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Norway Rat

Before one can get rid of any pest, one should know about these pests. Here we will tell you a little bit about the brown or Norway rat

The brown rat (Rattus norvegicus), also known as the common rat, street rat, sewer rat, Hanover rat, Norway rat, Norwegian rat, Parisian rat, water rat or wharf rat, is one of the best known and most common rats.

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 slightly shorter tail. It weighs between 140 and 500 g (4.9 and 17.6 oz). Thought to have originated in northern China, this rodent has now spread to all continents except Antarctica and is the dominant rat in Europe and much of North America, making it by at least this particular definition the most successful mammal on the planet alongside humans. With rare exceptions, the brown rat lives wherever humans live, particularly in urban areas.

Selective breeding of Rattus norvegicus has produced pet rats, as well as the laboratory rat - the white rats used as model organisms in biological research.

Diet

The brown rat is a true omnivore and will consume almost anything, but cereals form a substantial part of its diet.

Martin Schein, founder of the Animal Behavior Society in 1964, studied the diet of brown rats and came to the conclusion that the most-liked foods of brown rats include scrambled eggs, macaroni and cheese, raw carrots, and cooked corn kernels. According to Schein, the least-liked foods were raw beets, peaches, and raw celery.

Foraging behavior is often population-specific and varies by environment and food source. Brown rats living near a hatchery in West Virginia catch fingerling fish. Some colonies along the banks of the Po River in Italy will dive for mollusks, a practice demonstrating social learning among members of this species. Rats on the island of Norderoog in the North Sea stalk and kill sparrows and ducks.

Reproduction and life cycle

The brown rat can breed throughout the year if conditions are suitable, with a female producing up to five litters a year. The gestation period is only 21 days, and litters can number up to 14, although seven is common. They reach sexual maturity in about five weeks. Under ideal conditions (for the rat), this means that the population of females could increase by a factor of three and a half (half a litter of 7) in 8 weeks (5 weeks for sexual maturity and 3 weeks of gestation), corresponding to a population growing by a factor of 10 in just 15 weeks. As a result, the population can grow from 2 to 15 000 in a year. The maximum life span is three years, although most barely manage one. A yearly mortality rate of 95% is estimated, with predators and interspecies conflict as major causes.

When lactating, female rats display a 24-hour rhythm of maternal behavior, and will usually spend more time attending to smaller litters than large ones.

Brown rats live in large, hierarchical groups, either in burrows or subsurface places, such as sewers and cellars. When food is in short supply, the rats lower in social order are the first to die. If a large fraction of a rat population is exterminated, the remaining rats will increase their reproductive rate, and quickly restore the old population level.

Females are capable of becoming pregnant immediately after giving birth and can nurse one litter while pregnant with another. Females are able to produce and raise two healthy litters of normal size and weight without significantly changing their own food intake. However, when food is restricted, females can extend pregnancy by over two weeks, and give birth to litters of normal number and weight.

Mating behaviors

Males can ejaculate multiple times in a row, and this increases the likelihood of pregnancy as well as decreases the number of stillborn. Multiple ejaculation also means that males can mate with multiple females, and they exhibit more ejaculatory series when there are several oestrous females present. Males also copulate at shorter intervals than females. In group mating, females often switch partners.

Dominant males have higher mating success and also provide females with more ejaculate, and females are more likely to use the sperm of dominant males for fertilization.

In mating, female rats show a clear mating preference for unknown males versus males that they have already mated with (also known as the Coolidge effect) and will often resume copulatory behavior when introduced to a novel sexual partner.

Females also prefer to mate with males who have not experienced social stress during adolescence and can determine which males were stressed even without any observed difference in sexual performance of males experiencing stress during adolescence and not.

Social behavior

Rats commonly groom each other and sleep together. Rats are said to establish an order of hierarchy, so one rat will be dominant over another one. Groups of rats tend to "play fight", which can involve any combination of jumping, chasing, tumbling, and "boxing". Play fighting involves rats going for each other's necks, while serious fighting involves strikes at the others' back ends. If living space becomes limited, rats may turn to aggressive behavior, which may result in the death of some animals, reducing the burden over the living space.

Rats, like most mammals, also form family groups of a mother and her young. This applies to both groups of males and females. However, rats are territorial animals, meaning that they usually act aggressively or scared of strange rats. Rats will fluff up their hair, hiss, squeal, and move their tails around when defending their territory. Rats will chase each other, groom each other, sleep in group nests, wrestle with each other, have dominance squabbles, communicate, and play in various other ways with each other. Huddling is an additional important part of rat socialization. Huddling is often supposed to have a heat-conserving function. Nestling rats especially depend on heat from their mother, since they cannot regulate their own temperature. Huddling is an extreme form of herding. Other forms of interaction include: crawling under, which is literally the act of crawling underneath one another; walking over, also explained in the name; allo-grooming, so-called to distinguish it from self-grooming; and nosing, where a rat gently pushes with its nose at another rat near the neck.

Burrowing

Rats are known to burrow extensively, both in the wild and in captivity, if given access to a suitable substrate. Rats generally begin a new burrow adjacent to an object or structure, as this provides a sturdy "roof" for the section of the burrow nearest to the ground's surface. Burrows usually develop to eventually include multiple levels of tunnels, as well as a secondary entrance. Older male rats will generally not burrow, while young males and females will burrow vigorously.

Burrows provide rats with shelter and food storage, as well as safe, thermo-regulated nest sites. Rats use their burrows to escape from perceived threats in the surrounding environment; for example, rats will retreat to their burrows following a sudden, loud noise or while fleeing an intruder. Burrowing can therefore be described as a "pre-encounter defensive behavior", as opposed to a "post-encounter defensive behavior", such as flight, freezing, or avoidance of a threatening stimulus.