Rattus norvegicus norvegicus (Berkenhout)
Description: Like the black rat and house mouse, the Norway rat has been introduced into Kansas. It can be distinguished from other members of its family by: 1) short, coarse, grayish brown hair with black guard hairs on the upperparts, 2) pale gray underparts blending into the upper parts, 3) tail not noticeably bicolored, slightly grayer above, and nearly naked with distinct rows of scales; shorter than the head and body, and 4) large, nearly hairless ears. Young are grayer than adults.
Size: Adults may attain the following dimensions: total length 294-425 mm; tail 125-190 mm; hind foot 35-44 mm; ear 22-24 mm; weight 250-400 grams.
Range and Habitat: The Norway rat is common throughout Kansas. It is associated mainly with humans and their buildings. It is believed that Norway rats, natives of Central Asia, spread in the Middle Ages throughout Europe and were introduced into North America by shipping. Being more terrestrial than the black rat, the Norway rat can live in the wild, away from buildings.
Reproduction: The Norway rat is one of the most prolific breeders among mammals in Kansas. It breeds throughout the year, and has six to eight litters annually averaging five young per litter, with as many as fourteen young per liter. After a gestation period of 21 to 23 days, the young are born helpless and hairless with their ears and eyes closed. Their ears open in three days, and their eyes open as early as fourteen days. In three weeks the young are weaned. Sexual maturity is reached in about two months or earlier.
Habits: The Norway rat is responsible for considerable property damage. They are very aggressive, and can easily overcome and kill most native Kansas rodents. In contrast to the black rat, the Norway rat burrows more, especially around basements, and under floors, and among piles of debris although it is quite capable of climbing. Subterranean tunnels dug by this rodent provide shelter for raising its young and for protection while eating. Its nests are made of grasses, leaves, and other soft materials. Soils are excavated with its forefeet, and the dirt is pushed behind by the hind feet. When enough dirt is accumulated, it turns around and pushes the dirt out of the tunnel with its forefeet. Norway rats have a restricted home range and sometimes will not go beyond a particular building, although her are other buildings only a few meters away. They are very good swimmers and are adapted for dispersing along waterways. Fecal droppings are deposited at random in the home range.
Food: The Norway rat is omnivorous and will eat anything, vegetable or animal.
Remarks: Hawks, owls, snakes, skunks, weasels, foxes, and coyotes prey upon the Norway rat. This rodent has been bred to produce many strains of laboratory rats for use in research. Maximum longevity of this mammal is two or three years in the wild, and five years or more in the laboratory.
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