Chipmunks are forest-dwelling, squirrel-like rodents whose size is typically about half that of the average squirrel. In addition to their smaller size, chipmunks may be readily distinguished from squirrels by the linear stripes of white fur which chipmunks sport on their heads and backs. There are twenty-five recognized species of chipmunks, one of which lives in northeast Asia, another in eastern North America, and all of the others in western North America.
The omnivorous chipmunks eat grain, nuts, fungi, birds' eggs, small frogs, worms, and insects, and during the fall of each year chipmunks stockpile some of those foods in their underground burrows for consumption during the winter. Human vistors at forest parks in North America soon become familiar with the playful antics of the chipmunks, who often forage in campgrounds for scraps of food.
In July of 2004, researchers at the University of Illinois published the results of a field study they conducted of 244 chipmunks in the upper Midwest states of Illinois and Wisconsin. The chipmunks were captured in live traps, and the researchers removed a tiny sample of flesh from the tip of an ear of each chipmunk before releasing the animal close to the site of its capture. Back in the laboratory, the researchers isolated the mitochondrial DNA from each sample of chipmunk flesh and they studied the genetic structure of each sample.
The genetic patterns of the chipmunks from Illinois and Wisconsin, when compared with related communities of chipmunks in the eastern and southern USA, provided proof that the Illinois and Wisconsin chipmunks had remained in Illinois and Wisconsin throughout the last Ice Age Glacial Maximum. The researchers concluded that there must have been areas of forest that supported a chipmunk population which survived in close proximity to the great continental ice sheet throughout the Ice Age.
During an Ice Age Glacial Maximum, continental ice sheets up to two miles (or three kilometers) thick cover all of Canada, the Great Lakes, and large portions of the northern USA, including all of New York State, all of the New England states, and half of Alaska. In Eurasia, the continental ice sheets cover all of Scandinavia, the British Isles, Iceland, and large parts of Russia and Siberia.
The continental ice sheets that form during an Ice Age are created and enlarged by snowfall that subtracts water from the world’s oceans. As a result, the world’s ocean levels drop by as much as 425 feet (130 meters) during an Ice Age. During an Ice Age Glacial Maximum, the continental shelves and shallow seas will become dry land, and an examination of a good ocean-depth map will show you where the new coastlines will be during a Glacial Maximum.
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