By Eileen Dowd Stukel

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Be prepared. This well-known Boy Scout motto takes on heightened meaning when winter arrives in the Northern Great Plains. We prepare by winter-proofing our buildings and vehicles. We make accommodations for pets and livestock. We mentally fortify ourselves for the severe conditions to come.

Wildlife must also prepare for winter’s assault. Wild animals have three main strategies for surviving winter’s rigors. They can migrate to a milder climate, such as many breeding birds do. They may adapt to the conditions with added fat or thicker fur. Or they can hibernate until spring brings milder weather.

The woodchuck, or groundhog, is a true hibernator. This deep sleeper’s heart rate, respiration, and body temperature change dramatically during hibernation. Many of the deep sleepers, such as bats and ground squirrels, enter hibernation with extra body fat to help them last through their long winter slumber.

Other species are more restless hibernators. For these light sleepers, hibernation is a time of winter lethargy rather than true deep sleep. Light-sleeping hibernators may awaken frequently during winter and even appear aboveground on nice days.

South Dakota’s two chipmunk species are among nature’s light-sleeping hibernators. The least chipmunk (Tamias minimus) is found in western South Dakota, and the eastern chipmunk (Tamias striatus) resides in parts of the extreme northeastern counties.

Our two chipmunks share many characteristics with the other 19 North American species. These smallest members of the squirrel family, Sciuridae, are diurnal, or active during daylight hours. All chipmunks have some sort of light and dark striping on the head and body. They typically live in excavated underground burrows, but also inhabit rock piles and abandoned woodpecker cavities.

Unlike many hibernating mammals, chipmunks do not put on extra fat for the winter. Instead, they provide for themselves, much as rural residents did before winter trips to town became commonplace. All North American chipmunks are members of the genus Tamias, a Greek word for "storer."

Although industrious all year long, chipmunks gather and store food with a vengeance during the fall and early winter. Their burrow system may have several food storage chambers. In addition, their winter bed of crushed leaves lies on top of a store of nuts and seeds. When chipmunks awaken from their winter torpor, they feed on these food caches. Not only do they eat in bed, but you might also say that they eat their beds. The eastern chipmunk may store so much food that its bed may be nearly ceiling-high when the animal enters its winter quarters. When chipmunks awaken between their winter catnaps, which may last from one to several days, they not only feed, but use a toilet chamber in their burrow system or even come aboveground.

As spring approaches, males venture out in search of a mate, searching burrows for receptive females. Chipmunk mating is simply a brief encounter, since these animals generally lead a solitary life, except for a mother and her young. After a gestation of approximately one month, a female bears her litter of 4 to 6 young, with extremes of 1 to 8 per litter.

The mother cares for her helpless young in her burrow network. Young grow rapidly. They are weaned and essentially independent in about two months. The new arrivals must now secure their own home range, which may be near their mother’s territory.

Chipmunks are intolerant of each other and defend a small territory around their burrow system. Home ranges overlap, and chipmunks may travel through other individuals’ home ranges to find and secure food.

Chipmunks are extremely vocal and demonstrative, using a variety of calls and body postures to express their moods. The eastern chipmunk may give its common "chip" call as often as 130 times per minute.

A chipmunk’s summer diet is more diverse than its winter fare. Summer foods may include flowers, fruits, berries, invertebrates, and some small vertebrates. As fall approaches, chipmunks again begin their annual preparation for winter by gathering and storing nonperishable foods. They may fall prey to hawks, snakes, weasels, foxes, bobcats, raccoons, and domestic cats. Most chipmunks live less than two years.

South Dakota’s chipmunks, the least and eastern, share many habits and characteristics. So how do they differ? The least chipmunk’s name gives a clue, since this smallest chipmunk measures 6 to 9 inches long, including the tail. The eastern is larger, with a total length of 8 to 10 inches. Both species have the characteristic chipmunk stripes on the head and body. The dark central stripe of the least chipmunk extends from the base of its skull to the base of its tail. The eastern’s central stripe fades when it reaches the animal’s reddish rump. The least chipmunk’s coloration varies geographically. The subspecies found in South Dakota’s Badlands is paler than those of less arid habitats.

The eastern chipmunk is also aptly named, since all other North American chipmunk species range primarily in the western states and provinces. The least chipmunk seems adaptable to more habitat types than the eastern, which shows a preference for forested and brushy habitats. While the eastern is rarely observed far from protective cover, the least is sometimes seen in open areas. The least chipmunk appears to be a more social animal than the eastern.