Hibernation can last anywhere from a period of days to weeks to even months, depending on the species. Some animals, like groundhogs, hibernate for as long as 150 days, according to the National Wildlife Federation.
Animals such as these are considered true hibernators. They enter into a period of inactivity in which their metabolism is just 5 percent its normal rate, according to National Geographic. Their body temperature drops and heart and breathing rates are just a fraction of what they are during their active periods.
While hibernating, a groundhog’s body temperature drops from 99 degrees Fahrenheit to as low as 33 degrees, reports the National Wildlife Federation. Their heart rate plummets from about 80 beats per minute to 5, and their breathing rate goes from 16 breaths a minute to as few as 2.
In addition to groundhogs, ground squirrels and many species of bats are true hibernators. Some animals that hibernate are considered light sleep hibernators rather than true hibernators. Their state of hibernation is not as deep as a true hibernator’s and does not last as long.
“They are easily awakened,” Russell said of light sleep hibernators. “They are basically taking long winter naps that can last several days.”
Bears are the most famous example of this kind of hibernation. Closer to home, opossums, raccoons and skunks are also light sleep hibernators, she said.
One misconception about hibernation is that animals do not wake while hibernating. They do wake up, but how and how often they do depends on whether they are true hibernators or light sleep hibernators, Russell said.
True hibernating animals sleep so deeply that waking is difficult and takes a lot of time and energy, she said. These animals may wake every few weeks to eat and, like in the case of groundhogs, use the bathroom in their burrow. As spring inches closer, they wake more frequently.
Light sleep hibernators wake more often throughout winter and carry on as usual while they are awake. Their metabolic functions — body temperature, breathing rate and heart rate — return to normal when they wake, then drop again when they once again begin to hibernate.