Voles, Not Moles: Pine Vole, Microtus pinetorum

As we gaze at feeders outside our office window at Hilton Pond Center, we are sometimes distracted from birdwatching by a rustling among dead leaves that carpet the winter landscape. Most days, Eastern Chipmunks and Gray Squirrels forage frenetically in leaf litter for acorns and other goodies, but the activity that catches our eye is much more subtle. A leaf will move an inch or so for no obvious reason, followed by one more, then another, and another. When we focus our binoculars on these moving leaves, we see they follow an irregular line, and with patience we may even get to see the cause of the movements.

Occasionally, a tiny, blunt snout will appear from beneath a dead leaf, sniff the air, only to disappear a few seconds later. If we're really lucky a small, dark animal will emerge and scurry around in the open for a moment of two, revealing its identity as a Pine Vole.

The Pine Vole (eating a piece of apple, above) is a mouse-like rodent found almost everywhere in the eastern half of the U.S. except for northern Maine, southern Florida, and sandy coastal areas. Voles often are confused with moles because both animals make tunnels; however, the latter have oversized forefeet, are classified in the Insectivora, and don't bear chisel-shaped front incisors characteristic of voles and the rest of the Rodentia (left).

The Carolinas host three congeneric voles--Pine Vole, Microtus pinetorum; Meadow Vole, M. pennsylvanicus (which occurs mostly north of South Carolina); and Rock Vole, M. chrotorrhinus (found only in the Mountain Province and northward). A fourth more distantly related species--the Southern Red-backed Vole, Clethrionomys gapperi--occurs in North Carolina's mountains and up the Appalachians into Canada. Although the term "mouse" is sometimes used in place of "vole" for all these species, mice have tails about as long or longer than their body length, while vole tails are considerably shorter and their snouts are more blunt.

Pine Voles are our smallest species, measuring up to 5.5" in length with very short 1" tails; they weigh less than an ounce and a half. Fossorial in habit, Pine Voles have slightly elongated foreclaws (right) and spend most of their time digging and living in subterranean burrows. They excavate runways on or just beneath the soil surface, and sometimes under logs or planks. Orchardists detest Pine Voles because they tunnel right up to the main roots and trunks of fruit-bearing trees and gnaw on bark at the soil interface, sometimes girdling and killing the tree. Gardeners also have problems with Pine Voles because the little rodents may develop a liking for bulbs and the roots of ornamentals. In both cases, Pine Voles can be controlled by lightly tilling the soil, which destroys their shallow runway and burrow system.

Despite their name, Pine Voles are seldom found in coniferous forests, preferring instead to inhabit meadows or deciduous woods--hence their alternate and more descriptive name of "Woodland Vole." During an intensive three-year study at Hilton Pond Center by Billy Hilton III, 84% of all Pine Voles encountered were live-trapped in dense thickets dominated by Japanese Honeysuckle, Blackberry, Greenbrier, and/or Multiflora Rose (above right); the remainder occurred in hardwood stands. Voles are mostly herbivorous, eating subterranean fungi, fallen fruit, grass shoots, and other plant parts; they occasionally eat land snails and perform the valuable service of consuming larval and adult insects. Pine Voles cache large amounts of food--up to a gallon of tubers, berries, and seeds--and thereby can survive even when the ground is frozen. In seemingly random years their populations increase dramatically, at which time they become important prey items for hawks, owls, foxes, skunks, weasels, raccoons, and snakes. Free-roaming House Cats take tremendous numbers of Pine Voles and in some locales compete directly with native predators for this protein-rich food source.

Pine Voles have chestnut-brown pelage that blends to a silvery gray on the belly (male, below left); the back is lighter in juveniles. The velvety fur is short and dense and tends not to pick up soil particles; interestingly, each hair lies flat whether rubbed backward or forward--a nice adaptation for an animal that may need to reverse direction in a tunnel. A Pine Vole's eyes are dark and--like its external ears--relatively small.

In South Carolina's Piedmont Region the species may breed year-round, but north of here reproduction probably ceases in winter. Pine Voles aren't quite as prolific as some small rodents, producing only one to five young per litter rather than six or more. Gestation lasts about three weeks, and young are weaned another 18 days or so after birth. Females become reproductively active as young as two months of age and may produce up to five or six litters in their 18-month lifespans. Pine Vole pairs appear to be monogamous.

Since the species is semi-colonial, normal population densities of Pine Voles can reach 50 or so individuals per acre, with as many as 300 individuals reported in one acre of a New York apple orchard! With this kind of crowding, it's not surprising Pine Voles may suffer from heavy infestations of fleas, ticks, lice, mites, chiggers, and a variety of internal parasites.

Personally, we happen to like Pine Voles. They seldom bite when handled and we appreciate the way they fit into the natural scheme--sometimes as prey items, sometimes as consumers of beetle grubs and old persimmons. We welcome Pine Voles here at Hilton Pond Center and relish the opportunity to watch as they rustle up leaves while foraging for leftover seeds beneath our mid-winter bird feeders.

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