Winter 2003

Prairie Vole: Faithful Highway Engineer

In this era of fast living and high divorce rates, the prairie vole is an inspiration to us all. But before you get inspired, perhaps you need to know the basic biology of Microtus ochrogaster. Voles (also called "meadow mice") are heavy-bodied grassland rodents. They have short fur, a short tail, and small, rounded ears. The fur on the prairie vole's back is blackish-brown, while the belly is yellow to reddish-tan. Its body is from three to five inches long, slightly larger than that of a mouse, while its tail is about one inch long.

The meadow vole (Microtus pennsylvanicus), a close relative of the prairie vole, can also be found in the grasslands of Chicago Wilderness. Although the two species can occupy the same habitat, the prairie vole tends to be found in drier areas than the meadow vole.

Vole populations tend to fluctuate widely depending upon environmental factors, but during periods of high population, voles can be the most common mammal on the prairie. They're prolific breeders: females can give birth within 60 days of their own birth and can have several litters of three or four young during their one-year lifespan.

Although both prairie and meadow voles make the most of their short lives by being avid breeders, they do so in strikingly different ways. The polygamous meadow vole lives on the "wild side," roaming readily from mate to mate. The prairie vole, on the other hand, is famously monogamous. When a male and female prairie vole mate, they tend to stay together through the good times and bad. Even if one partner dies, the other seldom seeks out a new mate. And the young join in on the family togetherness, too: they may stay around and help raise later siblings.

Voles maintain an extensive network of runways that can be found in most grassy fields by parting the grasses above. These tunnels through the grass and duff allow the vole to move, unnoticed by predators, between underground burrows and food sources. Look for a main runway route and many branching side routes. In winter, these miniature highway engineers continue to use their runways to tunnel through the snow. As the snow melts in spring, their thoroughfares can be the last snow remaining, icy tubes of safety snaking across the brown leaf litter.

Vole runways can be especially evident after a prairie fire when the floor of the "tunnel," compressed and often somewhat damp, remains unburned. Land managers and visitors occasionally see these long, winding paths of grass surrounded by the blackened burned areas.

It is rare to get a good look at a prairie vole, as they are always wary of predators. If disturbed, prairie voles readily speed down their grassy escape routes back to their underground burrows. They are generally more nocturnal (active at night) during hot weather and more diurnal (active during the day) when the weather is cold.

Have you ever seen a marsh hawk making slow, low loops over a field, hunting for food? Voles are one of its favorite foods, so it's likely that the hawk was looking for one. The vole has even been called the "Big Mac of the prairie" because it is just the right size for the marsh hawk to get the most energy for its hunting effort. Prairie voles aren't especially safe at night either, when the night shift of predators, including coyotes and short-eared owls, takes over.

Besides being a critical part of predators' diets, prairie voles are important grazers, feeding on grasses and forbs. They also loosen and aerate the prairie soil as they build their underground burrows. Sometimes we forget that prairies are more than just plants, and unseen animals such as the prairie vole are crucial to these complex networks.

— Bill Glass