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If you’ve ever thrown your covers back over your head on a cold winter morning and wished that you could go back to sleep and hibernate until spring, you need to know that your morning fantasy has a serious factual error. Hibernating animals are not sleeping.

So, what is hibernation if it is not the Super Bowl of sleeping? It is a long bout of torpor—a physiological state in which metabolic processes are substantially slowed. Hibernating animals can reduce their body activity to as little as five percent of normal rates. Heart rate, breathing rate, and body temperature decline substantially. For example, during hibernation, bears’ heart rates can be just 14 beats per minute, their breathing rates can be as low as twice a minute and their body temperature reaches 86 degrees Fahrenheit. Such low levels provide animals with huge energy savings. In fact, the purpose of hibernating is to conserve energy when resources are scarce.

Though it is during extreme cold that many animals hibernate, including arctic ground squirrels, European hedgehogs, dormice and groundhogs, it’s the lack of food that makes this survival strategy so adaptive. Other harsh conditions that are unrelated to plummeting temperatures can also make it advantageous to conserve energy by hibernating. Echidnas in Australia hibernate after fires when food is scarce, resuming normal activity levels only once food becomes plentiful again. Dwarf lemurs hibernate in tropical conditions that can top 80 degrees Fahrenheit, but it is drought, rather than extreme temperatures, that triggers members of this species to hibernate.

However much our energy and activity levels seem to decrease during the winter, humans do not actually hibernate. Research into inducing human hibernation for medical purposes seeks to extend the time doctors have to treat and save trauma patients who would otherwise die from blood loss or organ failure if left in their normal metabolic state. Though lowering body temperature has been useful for this purpose, the suspended animation of science fiction (known as hibernation in the real world) has not yet been achieved in humans.

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A more promising area of research involves using knowledge about hibernation to develop ways to prolong storage times for transplant organs. (Hearts can only survive about six hours, kidneys for up to 30.) Hibernating animals slow their metabolic processes and return to normal energy levels months later without suffering organ damage. Currently, organs destined for transplantation after the death of a donor are kept cold, but are still prone to extensive damage within hours. By bathing these cold organs in chemicals like those that protect the organs of hibernating animals, medical researchers hope they will survive longer and in better condition than the ones that are just kept cold.

Hibernation has its purpose, but it is not sleep. In fact, many animals must periodically rouse themselves from their hibernating state so that they can get some much-needed sleep. So, go ahead and throw your covers back over your head, but remember to wish for more time to sleep rather to hibernate.

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Karen B. London, Ph.D. is a Certified Applied Animal Behaviorist, Certified Professional Dog Trainer, author, and an Adjunct Faculty in NAU’s Department of Biological Sciences.


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