Water vole (Arvicola terrestris)
|Size||Head-body length: 140 - 220 mm (2)|
Tail length: 95 - 140 mm (2)
|Weight||150 - 300 g (2)|
The water vole is classified as Least Concern (LC) on the IUCN Red List (1). Fully protected under Schedule 5 of the Wildlife and Countryside Act 1981 (3) (4).
The water vole (Arvicola terrestris) is the largest and most famous of the British voles (5). 'Ratty' in Kenneth Grahame's Wind in the Willows was not a rat, but a water vole; water rat is a local name for the species (5). Water voles have a short hair-covered tail, a blunt, rounded nose, and a small chubby face with small ears. They have a rich chestnut-brown coat (2), but individuals in Scotland often have black fur. The fur traps air that provides thermal insulation when swimming, and they also possess flaps of skin in the ear that prevent water from entering (5).
The water vole is widely distributed throughout Europe from the UK to eastern Siberia (5). It is widespread throughout Britain but is generally restricted to lowland areas beside water (2). Once a very familiar mammal of the British countryside, the population has undergone one of the fastest and most serious recent declines of any British mammal (5). The species has been in decline for many decades (6), and a national survey in 1996 to 1998 showed that the water vole had been lost from a massive 94 percent of sites (5) and had vanished from entire catchments in northeast Scotland, North Yorkshire and Oxfordshire (5).
Prime water voles sites are found along densely vegetated banks (2) of slow flowing rivers, ditches, lakes and marshes where water is present throughout the year (5).
Water voles are herbivores, feeding on a huge variety of waterside vegetation (2), and consume 80 percent of their body weight each day (5). Their burrow systems have several horizontal layers to guard against flooding (5), and there is usually an underwater entrance to provide this strong swimmer with a safe route in and out (2). Above-water entrances to the burrow can often be identified by a 'lawn' of cropped grass around the hole (2).
During the breeding season, the boundaries of female's ranges are marked with latrines, piles of flattened droppings where scent marking occurs. Each year between April and September, one to five litters consisting of three to seven blind, naked pups can be produced. Occasionally, dominant daughters may oust their mother from her territory after bouts of teeth chattering, tail beating and even boxing with the forefeet. In winter, a female, her daughters and unrelated males share a communal nest, but they do not hibernate (7).
The shocking decline in both range and numbers of the water vole is due to a number of factors. The large-scale loss and fragmentation of sensitive waterside habitats due to riverbank modification, drainage and flood defence works has been an important factor (5), as has the pollution of waterways and poisoning by rodenticides (3). Perhaps the most serious threat facing the beleaguered water vole is predation by the introduced American mink (3). When threatened, water voles often dive under water and kick up a cloud of mud to hide from predators. This does not fool the American mink, however, which is able to successfully hunt the water vole on land, in the water and even inside the burrow system. There is a correlation between the loss of water vole sites and American mink presence (5), and the introduced mink has even resulted in local water vole extinctions (2).
It is likely that the water vole will become extremely rare in areas colonised by American mink; the elimination of American mink is unrealistic, but numbers can be controlled in key areas in an attempt to ease the pressure on the water vole. Habitat enhancement such as the encouragement of a broad variety of waterside vegetation and recreation of natural features such as water meadows and oxbow lakes could benefit the species. Under the Wildlife and Countryside Act 1981, it is an offence to disturb, obstruct or damage water vole burrows. A booklet has been produced by English Nature, providing guidance on the water vole for planners and developers (8). Research into the ecology and habitat needs of this species is essential, as little work has been carried out on it due to its previously common status (3).
For more information on the water vole:
BBC Wildlife Finder:
Information authenticated by Dr Pat Morris.
- Hibernate: a winter survival strategy characteristic of some mammals in which an animal's metabolic rate slows down and a state of deep sleep is attained. Whilst hibernating, animals survive on stored reserves of fat that they have accumulated in summer. In insects, the correct term for hibernation is 'diapause', a temporary pause in development and growth. Any stage of the lifecycle (eggs, larvae, pupae or adults) may enter diapause, which is typically associated with winter.
- Territory: an area occupied and defended by an animal, a pair of animals or a colony.
IUCN Red List (March, 2011)
The Mammal Society (January, 2002)
UK Biodiversity Species Action Plan (January, 2002)
DEFRA News Release (May, 2008)
- Woodroffe, G. (2000) The Water Vole. The Mammal Society, London.
- Jefferies, D.J., Morris, P.A. and Mulleneux, J.E. (1989) An enquiry into the changing status of the Water Vole Arvicola terrestris in Britain. Mammal Review, 19: 111 - 131.
- Macdonald, D.W. and Tattersall, F.T. (2001) Britain's Mammals: The Challenge for Conservation. Wildlife Conservation Research Unit, Oxford University.
- English Nature. (1999) Water Vole: Guidance for Planners and Developers. English Nature, Peterborough.