By Dr. Jim Pease, Emeritus
Extension Wildlife Specialist (ISU - Retired)
The prairie vole (Microtus orchrogaster) is that small brown blur that slips beneath your feet as you take a walk on your prairie during the growing season. They come from the Muridae, the largest family of mammals in the world: the family of over 1,100 species of mice, rats, voles, lemmings, hamsters, and gerbils. The genus, Microtus, means “small ear” and the species, orchrogaster, means “yellow belly”. So, this critter is a small-eared brown rodent with a buff colored underside! In fact, the ears are rounded and somewhat hidden in the longish dark brown fur. Small eyes, a short tail (usually only about 1-1.75 inches in length), and short legs combine to create a compact animal well-adapted to life low on the prairie.
Found in the central grasslands of North America, the prairie vole ranges from the prairie provinces of Canada south to Oklahoma, and from the eastern slopes of the Rockies east to the edge of the eastern deciduous forest. That places Iowa wholly within its range. However, of the 50+ specimens in our collection at ISU, none were from north central or northeastern counties in the state. It may be that early mammal collectors didn’t trap there. It is more likely, though, that the prairie vole is a creature of xeric prairies, few of which are found in those areas of the state.
The prairie vole and its cousin, the meadow vole (Microtus pennsylvanicus) are both “semi-fossorial”—that means they dig shallow tunnel systems in the top1-3 inches of sod. While those grass tunnels in your lawn that appear just after the snow melts are more likely the work of meadow voles, prairie voles also line their well-maintained runways with vegetation they clip with their sharp incisor teeth. Strict vegetarians, they may eat their own weight daily in grasses, sedges, leaves, seeds, nuts, bulbs, tubers, and twigs and store them in shallow underground “pantries” for later use.
A vole’s life is busy, short, and has a strong family component. Unlike many rodent species, the prairie vole seems to form strong pair bonds, with both parents participating in the raising of the young (usually 3-4 in a litter) and in maintaining the enlarged nest area, burrow, and runway system. Though not considered a colonial species, they may form small colonies of several family groups in one area, probably reflecting abundant food supplies. They do not wander far: home ranges may be as small as .1 acre in tallgrass prairie regions or up to about .3-.5 acres in the drier, shortgrass prairie areas of their range. Females are sexually mature at about 1 month of age and can, if food is not limiting, have a litter about every 3 weeks. Because they are active year round and can have litters at any time there is sufficient food, they are prone to population “spikes” and “crashes” on somewhat regular intervals. Densities have been published of 2-4 voles/acre in sparse, western prairies to well over 100/acre in dry tallgrass prairies.
Few voles, however, reach the ripe old age of one year. Mortality rates are high as they serve as an important food source for many predators. Skunks, foxes, coyotes, weasels, raccoons, bobcats, hawks, owls, and snakes all use voles as a primary food source. Shorttailed shrews often invite themselves for dinner through the tunnel system and dine on the resident voles themselves! Good thing, though: with a litter of 3-4 (up to 7) every 3 weeks or so and sexual maturity at one month, it’s easy to see how a vole population could rapidly get out of hand without predators to harvest some of the growth!
In Iowa, prairie voles are listed as “statewide” but are restricted to drier sites. Not a prairie purist, they have adapted to other dry grassland sites across the state, including railroad right-of-ways, cemeteries, pastures, and some lawns. Their cousin, the meadow vole, tends to prefer more mesic to wet grassland sites and is also statewide, has a slightly longer tail, and doesn’t have the adult prairie vole’s “yellow” belly. Neither is a household pest, restricting their living to outdoor areas only.
As you walk your prairies and other grassland areas this summer, be on the lookout for that dark brown blur below you feet. Bend down and peer into the quarter-sized tunnel system of the prairie vole!