Brown Rat

## Description

The brown rat (Rattus norvegicus ), also known as the common rat, street rat, sewer rat, wharf rat, Hanover rat, Norway rat, Norwegian rat and Parisian rat, is a widespread species of common rat. One of the largest muroids, it is a brown or grey rodent with a head and body length of up to 28 cm (11 in) long, and a tail slightly shorter than that. It weighs between 140 and 500 g (5 and 17+3⁄4 oz). Thought to have originated in northern China and neighbouring areas, this rodent has now spread to all continents except Antarctica, and is the dominant rat in Europe and much of North America. With rare exceptions, the brown rat lives wherever humans live, particularly in urban areas.

Selective breeding of the brown rat has produced the fancy rat (rats kept as pets), as well as the laboratory rat (rats used as model organisms in biological research). Both fancy rats and laboratory rats are of the domesticated subspecies *Rattus norvegicus domestica*. Studies of wild rats in New York City have shown that populations living in different neighborhoods can evolve distinct genomic profiles over time, by slowly accruing different traits.

## Appearance

The Brown rat is one of the most common and widely distributed mammals around the globe, found in almost all parts of the world. This rodent is a very adaptable animal. The coloration of its coat is usually brown to brownish-grey. However, the animal can vary from white to pale reddish-brown and nearly black in color. Laboratories are known to use Albino versions of this species in research. In addition, the Brown rats are bred in captivity and may have various colorations as pet species. Female rats are a bit smaller and lighter in weight than males. The Brown rat is closely related to and frequently mistaken for the Black rat. However, the former is considerably larger, distinguished by shorter ears, smaller eyes and a comparatively shorter tale.

## Distribution

Native to northern China, the Brown rat has been introduced to Eastern Europe in the beginning of the 18th century. Currently, this animal is found in nearly any area, inhabited by humans, occurring on all continents around the globe, except for Antarctica. Originally, the Brown rats used to occupy forests and brushy areas, living in Asia. Nowadays, they are capable of living in a wide variety of habitats such as open fields, woodlands, basements, garbage dumps and sewers.

## Behavior

These animals are generally nocturnal or active at dusk, when they dig burrows, prepare the nests and look for food. As good swimmers, the Brown rats are also known as 'water rats' and can often inhabit areas near water. The Brown rats are highly social creatures, forming groups that are sustained on a dominance hierarchy. Each group has its own territory. Member of the group are usually extremely aggressive to outsiders. Each group is led by the dominant male, which occupies the best areas of the group's territory and can mate with multiple females. Collective nursing is a common activity in these groups with females, helping nurse offspring of another female. However, some females have their own separate nesting burrows. Their burrows are located under the surface of the ground, having 1 - 2 exits along with rooms, intended for nesting and serving as food stores. The area around the burrow has numerous scent-marked routes that are used for foraging and allow them to escape potential threats.

## Diet

As omnivorous species, the Brown rat has a rather diverse diet, composed of plant material such as grains, seeds, nuts and fruits, supplemented with mice, young rabbits, birds and their eggs, fish as well as invertebrates such as insects. This rodent is also known to hunt on larger animals, including poultry and young lambs. The animal is able to consume substances such as soap, paper and beeswax. In addition, this rat may also use carrion on occasion.

## Reproduction

Brown rats are polygynandrous (promiscuous), which means that both males and females have multiple mates. The Brown rats are cooperative breeders and may breed throughout the year in large groups that are formed up to 7 times per year. Gestation period lasts for 22 - 24 days, yielding about 8 young, which are born underdeveloped and are extremely small, weighing only 5 grams on average. The pups open their eyes at 14 - 17 days old. Young feed upon maternal milk during the first 3 - 4 weeks of their lives, after which they leave the nest. As these animals practice collective nursing, offspring of different females often live together in the same nest, cared for by various adults. The age of sexual maturity is 3 months old for males and 4 months old for females.

## Population

### Population threats

The Brown rat is considered one of the most prominent pests around the globe. In addition, it is highly dangerous to humans, due to carrying Weil’s disease, plague and numerous other diseases. Hence, this animal is persecuted and killed worldwide.

### Population number

According to IUCN, the Brown rat is abundant and widespread throughout its range but no overall population estimate is available. However, according to the People’s Trust for Endangered Species resource, Great Britain population of this species is around 6,790,000 individuals. Overall, Brown rats’ numbers are stable today, and this animal is classified as Least Concern (LC) on the IUCN Red List.

### Ecological niche

In some parts of their range, the Brown rats are a key prey species for local predators. Furthermore, these animals contribute to aeration of the soil due to digging burrows. And finally, when foraging, they disperse seeds of numerous plants, thus sustaining the ecosystem.

## Domestication

The brown rat is kept as a pet in many parts of the world. Australia, the United Kingdom, and the United States are just a few of the countries that have formed fancy rat associations similar in nature to the American Kennel Club, establishing standards, orchestrating events, and promoting responsible pet ownership.

The many different types of domesticated brown rats include variations in coat patterns, as well as the style of the coat, such as Hairless or Rex, and more recently developed variations in body size and structure, including dwarf and tailless fancy rats.

## Fun Facts for Kids

These rodents are known to spend a great part of their active time washing and grooming. They remain clean in spite of living among rubbish tips and sewers.

Rats occasionally emit a cheerful, laughter-like sound when playing or when they feel happy.

In spite of the poor sense of vision, rats possess adorable whiskers, helping them perceive their environment.

Rats are highly intelligent animals, able to learn their own name and perform numerous tricks.

These rodents are stupendous nappers, and as much as 76% of their daytime hours is spent sleeping.

Rats also possess a well-developed sense of taste. For example, they are able to identify poison and remember its taste. In addition, they have an excellent memory.