Like most mammals, Norway rats use a variety of communication avenues. They are vocal, and also use visual cues such as body postures when communicating. Norway rats have relatively good hearing and tactile capabilities. They are able to sense very minute vibrations in the ground, and feel their way through total darkness with their paws and whiskers. However, these rats would not have such an advantage over all other foragers if it were not for their spectacular sense of smell. Scent is the Norway rats' best sensory channel, and it is used to find food and distinguish between individuals of a group.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: pheromones ; scent marks
Perception Channels: visual ; tactile ; acoustic ; vibrations ; chemical
These animals are not a conservation concern. In fact, humans spend a great deal of effort trying to eradicate them.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Some consider Norway rats to be the greatest mammal pest of all time. They have caused more deaths than all the wars in history. Rat-borne diseases are thought to have killed more people in the last 1000 years than all of the wars and revolutions ever fought. They harbor lice and fleas that carry bubonic plague, typhus, trichinosus, tularemia, infectious jaundice, and many other serious diseases. These rats also cause considerable damage to property including crops, destroying and pollution of human food storage, and damage to insides and outsides of buildings. It is estimated that rats cause almost 1 billion dollars in damage in the United States each year. Rats kill poultry, domestic livestock, and game birds and are responsible for the endangerment or extinction of many species of wildlife, especially those found on islands.
Negative Impacts: injures humans (bites or stings, causes disease in humans , carries human disease); crop pest; causes or carries domestic animal disease ; household pest
Norway rats have been widely used in medical and genetic research. This research has led to important advances in physiology, genetics, immunology, pathology, and epidemiology. They are also popular pets and have been important in research on behavior because of their ability to learn quickly and because it is easy to keep them in laboratory settings.
Positive Impacts: pet trade ; research and education
Norway rats are excellent competitors and will readily drive out competing rat species, such as Rattus rattus. Because of their foraging habits, Norway rats act as seed dispersers. Their burrows also tend to aerate the soil. As prey, they help to sustain predator populations. Norway rats are commensal species with humans.
Ecosystem Impact: disperses seeds; soil aeration
Mutualist Species:
Norway rats are excellent foragers. Using their sense of smell and touch, they are able to survive quite easily given that there is a steady supply of any type of food. In metropolitan areas, they survive mainly on discarded human food, and anything else that can be eaten without negative consequences. Some Norway rats living near the sea have been observed catching fish with their paws. Also preyed upon by Norway rats are chicks, mice, birds, and small lizards. They have even been known to attack infant human beings.
Examination of a wild R. norvegicus stomach in Germany revealed 4000 items, most of which were plants, although studies have shown that Norway rats prefer meat when given the option.
Animal Foods: birds; mammals; amphibians; reptiles; fish; eggs; carrion ; insects; terrestrial non-insect arthropods; mollusks; terrestrial worms; aquatic crustaceans; echinoderms; other marine invertebrates; zooplankton
Plant Foods: leaves; roots and tubers; wood, bark, or stems; seeds, grains, and nuts; fruit; nectar; flowers; sap or other plant fluids
Other Foods: fungus; detritus
Foraging Behavior: stores or caches food
Primary Diet: omnivore
Norway rats (Rattus norvegicus) are originally native to northern China. Following a series of introductions, the species had found its way to Eastern Europe by the early eighteenth century. By the year 1800, they occurred in every European country. Records show the first sighting of R. norvegicus in the New World occur in the 1770's as ship stowaways. Today, Norway rats (also known as brown rats) can be found on every continent of the world except Antarctica.
Biogeographic Regions: nearctic (Introduced ); palearctic (Native ); oriental (Introduced ); ethiopian (Introduced ); neotropical (Introduced ); australian (Introduced ); oceanic islands (Introduced )
Other Geographic Terms: cosmopolitan
In Asia, R. norvegicus was native to forests and brushy areas. Today, however, Norway rats find preferred habitat to be alongside the rapid expansion of the human population. Nearly every port city in the world has a substantial population of these rodents. They occupy a variety of habitats including garbage dumps, sewers, open fields and woodlands, basements, and nearly anywhere else that food and shelter might be found. Anywhere that humans are located, R. norvegicus will most likely follow.
Habitat Regions: temperate ; tropical ; terrestrial
Terrestrial Biomes: taiga ; desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Wetlands: marsh ; swamp ; bog
Other Habitat Features: urban ; suburban ; agricultural ; riparian
The maximum lifespan of R. norvegicus is 4 years (in captivity). In the wild, it is assumed that they live for upwards of 2 years.
Range lifespan
Status: captivity: 4 (high) years.
Average lifespan
Status: wild: 2 years.
Typical lifespan
Status: captivity: 2 to 3 years.
Rattus norvegicus is a rather large member of the mouse family. On average, these rats reach nearly 400 mm nose-to-tail, and weigh 140 to 500 g. Males are usually larger than females. In natural populations, these rats are covered with coarse, brownish fur (sometimes splotched with black or white hairs) on their dorsal surface, which usually lightens to a gray or tan color nearing the underside. Various strains of these rats bred in captivity may be white, brown, or black. The ears and tail are bald. The length of the tail is shorter than the length of the body. Molars are lophodont and the dentary is 1/1-0/0-0/0-3/3. The ears of Norway rats are typically shorter than those of related species, and do not cover up the eyes when pulled down. Norway rats can be easily mistaken for black rats, however, the temporal ridges of the Norway rat are straight, whereas those of the black rat are curved.
Range mass: 140 to 500 g.
Average mass: 400 g.
Average length: 399 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Average basal metabolic rate: 1.404 W.
Rattus norvegicus is preyed on by any number of carnivorous mammals, birds, and reptiles. Humans also kill very large numbers of Norway rats as pests.
Known Predators:
The mating system of R. norvegicus is best described as polygynandrous. Social animals, Norway rats tend to breed in large groups. Once a female enters her six-hour estrus period, she may mate as many as five-hundred times with competing males.
Mating System: polygynandrous (promiscuous) ; cooperative breeder
Although not technically a seasonal breeder, a mating increase occurs in the warmer months of the year. An average female is capable of giving birth approximately seven times per year. Around 18 hours after giving birth, females experience postpartum estrus, and mate again. This reproductive function is responsible for the huge birthrates of Norway rats, which can reach 60 young each year per female. After a short gestation period of 22 to 24 days, the litter of approximately 8 pups is born. The young are very small and underdeveloped. It takes 14 to 17 days for the young's eyes to open. Newborns weigh an average of 5 grams and are milk-fed until weaning occurs at 3 to 4 weeks, and the young then leave the nest.
Often, the litters of numerous females will occupy the same nest, and all the young are cared for by the adults, regardless of who the true mothers are. This communal care makes the species something of a cooperative breeder.
Males usually reach sexual maturity at 3 months and females at 4. However, it is usually the female who mates first because competition for mates among males prevents the smaller, less-dominant individuals from succeeding immediately. Rattus norvegicus is capable of mating for up to two years.
Breeding interval: Norway rats may breed up to 7 times per year
Breeding season: Breeding occurs year round, but is less pronounced during colder months.
Range number of offspring: 2 to 14.
Range gestation period: 22 to 24 days.
Range weaning age: 3 to 4 weeks.
Range time to independence: 4 to 5 weeks.
Range age at sexual or reproductive maturity (female): 3 to 4 months.
Range age at sexual or reproductive maturity (male): 3 to 4 months.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous ; post-partum estrous
Average birth mass: 5.81 g.
Average number of offspring: 9.9.
Parental care is provided by females. Because these animals often nest communally, the litters of several different females often occupy the same nest. In nesting groups of more than one female, if a mother is killed, the other females will take over nursing the newborns. Males do not particupate in parental care.
Parental Investment: no parental involvement; altricial ; female parental care ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Protecting: Female)
