Tundra Voles are one of the six mammal species endemic to Kodiak Island. Seven species of voles live in Alaska. Two belong to the genus Muridae, and the other five belong to the genus Microtus. The name Microtus means “small ear,” referring to the tiny ears that are nearly hidden in the fur. The tundra vole or root vole, (Microtus oeconomus) is the only species of vole that lives on Kodiak Island. Microtus oeconomus has the northernmost distribution of any Microtus species and exists on all northern continents. In North America, tundra voles are only found in Alaska and northwest Canada.
Tundra voles live in colonies of a few to as many as 300 individuals. They live in a variety of habitats from tundra to sedge meadows, but they favor areas with abundant cover. In grassy meadows, they build distinctive runways that crisscross the ground. They also dig burrows, complete with food and nesting chambers. Tundra voles do not hibernate and are active all winter. In areas covered with snow, voles make extensive tunnel systems, sometimes hundreds of meters long, under the snow where they feed on snow-flattened grass and plants. Research has shown that they memorize their tunnel routes and become so accustomed to them that if a rock is placed in the middle of a tunnel, the vole will probably run into the rock.
Voles are highly dependent on their sense of smell, and scents are probably used to identify individuals or to determine age, sex, and reproductive condition of other voles. Voles have scent glands and display common scent-marking behaviors such as scratching or rubbing. Tundra voles also have a well-developed sense of hearing, and it is believed that they may use vocalizations for communicating.
Tundra voles breed from late April through September. The gestation period lasts 20 to 21 days, and females can produce three litters a year. Females give birth to between four and eight offspring, and when they are born, the babies are naked and blind. After five days, the young are covered with hair, and they open their eyes 11 to 13 days after birth. The young develop quickly and are weaned after 18 days. They attain their maximum size approximately two months after they are weaned. Females reach sexual maturity at an age of only three weeks, but males are not sexually mature for six to eight weeks. Biologists think this delay in sexual maturation for males guards against inbreeding since females are usually fertilized before their males siblings are ready to mate. Tundra voles may live as long as two years but rarely live longer than one year in the wild.
Tundra voles are vegetarians and eat sedges, grasses, mosses, lichens, small woody shrubs, and other plants. Voles play a critical role in the food chain in Alaska. They are the primary food source for many small mammals and birds, including weasels and foxes. Even bears will sometimes eat voles. Vole populations cycle through boom and bust periods. During the high point of a cycle, the vole population may be 50 to 100 times higher than it is at the low point of the cycle. These boom times occur every four to five years, and predators that depend on voles for food also cycle in response to the size of the vole population.
Next week, my post will be about the little brown bat, another mammal endemic to Kodiak Island. Don’t forget to sign up for my free monthly mystery newsletter to read about true crime in Alaska.