norwegian rat

The Norway rat or Norway rat (Rattus norvegicus) is une species de rat. This is a rodent stocky family des Muridae. It has a long body of about 25 cm and a tail of about the same size. Adult, it weighs about 300 g. It is therefore larger and heavier than its close relative le black rat.

It is called brown rat1, brown rat or brown rat, sewer rat, Norway rat or gray rat to distinguish it from the black rat. Like all rats of the genus Rattus, the brown rat is native toFar East, specifically from la China. It is the northernmost of the rats, most species of which live under tropics and the equator. It spreads towardsEurope through steppes d'Central Asia  much later than the black rat, since the first were reported on the Old Continent in the 16th century; however, it was mainly during the 18th century that it massively invaded all of Europe. The brown rat is now present on all continents, except theAntarctic. He lives in contact with Human being  and more particularly in the urban spaces  equipped with sewers. It's an animal nocturnal, omnivorous  with a carnivorous tendency that feeds on the waste of city dwellers. Most brown rats nest in the sewers, which provide predator-free shelter and nesting opportunities, hence the name "sewer rat". Gregarious, the Norway rat mostly lives in very large groups hierarchical.Extremely prolific, this species is known as a possible vector of many diseases, which makes the brown rat considered an animal harmful and potentially invasive, as well as several other species of rats. However, this intelligent, sociable and easy-to-tame rat is also thestock species du domestic rat breeding.

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Physical characteristics

 

General aspects of black and brown rats and comparison between rattus rattus and Rattus norvegicus.

The adult rat has a size between 20 and 28 cm without counting the tail. Its tail is between 17 and 23 cm long. In the brown rat, the tail of the rat is shorter than its body with its head, contrary to the black rat which is smaller and has a tail longer than its body.

The various studies consulted report body weights of 200 to over 650 g for adult rats, with male rats generally being larger and taller than females. Urban Norway rats are larger than rural rats. Similarly, domestic rats have a larger body mass than wild rats, with the size/weight ratio varying greatly between lineages.

The brown rat in the wild has a brownish-gray color on its back and whitish-gray on its belly, the domestic rat can have different colors, markings and mutations. There are also black animals.

The brown rat has a pointed and thin head, surmounted laterally by two rather small ears, the muzzle carries the vibrissae which are very useful to rats to locate themselves. The rat's eyes are quite small and its masseters are quite developed. The rat has an almost non-existent neck and a relatively thin and slender trunk, which becomes more prominent at the level of the intestines and the hind legs. The rat's body ends in a ringed tail with very little hair.

The number of toes on each leg, front or back, is 57. The rat also uses its front paws to groom itself, to feed itself... The developed musculature of the rat allows it to run and jump (sometimes up to 1 m high and 1.20 m long)3,8. The rat is also a very good swimmer, it can swim 800 m.

Compared to the black rat, the brown rat has a less pointed, more beveled snout and smaller ears as well as larger rear legs.

 

The storage capacity of the rat's stomach is large, and it always contains food as it does in rodents. The intestines of the rat play an essential role since they allow the digestion of cellulose. Its digestive system makes it impossible for it to vomit. The digestive transit of the brown rat is from 12 to 24 hours. The rat is a caecotrophic animal, which means that it ingests part of its excrement. Soft, green excrements pass a second time through the digestive tract and through the cecum to be rejected as hard and dry droppings. This ingestion allows them to recover some nutrients but also to completely absorb the cellulose.

The heart of a 300g adult rat weighs about 0.25g. An adult has a heart rate of 250 to 450 beats per minute.

The body temperature of the rat is between 36°C and 38°C. Its chromosome number is 424.

The respiratory system of the rat consists, as in all mammals, of an upper part (nostrils, nasal cavities, larynx, trachea) and a lower part (bronchi and lungs)7. The rat has a reduced thoracic volume with a lung volume of 25 mL and a respiratory rate of 70 to 115 breaths per minute4,8.

The rat has no penile bone, and its penis can easily be exteriorized from the prepuce. The anogenital distance is greater in males than in females.

 

Farmed brown rats have a lifespan of 2 to 3.5 years, while wild rats have a lifespan of only 18 months. Nevertheless, the record longevity is 56 months, or a little over 4.5 years. In the wild, the main cause of rat mortality is extermination by humans; predation by canines and felids is anecdotal, and mustelids, snakes or raptors are practically only found in the countryside. The reduction of trophic resources of a colonized environment can cause famine and sometimes pathogenic diseases.