray. Tail is shorter than body, dark above and pale below. Blunt nose. Ears are relatively small and close to body. Large and protruding eyes. Similar Species: The Norway rat is similar to the Roof Rat; but differs in that the Norway rat is large and robust and the roof rat is sleek and agile. The tail of the Norway rat is shorter than the tail of the roof rat. The nose of the Norway rat is blunt while the nose of the roof rat is pointed. The eyes and ears on Norway rats are small while the roof rats’ are large. Range: Live throughout the 48 contiguous United States. Native to China, Japan, and Russia. Occurs worldwide. Habitat: In the wild present in lowland and coastal regions. Lives as a commensal in close association with humans, principally in basements, ground floor, or burrows under sidewalks or outbuildings. Diet: Cereal grains, meats, fish, nuts, and some fruits. Activity: Nocturnal. Most feeding occurs half hour after sunset and before sunrise. Reproduction: At low densities in a burrow: Polygynous, one male mates with multiple females. At high densities: Polygynandrous, multiple males mate with multiple females. Prolific breeders, usually have 4-7 litters per year. Gestation is 21-23 days. Litter size from 2-14. Born naked and blind. Eyes open in 14-17 days. Weaned at 3-4 weeks old. Lifespan: In the wild 5-12 months. As a commensal 2-3 years.