The Field Vole (Microtus agrestis)
FACTS AND FIGURES
Recognition: Grey-brown fur above, creamy-grey fur below, has tail much shorter than the bank vole, and fur is shaggier, covering the ears. Rounded snout, less prominent eyes than mice and ears are furry. Head/body length: 90-115mm; tail is <40% of head and body. Weight: 20-40g. Lifespan: The average life span of a field vole is up to 1 year. Diet: Grass is the field voles' major food source, with bents, fescues and hair grasses being preferred.
Field voles are found throughout mainland Britain and remains date back to before the end of the last glaciation, 11000 years ago. They are absent from a number of islands including Shetland, the Isle of Man, Isles of Scilly, Lundy and Ireland; they are replaced by larger Orkney and Guernsey voles on the respective islands. The field vole occurs typically in ungrazed grassland or in the early stages of forestry plantations but may also live in woodland, hedgerows, dunes, scree or moorland, wherever grass is available. Shredded grass leaves are used to make their nests which are about 10cm in diameter and may be built at the base of grass tussocks, in underground burrows or even under sheets of corrugated iron. The breeding season begins in March/April and ends between October and December. Four or five young are normally found in each litter and females will give birth to five or six litters each year. Although this gives rise to large numbers, population turnover is rapid. Voles do not hibernate but moult to cope with the inevitable change in temperature with the seasons. Moulting provides a dense layer of fur for winter and a "lighter" coat in spring. Like all small mammals, the field vole is host to a number of parasites, carrying fleas and possibly ticks and worms. It must be particularly careful to avoid predators which include kestrels and owls, together with foxes, weasels and stoats. The number of young reared by kestrels and owls has been shown to increase when vole numbers increase. In extensive grasslands, field vole populations may fluctuate on a 4-year cycle with numbers increasing tenfold between the lows and highs.
Field voles are very widespread and are currently thought to be the most common British mammal; a recent population estimate put the number of field voles in Britain at 75,000,000. They occur at densities of 100/ha in spring. Although the field vole is numerous, it is still important to consider conservation methods and maintain biodiversity within habitats, not least because field voles are so important to owls and other predators. Leaving wide field margins beside hedgerows provides cover and food which will encourage and maintain populations. Long grass on roadside verges is also important. A varied woodland area will encourage small mammals and groups of branches should be left when clearing patches of ground.
Gurnell, J & Flowerdew J.R. (2006) Live Trapping Small Mammals: A Practical Guide. The Mammal Society, Southampton. Harris, S. & Yalden, D.W. (2008) Mammals of the British Isles: Handbook (4th edn.) The Mammal Society, Southampton.