Figure 1. Pine vole, Microtus pinetorum (left), and prairie vole, M. ochrogaster (right).
Voles, also called meadow mice or field mice, belong to the genus Microtus. Voles are compact rodents with stocky bodies, short legs, and short tails. Their eyes are small and their ears partially hidden. Their underfur is generally dense and covered with thicker, longer guard hairs. They usually are brown or gray, though many color variations exist.
There are 23 vole species in the United States. This chapter provides range maps, descriptions, and habitat characteristics for seven species that are widespread or cause significant economic damage. Tentative identification of a particular animal may be made using this information. For positive identification, use a field guide or contact an expert.
Prairie Vole (Microtus ochrogaster). The prairie vole is 5 to 7 inches (13 to 18 cm) in total length (nose to tip of tail). Its fur is gray to dark brown and mixed with gray, yellow, or hazel-tipped hairs, giving it a “peppery” appearance. Underparts are gray to yellow-gray. It is the most common vole in prairie habitats.
Meadow Vole (M. pennsylvanicus). The meadow vole is the most widely distributed Microtus species in the United States. Its total length is 5 1/2 to 7 1/2 inches (14 to 19 cm) and its fur is gray to yellow-brown, obscured by black-tipped hairs. Northern subspecies may also have some red in their fur. Its underparts are gray, at times washed with silver or buff. The tail is bicolored.
Long-tailed Vole (M. longicaudus). The long-tailed vole can be distin-guished from other Microtus species by its tail, which comprises 30% or more of its total length of 6 to 8 1/2 inches (15 to 21 cm). The long-tailed vole has gray to dark brown fur with many black-tipped hairs. The underparts are gray mixed with some white or yellow. The tail is indistinctly to sharply bicolored.
Pine or Woodland Vole (M. pine-torum). The pine vole is a small vole. Its total length is 4 to 6 inches (10 to 15 cm). Its brown fur is soft and dense. The underparts are gray mixed with some yellow to cinnamon. The tail is barely bicolored or unicolored.
Montane (or Mountain) Vole (M. montanus). The montane vole is 5 1/2 to 8 1/2 inches (15 to 20 cm) in total length. Its fur is brown, washed with gray or yellow, and mixed with some black-tipped hairs. Its feet are usually silver-gray and its body underparts are whitish. The tail is bicolored.
Oregon Vole (M. oregoni). The Oregon vole is 5 1/2 to 6 1/2 inches (14 to 16 cm) in length. Its fur is gray to brown or yellow-brown. Underparts are darkish, washed with yellow to white. The tail is indistinctly bicolored.
California Vole (M. californicus). The California vole is 6 to 8 1/2 inches (15 to 20 cm) in total length. Its fur is tawny olive to cinnamon brown with brown to black overhairs. The under-parts are grayish. The tail is bicolored.
Voles are active day and night, year-round. They do not hibernate. Home range is usually 1/4 acre (0.1 ha) or less but varies with season, population density, habitat, food supply, and other factors. Voles are semifossorial and construct many tunnels and surface runways with numerous burrow entrances. A single burrow system may contain several adults and young.
Voles may breed throughout the year, but most commonly in spring and summer. In the field, they have 1 to 5 litters per year. They have produced up to 17 litters per year in a laboratory. Litter sizes range from 1 to 11, but usually average 3 to 6. The gestation period is about 21 days. Young are weaned by the time they are 21 days old, and females mature in 35 to 40 days. Lifespans are short, probably ranging from 2 to 16 months. In one population, there was 88% mortality during the first month of life.
Large population fluctuations are characteristic of voles. Population levels generally peak every 2 to 5 years; however, these cycles are not predictable. Occasionally during population irruptions, extremely high vole densities are reached. Dispersal, food quality, climate, predation, physiological stress, and genetics have been shown to influence population levels. Other factors probably also play a part.
Population densities are variable. Smolen and Keller (1987) list densities of long-tailed vole populations. A California population ranged from about 2 to 7 voles per acre (5 to 16/ha) and a New Mexico population ranged from around 8 to 49 voles per acre (20 to 121/ha). Cole and Batzli (1979) found that prairie vole populations averaged 15 per acre (38/ha) in prairie, 52 per acre (128/ha) in bluegrass, and 99 per acre (244/ha) in alfalfa. Another vole population ranged from 1 to 14 per acre (2 to 35/ha) over 3 years in western mixed prairie. Variability in meadow vole population density was reported by Taitt and Krebs (1985). An Ontario, Canada population ranged from 32 to 162 per acre (80 to 400/ha) over 1 year while an Illinois population ranged from 2 to 6 per acre (5 to 15/ha) also over 1 year. Other populations show similar year-to-year variability. Much higher densities may be reached during population irruptions. In Klamath Basin, Oregon, montane vole densities ranged from 200 to 500 per acre (500 to 1,250/ha) and may have reached 4,000 per acre (10,000/ha) in some instances during a 1957 to 1958 irruption.
Many voles are excellent swimmers. The water vole, in fact, escapes predators by swimming and diving. The climbing ability of voles varies. The long-tailed vole, for example, is a good climber (Johnson and Johnson 1982) while the pine vole is a bit clumsy in this regard.
Voles are prey for many predators (for example, coyotes, snakes, hawks, owls, and weasels); however, predators do not normally control vole populations.
Voles eat a wide variety of plants, most frequently grasses and forbs. In late summer and fall, they store seeds, tubers, bulbs, and rhizomes. They eat bark at times, primarily in fall and winter, and will eat crops, especially when their populations are high. Occasional food items include snails, insects, and animal remains.
Read the images from top to bottom. Figure 2. Distribution of the prairie vole in North America. Figure 3. Distribution of the meadow (light) and California voles (dark) in North America. Figure 4. Distribution of the long-tailed vole in North America. Figure 5.Distribution of the pine (light), montane (medium), and Oregon voles (dark) in North America.
Voles occupy a wide variety of habitats. They prefer areas with heavy ground cover of grasses, grasslike plants, or litter. When two species are found together in an area, they usually occupy different habitats. Though voles evolved in “natural” habitats, they also use habitats modified by humans, such as orchards, windbreaks, and cultivated fields, especially when vole populations are high. Characteristic habitat descriptions for the seven described species follow.
Prairie Vole. The prairie vole, as the name suggests, is the most common vole of the Great Plains grasslands. It is found in a variety of habitats, such as old fields, marshlands, and grass prairies. When in association with the meadow vole, it is generally in drier habitats.
Meadow Vole. The meadow vole is found in the northern United States and Canada. It prefers wet meadows and grassland habitats. When in association with the montane vole or prairie vole, it is generally in moister habitats.
Long-tailed Vole. The long-tailed vole is found in a wide variety of habi-tats (for example, sagebrush grass-lands, forests, mountain meadows, and stream banks) in the western United States and Canada.
Pine Vole. The pine vole is found in the eastern United States. It inhabits a variety of habitats such as deciduous and pine forests, abandoned fields, and orchards. Heavy ground cover is characteristic of these habitats.
Montane Vole. The montane vole is found primarily in mountainous regions of the western United States. It is found in alpine meadows, dry grasslands, and sagebrush grasslands. It avoids forests. When in association with the meadow vole, it is generally in drier habitats.
Oregon Vole. The Oregon vole is most often found in forested areas of northern California, Oregon, and Washington where there is an under-story of forbs and grasses such as in burned or clear-cut areas.
California Vole. The California vole inhabits the chaparral woodland shrubland of California. It is found in both wet and well-drained areas.
John M. O’Brien. Agricultural Programs Coordinator. Nevada Department of Agriculture. Reno, Nevada 89510