Field vole  (Microtus agrestis)

Not legally protected in the UK. No conservation designations (3).

Like all voles, the field vole has a small, stocky body and a blunt, rounded muzzle (4). The fur is greyish-brown on the upperparts, and creamy-grey below. The rounded ears are covered with fur, and the eyes are less obvious than in mice (2).

This species is believed to be the most numerous of the British mammals; it has a wide albeit patchy distribution throughout Britain. They are not present on the Scilly Isles, Orkney, Shetland or Lundy Island (5). This vole is also widespread throughout central and northern Europe (5).

Inhabits ungrazed grasslands, with plenty of vegetation cover (5). Main habitats include meadows, the margins of fields, and forestry plantations, but they may also be found in hedgerows, dunes, open moorland and blanket bogs (5).

Although active throughout the day and night, this vole is most active at dusk (5). It feeds primarily on the stems and leaves of grasses (5). Males defend territories, whereas females do not (5). Breeding typically takes place between April and September, but births may occur throughout the year when conditions are good (5). Between 2 and 7 litters are produced each year, each consisting of 4-6 young. Sexual maturity is reached at 40 days in males, and 28 days in females (5). Most predatory birds and mammals take field voles; indeed this species is a very important component of the diet of many of Britain's birds of prey, so much so that creation of grasslands suitable for field voles has been shown to boost populations of kestrels (Falco tinnunculus) and barn owls (Tyto alba) (4). The maximum lifespan for field voles is 18 months, although very few individuals survive to reach their second autumn (5). When it occurs in high densities, the field vole can be a pest in grasslands, young plantations and crops (5). Although there are few data to show populations sizes of field voles, there is a general belief that populations may have been declining since 1970 (5).

Overgrazing, reductions in the amount of rough grassland, development, scrub growth and removal of linear features such as hedgerows, all impact negatively on this vole. Furthermore, poisoning by rodenticides is also a threat (5).

The precise status of the field vole is not clear at present. Although a common species, it may well have declined, and its importance as a food source for predatory birds makes it more pertinent that its status should be assessed (5). Conservation measures and the maintenance of biodiversity are important, even though this vole is common. The creation of grassy field margins and set-aside areas encourages this species (2), and has the added bonus that birds of prey also benefit (4).

For more on this species see The Mammal Society, field vole fact sheet:
http://www.abdn.ac.uk/mammal/field_vole.shtml

• Biodiversity: short for biological diversity, biodiversity is a term used to define the great diversity of life on earth. For more on biodiversity see the IUCN's Biodiversity is Life website at http://www.iucn.org/bil/whatis.html

1. National Biodiversity Network Species Dictionary (May 2002) http://www.nhm.ac.uk/nbn/
2. The Mammal Society, field vole fact sheet. (August 2002) http://www.abdn.ac.uk/mammal/field_vole.shtml
3. The Environment Agency (1998) Species and Habitats Handbook. The Environment Agency, Bristol.
4. Buisson, R. (2001). Habitat Management News. British Wildlife12 (4): 272.
5. Macdonnald, D. W. & Tattersall, F. T. (2001) Britain's mammals- the challenge for conservation. The Wildlife Conservation research Unit, Oxford University. www.wildcru.org