Eastern chipmunks are more like woodland squirrels.

While they climb trees, each spends most of its time in a complex underground burrow, which has food storage chambers and two or more entrances. This makes them woodland ground squirrels.

Like many other ground squirrels, chipmunks hibernate. Their body temperature decreases, and they fall into a relatively deep sleep from October through March.

Yet unlike the thirteen-lined ground squirrels and woodchucks, chipmunks do not put on much fat before they hibernate. They awaken frequently during the winter and feed in their underground pantries, eating stored acorns and other seeds.

Because they are light hibernators, eastern chipmunks sometimes emerge during warm spells in the winter. But we can expect to see the first one out for sure by late February or early March. The period coincides with mating season.

The first litter could be born in April, the second in late August.

Last year I spotted my FOY (first of year) active eastern chipmunk above ground Feb. 21. I was walking a woodland trail at the University of Minnesota Landscape Arboretum. There were many more above ground in March.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.