Water Vole – Arvicola terrestris
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: 140-220mm; tail 95-140mm
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.
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.