The groundhog is also known as the woodchuck or whistlepig and is a rodent belonging to the group of large ground squirrels known as marmots. It is widely distributed in North America and common in the northeastern and central United States. They hibernate in their winter burrows during the late fall and winter months, going into hibernation during October and emerging during the months of March and April. They are excellent burrowers, using burrows for sleeping, rearing young, and hibernating.

The etymology of the name woodchuck is unrelated to wood. It stems from an Algonquian name for the animal (possibly Narragansett), wuchak. Groundhog Day is a traditional festival celebrated in the United States and Canada on February 2. In traditional weather lore, if a groundhog emerges from its burrow on this day and fails to see its shadow because the weather is cloudy, winter will soon end. If the groundhog sees its shadow because the weather is bright and clear, it will be frightened and run back into its hole, and the winter will continue for six more weeks.

Groundhog Links:
Great Canadian Site!
Wikipedia
Punxsutawney Phil's Official Site