The water vole (Microtus richardsoni) is the largest North American vole. It is found in the northwestern United States and southern parts of western Canada. This animal has been historically considered a member of genus Arvicola, but molecular evidence demonstrates that it is more closely related to North American Microtus species. Water voles are on the USDA Forest Service Region 2 sensitive species list because they maintain very small populations and there is high concern that their required habitat may be declining. These animals have gray-brown or red-brown fur with gray under parts. Their large hind feet help make them excellent swimmers, and they are found in alpine or semi-alpine meadows near water. They feed on grasses, leaves, roots and seeds, also eating small invertebrates. Water voles dig burrows that are connected to water sources, and are considered a semi-aquatic species. They are active year-round, tunneling through snow during the winter. Their burrows often have entrances at the water's edge or under water, and they usually live in colonies of 8-40 individuals along the waterway. Etymology 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. 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 would lead us to believe it is the primitive form of the genus Microtus, and that the morphological similarities between M. richardsoni and Arvicola are likely convergent traits. Approximately 62 species are now considered to be in the genus Microtus''. Appearance and anatomy Water voles have unusually large hind feet, ranging between 25 and 34 mm in length, which can help distinguish the water vole from other similar rodents, and contribute to its speed in the water. Males