Arvicola amphibius
Eurasian water vole
(Also: European water vole)

Water voles (Arvicola terrestris) inhabit the Paleartic region, spanning most of central and western Europe, Siberia, Mongolia and some parts of southwest Asia (Nowak, 1991).

Water voles live in the banks of rivers, streams, ponds, and other bodies of water that maintain a fairly constant water level. They prefer areas with good vegetation cover. They are mainly found in lowland areas near waterways but also sometimes occur in gardens and fields. Water voles dig lengthy burrows, ranging from 34 m in the winter up to 74 m in the summer. Burrows contain one or two nests and in the winter contain storage chambers for food (Niethammer, 1989; Nowak, 1991). (Niethammer, 1990)

Average male body length is 210 mm, with females averaging 187 mm. Tail length averages 124 mm in males and 116.5 in females. Males average 263 g, while females average 232 g (Thompson, 1964).

With a dense coat of fur, small, rounded ears, and short tail, A. terrestris resembles other voles of similar size. Water voles are relatively large voles. Their pelage is thick and extends from the head to the end of the tail. Coloration ranges from light to dark brown on top (sometimes black); and from white to slate gray on their underside. This coloration makes them difficult to see in the dense vegetation they prefer. Claws on each of the feet are well developed, and flank glands on the sides of the body used to mark territory are visible most of the time as well. Water voles possess the typical rodent dental formula and posses continuously growing cheek teeth (Niethammer, 1990; Nowak, 1991).

Male home ranges overlap those of several females and males continually compete for access to receptive females. Research using microsatellite analysis of genetic patterns confirmed that the mating system was promiscuous (Stewart et. al., 1999).

Arvicola terrestris undergoes one mating season per year, usually ranging from early spring (April/March) to late summer/early autumn (August/October). During this time water voles can have up to four litters with an average number of four to six young each. The gestation period is short, 21 days, and postpartum estrus and mating usually occurs shortly after birth. Newborn weight is usually 5g, with young opening eyes around 5 days, and becoming weaned 14 to 21 days after birth. Sexual maturity is reached during their first summer, if born early in the season, or in the following mating season (Bazhan et al., 1996; Nowak, 1991). Females may mature as early as 5 weeks of age. (Bazhan, et al., 1996; Nowak, 1991)

While males sometimes participate in the raising of the young, the females are the main care givers (Niethammer, 1990). The young are born helpless but rapidly develop and become independent.

Water voles are short-lived, probably suffering the highest mortality rates in their first year. They can live up to 5 years in captivity but average lifespan is less than a year in the wild.

While sometimes living in close proximity to large numbers of other individuals, water voles tend to live in smaller family units, usually comprised of several individuals. Usually present in these family units is the adult generation and up to two generations of young (Niethammer, 1990; Nowak, 1991).

Water voles are mainly active during the day or during dusk and dawn. In addition, water voles tend to limit the extent of their activity to a set range. Some accounts list the maximum "home range" as being 200 square yards, while other experiments have shown the range to extend up to 300 square yards or more from the burrow (Thompson, 1964).

Territories are delimited by scent marking using the flank glands. In marking the territory, these voles wipe the flank glands with their feet, and then proceed to stamp the ground (Niethammer, 1990).

Other behaviors of water voles include the building of latrines for defecation. There is also some reason to believe that latrines serve a dual purpose during mating season of helping to mark territory (Woodroffe, 1990).

The diet of Arvicola terrestris is comprised mainly of various forms of vegetation. This includes different types of grasses, herbs, and sometimes fruits and seeds. Water voles also feed on the roots of some plants, causing extensive root damage and sometimes destruction of crops. In addition to vegetation, water voles will sometimes supplement their diet with water snails, freshwater mussels, and mollusks (Cobet, 1966; Thompson, 1964).

In the winter, water voles usually maintain at least one chamber in the burrow as a place to store grasses and other food to feed on during lean winter months. They do not live entirely off this store, and will still forage for food during the winter (Nowak, 1991).

Common foods eaten include: reed grass, reeds, flote-grass, water snails, freshwater mussels, grasses, sedges, rushes, mollusks, dandelions, cattail, soft grass, moor grass, water milfoil, water crowfoot, herbs, twigs, buds, bulbs, fallen fruit (Thompson, 1964; Niethammer, 1990; Nowak, 1991).

Water voles seek safety in their burrows and restrict their movements mainly to areas of dense vegetative cover to avoid predation. Their prodigious reproductive rates generally help to maintain viable populations under predation stress by natural predators. However, non-native American mink (Mustela vison) are decimating water vole populations in the British Isles.

Water voles are an important prey base for many small to medium-sized predators. They are also important in nutrient cycling through their burrowing and grazing activities in the ecosystems in which they live.

Although their economic benefit is somewhat limited, in some regions (such as that once occupied by the former Soviet Union), water voles are hunted for fur. (Niethammer, 1990)

Negative economic impacts from A. terrestris on humans stems mainly from the destruction of human crops such as beans, peas, and some forms of apple trees (Niethammer, 1990). In rare circumstances they have also been known to weaken river banks due to their extensive burrowing (Thompson, 1964)

In addition to crop damage and bank damage, A. terrestris is also known to sometimes carry and transmit tularemia. The disease affects mostly wild rodents and rabbits, but can be transmitted to humans by contact with animal flesh or tick bites (Nowak, 1991; WebMD, 1999).

Some humans have attempted to take actions against water voles in efforts to minimize damage to crops (Neithammer, 1990). However, water voles are on the decline in some regions. For example, in England changes due to habitat and introduction of American mink, Mustela vison, is thought to be playing a large role in the decline of water vole populations (Storey, 2001). Conservation efforts are underway in various parts of the British Isles to protect water vole populations.

One interesting piece of information is that water voles (sometimes also known as "water rats") are thought to be the inspiration for the character of "Ratty" in the British novel "The Wind in the Willows" by Kenneth Grahame (Mammal Society, 2001).