This is called hibernation.
Some folks have wondered whether there might yet be something scientific behind the groundhog tale. After all, the groundhog is a hibernating species that occasionally rouses itself during the winter, and perhaps the creature can sense something that tells it whether to wake up for the warm weather or go back into its torpor in early February.

"There's a little bit of truth to that, but with modifications," said Hannah Carey, a professor of veterinary medicine at the University of Wisconsin at Madison. Carey specializes in the study of hibernating animals.

"For hibernators like groundhogs and the ground squirrels that we study, they're on a biological clock that tells them when to start [to hibernate] in the fall and when to finish in the spring, regardless of external conditions," she told me. "They do arouse periodically throughout the winter. They do this spontaneously while they're underground, but there are no external signals."

During hibern ...more

Hibernation