Norway rats


 * See Rattus Norvegicus (album) for the album by the Stranglers.

The brown rat, common rat, Norway rat, Norwegian rat or wharf rat (Rattus norvegicus) is one of the best-known and common rats, and also one of the largest. It is not known for certain why it is named Rattus norvegicus (Norwegian rat) since it doesn't originate in Norway, but John Berkenhour, the author of the 1769 book Outlines of the Natural History of Great Britain, is most likely responsible for the misnomer. Berkenhour gave the brown rat the binomial name Rattus norvegicus believing that the rat had migrated to England from Norwegian ships in 1728, although no brown rat had entered Norway at that time, instead coming from Denmark. Thought to have originated in northern China, this rodent has now spread to all continents and is the dominant rat in Europe and much of North America. It lives wherever humans live, particularly in urban areas. Selective breeding of Rattus norvegicus has produced the laboratory rat, an important model organism in biological research, as well as pet rats.

Food & habitat
The brown rat is a true omnivore and will consume almost anything, but with cereals forming a substantial part of the diet. Martin Schein, founder of the Animal Behavior Society in 1964, studied the diet of brown rats and came to the conclusion in his paper "A Preliminary Analysis of Garbage as Food for the Norway Rat" that the most-liked food of brown rats was (in order) scrambled eggs, macaroni and cheese, and cooked corn kernels. Their least-liked food was raw beets, peaches, and raw celery. They are usually active at night and are good swimmers, both on the surface and underwater, but (unlike the related Black rat Rattus rattus) are poor climbers. They dig well, and often excavate extensive burrow systems.

Physiology
The fur is coarse and usually brown or dark grey, the underparts are lighter grey or brown. The length can be up to 25 cm, with the tail a further 25 cm (the same as the body length). Adult body weight averages 350 g in males and about 250 g in females, but a very large individual can reach 500 g. Rats weighing over a kilogram are exceptional, and stories of rats as big as cats are exaggerations, or misidentifications of other rodents such as the coypu and muskrat. Brown rats have acute hearing and are sensitive to ultrasound, and also possess a very highly developed olfactory sense. Their average heart rate is 300 to 400 beats per minute, with a respiratory rate of around 100 per minute. Their vision is poor and they are unable to detect colour and are blind to long-wave light.

Breeding
The brown rat can breed throughout the year if conditions are suitable, a female producing up to five litters a year. The gestation period is only 21-23 days and litters can number up to fourteen, although seven is common. The maximum life span is up to three years, although most barely manage one&mdash;a mortality rate of 95% is estimated, with predators and intraspecific conflict as major causes. 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.

Rats live wherever people live. It is often said that there are as many rats in cities as people, but this varies from area to area depending on climate, etc. It is probable that New York City (with a severe winter climate), for instance, has only 250,000 rats, not eight million. However, the UK official National Rodent Survey found a 2003 UK population of 60 million brown rats, about equal to the UK human population; winters in Britain are much warmer, making rat survival higher. Brown rats in cities tend not to wander extensively, often staying within 20 meters (65 ft) of their nest if a suitable concentrated food supply is available, but they will range more widely where food availability is lower.

The only way to truly combat the rat problem is reduce the food supply, i.e., garbage left out on the street.

Rat-free zones
The only rat-free zones are the Arctic, the Antarctic, and, since the 1950s, the province of Alberta in Canada. Provincially appointed rat catchers, a lack of sea ports, an alert population (mainly grain farmers), and a prohibition on holding rats as pets have succeeded in keeping the province free of rats, resulting in substantial savings to the farmers. The similarly landlocked province of Saskatchewan has been discussing a similar programme.

Diseases
Brown rats are supposed to carry some diseases, including Weil's disease, cryptosporidiosis, Viral hemorrhagic fever (VHF), Q fever and hantavirus pulmonary syndrome. Unlike the black rat, brown rats rarely if ever carry bubonic plague.

Brown rats in science
Selective breeding of the brown rat has produced the albino laboratory rat. Like mice, these rats are frequently subjects of medical, psychological and other biological experiments and constitute an important model organism. This is because they grow quickly to sexual maturity and are easy to keep and to breed in captivity. When modern biologists refer to "rats", they almost always mean Rattus norvegicus.

Scientists have bred many strains or "lines" of rats specifically for experimentation. Generally, these lines are not transgenic, however, because the easy techniques of genetic transformation that work in mice do not work for rats. This has disadvantaged many investigators, who regard many aspects of behavior and physiology in rats as more relevant to humans and easier to observe than in mice, but who wish to trace their observations to underlying genes. As a result, many have been forced to study questions in mice that might be better pursued in rats. In October 2003, however, researchers succeeded in cloning two laboratory rats by the problematic technique of nuclear transfer. So rats may begin to see more use as genetic research subjects.

Brown rats as pets
Brown Rats make excellent pets and are the focus of attention at shows of fancy rats. Brown rats are clean, social and intelligent pets. They will suffer severe psychological stress when not kept with at least one other rat. The source of the pet's litter should be carefully monitored, as wild animals make poor pets.

Rats can live 2 to 3 years, are easy to house and feed, and are mostly odorless. They are inexpensive, small, and are considered lovable by their owners. Rats also tend to be hardy and disease-resistant. When kept as pets, rats require 2 cubic feet per animal of cage space to provide suitable living, playing and stashing space. Crowding rats in less-than-optimal space can result in stress, aggression and fighting among animals housed together.

When looking for a rat to purchase as a pet, it should be a young, healthy animal. It should ideally be up to 8 weeks old. Make sure it is plump, has bright eyes, good sound teeth, and a healthy coat. Either sex will make a good pet, however if you plan to purchase more than one, it is recommended that they are of the same sex, as rats breed quickly and often. Females tend to be more active but males are more likely to sit on your lap and let you pet them.

Brown rats as pet food
Because of their quick reproduction, rats are also used as live food for captive animals, commonly large reptiles such as snakes. Care must be taken to select rats from breeders who provide a good quality diet and captive living conditions.

There is a large risk to captive animals if live rats are fed. An animal that is not hungry may become food for the rat. An animal that does not kill the rat quickly will suffer injuries. Even supervised feedings can result in an injured or dead animal, as rats are fast.