Black Rat

Maximum longevity: 4.2 years (captivity) Observations: One captive specimen lived for 4.2 years (Richard Weigl 2005).

Known predators of R. rattus vary depending on environment. In urban or suburban areas, house cats are the main threat to its survival. In less populated areas, birds and other carnivorous animals prey upon it. One possible anti-predator adaptation is the array of color patterns found in this species. Some evidence suggests that color is related to geographical location and therefore ability to remain less conspicuous in the local environment. Also, rats are often aggressive toward other rats. Captive studies have shown R. norvegicus will kill R. rattus. Rattus rattus has a typical threat pose in which it stands on its hind feet and bares its teeth.

Known Predators:

• domestic cats (Felis silvestris)

Anti-predator Adaptations: cryptic

Rattus rattus is a medium sized rat with relatively large ears and a tail that is nearly always longer than the body. Individuals weigh between 70 and 300 g, and are between 16 and 22 cm in head and body length and a tail length of 19 cm or longer. Males are longer and heavier than are females.

Many members of the species are black in color with a lighter colored ventral belly. The species is often divided into subspecies based upon color patterns which can occur in any combination of black, white, grey, and agouti.

The skull and nasal bones are relatively narrow. One of the main ways to differentiate between R. rattus and R. norvegicus is that R. rattus has a finer covering of hair, a lighter skull, and a slightly differently shaped upper first molar.

Range mass: 70 to 300 g.

Average mass: 200 g.

Range length: 16 to 22 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Average basal metabolic rate: 0.77 W.

Rattus rattus tends to live for about a year in the wild with an annual mortality rate of 91 to 97%. In captivity, it has been reported to live for up to 4 years.

Range lifespan
Status: wild: 1 (high) years.

Range lifespan
Status: captivity: 4 (high) years.

Typical lifespan
Status: wild: 1 (high) years.

Typical lifespan
Status: captivity: 1 (low) years.

Rattus rattus is most often found in large numbers in coastal areas because of the way the species is spread through human sea faring. It is generally found in any area that can support its mainly vegetarian diet. Because R. rattus is an agile climber, it often lives in high places, such as top floors of buildings in populated areas or trees in forested areas. Even though it can be found near water, this species rarely swims and unlike its close relatives, rarely finds a home in sewers or in aquatic areas. Although it was formerly common in towns and farms of temperate regions, it has been largely driven out by the more aggressive Norway rat as well as killed off by increasing chemical pest control programs. Data have shown that R. rattus can reach elevations up to 250 m above sea level.

Range elevation: 0 to 250 m.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest

Other Habitat Features: urban ; suburban ; agricultural

Rattus rattus, is found on all continents of the earth. Although the species is believed to be native to India and possibly other Indo-Malayan countries, it has been introduced through human travel overseas to all continents. It is most common in coastal areas because it is a rodent that flourishes in areas inhabited by humans as well as on large ships. For this reason, these animals are often called ship rats. Some other common names for this species include house rat, black rat, and roof rat. Rattus rattus thrives in tropical regions but has been largely driven out of more temperate regions by Noway rats, R. norvegicus. Norway rats, are closely related to black rats, but are more successful in colder climates. However, some data show that R. rattus has been able to adapt to more extreme cold and harsh climate conditions.

Biogeographic Regions: nearctic (Introduced ); palearctic (Introduced ); oriental (Native ); ethiopian (Introduced ); neotropical (Introduced ); australian (Introduced ); antarctica (Introduced ); oceanic islands (Introduced )

Other Geographic Terms: cosmopolitan

Rattus rattus generally feeds on fruit, grain, cereals, and other vegetation. It is an omnivore, however, and will feed on insects or other invertebrates if necessary. It consumes about 15 g/day of food and 15 mL/day of water. Because it consumes and destroys the food source during feeding, it can cause devastating damage to farms and livestock. Not only does it gnaw through many materials but it ruins more than that by excreting on the remains of its foraging efforts.

Animal Foods: insects

Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts; fruit

Primary Diet: herbivore (Granivore )

Impact of these animals on their ecosystems has not been studied. However, we may infer from their feeding habits that they have some impact on plant communities. As a prey species, they may impact populations of those animals which feed upon them. Also, they compete with other species of rodents, such as Rattus norvegicus. Rattus rattus is a disease vector, responsible for bubonic plague outbreaks and other diseases. This cosmopolitan species hosts a wide variety of internal and external parasites, up to 18 species of gastrointestinal helminths in some areas.

Mutualist Species:

• Homo sapiens

Commensal/Parasitic Species:

• Oriental rat flea (Xenopsylla cheopis)
• rat flea (Nosopsyllus fasciatus)
• cestodes (Hymenolepis diminuta)
• cestodes (Taenia taeniaeformis)
• cestodes (Raillietina sp.)
• nematodes (Mastophorus muris)
• nematodes (Trichuris muris)
• nematodes (Syphacia sp.)
• nematodes (Nippostrongylus brasiliensis)
• acanthocephalan (Moniliformis moniliformis)
• trypanosomes (Trypanosoma lewis)

There are no known benefits of R. rattus for humans. Norway rats, the closest related species, is often used for research and as pets.

Rattus rattus is a pest and is dangerous to humans in several ways. First, these animals are severely destructive to crops, farms, and fruit trees. Not only do they feed on these but they tend to destroy what they are unable to consume. By urinating and defecating on remains of their meals, they ruin grain, cereals, and other food sources. This species is famous for its role in spreading the bubonic plague (Yersinia pestis) that took millions of lives in the middle ages. The fleas that live on these rats carry a number of diseases that can seriously harm humans, livestock, and other animals.

Negative Impacts: injures humans (causes disease in humans , carries human disease); crop pest; causes or carries domestic animal disease ; household pest

Rattus rattus is a somewhat vocal animal, producing squeaks when threatened or socializing. It also produces oil smears that are left along particular areas to illustrate territorial boundries. Hierarchy in groups is determined using aggressive threat postures and physcial contact. Vision, hearing, touch, and smell are all used in sensing the environment.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: pheromones ; scent marks

Perception Channels: visual ; tactile ; acoustic ; chemical

Rattus rattus has no special conservation status. They are widespread and abundant, especially in areas where humans live.

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

Social groups of R. rattus are often formed of multiple males and multiple females. One male is dominant and a linear male hierarchy may form. Two to three females are often dominant to all other group members except the dominant male. Females are generally more aggressive than males. The species is polygynous, and generally, the dominant male is the most successful breeder. Territories and mates are defended through aggressive behavior. If environmental conditions allow it, successful breeding may occur all year.

Mating System: polygynous

Rattus rattus is able to breed throughout the year if conditions allow. The peak breeding seasons are summer and autumn. Females can produce up to 5 litters in one year. The gestation period ranges between 21 and 29 days, and young rats are able to reproduce within 3 to 5 months of their birth. Neonates are altricial, like most rodents, and their eyes do not open until 15 days of age. Young remain hairless for much of their nursing period. Weaning and independence from the mother occur at about 3 to 4 weeks of age.

Breeding interval: R. rattus breeds year-round producing up to five litters in that time.

Breeding season: R. rattus mates throughout the year if environmental conditions permit, however peak times are summer and autumn seasons.

Range number of offspring: 6 to 12.

Average number of offspring: 8.

Range gestation period: 21 to 29 days.

Range weaning age: 3 to 4 weeks.

Range time to independence: 3 to 4 weeks.

Range age at sexual or reproductive maturity (female): 3 to 5 months.

Range age at sexual or reproductive maturity (male): 3 to 5 months.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous

Average birth mass: 4.55 g.

Average number of offspring: 7.3.

Because male members of R. rattus copulate with one female and then move on to the next, they don't contribute much to the care of the young. The young remain relatively helpless for about 2 weeks, until they begin to grow a pelage, their eyes open, and they are able to move around more. Weaning is accompanied by increased independence from the mother. Until these rats reach their full adult size, they stay in the nest built by their mother. Young rats are capable of reproducing by about 3 to 5 months of age.

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)

The black rat is nocturnal, although it may become more active in the day in undisturbed areas (4). It is an omnivore, but tends to prefer plant matter (4) such as fruits and seeds, although it will also feed on insects, carrion, refuse and faeces (2). On Lundy Island these rats feed on crabs along the shore (4). This rat lives in groups called 'packs', consisting of several males and two or more dominant females (4). They are skilled climbers and can also swim well (2). Nests are constructed from grass and twigs, often in roof spaces, a habit which earned the species the further common name of 'roof rat' (2). Breeding takes place between March and November; 3 to 5 litters can be produced in a year, each litter containing 1-16 young (although the average is 7). A single female can therefore produce a huge number of offspring; 56 young were recorded on a London ship for a single female (4). At 12-16 weeks of age, females are capable of breeding; they are also able to conceive whilst still suckling the previous litter, which further maximises their reproductive capability (1).Maximum lifespan in the wild is less than 18 months; populations have very high mortality rates, mainly as a result of widespread pest control measures (4). The black rat is a notorious pest, and was the host of the fleas that carried bubonic plague (2). It also carries a host of other diseases and is damaging to property and food stores (1).

The question as to whether this species should now receive a level of protection due to its poor status is a highly contentious issue (4).

Also known as the ship rat (2), the black rat was introduced to Britain with the Romans (4). Generally smaller than the brown rat (Rattus norvegicus), the black rat is typically a uniform black to tawny brown colour, with lighter underparts (1). The tail, which is longer than the head and body, is hairless, and is used for balance (2).

This species is closely associated with buildings around the world, although in Britain it tends to inhabit rocky shores and cliffs. On the islands it occasionally occurs on rubbish dumps and around buildings (4).

This species was once widespread throughout Britain until the brown rat was introduced (4). It originates from Asia, and today is widely distributed around the globe (4). It has been restricted to largely transient populations in Southwark, London and Avonmouth since 1884, and has undergone a drastic decline in range since the 1950s (4). It also persists on Lundy Island in the Bristol Channel and the Shaint Islands in the Outer Hebrides (4).

Not legally protected in the UK. No conservation designations (3).

The future of this once devastating pest in Britain is now uncertain. Improved hygiene and control measures on ships makes further introductions highly unlikely, and control measures such as poisoning with rodenticides are ever-prevalent, particularly close to human habitation, where this species occurs (4).

Widespread.

Non-native, resident.

Although not generally viewed fondly by humans, Black Rats are welcome at the Karni Mata Temple in northern India, where the rats are treated as sacred.