Living Organisms / Animalia / Craniata / Mammalia / Rodentia / Muridae / Rattus / Species
Rattus norvegicus - Brown rat (Click photographs/illustrations: full picture & further details)
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INFORMATION AVAILABLE

GENERAL & REFERENCES

APPEARANCE / MORPHOLOGY

LIFE STAGES / NATURAL DIET / PHYSIOLOGY

BEHAVIOUR

HABITAT & RANGE

CONSERVATION

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General and References

Alternative Names (Synonyms)

  • Norway Rat
  • Common Rat
  • Rat d'egout (French)
  • Surmulot (French)
  • Rat surmulot (French)
  • Wanderratte (German)

Names for new-borns / juveniles

Pup
Names for males  
Names for females  

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General Appearance

Typical rat with pointed muzzle, large eyes, large ears and long naked tail (D30)

Similar Species

  • Distinguished from Rattus rattus - Roof rat by: smaller and haired ears, paler overall colouring and shorter, thicker bicoloured tail (B142, D30)
  • Distinguished from mice, voles and squirrels by: size, relatively pointed muzzle and long scaly tail; compared with Arvicola terrestris - Water vole, muzzle is more pointed, ears larger and tail longer (B142).
Sexual Dimorphism Sexes similar. Males generally larger than females (B142).

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References

Species Author

Debra Bourne

Major References

Husbandry references:
B142, B169.24.w24

Other References

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Click image for main Reference Section

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TAXA Group (where information has been collated for an entire group on a modular basis)

Parent Group

  • Rats (Rodents)

Specific Needs Group referenced in Management Techniques

  • Rats (Rodents)

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Husbandry Information

Notes

  • Unlike domestic and laboratory rats, even hand-reared wild rats become nervous and difficult to handle from an early age (B142).
  • Wild rodents may carry diseases transmissible to humans. Care should be taken in all handling of wild rodents. B169.24.w24
  • Wild rodents are liable to bite. B169.24.w24
  • Wild rodents are generally less stressed by indirect (e.g. being tipped gently from one container into another) than direct handling. B169.24.w24
  • Wild rodents are less stressed if handled in reduced light conditions (B169.24.w24).
  • Wild rats should be considered dangerous and never handled directly without being anaesthetised. (B169.24.w24)
  • Transfer from one cage to another may be carried out without direct contact, by quietly allowing the rat to move from the container into a strong black cloth bag, and then encouraging it out of the bag into the other container. (B169.24.w24)
  • The cloth bag should be secured tightly e.g. with a rubber band while being carried. B169.24.w24

Accommodation: wild rats will quickly chew through plastic laboratory cages. Stainless steel mesh cages (29cm x 35cm x 25cm high for an individual rat) are used for laboratory housing of wild rats, with a metal hideaway clipped onto the back of the cage and shredded paper (replaced 2-3 times a week) for bedding/concealment (B169.24.w24).

Euthanasia:

  • CO2/O2 until loss of consciousness, then increase CO2 to 100% and keep there for at least 10 minutes. N.B. neonatal rats and mice are relatively resistant to CO2.
  • Stunning
  • Decapitation
  • Lethal dose of inhalation anaesthetic e.g. halothane (B169.24.w24).

Management Techniques

  •  

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Appearance / Morphology

Measurement & Weight

Length Head-body length: up to 280mm (B142, D30)

Tail: 80-100% of head-body length (B142)

Hind foot: 40-44mm (B142).

Ear: 20-22mm (B142)

Height --
Adult weight General 500g, maximum recorded 794g (B142); usually 200-400g, few to 500g (B147).
Male --
Female --
New-born weight 5-7g (B147).
Growth rate 110mm and 40g at weaning (B142).

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Head

General --

Skull: Larger, heavier and more angular than skull of Rattus rattus  - Roof rat. May reach 54mm condylobasilar length (B142).

Nose: relatively pointed

Ears: 20-22mm long, haired.

(B142, D30)

Dentition (Teeth) --
Eyes Large, dark (B142, D30)

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Legs and Tracks

Hind feet 40-44mm (B142)

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Tail

Length just less than head-body length (80-100%). Dorsal surface dark,ventral surface lighter (B142, D30).

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Coat / Pelage

Adult Female Shaggy. variable colouration.
  • Dorsal: grey-brown.
  • Ventral: pale grey.
  • Tail: dorsal sparse, dark and ventral sparse pale

(B142, D30)

Variations (If present)
  • Melanic: - common in some populations, e.g. 1-2% of London population.
  • Albino: rare.
  • Ventral: white stripe or blaze.

(B142)

Moult --
New-born / Juvenile Juveniles to three months fur shorter, sleeker, greyer (B142)

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Neonate (New-born) Characteristics

Altricial: naked and blind (B142, B147).

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Detailed Anatomy Notes
(Summary information provided for pertinent species-specific data cross-referenced in Wildpro)

Reproductive: Six pairs of nipples (B142).

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Life Stages / Natural Diet / Physiology.

Reproductive Stages

Breeding Season May be all year if food available. Other habitats mainly summer and autumn (B142).

Usually spring and autumn peaks but some populations all year (B147).

Oestrus / Ovulation
  • Often post-partum oestrus within 18 hours of birth. (B142, B147).
  • Polyoestrus (B147)
  • Oestrus cycle 4-6 days, oestrus lasts 20 hours (B147)
Gestation / Pregnancy 21-24 days (B142); 21-16 days (B147)
Parturition / Birth --
Neonatal development
  • Birth: naked, blind
  • Six days: eyes open
  • Three weeks: weaned 
  • (B142)

15 days: eyes open, fully furred; 22 days: weaned, leave nest (B147).

Litter size
  • Varies with size of mother: average 7-8, 500g female may produce 11 but 150g female only 6 (B142).
  • 2 to 22, average 8-9 (B147).
Time between Litters / Litters per year
  • Usually up to five litters per year, rarely more (B142).
  • 1-12 litters per year (B147).
Lactation / Milk Production
  • Three weeks (B142).
Sexual Maturity
  • Females by about 11 weeks (115g). (B142); 2-3 months (B147).
Longevity
  • Usually one to two years (B142).

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Natural Diet

  • Omnivorous.
  • Starch-rich and protein-rich foods prefered, e.g. cereals.
  • Meat, fish, bones etc. may be eaten in urban environments.
  • Cereals and root crops but also e.g. brassicas in agricultural areas.
  • Also earthworms, rice grass and crustaceans on sea shores, molluscs by rivers.

(B142, B147).

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Detailed Physiology Notes
(Summary information provided for pertinent species-specific data cross-referenced in Wildpro)

Temperature --
Pulse --
Respiration --
Faeces Coarse-textured, about 12mm long, may be tapered at ends, often deposited in groups (B142).
Haematology / Biochemistry --
Chromosomes 2n = 42, FNa = 62 (B142).
Other --

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Behaviour

Feeding Behaviour

  • Opportunist.
  • May carry food to safe place before eating.
  • Sometimes hold food in forepaws while eating.
  • Hoard food.
  • New sources of food approached cautiously and initially only sampled

(B142)

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Parental Behaviour

--

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Social Behaviour / Territoriality

Intra-specific
  • Colonies made up of aggregations of smaller 'clans'.
  • Clans may be pair or male and several females defending a territory.
  • Home range and movement depends on food availability.
  • Females range less widely and defend smaller territories than males.
  • Aggression shown to strangers entering a colony.
  • Aggression within colony increases as population density increases.
  • Injuries on rump from aggressive encounters.

(B142)

Inter-specific --

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Sexual Behaviour

  • High ranking males male with several resident females and exclude other males (B147)..
  • Within packs of low-ranking animals, oestrus female followed by numerous males and mounted repeatedly (B147).

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Predation in Wild

Most predators including foxes, cats, owls, but mainly juveniles taken (B142).

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Activity Patterns

  • Urban areas: no obvious seasonal rhythm (B142).
  • Agricultural: transient rats in summer and autumn - displaced males. Increased population on farm premises in winter (B142).
  • Fast trot along familiar runs, also slower amble while searching for food.
  • Swim well, dive well.
  • Climb in buildings; rarely climb trees.
  • Dig burrows.

B142, B143.

Circadian --

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Habitat and Range

General Habitat Type

  • Urban and rural habitats - widespread (D30).
  • Adaptable, versatile. 
  • Use habitats where no or few competitors or where human activity increases food supple.
  • Farms, refuse tips, sewers, urban waterways, warehouses, also around cereal and root crops.
  • Areas with dense ground cover preferred.
  • Areas close to water preferred.
  • Use lower, damp areas of buildings.

(B142, B147)

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Nests / Burrows / Shelters

  • Usually below ground. 
  • Also use straw bales, or nest among sacks.
  • Burrows are usually 6-9cm diameter, often on sloping ground or under cover such as tree roots, flat stones. Dug earth remains as heap near entrance.
  • (B142).

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Distribution and Movement (Migration etc.)

Normal Native to north-east Asia (northern China) (B143, B147); probably originally south-east Asia (B51)
Occasional and Accidental --
Introduced Now worldwide (tropics and warm temperate) as human commensal (B51, B147); worldwide in urban areas except mainland low altitude inland towns in tropics and subtropics. Found both in cultivated areas and areas away from humans, in temperate areas and tropical islands with few indiginous competitors (B142).
  • In Europe: widespread but less in Mediterranean than further north, and sporadic in sparsely-populated areas of Fennoscandia (B143)
  • Britain: introduced in the first half of the 18th century; found everywhere except very exposed mountain areas and some small offshore islands (B142, B221)

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Conservation

Intraspecific variation

Two subspecies:
  • Rattus norvegicus norvegicus
  • Rattus norvegicus caraco (Pallas, 1779) (in Asia).

(B143)

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Conservation Status

Wild Population -
(Importance)
  • Common. Generally considered a pest. (B143)

  • In Britain: common. Pre-breeding population estimate of about 6,790,000, including 5,240,000 in England, 870,000 in Scotland, 680,000 in Wales. Population estimate was "based on a very limited amount of information for the species" although additional knowledge "may not necessarily have made a substantial difference to the estimate". Population estimates considered minimums (B221)

General Legislation --
CITES listing --
Red-data book listing --
Threats
  • Locally, improved environmental hygiene and intensive rat control measures (B221).
Captive Populations --
Trade --

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