Is hibernation more of a nightmare than a pleasant dream?

Each year, on 2 February, North Americans watch someone drag a groundhog from hibernation for clues about how long winter will last. According to legend, if the groundhog sees his shadow, there will be six more weeks of winter weather and if he doesn’t, an early spring is predicted.

Sometimes during an especially long winter, hibernation sounds like a good thing. Just crawl into bed and wake up in the spring. Scientists are now weighing the costs and benefits of spending half your life disconnected.

Hibernation is when an animal alternates between torpor (deep sleep) and arousal while holed up in a winter den. The state of torpor is defined as a coma-like state where body temperature, heart rate, and breathing are lowered drastically. 

Torpor is a response to food scarcity and decreasing day length during the cold winter months, but it doesn’t come without serious risks. During torpor, sensory and motor capabilities are reduced severely. Groundhogs move into a near brain-dead state and many basic body functions are shut down. Brain activity is arrested to such a degree that animals must rouse themselves occasionally just so they are able to sleep.

Most hibernators come out of torpor for only a few hours at a time and remain relatively inactive. During arousal, groundhogs usually stay in their burrows except perhaps for an early emergence in February to survey their territories, assess food availability and establish bonds with females. Groundhogs then return to the den to recover and for some more deep sleeping episodes before the final arousal in March.

During hibernation animals are not only incapacitated and vulnerable to an attack from predators, their body is under such stress that temporary brain damage, disorientation and memory loss is commonplace. Also muscles can begin wasting away and, in fat-storing species like groundhogs, the gut undergoes profound atrophy. Most of these negative effects of torpor are reversible but a more thorough examination of hibernation needs to be made before the physiological consequences of this remarkable and widespread phenomenon are understood.

Source: The Role of Energy Availability in Mammalian Hibernation: A Cost-Benefit Approach http://biology.mcgill.ca/faculty/kramer/articles/Humphries%20et%20al_97.pdf

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