Common Vole
Encyclopedia
The Common Vole, Microtus arvalis, is a Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

.

Distribution and habitat

The common vole is hardly restricted in means of distribution and habitat and inhabits large areas of Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...

. As Microtus arvalis followed human civilisation, primary and secondary habitats can be distinguished. The primary habitats are everything but dense forests, such as meadow
Meadow
A meadow is a field vegetated primarily by grass and other non-woody plants . The term is from Old English mædwe. In agriculture a meadow is grassland which is not grazed by domestic livestock but rather allowed to grow unchecked in order to make hay...

s, heath lands, and fallow land. The secondary habitats are mainly agricultural fields whereby shallow sloped areas are preferred. The natural food of the common vole is grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...

, but it also feeds on many agricultural crops (within secondary habitats) and here its reproduction is faster than in primary habitats.

Reproduction, demography, and predation

After pregnancy
Pregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...

 of 16 to 24 days, females give birth to 3 to 8 juveniles, weighing between 1.0 and 3.1 g. Weaning is around the 20th day. Female juveniles can be impregnated from the 13th day after birth. Hence, first birth can be given from the 33rd day. During annual reproduction, which starts in March and ends in October, females usually have three reproductive cycles. The average life span is 4.5 months, which means that most animals die after the last reproduction in October, while the latest offspring in the year survives the winter and starts reproduction the following spring. Weights can reach 51 g in males and 42 g in non-pregnant females. Sex ratio at birth is equal, but becomes female-biased as the animals mature or with increasing population density when the ratio can level off to 3:1 or even 4:1 in favour of females. These ratios depict an intense competition for female mates, which leads to higher mortality and dispersal rates among the males. Population density varies seasonally and exhibits a considerable long-term fluctuation that shows typically three-year or five-year cycles. Densities can range from 100 individuals per ha (very low level) over 500 individuals per ha (medium level) up to 2000 individuals per ha in some years. As reaction females’ reproduction can decrease or even stop. Not only influenced by population level, reproduction rate can change with the amount and quality of food and light. Self regulation (e.g. decrease of reproduction rate) has been addressed to be a response to increased population densities. However, M. arvalis is one of the main food sources of a considerable number of predators in Central Europe
Central Europe
Central Europe or alternatively Middle Europe is a region of the European continent lying between the variously defined areas of Eastern and Western Europe...

. Buzzard
Hawk
The term hawk can be used in several ways:* In strict usage in Australia and Africa, to mean any of the species in the subfamily Accipitrinae, which comprises the genera Accipiter, Micronisus, Melierax, Urotriorchis and Megatriorchis. The large and widespread Accipiter genus includes goshawks,...

, kestrel
Common Kestrel
The Common Kestrel is a bird of prey species belonging to the kestrel group of the falcon family Falconidae. It is also known as the European Kestrel, Eurasian Kestrel, or Old World Kestrel. In Britain, where no other brown falcon occurs, it is generally just called "the kestrel".This species...

, long-eared owl
Long-eared Owl
The Long-eared Owl - Asio otus is a species of owl which breeds in Europe, Asia, and North America. This species is a part of the larger grouping of owls known as typical owls, family Strigidae, which contains most species of owl...

, tawny owl
Tawny Owl
The Tawny Owl or Brown Owl is a stocky, medium-sized owl commonly found in woodlands across much of Eurasia. Its underparts are pale with dark streaks, and the upperparts are either brown or grey. Several of the eleven recognised subspecies have both variants...

, and barn owl
Barn Owl
The Barn Owl is the most widely distributed species of owl, and one of the most widespread of all birds. It is also referred to as Common Barn Owl, to distinguish it from other species in the barn-owl family Tytonidae. These form one of two main lineages of living owls, the other being the typical...

 are some of the birds that feed on the common vole and so delimit population sizes. Ground-predators are mainly weasel
Weasel
Weasels are mammals forming the genus Mustela of the Mustelidae family. They are small, active predators, long and slender with short legs....

, stoat
Stoat
The stoat , also known as the ermine or short-tailed weasel, is a species of Mustelid native to Eurasia and North America, distinguished from the least weasel by its larger size and longer tail with a prominent black tip...

, adder
Adder
Adder may refer to:Snakes:* Any of several groups of venomous snakes of the Viperidae family including Vipera berus, the common European adder, found in Europe and northern Asia...

, polecat, fox
Fox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...

 and boar
Boar
Wild boar, also wild pig, is a species of the pig genus Sus, part of the biological family Suidae. The species includes many subspecies. It is the wild ancestor of the domestic pig, an animal with which it freely hybridises...

.

Territories and nests

Microtus 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
Polygyny
Polygyny is a form of marriage in which a man has two or more wives at the same time. In countries where the practice is illegal, the man is referred to as a bigamist or a polygamist...

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.
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