Chipmunks

The eastern chipmunk is a small, brown, burrow-dwelling squirrel. It typically measures 5 to 6 inches long and weighs about 3 ounces. It has two tan and five blackish longitudinal stripes on its back, and two tan and two brownish stripes on each side of its face. The longitudinal stripes end at the reddish rump. The tail is 3 to 4 inches long and is hairy but not bushy.

Chipmunks sometimes are confused with red squirrels. Chipmunks are very vocal and emit a rather sharp “chuck-chuck-chuck” call. The red squirrel also is very vocal but has a high-pitched chatter. Red squirrels spend a great deal of time in trees; chipmunks, although they can climb trees, spend most of their time on the ground.

General Biology

Eastern chipmunks typically inhabit mature woodlands and woodlot edges, but they also inhabit areas in and around suburban and rural homes. Chipmunks are most active during the early morning and late afternoon. Population densities of chipmunks are typically two to four animals per acre, although densities may be as high as ten animals per acre if sufficient food and cover are available. The home range of a chipmunk may be up to 1/2 acre, but adult animals defend a territory only about 50 feet around their burrow entrance. Consequently, home ranges often overlap among individuals.

The diet of chipmunks consists primarily of grains, nuts, berries, seeds, mushrooms, insects, and carrion. Chipmunks also prey on young birds and bird eggs. Chipmunks spend most of their time on the ground, but regularly climb trees in the fall to gather nuts, fruits, and seeds. Chipmunks cache food in their burrows throughout the year. By storing and scattering seeds, they promote the growth of various plants.

Burrowing

Chipmunk burrows often are well hidden near objects or buildings (for example, stumps, wood or brush piles, basements, and garages). The burrow entrance usually is about 2 inches in diameter and is not surrounded by obvious mounds of dirt, because the chipmunk carries the dirt in its cheek pouches and scatters it away from the burrow. In most cases, the burrow’s main tunnel is 20 to 30 feet long. Complex burrow systems occur where cover is sparse, and normally include a nesting chamber, one or two food storage chambers, various side pockets connected to the main tunnel, and separate escape tunnels.

With the onset of cold weather during late fall, chipmunks enter a period of inactivity that continues through the winter months. They do not enter a true hibernation as woodchucks do during the fall, but instead rely on the cache of food they store in their burrows. Some individuals become active on warm, sunny winter days. In Pennsylvania, chipmunks emerge from their burrows from late April to early May, although they can be observed above ground in early March during a brief breeding season.

Longevity and Reproduction

Chipmunks mate two times a year, in early spring and again early in the summer. After a 31-day gestation period, they give birth to two to five young in April to May and again in August to October. Chipmunks live for two to three years in the wild and five to eight years in captivity. Females have two estrus cycles per year: one in March or early April, one in late July or early August. Males make long trips out of their home ranges to locate females and check on their reproductive condition. Females raise their litters alone. No pair bonding between individuals takes place. Gestation is about thirty days after which the female gives birth to a litter of four to six young in the nest chamber of her deep burrow. The young (which weigh about 3 grams at birth) are born toothless, furless and with closed eyes and ears. Fur (and stripes) becomes visible 10 days after birth along with the emergence of the teeth (incisors at one week, first molars by three weeks, adult molars by three months). Ears open by twenty-eight days and eyes open a few days later. Juveniles starting at four to six weeks leave the nesting burrow during the day to forage and frolic. Mortality rates for these frolicking juveniles (primarily due to predation) is approximately thirty percent. The young are sexually mature within one year. Adults may live up to three years in the wild.

Damage Identification

Chipmunks present in large numbers can cause structural damage by burrowing under patios, stairs, retention walls, or foundations. They also may consume flower bulbs, seeds, or seedlings, as well as bird or grass seed and pet food not stored in rodent-proof containers. So although they are cute, chipmunks too, can be pest!

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