some of the birds that feed on the common vole and so delimit population sizes. Ground-predators are mainly weasel, stoat, adder, polecat, fox and boar. Territories and nests M. arvalis maintains aboveground runways, which expand like a railway-system through the entire home range. Voles are seldom seen outside these runways, which enable a faster and safer locomotion and easier orientation. The climbing ability of the common vole is very poor. Underground nests are dug 30 to 40 cm deep into the ground and are used for food storage, offspring raising, and as a place for rest and sleep. Nests can be shared and defended by up to five females with juveniles that are related in most cases. Females are territorial and an overlap of occupied areas does not occur. Hence, the number of colonies increases with individual number (i.e. population density). As common voles have a polygynous mating system the males do not maintain territories and move as so-called "floaters" between several females' territories in order to mate as often as possible. They can show overlap in territories. These findings are supported by the different home range sizes of males (1200–1500 m2) and females (300–400 m2) that can decrease in both males and females as population density rises. Another response to population growth is to leave the original habitat and move towards another one. Males predominantly conduct dispersal, being most often caused by the competition for mates. See also Orkney vole 2007 vole plague in Castile and León References Baillie, J. 1996. Microtus obscurus. 2006 IUCN Red List of Threatened Species. Retrieved 9 July 2007. Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. pp. 894–1531 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore. Niethammer, J. and Krapp, F. 1982. Handbuch der Säugetiere Mitteleuropas. – Akademische Verlagsgesellschaft Wiesbaden External link Microtus Mammals of Asia Rodents of Europe Mammals of Russia Mammals of Central Asia Mammals of Azerbaijan Mammals of Turkey Vole, Common Mammals described in 1778