Rattus rattus Linnaeus, 1758
Muridae

Description

Together with the common rat (R. norvegicus), they are the two representative species of the genus Rattus. The black rat and the common rat are very similar externally, but they differ in the fact that the black rat is more graceful, with a more elongated body, longer tail and ears, and a more pointed snout. The head and body length of the black rat ranges from 17.6 to 21 cm. The tail is long, scaly, and practically hairless, measuring between 18.4 and 23.5 cm, thus exceeding the length of the head and body together (this is not the case with the common rat). Females are slightly smaller than males. The dorsal colouration of the black rat is dark (darker than the one of the common rat) and the belly is lighter (a combination of white, yellow and grey).

The black rat is a crepuscular and nocturnal animal, although some individuals can be seen during the day. It is organized in hierarchical groups dominated by an adult male and two subordinate females.  

The black rat is rarely found occupying edible dormouse nest boxes.

Distribution

The black rat is a Palaearctic species, probably originated in southern Asia and currently distributed in the tropical and temperate environments of this region. In Europe, it has been associated with humans since the Bronze Age. The strong link it maintains with man has enabled it to colonize practically the entire world, including the Americas, the Caribbean and many Pacific islands. In Europe, it is found practically everywhere except Scandinavia, and it is abundant in the Mediterranean area. Although scattered, this species inhabits the entire Iberian Peninsula, including the Balearic and Canary Islands. Its distribution is conditioned by the common rat, which is more resistant, stronger and aggressive and tends to displace it.

Habitat and feeding

It is an animal present in numerous types of habitats and, thanks to commensalism, it can be distributed throughout the whole territory, from very low altitudes near the sea to the Pyrenees. It can be found in wooded areas with significant undergrowth, as well as in cultivated fields, mainly with fruit plantations, and occupying human buildings. The territorial competition with its relative, the common rat, have distanced it from anthropic areas and moved it towards wooded areas and higher ground. It is a species with a great climbing capacity and this favours its presence in this type of environment. For this reason, it can also occupy nest boxes occasionally. As we approach the Pyrenees, it seems that R. rattus remains the only representative of its genus, linked to human constructions. 

It is an omnivorous species, capable of eating any type of food.

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Feeding

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Breeding

The reproductive cycle varies according to the place where it lives. The wild populations that live outdoors have a seasonal cycle, although males are active all year round, their percentage of activity decreases considerably in winter. Females are active from February to October, largely governed by the length of the photoperiod. In these populations, they usually develop two gestations per year. Southern populations might produce a summer break in the breeding period. Populations inhabiting human constructions are sexually active all year round, as neither environmental conditions nor food resources are limited. Under these conditions, females can reproduce uninterruptedly and produce up to five litters per year. Forest-dwelling animals build nests in the canopies with branches and leaves that they cut with their teeth. The nests are usually spherical, with a single entrance and a tightly packed center of leaves in which the young are born. Commensal populations usually build their nests in attics or under roofs, also accumulating plant debris, rags, or plastics.

Gestation lasts about 21 days and lactation one month. Females reach sexual maturity at 6 or 7 weeks of age and males at 7 or 8 weeks. The number of offspring can range from 1 to 12, but normally is 7. The average lifespan of the species hardly exceeds one year (typical of species with a high turnover rate).