What is Hibernation?

Animals enter hibernation during winter to conserve energy by going into a deep sleep-like state. Mammals, such as gophers, bears, skunks, raccoons, hamsters, and bats, lower their metabolism and enter a state of torpor, but they are not asleep. With a slowed heart rate and lowered body temperature, these animals have adapted to survive cold winters with little or no sustenance.

The dormant state means the hibernating animals minimally eat, drink, move, think, or defecate. Some "deep" hibernators, like bears, almost never rouse themselves once they are secure in their den. Other animals, especially rodents, frequently come out of this state to snack on food harvested during the summer and fall. Cold-blooded creatures, such as reptiles and amphibians, also can be said to hibernate. They are always the same temperature as their surroundings, however, so this "sleep" means something different. For instance, wood frogs actually freeze solid over winter, while a natural antifreeze, glucose sugar, protects their organs.

Once in wintering mode, in a snug den, most animals do not need significant external energy sources. They survive plummeting temperatures by lowering their own body temperature, sometimes to within degrees of the freezing point of water. Physiologically, their bodies reduce their need for energy by almost stopping their heartbeat.

In the months leading up to the cold season, the animal has stored fat by eating more than usual. It receives the little energy it does need by breaking down stored carbohydrates and fats. Organs and muscles even donate some sustenance. A bear actually borrows protein and water from its organs, because it can regenerate them to healthy levels once spring comes.

No one knows exactly what triggers hibernation in various animals. It might be a change in light exposure, measured by melatonin levels, which alerts animals to the coming winter and nudges them to seek out a burrow. A lessening food supply might be what makes them drowsy and lethargic. Biologists have been successful at triggering this state in certain species, like rodents, in the laboratory.

Of course, biologists also use their research to solve human problems. Some scientists think that humans might hibernate one day, such as in order to travel to Mars or lose weight. Researchers are looking for clues to healing people's liver disorders, kidney disease, starvation, or obesity, by studying mammals in this state as well. Humans might carry dormant genes that, when triggered, could regenerate damaged muscles and organs.

Hibernation is a state of inactivity and metabolic depression in endotherms. During hibernation, animals conserve energy by significantly lowering their body temperature, slowing breathing and heart rate, and decreasing metabolic rate. This adaptation allows them to survive periods when food is scarce, particularly in winter, by utilizing their stored body fat as energy.

Common hibernators include species adapted to cold climates, such as ground squirrels, bats, and certain bear species, although bears experience a less intense form of hibernation known as torpor. Other hibernators are hedgehogs, dormice, and some species of turtles and frogs. Each species has evolved hibernation strategies suited to its environment and biological needs.

Animals prepare for hibernation by eating extra food and storing it as body fat to use as energy during their dormant period. Some, like the American black bear, can gain up to 30 pounds of body weight per week before hibernation. They also seek out or create a hibernaculum—a safe, sheltered space to hibernate, such as a burrow or cave.

No, hibernation is not the same as regular sleep. While both involve rest, hibernation is a deeper state of dormancy. The animal's physiological processes slow dramatically, conserving energy at a much higher level than during sleep. Hibernating animals are not alert and do not respond to stimuli as they would when sleeping.

Yes, hibernating animals can wake up during their hibernation period, although it's not common. These arousals can be spontaneous or triggered by external disturbances. However, waking up is energetically costly, and animals will return to hibernation as soon as possible to conserve energy. The frequency and duration of these arousals vary among species.

Hibernation can positively affect an animal's lifespan. By avoiding harsh winter conditions and conserving energy when food is scarce, hibernating animals reduce the risk of predation and starvation. According to research, some hibernating species, like the European hedgehog, can have extended lifespans due to the reduced wear and tear on their bodies during hibernation.