North American water vole

The North American water vole or just water vole (Microtus richardsoni) is the largest North American vole. It lives in the northwestern United States and southern parts of western Canada. This animal has gray-brown or red-brown fur with gray under parts, and its large hind feet help it swim very well.

Water voles enjoy eating grasses, leaves, roots, seeds, and small invertebrates. They dig burrows connected to water sources, making them semi-aquatic creatures. These burrows often open at the water's edge or underwater, and water voles usually live together in groups along waterways.

They stay active all year, even tunneling through snow during the winter months. Because their populations are very small and their habitat may be disappearing, water voles are considered a sensitive species.

Etymology

The word "vole" started being used around 1805. It is a shorter way to say "vole-mouse," which means field mouse. The word comes from a Norwegian word, "vollmus," where "voll" means field and "mus" means mouse. It might also have been influenced by a Swedish word, "vall," which also means field.

The scientific name Microtus richardsoni has many common names, such as Richardson's water vole, Richardson vole, and giant water vole. This name honors a Scottish naturalist named Sir John Richardson.

Taxonomy and evolution

This animal was once thought to belong to a group called Arvicola, but tests show it is closer to North American Microtus animals. The closest relative of Microtus richardsoni seems to be Microtus pennsylvanicus, known as the meadow vole. Old bone evidence suggests that M. richardsoni split from an ancient group in Siberia long ago. Today, about 60 species are recognized in the Microtus group.

Appearance and anatomy

Water voles have big hind feet that help them swim fast. Males are usually bigger than females. They are about 20–27 cm long, including their tails, which are 6–10 cm long. They weigh between 125 and 178 grams. Their fur can be grey-brown, dark brown, or reddish-brown on top and grayish-white on the bottom. They have large teeth and strong jaws, which help them dig tunnels and chew through tough plants. They are the second largest arvicoline in their area, after the muskrat.

Behavior and ecology

Water voles live in groups in western United States and Canada, from British Columbia and Alberta through parts of Oregon, Washington, Montana, Idaho, Wyoming, and Utah. They like areas near water in mountains and meadows, usually between 914–3,201 meters high. Their homes change because of forests and valleys, but they can move over land to find other groups.

These voles mostly eat plants like leaves, stems, grasses, and willows, and sometimes seeds or insects. They need to eat a lot because they use a lot of energy. In winter, they dig tunnels under the snow and stay below the surface when there is about 6 cm of snow. They are mostly active at night and make small paths through plants to move around. During summer, they build tunnels and nests under plants where the mothers care for their babies.

Water voles live near water and have groups where females stay in one area and males move around to find mates. Males are usually more aggressive, especially during breeding time. They breed during the summer, and females can have about 5-6 babies at a time after a short pregnancy. The babies are born without fur and can’t see, but they grow quickly, getting fur in a few days and learning to swim in about two weeks. Mothers nurse their babies for three weeks, and the young stay with their mother for about a month before moving out on their own. Most babies grow up to have their own families the next breeding season.

Life span

Water voles usually only live through one winter. Most of them die by the end of the next breeding season. Very few see a third winter.

Loss of habitat and endangerment

Scientists study where water voles live to learn how things like rain and animals affect their numbers. More rain gives water voles more space and helps them have more babies. But when animals like cows eat grass nearby, it can hurt the voles.

Light or moderate grazing means fewer baby voles survive and groups get smaller. In places with very heavy grazing, the stream banks can get damaged and are no longer a good home for voles.

Livestock can change the land in harmful ways. They can press down the soil, cause more water to run away, and damage the plants voles need for food and shelter. Plants like ferns, mosses, and shrubs help protect voles, but these plants often disappear when livestock graze, making it hard for voles to survive.