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Chipmunk

Eastern Chipmunk
(Tamias striatus Richardson)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry. 216pp.

Order: Rodentia

Family: Sciuridae

Description: This brightly colored, conspicuously patterned rodent averages 243 mm (9.6 in) in length. A rusty rump, two buffy to whitish eye stripes, and narrow dark brown to blackish stripes on the back and sides-the lower two on each side bordering a white or buffy white stripe-distinguish the “grinny” or ”ground hackee” (two colloquial names). The grizzled tan upper parts and buffy white under parts are additional characters. The tail, about 93 mm (3.7 in) in length, is moderately furred and slightly flattened. Adults weigh about 80-92 g (2.8-3.2 oz).

Range and Habitat: The range includes much of eastern North America from southern Canada south to the Gulf of Mexico except for parts of the Southeast. In the Adirondacks, where the eastern chipmunk occurs at elevations to 1220 m (4000 ft), it prefers deciduous and mixed forests, and is most abundant in mature (old-growth) hardwoods containing sugar maple, beech, and a relatively open understory.

Within these plant communities, the chipmunks best home is an elaborate maze of inter-connecting tunnels, 4-10 m (12-30 ft) in length and 5 cm (2 in) in diameter. This burrow system usually has one unobstructed entrance with the opening of other tunnels that lead to the surface plugged with leaves. Most tunnels are 45-91 cm (18-36 in) deep, but few penetrate deeper and serve as drains to minimize flooding. A chamber, 15-25 cm (6-10 in) in diameter contains a nest of leaves and several passageways to food galleries. A chipmunk may dig part of the burrow system using its forefeet and cheek pouches to loosen and transport soil, but the renovation of old root channels and existing burrows of other mammals is the primary method of burrow construction. The presence of these pre-formed tunnels may be one of the requirements for a suitable home range.

Burrow structure of a chipmunk

From: Elliot, L. 1978. Social behavior and foraging ecology of the
eastern chipmunk (Tamias striatus) in the Adirondack Mountains.
Smithsonian Contributions in Zoology, 265:1-107.

Food and Feeding Behavior: The chipmunk's feeding habits reflect the woodland's seasonal supply of seeds, fruits, nuts, fungi, and tubers. Of this supply, striped, red and sugar maple seeds, beechnuts, the fruit of black cherries, and yellow trout lily bulbs form the bulk of the diet. Chipmunks prefer beechnuts, and can stuff their two internal cheek pouches with as many as 32 of the husked nuts at one time for transport to an underground cache, which by the end of autumn may contain 5000-6000 nuts. When the beechnut crop is poor, rough barked maple trees serve as “ladders” for entry to the canopy of mature beech trees whose smooth bark acts as a barrier to this “ground squirrel”. Once in the canopy, chipmunks locate cluster of beechnuts by sight and then nip them off, returning to the ground a few minutes later to retrieve them. During years of abundant beech mast, nuts are gathered from leaf litter by ground foraging.

Scatter hoarding is a common means of temporary storage for seeds and bulbs. The small supplies, located throughout the home range, may later be eaten on the spot if perishable or consolidated in one of several large galleries in the burrow system of even in the underground nest. Scatter hoards may offer an alternative food supply if the chipmunk's main food cache is stolen or destroyed. Food stores provide crucial nourishment during the winter, mid-summer early spring and occasionally when seed and nut crops fail throughout the entire year.

Other foods important to Adirondack chipmunks include fungi (particularly false truffles), invertebrates, and even small vertebrates. Chipmunks occasionally kill and eat birds, especially nestlings. The use of fungi may be significant to forest regeneration by spore dispersal, because some fungi create conditions favorable to tree seedling survival and growth.

Activity and Movement: The eastern chipmunk spends most of the winter in its burrow. This inactive phase extends from about mid November until early March - late April, with local snow depth and temperatures influencing the duration. This species is not a true hibernator and accumulates little body fat prior to winter. Underground caches of food are sources of energy for individuals arousing from short, recurring periods of torpor. During mid-winter thaws, some chipmunks may leave their burrows, even digging through several feet of snow to forage for seeds in nearby areas where the snow has melted, exposing the forest floor. Chipmunks residing at low elevation and near bird feeding stations in yards may come above the ground throughout the winter to consume sunflower seeds. At all seasons, chipmunks are diurnal, i.e., leaving their burrows only during day light. They are least active during hot, windy, or rainy weather, and during some years, may seldom venture from their burrows in July and August, a response to scarce food and botfly parasitism rather than hot temperatures.

Chipmunk cache containing

Chipmunk cache containing
beech nuts and maple seeds

Reproduction: Females mate repeatedly with one or more males during an estrous period that lasts 6-7 hours. Each bears a litter of 2-9 young, (average 4-6) 31 days later within the underground nest. A female may bear two litters, the first in April - June, and a second in August - October, or just one litter in late summer. Age, available food, and the duration of snow cover are some factors influencing litter frequency. At birth the young are 64 mm (2.5 in) long, blind, naked, and weigh about 2-3 g (0.1 oz). The eyes open at 30-31 days. Young chipmunks begin to emerge from the burrow at 40 days. The female weans and abandons her litter once they come above ground, by either moving them to a nearby burrow, or by leaving her young in the natal burrow while she moves to a new one. In either case, the young disperse about two weeks later. Sexual maturation takes place during the spring or summer following birth. Potential life span for an adult chipmunk is 8 years, but few adults live longer than 2-3 years.

Predators: Owls, hawks, coyotes, foxes, martens, fishers, bobcats, raccoons, and even red squirrels are some of the predators of the eastern chipmunk.

Social Behavior:

  • Social System - The eastern chipmunk is polygamous, sedentary, and usually solitary. Adults have a home range of 0.2-0.4 ha (0.5-1.0 acre) which may overlap with others. An individual defends the area around the burrow entrance, and is dominant to other chipmunks in this area. Excursions of several hundred feet beyond the boundaries of the normal home range may occur, usually by males seeking females during peaks of breeding, and by both sexes when food is scarce.
  • Communication - Chipmunks are quite vocal, producing loud “chips,” “chip-trills,” and soft “cuk-cuk-cuk...” calls which function to announce the intrusion of predators, and to advertise occupied areas. The same calls accompany aggressive encounters. High intensity chases with frequent reversals establish temporary hierarchies among small groups of males competing for access to females in estrous. Chases may lead to fighting in which opponents bite each other. Rushing, chasing, and particularly posturing, e.g., flattening the ears, moving jerkily, and erecting the tail hairs, provide important visual cues to motivation. Chipmunks touch noses and sniff each other's hindquarters during some encounters, responding to chemical signals such as those produced by secretions of the anal glands.

Additional References

Elliot, L. 1978. Social behavior and foraging ecology of the eastern chipmunk (Tamias striatus) in the Adirondack Mountains. Smithsonian Contributions in Zoology, 265:1-107.

Linck, D. B. 1971. Summer activity patterns of the eastern chipmunk in an Adirondack forest. Unpubl. M.S. Thesis SUNY CESF, Syracuse, NY 54pp.

Snyder, D. P. 1982. Tamias striatus. Mammalian Species, 168:1-8.

Van Etten, R. 1957. The ecology and population distribution of the eastern chipmunk, Tamias striatus lysteri on the Huntington Forest. M.S. Thesis, SUNY CESF, Syracuse, NY. 132pp.



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