Prairie Vole (Microtus ochrogaster)
Photo courtesy of Dr. Zuoxin Wang
Scientific name:
Microtus ochrogaster
Common name: Prairie vole
General Description:
Prairie voles are small, compactly built rodents that could easily be mistaken for mice or rats except that voles have more rounded muzzles, smaller eyes and ears, and short tails. The prairie vole is grizzled brown or yellowish brown in color. The color can also be described as grayish to dark brown, with a good mixture of tawny-tipped hairs. They tend to be darkest in the southern and eastern portion of their range and palest in the northwest. The belly is either whitish or yellowish in color with six mammae. The measurements of the torpedo-shaped body are as follows: Head and body 89-127mm (3 ˝ - 5 in.); tail 30-41mm (1 1/5 - 1 3/5 in.); weight 1 - 1 ˝ oz. (28-42g). The incisors of the prairie vole are ungrooved. The dental formula for this species animals is: I 1/1 C 0/0 PM 0/0 M 3/3. Similar species include the meadow vole which has a silvery-gray belly and a longer tail (more than 1 3/5 in. or 41mm). The longtail vole has a tail 2 in. (51mm) or more. The mountain vole, mountain phenacomys, and the boreal redback vole are also similar species. The sagebrush vole is ash-gray. The pine vole is auburn with a tail 25mm (1 in.) or longer. Finally, the southern bog lemming has grooved upper incisors.
Habitat:
Prairie voles tend to prefer dry habitats such as dry grass prairies or mixed grass-weed areas. Microhabitats may include open prairies, fence rows, railway rights-of-way, and old cemeteries. When prairie voles and meadow voles occur together the prairie vole inhabits the drier microhabitats with less cover and the meadow vole inhabits the moist microhabitats. Prairie voles also live in suburban areas and often occupy golf courses and vacant lots. Prairie voles prefer a full canopy of ground cover for protection from predators. These voles build extensive underground burrow systems as well as runways on the ground surface under thick mulch. The runways are usually 1 to 2 in. wide and all connect to shallow, mounded underground burrows. These underground burrows contain the nests and they may be padded down with grass cuttings. The homerange size varies from 25m (82ft) when the population density is low (less than 1 vole/hectare) to 10m (33ft) when the population density is high (more than 15,000 voles/hectare).
Distribution:
The prairie vole is perhaps the most abundant mammal in grassland communities of the North American Midwest. Prairie voles range from Texas to Indiana, New York, Minnesota, Kentucky, Utah and east to Rhode Island. Populations of prairie voles in Louisiana and Texas are often classified as a separate species, M. ludovicianus. Populations of the prairie voles undergo periodic fluctuations or cycles in population densities every two to four years. Despite these population fluctuations, the prairie vole is abundant throughout the state of Indiana and reproduces yearly.
Diet / Feeding Habits:
Voles, unlike other rodents, are adapted to eat and digest grasses and other course vegetation. This ability allows them to access an extremely abundant food supply. Their diet consists of green vegetation and many different species of grasses and forbs, such as, bluegrass, brome grass, curly dock, clover, alfalfa, ambrosia, goldenrod, dandelions, penstemon, and lespedeza. Their diet may also include some insect material and mosses. Prairie voles consume grass blades, leaves, and shoots, as well as, seeds, berries, nuts, lichens, twigs, and bark.
Prairie voles forage on the surface or underground. They dig to access roots and bulbs. Prairie voles can damage orchards and other crops by feeding on underground roots. The feeding range of an active vole colony can range from 92.9m to 16,200m. Prairie voles feed for several hours per day and may consume its own body weight in food within in a 24-hour period. As the weather fluctuates throughout the year, prairie voles change their feeding habits by feeding underground more in the winter. When foraging on the ground surface, voles may change from green herbage in the summer months to less nutritious foods still available in the winter. While they are in their underground burrows, they feed on the underground portions of plants, such as roots, bulbs, and tubers.
Reproduction:
The prairie vole reproduces throughout the year. Each female can produce several litters per year, each containing from 2 to 6 young. The gestation period is 20 to 30 days and the young are generally born between the months of March and September. The newborns are tiny, blind, and capable of only staggering movements. They huddle together in the nest and move only when searching for the lactating female. After a few days, their fur appears, and in 4 to 5 days, they open their eyes. Around two weeks of age the young are weaned and they begin to feed for themselves. At this time, the young female prairie voles may already be ready for breeding as females are capable of breeding at 30 days of age. The males take about two weeks longer to reach sexual maturity. Young that are born early in the breeding season can raise their own young before the season is over. Many juvenile males disperse from their natal site to seek unrelated mating partners. Also, many young pregnant females disperse, enabling them to rapidly colonize vacant habitats.
The reproductive behavior of prairie voles is unique compared to other voles, in that prairie voles are monogamous. Most other species of voles are polygamous, in that the male mates with several females. A mated pair of prairie voles share the same burrow and the male helps with parental care by grooming the young and retrieving them when they stray too far from the nest. The males also keep the burrow and surface runways clear of debris. Prairie voles display three types of social groups or families: groups of single females, male-female pairs and communal groups. The type of group that predominates in a population depends on several factors, including the season and the activity of the predators. Females conduct mate selection during the 24-hour period when they are reproductively receptive. Female reproductive hormones are triggered by the presence of a male.
Behavior:
Prairie voles are active day and night. Voles spend most of their time hidden from view, forcing them to communicate with one another largely by sound and scent. Each individual species has its own unique call. Prairie voles leave scent marks in their habitat, indicating its presence to others. Scent marks may be left in the form of feces, droplets of urine, or secretions from scent glands. Prairie voles often leave a trail of urine from their burrow that helps them find their way back home. During the breeding season territories are defended by the males and females against intruders. Outside of the breeding season, territoriality breaks down to such an extent that groups of prairie voles share communal burrows and even huddle together for warmth while nestling. Aggression towards other voles could cause young males to disperse at this time to new grounds. Also, during peak periods of intense overcrowding, behavior changes immensely with much more aggression.
Predators / Defense Mechanisms:
Because prairie voles are small in size and widely abundant, they have an array of predators. Common predators include cats, foxes, weasels, owls, falcons, snakes, coyotes, minks, badgers, skunks, or bobcats. A coyote killed near West Point, Indiana had 14 Prairie Voles in its stomach. In a stable breeding population, monthly mortality rates may be as high as 30% of the total population size. The burrows in the soil that prairie voles make and the adaptation of pushing through leaf litter and dense ground cover provides them with protection from predators. Burrows also protect them from harsh weather and open up new food sources underground. Dispersal by male prairie voles greatly increases their chance of getting killed by a predator. Thus, the adult sex ratio is female based.
Commercial Use and Economic Value:
Prairie voles are of little positive economic value. Their pelts are not valuable compared to other vole species, therefore, they are not hunted in large numbers by humans. Prairie voles pose a threat to many farmers and to keepers of orchards and vineyards, as they can damage pastures, crops, and seedlings. Dense populations of prairie voles can reduce plant stands by 80 - 100%. However, prairie voles are not under direct persecution by humans, as are, house mice and rats.
Status and Conservation:
Prairie voles are abundant and not endangered. Some farmers attempt to provide an alternative food sources for prairie voles instead of killing them with toxic pesticides such as, zinc phosphide.
References:
Burt, Whilliam and Grossenheider, Richard. 1980. Peterson Field Guides Mammals.
Encyclopedia of Mammals. 1997. Vol. 15; Marshall Cavendish Corporation.
Getz, Lowell and Carter, Sue. 1996. “Prairie-Vole Partnerships” The American Scientist. Jan.-Feb.
Hauser, Marc D. 2000. Wild Minds: What Animals Really Think. Henry Holt and Company, Ltd.,
Jackson, Marion. 1997. The National Heritage of Indiana. Indiana University Press.
MacDonald, David. The Encyclopedia of Mammals: Marsupials, Insect eaters, and Small Herbivores. 2001. Vol. 11; Andromeda Oxford Ltd.
Page, George. 1999. Inside the Animal Mind: A Groundbreaking Exploration of Animal Intelligence. Educational Broadcasting Corp.
Whitaker, John O. Jr. 1996. National Auduban Society Field Guide to North American Mammals. Chanticlear Press, Inc.