THE WATER VOLE Arvicola terrestris

 

Recognition:

Rat-sized with blunt nose; chestnut-brown fur; short rounded ears; long hair-covered tail.
Head/body length: 140-220mm; tail 95-140mm.
Weight: 150-300g.

General Ecology:

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 Ireland. It is usually found near open water and dives and swims with great ease. Water voles are sometimes confused with brown rats which often also live near water courses. Indeed, it is sometimes called "the water rat", which is the origin of the water voles' fame as "Ratty" from Kenneth Grahame's book The Wind in the Willows.

Water voles occur mainly along well vegetated banks of slow flowing rivers, ditches, dykes and lakes. They eat grasses and waterside vegetation: 227 plant species have been identified in their diet, though other broadleaved plants may also be eaten at certain times. 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.

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. On average, water voles only live about five months in the wild. Their most important predators are mink and stoats; though herons, barn owls, brown rats and pike are also known to take them.

Conservation:

Water voles are not legally protected in Britain. On the continent they behave quite differently, living away from open water and are regarded as serious agricultural pests. In Britain, water voles occasionally undermine river banks, but otherwise they are harmless and cause no damage.

Recent evidence suggests that water voles have undergone a long term decline in Britain. On current trends it is predicted they may eventually disappear from 94% of their former sites, a decline exceeding even that for the otter.

Predation by the introduced American mink is thought to have a severe impact on water vole populations, even causing local extinctions. This may be because their usual way of evading predators, by diving and using burrows with underwater entrances, does not protect water voles from the mink. Removal of mink is unrealistic for large areas but can be carried out locally in nature reserves and along key sections of rivers to protect remaining water vole populations.

Habitat degradation and pollution are also thought to have contributed to the decline of the water vole. Riverside works such as dredging and clearance of bankside vegetation removes large amounts of the plants water voles depend on for food and causes disturbance. A more sensitive approach to riverbank management needs to be encouraged to protect water voles. Dredging and other work should be scheduled so it does not affect both banks simultaneously and retention or planting of bankside vegetation carried out wherever possible.

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 water vole food plants.

Frequent Questions:

How do I distinguish water voles from brown rats?
The ears of the water vole are hardly visible, unlike those of the rat which stand out. The tailed is furry whilst that of the rat is naked. The muzzle of the water vole is blunt, not pointed, its fur is more red and the tail is shorter. When disturbed they dive with a marked "plop".

What are the main field signs of water voles?
They leave characteristic tracks in mud flats close to the water. The forefoot has four toes which leave a distinctive star shaped pattern, while the hind foot has five toes with the first and fifth toes leaving prints almost at right angles to the three central toes.

Further Information:

 

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