Alternative Names (Synonyms)

• Water rat
• Water vole
• Campagnol terrestre (French)
• Ostschermaus (German)
• Schermaus (German)
• Mus terrestris Linnaeus, 1758; Upsala, Sweden
• Mus amphibius Linnaeus, 1758; England
• Arvicola ater MacGillivray, 1832; Scotland
• Arvicola amphibius amphibius (J42.81.w1).

Alternative species names (the second part of the binomial species names): [Genus] abrukensis; [Genus] albus; [Genus] americana;  [Genus] amphibius; [Genus] aquaticus; [Genus] argentoratensis; [Genus] argyropus; [Genus] armenius; [Genus] ater; [Genus] barabensis;  [Genus] brigantium; [Genus] buffonii; [Genus] cantabriae; [Genus] canus; [Genus] castaneus; [Genus] caucasicus; [Genus] cernjavskii;  [Genus] cubanensis; [Genus] destructor; [Genus] djukovi; [Genus] exitus; [Genus] ferrugineus; [Genus] fuliginosis; [Genus] hintoni;  [Genus] hyperryphaeus; [Genus] illyricus; [Genus] italicus; [Genus] jacutensis; [Genus] jenissijensis; [Genus] karatshaicus; [Genus] korabensis; [Genus] kuruski; [Genus] kuznetzovi; [Genus] littoralis; [Genus] martinoi; [Genus] meridionalis; [Genus] minor;  [Genus] monticola; [Genus] musignani; [Genus] niger; [Genus] nigricans; [Genus] obensis; [Genus] ognevi; [Genus] pallasii;  [Genus] persicus; [Genus] pertinax; [Genus] reta; [Genus] rufescens; [Genus] scherman; [Genus] seythius; [Genus] stankovici;  [Genus] tanaiticus; [Genus] tataricus; [Genus] tauricus; [Genus] turovi; [Genus] uralensis; [Genus] variabilis; [Genus] volgensis (B141).

Names for new-borns / juveniles

General Appearance

Similar Species

• Differentiated from Rattus norvegicus - Brown rat by darker fur, rounder body, blunter muzzle, smaller eyes, smaller ears mainly hidden in fur and shorter, haired tail.
• Differentiated from other voles in Britain by much larger size.
• Juveniles differentiated from field voles by larger head and feet, and longer tail.

(B142, B155, D30)

References

Species Author

Major References

• B51, B141, B142, B143, B144, B147, B155, B221
• D30

Husbandry references:

• Wildlife and Countryside Directorate, Department of the Environment, Transport and the Regions (DETR)
• The Mammal Society
• Mammals Trust

• British Mammal Factsheets

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

Parent Group

• Voles (Rodents)

Specific Needs Group referenced in Management Techniques

• Voles (Rodents)

Husbandry Information

Notes

• Accommodation of Casualty Mice & Voles
• Hand-rearing Mice & Voles
• Catching and Handling of Mice & Voles
• Feeding of Casualty Mice & Voles
• Release of Casualty Mice and Voles

Measurement & Weight

• 5.6-8.0in./14-20cm (B144); 120-260mm (D30).
• Males 121-261mm; females 119-247mm (B142).

• First litter of the year: 160g by 5 weeks old; second litter 160g by 12 weeks old (County Durham) (B142).
• 42g at 3 weeks, 120g at about 3.5 months (B155).

Head

Skull: Nuchal crest develops over first winter (B142).

Nose: Blunt.

Ears: Small.

(B142, B155)

• Upper incisors large, orthodont. Enamel on outer surface bright orange.
• Molars high crowned and rootless - grow throughout life.

(B142, B147, B155)

Legs and Tracks

• Four toes from fore feet tracks, five on hind feet (B142).
• Hind Foot length: males 26-42mm, females 25-41mm (B142).

Tail

• Length 60% (55-70%) of head-body length. 
• Lightly haired

(B142, B155, D30).

• Length: 2.4-4in./6-10cm (B144); Males 82-174 mm, females 80-161mm (B142).

Coat / Pelage

• Dorsal: red-brown, medium-brown, dark brown or black. Grades to:
• Ventral: paler: grey-white/brownish-white/greyish-ochre.
• Long glossy guard hairs.

(B142, B155, D30)

• Melanic form: proportion of individuals with black fur varies between populations: common in Scotland.
• Partial albinism: (white patches), most often white patches on tail tip, forehead. Also occur on chest, front paws, flanks, shoulders.
• Older animals: fur thin and greyish after second winter and no spring moult.

(B142, B147, B155)

• Autumn moult (main moult) in adults and juveniles.
• Spring moult after first winter.
• No moult if survive second winter: fur becomes thin.

(B142, B147)

Neonate (New-born) Characteristics

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

• Reproductive: Four pairs of nipples in females (B147).
• Scent glands: flank glands in both sexes (B147)

Natural Diet

• Green and subterranean parts of grasses and sedges, also tree roots and bark.
• Grasses (Graminae), sedges (Cyperacae), Phragmites australis - common reed, and Ranunculus fluitans - river crowfoot) commonly eaten.
• Grasses usually only growth meristem eaten, but whole of young shoots may be eaten.
• Rushes and dicotyledons such as Urtica dioica - Nettle and Lamium album - Dead-nettle eaten less commonly.
• Insects, molluscs (freshwater mussels and snails), fish (carrion) taken only exceptionally.
• More reeds and rhizomes eaten by adults than by juveniles.
• Fruits eaten in winter, with apple a preferred food
• Tree roots, tree bark, herbaceous roots, bulbs and rhizomes eaten in winter.
• Hay (kept green in burrows) also eaten in winter
• Eat about 80% of body weight per day.

(B142, B143, B144, B147, B155)

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

• 8-12mm long, cylindrical, blunt-ended, often greenish.
• Left in latrines marking range boundaries and at water edge and near burrows.

(B142)

Feeding Behaviour

• Feed while sitting on hind legs, holding food in forefeet.
• Often leave piles of grass and reed stems when only nodes and stem bases eaten.
• Harvest hay in autumn, keep in burrows for winter.

(B142, B155)

Parental Behaviour

Social Behaviour / Territoriality

• Variations with season and population density.
• Larger home ranges for males than females.
• Smaller home ranges for juveniles, except for young males moving between females's territories.
• Winter ranges smaller than breeding ranges
• Communal nests in winter: female, daughters and unrelated males
• Spring: fights, with losers dispersing.
• Males fight more aggressively than do females.
• Breeding females defend exclusive territory
• Territory of breeding females marked with latrines, which mate then scent-marks
• Males disperse by four months old, moving between territories of females, then settle.
• Dominant daughters settle within territory, subordinate daughters disperse.
• Adult females may disperse following fights with daughters (even while pregnant).
• Males mark territories using flank gland secretions.
• Populations may be 20-114 per kilometre along waterway (B155).

High population density differences:

• Home ranges of males and females smaller.
• Female home ranges overlapping and undefended.
• Fewer fights between breeding females.
• Less overlap between home ranges of males.

Fossorial populations:

• Fluctuate 0-1000 individuals per hectare, in 5 to 8-year cycles.(B143); 46 year cycles (B147).

(B142, B143, B144, B147, B155)

Sexual Behaviour

• Females have only single mate throughout breeding season.
• Male may have two or three mates during breeding season.
• Some males have no mate.
• Male grabs female by scruff during copulation

(B142, B155)

Predation in Wild

• Avian predators include Ardea cinerea - Grey heron, Tyto alba - Barn owl, eagle owl, tawny owl, marsh harriers.
• Mammalian predators include Mustela erminea - stoat, Mustela nivalis - weasel, Mustela vison - mink, otters, domestic cats, Vulpes vulpes - Red fox, Meles meles - Badger.
• Rats take nestlings and juveniles.

(B142, B155)

Activity Patterns

• Use runways, remembering direction of runway.
• Good and frequent swimmer.
• Dive well.
• Jump well.
• Juvenile males disperse on runways on land.
• Juvenile females usually disperse by swimming.
• Away from water, use burrow systems.
• Able to climb in trees to feed.

(B142, B144, B155).

• Active about every 2 to 4 hours.
• More active in daytime in some areas.
• Less active in middle of night on cold nights.
• Less active in middle of day on hot days.
• Out of nest about 25% of time over 24 hours, and longer (peaking at 38%) during breeding season.
• Active all year, but spend more time in burrows in winter.

(B142, B155)

General Habitat Type

• Mainly lowlands.
• Densely vegetated ditch, dyke, river and stream banks, usually with slow currents and continuous presence of water.
• Less common on ponds.
• Require certain depth of water: do not use very shallow areas .
• Also away from water, living mainly below ground in burrows.
• N.B. Away from water more commonly in continental Europe than in Britain.

Fossorial populations:

• Dry and mesic grasslands: meadows, pastures.
• Occasionally wooded areas.

(B142, B143, B144, B147, B155)

Nests / Burrows / Shelters

• Make complex burrow systems.
• Nest within burrow system.
• If water table high, may nest in tussock sedges.
• Sometimes plug exits from nursing chambers with loose soil or with grass.
• Rarely build nests of large balls of reeds or grass above ground.
• Burrow may average 40.2m long, with one or two nests, also with storage chambers in autumn and winter.

(B142)

Distribution and Movement (Migration etc.)

• Palearctic: Great Britain to eastern Siberia (Lena Basin), and from Arctic circle to Lake Baikal, north of Aral Sea, northern Iran, Near East.
• In Britain: Throughout mainland Britain, and on Bute, Anglesea, Isle of Wight.
• Not present: Ireland, western and southern France, southern Iberian peninsula, southern Greece.
• Not found at very high altitudes in Alps.

Migration:

Some populations migrate, e.g.:

• a population in north-west Scotland, wintering on higher ground.
• German and Russian populations, seasonally moving from wet to dry habitats.

(B51, B142, B143, B155)

--.

Intraspecific variation

• Large number of subspecies described (at least 36).
• Polymorphic.
• Aquatic populations larger (150-300g) and more commonly dark furred.
• Fossorial populations smaller (60-150g), more commonly pale furred and with incisors more protruding. Found in Carpathians, Alps, Massif Central, Pyrénées, north of Spain, north of Portugal.

(B143).

Conservation Status

• Under threat in western Europe: Britain, Italy, Netherlands.
• In Britain: disappeared from 70% of sites by 1993, and decline continuing (B155, D30, V.w30)
• Fossorial populations may cause agricultural damage at high densities (B147).
• In Britain: native, and declining but still moderately common (1995). Pre-breeding population estimate of about 1169,000, with 752,000 in England, 376,000 in Scotland, 41,000 in Wales. Population estimate of this widely-distributed species was based on a limited amount of data and considered likely to be inaccurate by up to 50% in either direction (B221).

• This species is listed on Schedule 5 (Protected animals) of the LUK2 - Wildlife and Countryside Act 1981 of the United Kingdom. (W5.Oct01) (Section - 9(4)(a) and (b) "damaging etc. a place used for shelter" and disturbing an animal while occupying a structure or place of shelter" only)