Field vole  (Microtus agrestis)

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).