Mice and Voles

Deer mice inhabit nearly every type of land habitat in Pennsylvania: farm fields, fencerows, grassy berms of roads, brushland, and deep woods, both dry and damp, pine, and hardwood. Some taxonomists recognize two forms of Peromyscus maniculatus, the “woodland deer mouse” and “prairie deer mouse.” Deer mice eat seeds of many plants, cultivated grains, soybeans, corn, berries, buds, nuts, and mushrooms. They consume beetles, grasshoppers, crickets, caterpillars (including those of the gypsy moth), other invertebrates such as earthworms, centipedes, slugs, spiders, and even carrion.

Deer mice have sharp hearing and good eyesight. They locate most of their food by smell. They can swim if necessary and even run at nearly five miles per hour for short distances. The tail, covered with fur, acts as a tactile organ and a balancing aid; when climbing, a deer mouse wraps its tail around twigs or branches to gain steadiness.

The species weaves ball-shaped nests, six to eight inches in diameter, out of leaves, grasses, and other plants, lined with fur, feathers, and shredded plant matter. Deer mice nest in hollow logs, stumps, fenceposts, beneath rocks, in root channels underground, and rather frequently in abandoned squirrels’ and birds’ nests in trees up to 50 feet above ground. Deer mice rest in their nests during the day, and there they rear their young. Nests at ground level may have a nearby burrow with a latrine area for waste and a chamber for storing food.

In winter, if snow covers the ground, deer mice spend most of their time beneath the white blanket, where the temperature is warmer than in the open air. Here, they eat stored food. In extreme cold, deer mice cut down on their activity, sometimes sleeping for several days, perhaps huddled in a communal nest with two to four other mice (some of which may be white-footed mice, a different, although closely related, species).

Deer mice breed from March to October. Females raise three or four litters per year, each with three to seven young. In one year, a single female can produce nearly 30 young, although few survive long enough to do so. Young mice, called pups, utter high-pitched squeaking sounds. Males do not help females raise the litters. Deer mice are preyed on by foxes, cats, short-tailed shrews, mink, weasels, hawks, owls, and snakes. Home ranges vary in size from 0.05 to 2.5 acres, with 3 to 36 mice per acre of habitat. Like most other small mammals, deer mice are very abundant in some years and rather scarce in others, depending on environmental conditions.

Norway rats have poor vision, but their senses of smell, taste, hearing, and touch are well developed. Extremely adaptable, they live in and under barns and farm buildings, in city sewers and dumps, along streams and rivers, and in marshes and open fields. They dig burrows about three feet long with several escape holes lightly plugged with weeds or dirt and hidden in grass or under rubbish. Rattus norvegicus lives in colonies composed of several family groups that share feeding and nesting areas. Although they’re mainly nocturnal, rats also move about and feed during the day. Rats eat anything they can find or subdue, including fish, eggs, vegetables, grain, fruits, nuts, garden crops, carrion, and garbage. They kill poultry, snakes, young rats from neighboring colonies, and wild birds. In local areas, rats may suppress or wipe out native birds and mammals, especially ground-nesting birds. In turn, rats are preyed on by dogs, cats, minks, snakes, and large hawks and owls

Norway rats breed throughout the year, with peak activity in spring and autumn; a female may bear six to eight litters per year, with an average of six to nine young per litter. Rats carry many diseases, including rabies, tularemia, typhus, and bubonic plague. Another introduced Old World rat, the black rat (Rattus rattus) is found in small numbers in southeastern Pennsylvania.

Meadow jumping mice inhabit moist grassy and brushy fields, thick vegetation, and woodland edges. The home range is usually less than an acre. The name “jumping mouse” is something of a misnomer, as these animals do not normally travel by jumping, rather, they prefer taking short hops of a foot or two. Active at night, they eat seeds, grasses, berries, nuts, roots, fungi, earthworms, insects, spiders, and slugs.

The species breeds from May to October, with two litters of three to six young born yearly, in nests beneath boards, in hollow logs, and in grass tussocks. Zapus hudsonius hibernates in winter; after adding up to 0.2 ounces of body fat (a third of its body weight). In October or November, the meadow jumping mouse retires to a nest about 18 inches below the ground. The creature curls into a tight ball, buries its nose in its belly, coils its tail around itself, and sleeps. Its breathing lags, its temperature falls to a few degrees above freezing, and its heart rate slows to a few beats per minute. After six months’ suspended animation, the meadow jumping mouse emerges in late April or early May.

Meadow voles thrive in moist meadows and fields thick with grasses and sedges. They do not live in forests but may inhabit small clearings, bogs, and grassy openings in the woods. They are good swimmers and can run at five miles per hour. Meadow voles move about in low, thick grass and weeds that screen them from hawks and owls

Meadow voles eat grasses and sedges (cut stalks with seedheads are stored in small piles in the runways to be eaten later), tubers, roots, grains, and the inner bark of shrubs and trees; voles sometimes girdle small trees, killing them. Meadow voles are active all year, by night and by day, especially around dawn and dusk. Voles nest in shallow burrows three to four inches underground or hidden in grass. During winter, voles huddle together in the nests or move about and feed in runways beneath the snow.

In breeding season, meadow voles vigorously defend individual territories of 0.1 to 0.8 acres, which fluctuate from larger in summer to smaller during peak population years—when up to 166 voles may live on a single acre. Usually, a high population crashes to a low level, then builds up again to another high. Females produce from eight to ten litters in a high population year and five or six litters in a year when food is scarce, with each litter averaging four to seven young. Among the myriad of predators that attend to the vole population are herons, crows, gulls, foxes, house cats, weasels, opossums, skunks, shrews, bears, bass, pickerel, and snakes. Many voles are snatched up by hawks and owls, particularly barn owls. Maximum longevity is around a year and a half in the wild

A reddish band down the back and a pale gray belly distinguish the species, found in much of upland Pennsylvania. A woods dweller, the red-backed vole favors cool, damp forests with hemlocks, mossy rocks, stumps, and rotten logs. It also inhabits deciduous and mixed woodlands with mosses and ferns, rocky outcrops, stone walls, reverting fields, and grassy clearings. When traveling, it uses the burrows of moles and shrews and casts about beneath the fallen leaves. It also climbs into low trees. This species breeds from late March through November, nesting in cavities or appropriating abandoned nests of other species. It feeds on nuts, seeds, berries, green vegetation, roots, and fungi.

White-footed mice live in shrubby areas, woods, cultivated fields, pastures, rhododendron thickets, fencerows, stream margins, ravines, revegetated strip mines, and in farm buildings and houses. Some authorities believe the white-footed mouse prefers a slightly drier habitat than the deer mouse. White-footed mice nest in stones walls and rock crevices, under old boards, and in woodchuck burrows, tree cavities, and the abandoned nests of squirrels and birds. Like deer mice, white-footed mice do not dig burrows but use the runways of other small mammals. They are very agile and can climb trees. Individual home ranges vary from 0.11 to 0.86 acres, with ranges being slightly larger for males. From 1 to 13 white-footed mice may inhabit one acre.

White-footed mice eat about a third of their body weight daily, or around 0.2 ounces: seeds, nuts, berries, fungi, green plant matter, insects (chiefly caterpillars and ground beetles), centipedes, snails, and even small birds and other mice. They cache food in autumn, carrying seeds in their cheek pouches to chambers beneath logs and stumps. They breed from March through October; the three or four annual litters have three to seven young apiece. Females can mate when two months old. Males sometimes help females rear the young.

Woodland jumping mice eat seeds, berries, nuts, green plants, fungi (particularly subterranean fungi of genus Endogene), insects, worms, and millipedes. An individual home range is 1.2 to 8 acres. Although mainly nocturnal, woodland jumping mice venture out on cloudy days. They use burrows and trails made by moles and shrews. Normally they travel on all four feet, but for greater speed they hop with their long hind legs and can leap up to ten feet. They evade predators by taking several bounds, then stopping suddenly under cover. Screech owls, weasels, skunks, minks, bobcats, and snakes prey on woodland jumping mice. Like its cousin the meadow jumping mouse, the woodland species hibernates from October to late April or early May (about half the year) in an underground nest, singly or in pairs. Females bear three to six young in late June or early July; a second litter may be born in August.

The woodland vole is a molelike species that burrows into the soil just below the leaf litter. It breaks up the dirt with its head, incisors, and forefeet, turns around, and shoves the dirt out the tunnel’s entry, forming a cone-shaped pile two or three inches high. Meadow voles, hairy-tailed moles, and shrews use the burrows of Microtus pinetorum. Woodland voles seldom leave their burrows, and an individual’s home range is small, around a hundred feet in diameter. Foods include roots, stems, leaves, seeds, fruits, and tree bark. In gardens, these voles eat potatoes and flower bulbs. Woodland voles kill fruit trees by girdling the bark or damaging the roots. They cache food in storage chambers as deep as 18 inches underground, and they rear their young in nests under rocks, logs, and stumps. Woodland voles breed less prolifically than other voles, bearing one to four litters per year, each with one to five young.