What Happens During a Groundhog's Hibernation?

Several types of animals go into hibernation for the winter, but the groundhog is probably among the most well-known. Groundhog Day and the legend that goes with it is familiar throughout the United States and Canada, as every year, a groundhog is pulled out of hibernation so that we can find out if it will see its shadow and predict six more weeks of winter. Beyond the folklore, hibernation is a complex state during which many things are happening inside a groundhog's body.

  1. Body Temperature

    • A groundhog burrows underground to hibernate, and the hibernaculum, or the deepest part of the burrow where the groundhog falls into its winter slumber, is below the frost line. Because of this, a hibernating groundhog's body temperature can drop to as low as 39 or 40 degrees Fahrenheit. This is not much warmer than the temperature outside, but the groundhog is insulated by the body fat it stores up just before hibernation.

    Metabolism

    • A hibernating groundhog's metabolic rate, like the body temperature, plummets during hibernation. This is why a groundhog binges all summer, trying to reach its maximum weight around August of each year. As winter approaches, the animal's metabolism begins to slow. Just before going into its winter sleep, a groundhog will become sluggish and lethargic, and once in hibernation, the slowed metabolism will not require as much energy. The groundhog will live off its fat store all winter and emerge much slimmer in late February to early April, depending on how far north it lives.

    Heart Rate

    • Once a groundhog enters its annual sleep, its heart rate drops significantly, to about four or five beats per minute. Scientists are still trying to determine how the groundhogs remain alive and unharmed with such a slow heart beat, and some studies have suggested that the animals are somehow able to store large amounts of ascorbic acid and other antioxidants so that their brains are not damaged when they begin to awaken and blood flow increases. Another answer may be that groundhogs do awaken briefly several times during their hibernation, perhaps increasing their breathing and heart rates long enough to stave off any harm.

    Waking

    • Though the groundhog is in a kind of deep slumber, its body's hormones and internal clock still seem to be in tune with the slowly changing season. It is believed that the gradually increasing amounts of daylight somehow affect the groundhog's internal clock and trigger changes in the production of melatonin, a hormone related to sleep. This may be what tells the groundhog it is time to awaken.