The eastern chipmunk is a small, agile rodent found throughout Pennsylvania. Colloquial names include grinny, chippie, hackle and rock squirrel. A member of the squirrel family, Sciuridae, the chipmunk, is closely related to red, gray, fox and flying squirrels and, surprisingly, the woodchuck.
The chipmunk’s taxonomic name is Tamias striatus (tamias means collector and keeper of provisions, and striatus refers to the animal’s prominent body stripes). The species ranges from Quebec south to northern Florida and Louisiana, and from the eastern seaboard west to Oklahoma, Kansas, the Dakotas and Saskatchewan.
Adult chipmunks are 8 to 10 inches long (including a 3- to 4-inch tail) and weigh 2½ to 4 ounces. Sexes are the same size. A chipmunk’s head is blunt with rounded, erect ears. The legs are short. Each hind foot has five clawed toes, and each forefoot has four clawed toes and a fifth, thumb-like, digit with a soft, rounded nail. The tail is well-furred and flattened. The front incisor teeth are broad and chisel-shaped like those of other rodents. A chipmunk has internal cheek pouches for carrying food or excavated dirt.
The short, dense body fur is colored alike for both sexes: reddish-brown sprinkled with black and white hairs, brightest on the rump and flanks. Cheeks and sides of the body are grayish-tan to tawny brown, and the underparts are whitish. The most prominent field marks are five dark brown to blackish stripes on the back and sides. The narrowest stripe centers on the backbone, while on each side from shoulder to rump two more dark stripes sandwich a cream-colored band. On the sides of the face two buffy stripes outline the eye, and a black stripe runs through it. Adults molt in late spring or early summer and again in late fall or early winter. Winter pelage is slightly paler than summer. Albino and melanistic individuals occur.
Chipmunks are graceful and spry, quick to dart for their underground burrows when startled. They run with their bushy tails held straight up. Although largely ground-dwelling, they sometimes climb trees, descending head first in squirrel-like leaps. Their senses of sight and hearing are keen. When eating they often perch on stumps, rocks or logs, to survey their surroundings. Tamias striatus is a vocal creature. It sounds a loud, repetitive “chip” similar to a robin’s note; a more rapid chipping (three or four chips per second, perhaps to warn other chipmunks away from its individual territory); and a single, sharp alarm whistle.
Chipmunks are omnivorous. They feed on nuts, (acorns, hickory nuts, beechnuts) and seeds of woody and herbaceous plants including cherry, box elder, maples, shadbush, dogwood, viburnum, ragweed, wintergreen and wild geranium. They also eat mushrooms, berries, corn, and the flesh and seeds of apples, peaches, pears and garden vegetables. Birds’ eggs, insects, snails, earthworms, millipedes, salamanders, small snakes, frogs and young mice and birds supplement their vegetable diet. Chipmunks eat food on the spot (evidenced by piles of shelled seeds or nut fragments) or carry it away for hoarding. A chipmunk can transport large amounts of food: one observer noted 31 corn kernels, another 32 beechnuts, and a third 70 sunflower seeds in the cheek pouches. A chipmunk uses its forepaws to manipulate food for eating or transporting.
Food foraging and other above-ground activities are carried on during daylight. Chipmunks are most active in early morning and late afternoon. In hot weather they spend much time in their cool underground burrows; this mid-summer adaptation is called estivation. A chipmunk’s activities and individual territory center on its burrow, which may be simple or intricate. The entrance, about two inches wide, is usually hidden under a rock, tree stump, log, or at the base of a fencepost or stone wall. Burrows plunge straight down for several inches, then level off and extend 30 feet or more, sometimes branching into offshoot tunnels with separate entries.
Chipmunks dig their burrows, pushing or carrying excavated dirt away from the entrance. Somewhere in the system is a foot-square nest chamber lined with crumbled dry leaves and grass. A chipmunk stashes nuts, seeds, corn, etc. under the leaf bed or in a storage chamber nearby. In autumn, chipmunks gather winter food, storing it in their burrows or in aboveground caches in their home territories. They do not enter winter with a thick layer of body fat, as do true hibernators. In late October or early November, they go underground to live on stored food until spring.