North American water vole

The word vole originated in approximately 1805, and is short for vole-mouse, which means field mouse. Vole originated from the Norwegian word vollmus; voll, meaning field, and mus, meaning mouse. It is also possible that there were influences from Swedish vall, which translates to mean field. Microtus richardsoni is also known as Richardson's water vole, Richardson vole, Richardson's meadow vole, Richardson meadow mouse, water rat, big-footed mouse, giant water vole, and water vole. The specific name is after Scottish naturalist Sir John Richardson. == Taxonomy and evolution ==

Although this animal has been historically considered a member of genus Arvicola, molecular evidence demonstrates that it is more closely related to North American Microtus species. Genetic tests have been done that suggest that the closest relative to Microtus richardsoni is Microtus pennsylvanicus (the meadow vole). Paleontological evidence suggests that M. richardsoni diverged from a Mimomys ancestral form in Siberia approximately 1.5 million years before Arvicola evolved in Europe. This could indicate that it is the primitive form of the genus Microtus, and that the morphological similarities between M. richardsoni and Arvicola are likely convergent traits. Approximately 60 species are now considered to be in the genus Microtus. == Appearance and anatomy ==

Water voles have unusually large hind feet, ranging between in length, which can help distinguish the water vole from other similar rodents, and contribute to its speed in the water. Males tend to be larger than females. On average these animals are about in total length (including the tail), with tails long, and weigh . The water vole is the second largest arvicoline in its range (after the muskrat). Their fur is grey-brown, dark brown, or reddish-brown on the upperparts, and is grayish-white on their underside. The water vole's large incisors, combined with its very large skull and well developed zygomatic arch (which strong chewing muscles attach to), contribute to its ability to efficiently dig tunnels and chew through tough roots. == Behavior and ecology ==

Habitat and feeding Water voles live in two distinct bands through the western United States and Canada, extending from British Columbia and Alberta through parts of Oregon, Washington, Montana, Idaho, Wyoming, and Utah. They are found in alpine or semi-alpine meadows near water, usually between in elevation. The distribution of habitats is found to be extremely variable, due to the geographical barriers of large coniferous forests, mountains, and expansive valleys without readily available waterways. Their main source of food is vegetation, including leaves, stems, grasses, sedges, willows, and sometimes seeds or insects. Their food source varies significantly depending on geographic location. Studies have shown that water voles have a very high metabolic rate, and therefore have to consume more food than other rodents their size. Most often, water voles feed on the subterranean portion of plants, which are available to them year round. There is no evidence that they store food for the winter. During the winter they are seen to dig tunnels through the snow, and usually do not surface above the snow once have accumulated (approx. 7 to 8 months of the year). This may be due to the very short breeding season compared to other rodents who breed for 6 months or more. Birthing and parental care Newborn voles are naked and blind, and weigh about 5 g. They are able to vocalize immediately, and within 3 days start to show fur. By day 10 they are running and climbing, and by day 17 they are swimming on their own. Mother feeds them by lactation until they are 21 days old, and they nest together for approximately 32 days, during which time the pups are growing about 1.24 grams per day. Evidence shows that although they may still be nesting with their mother, she provides very minimal parental care after weaning. Around the time they reach 40 days of age, they move to their own nests and about 3 weeks later reach sexual maturity. Approximately 26% of young males and females begin to reproduce during the breeding season of their birth, but overwintered adults are responsible for most of the reproduction. Some adult females may have up to two litters during one breeding season. Among overwintered adults, 90% of females and 100% of males are reproductively active. == Life span ==

The age distribution studied among populations show a 1:1 replacement of adults by young. Most water voles only live through one winter, and die at the end of the second breeding season. Very few adults survive two winters. == Loss of habitat and endangerment ==

There have been several studies done on the habitat of the vole, given its very specific requirements, to find out if grazing or precipitation levels affect the vole populations so that we can protect them. It has been found that higher precipitation levels create increased availability of usable habitat for water voles. In years of that are wetter than usual it has been observed that young water voles become reproductively active sooner, and therefore can have more offspring. The mean number of pups in each litter increased as well. The abundance of ferns, mosses and shrubs are imperative as ground cover to protect water voles from predation, and in areas of grazing these plants were scarce or non-existent, and therefore water voles weren't often found in these areas. ==References==