Bears are considered “deep” hibernators, rarely coming out of their dens in winter.
Animals hibernate during the winter to conserve energy, entering a state of deep sleep. Mammals, such as squirrels, bears, skunks, raccoons, hamsters, and bats, slow down their metabolism and go into a state of torpor, but they don’t sleep. With a slow heart rate and reduced body temperature, these animals have adapted to survive cold winters with little or no sustenance.
Bats are one of the creatures that slow down their metabolism and go into a state of torpor during the winter.
Dormancy means that hibernating animals eat, drink, move, think, or defecate minimally. Some “deep” hibernators, like bears, almost never wake up when they are safely in their den. Other animals, especially rodents, often leave this state to nibble on food harvested during the summer and fall. Cold-blooded creatures, like reptiles and amphibians, also hibernate. They are always at the same temperature as their surroundings, however this “sleep” means something different. For example, wood frogs freeze during the winter, while a natural antifreeze, glucose sugar, protects their organs.
Many frogs hibernate.
Once in winter mode, in a comfortable den, most animals do not need significant external power sources. They survive the temperature drop by lowering their own body temperature, sometimes to a few degrees below 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 stored fat by eating more than usual. It gets what little energy it needs by breaking down carbohydrates and stored fats. Organs and muscles even donate some sustenance. In fact, a bear borrows protein and water from its organs because it can regenerate them to healthy levels come spring.
Skunks hibernate.
No one knows exactly what triggers hibernation in various animals. It could be a change in light exposure, measured by melatonin levels, that alerts animals to the approach of winter and encourages them to seek out a burrow. The decreased food supply may be what makes them sleepy and lethargic. Biologists have managed to trigger this state in certain species, such as rodents, in the laboratory.
Raccoons are mammals that hibernate.
Of course, biologists also use their research to solve human problems. Some scientists believe that humans could one day hibernate, for example to travel to Mars or lose weight. Researchers are looking for clues to curing people’s liver disease, kidney disease, hunger or obesity, also studying mammals in this state. Humans may carry dormant genes that, when activated, can regenerate damaged muscles and organs.