Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Rodentia
Family Muridae
Genus Rattus
Species norvegicus
Classification Berkenhout, 1769
Common name norway rat
Size 40 centimeters with the tail
Male weight 195 - 485 grams
Female weight 200 - 500 grams

Geographic Range it originated in northern China; now it is widespread almost all over the world.
Physical Characteristics the body is covered with hairs, while ears and tail are naked. The tail is shorter than the body. The molars of the upper jaw have tubercles arranged in three longitudinal rows. The colour of the upper part of the body is brown-dark grey with scattered black hairs, while the underparts are pale grey.
Notes it adapts to different situations, its main constraint is that it cannot survive for a long time without water unless its diet contains other liquids in adequate amounts. It is active all year round; it is mainly nocturnal and it leaves the nest as dusk approaches. It forages on the ground even if it swims and climbs very well. When at night it goes out from its nest to search for food it always follows the same route: the diameter of its home range isn't generally larger than 50 meters. It usually lives in large groups in which a large male is dominant and maintains the privilege to be the first to have access to food and water. This male continuously defends its harem of females from other males which might want to come in. The females defend strenuously group resources against strangers and they often build their nest together. Dominance within the group is based on weight and size rather than age. Some rats may be seen foraging during the day: they are probably socially low-ranked individuals to which the access to food has been denied by dominant rats during the night.
Habitat it is found in human settlements, or where there is abundance of food and shelter and in salt marshes.
Food habits it is a true omnivore, its appetite is prodigious: it can eat in a day the quantity of food equivalent to one third of its weight. It can catch fish and small rodents.
Reproduction it is a very prolific animal, if food is abundant it can breed all year round, although in winter litters can be few. The number of the young per litter can range from 2 to 14, but it is usually 7. At birth they are born blind, naked and helpless, they open their eyes at 14-17 days and are weaned at the age of three weeks. The nest is built with leaves, bits of paper and cloth, twigs. If it cannot find a suitable cavity, it makes holes in the ground, arranging them as a series of galleries communicating to each other, with rooms for nest building and for food storage, one or more main entrances and lots ways of escape.

References Animal Diversity Web, University of Michigan
Web References http://animaldiversity.ummz.umich.edu/
Source of the photo www.zoologi.no/patlas/ pat_foto.htm

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