The Mammal Society

For Evidence Based Conservation

Water Vole – Arvicola amphibius

 
 
Habitat: Rivers and wetland, mixed woodland.
 
Description: Rat-sized with blunt nose; dark chestnut-brown to black fur; short rounded ears; hair-covered tail, which is about half length of head and body.
 
Size: 14-22cm; tail 9.5-14cm
 
Weight: 150-300g
 
Lifespan: 5 months on average. Maximum longevity in captivity is 2.
 
Origin & Distribution: Native. The water vole is found throughout Britain, though it is less common on higher ground. It is infrequently recorded from parts of northern Scotland and is absent from Ireland. Water voles occur mainly along well vegetated banks of slow flowing rivers, ditches, dykes and lakes.
 

Water vole distribution (in green), taken from ‘Britain’s Mammals 2018: The Mammal Society’s Guide to their Population and Conservation Status.’

  
Diet: They eat grasses and waterside vegetation: 227 plant species have been identified in their diet, and additional broadleaved plants may also be eaten at certain times.
 
General Ecology: Water voles occur mainly along well vegetated banks of slow flowing rivers, ditches, dykes and lakes. They are sometimes confused with brown rats which often also live near water courses. Water voles excavate extensive burrow systems into the banks of waterways. These have sleeping/nest chambers at various levels in the steepest parts of the bank and usually have underwater entrances to give the animals a secure route for escape if danger threatens. “Lawns” of closely cropped grass, occasionally with piles of chopped food, may surround burrow entrances. Water voles tend to be active more during the day than at night. Male voles live along about 130 metres of water bank, while females have ranges about 70 metres long. They deposit distinctive black, shiny faeces in latrines. Latrines occur throughout and at the edges of their range during the breeding season.
 
Breeding: Water voles usually have three or four litters a year, depending on the weather. In mild springs the first of these can be born in March or April, though cold conditions can delay breeding until May or even June. There are about five young in a litter, which are born below ground in a nest made from suitable vegetation, notably grasses and rushes. Although blind and hairless at birth, young water voles grow quickly, and are weaned at 14 days.
 
Conservation Status: Water voles are legally protected in Britain. Recent evidence indicates that water voles have undergone a long term decline in Britain, disappearing from 94% of their former sites. Predation by the introduced American mink has had a severe impact on water vole populations, even causing local extinctions. Habitat degradation and pollution are also thought to have contributed to the decline of the water vole. Predator exclusion, bank side management and pollution control provide viable tools for sustaining local populations. Water voles are also probably affected by poor water quality, both directly through contamination of water bodies with pollutants and indirectly through eutrophication, the build up of nitrogen levels in water which causes algal blooms and loss of their food plants.
 

Identification

Rat-sized with dark chestnut-brown/black fur. Blunt muzzle and short rounded ears. Hair-covered tail about half the length of head and body. Makes a characteristic ‘plop’ when entering the water. Swims with much of the body showing above the surface but may also swim totally under the water.

Field Signs
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Droppings: Water vole droppings are particularly distinctive as they are often described as having a tic-tac shape—no other mammal has droppings comparable to the water vole. Droppings are usually found in latrines and in small heaps close to water. Width 8-12mm, 4-5mm thick. Variable in colour – usually dark green when broken up. Odourless.

Feeding signs: Nibbled stalks of grass in small piles along tunnels in long grass indicate the presence of water voles. However, field voles and bank vole do leave similar feeding signs, so always look for supporting evidence, ideally droppings. Water voles can be seen during the day feeding on grasses and reeds, sitting on their hind feet and holding a stalk in front of their paws. They will bite the grass at 45 degree angles, as shown in the photo.

Confusion species

Brown rat (Rattus norvegicus)
Grey/brown coat on top with grey underside, compared to chestnut brown colour of water vole. More pointed muzzle than water vole, which has more of a blunt muzzle. Hairless tail, 90% length of body, proportionately longer than water vole’s, which is 60%. Rat ears are bigger and much more prominent than water voles, which are very subtle, usually covered by fur.

Field vole (Microtus agrestis)
Much smaller than water vole, with head and body length of 9-12cm, compared with 14-22cm for water vole. Yellowish or grey/brown, much lighter than water vole which has darker chestnut brown fur. Tail shorter than water vole tail, only 30% length of head & body, whilst water vole’s is 60%.

Bank vole (Myodes glareolus)
Bank vole much smaller than water vole with head and body length of 9-11cm compared to 14-22cm. Water vole tail is slightly longer than that of bank vole, with it being 60% head and body length compared to 50%.

 

Derek Crawley, Staffordshire Mammal Group, says:

“Water voles can be quick and very hard to see on the bank of a water course, but once they start swimming then the movement catches the eye. Here, the fact that their whole body is above the water, whereas a rat shows just the head, makes recognition easier.”

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