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Brown Rat (Rattus norvegicus)

Diputación de Málaga

Brown Rat (Rattus norvegicus)

Identification

It is a medium sized (head-body length 17 to 27 cm) rodent (animal with a pair of incisor teeth in continuous growth), bigger than the black rat. It has a dark grey coat, a bit lighter on the belly. It has a large head, a blunt snout and small ears (smaller than in the black rat). The tail is long (15 to 23 cm), without exceeding the body-length, and covered by scales. There is no differences between both sexes.

Where does it live?

It is an exotic species, native from China and the rest of Asia, which has been expanding and colonizing almost all the planet since the 16th and 17th centuries. It successfully competes with the native or black rat (Rattus rattus), expelling it from many places.  Its typical habitats are villages, towns and urbanized environments in general. It often occupies the lower parts of the city, at ground level (cellars, sewers, drains, corrals, weedy areas ...) since it can not climb. The other rat occupies lofts, roofs and niches at higher altitudes, since they can climb very well. It requires the presence of water, since it ingests daily up to 38 ml. That is why it is also very linked to wet areas (culverts, edges of banks with dense vegetation). 

How does it live?

It is an omnivore animal. It mainly eats everything, but it focuses on harnessing waste and rubbish. It is a very opportunistic species and a banqueter of human. It digs tunnels with different habitats on embankments and areas with a certain slope having a vegetation cover. Tunnels can be very long. It is a gregarious species, very territorial and even aggressive with specimens that are not from its colony; with a very organized and hierarchical social structure. The colony is lead by an adult male and two subordinate females. The colony members are very disciplined and submit to the dominant male, although there are usually internal fights to take the power and control over the colony. They distrust unusual food. In those cases, the dominant male sends a taster to taste the food. If it dies, the colony will always distrust this kind of food. This strategy helps them to successfully overcome the deratization campaigns with poisons. They are dusk and night animals, but they can also be seen during the day. They can swim very well. 

How does it reproduce?

Rats mate all year round. They are sexually active at the age of two months, each female being able to get from 5 to 8 litters per year. From 2 to 16 offspring are born in each litter. The colony breeds almost every six weeks. The offspring are born into the rooms or nest located at the bottom of the tunnels; they are naked, blind and without a sense of hearing. They develop within less than three weeks. The medium lifetime of a rat lasts less than a year, with a very high death rate of its population (90-95%).  It is considered that the colony is renewed every year.

Where can we see it in Málaga?

This species is present in the whole province, being scarcer in high mountain areas (more than 1000 meters above sea level). It is a very abundant and common species. We can find it on almost every stage of the Great Path (Gran Senda).

Curious facts

The brown, grey or sewer rat is also named the Norwegian rat.  This surname refers to its specific name in Latin, which incidentally coincides with that of the Norway lobster (Nephrops norvegicus). This misnomer was granted by John Berkenhout in 1769. This English physicist and naturalist named the Norwegian rat in the belief that they had arrived in England on ships from Norway, which had crossed the English Channel loaded with wood. The Latin name has remained, but today it is known that actually it should be called the Chinese rat because of its true origin. The Norway lobster was described from specimens caught in the Norwegian Sea. Linneo gives it its correct Latin name.

Similar species

It can be confused with the back or country rat. This rat is smaller, with a less strong are more stylised body, a longer tail, smaller sized ears and a more pointed snout. Moreover, the black rat occupies more rural habitats than the brown rat. In the city, it is only present in high areas, as it can climb very well and since at ground level, the brown rat expels it very aggressively.

Routes where it can be observed

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