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Hibernation: Not Just Sleep

Updated: Jul 1, 2021

Author: Ioannes Salamanes

Editors: Ken Saito and Michael Zhu

Artist: Gianluca Zhang

Hibernation is a familiar word for many of us. However, not everyone knows about how it really works, or what different things are required to make hibernation practical and effective. Read this article to learn more about how different animals hibernate.

From a young age, we’ve learned that hibernation is when animals enter a sleep-like state for the whole winter season. While this is somewhat true, there is more to hibernation than just sleeping. Hibernation is the involuntary biological process where some animals undergo physiological changes like slowed metabolism and a drop in body temperature. Animals hibernate to conserve energy when there is a lack of food during harsh weather conditions. It is critical for the survival of many animals.

Many people think hibernation equals sleep but these are two distinct processes. Hibernation can last days, weeks, and months and sleep is a daily, normal process. The largest distinction between sleep and hibernation is brain activity. When we are sleeping, our brain waves change while we cycle through the different stages of sleep but when animals are hibernating, their brain waves are similar to how they are while awake, just slowed down. When waking up from hibernation, animals appear sleep-deprived and need to catch up on deep sleep. Slowed breathing and heart rate are physiological changes associated with sleep, however physiological changes are more dramatic during hibernation. Sometimes, the body temperature of certain animals can drop below the freezing point of water and some animals even stop breathing for over an hour at a time. This happens because the purpose of hibernation is to allow animals to reduce their energy consumption.

To fully understand hibernation and why it’s necessary for some animals, one must know the difference between endothermic and ectothermic animals. An ectotherm is an animal whose body temperature depends on the surrounding temperature and an endotherm is an animal that can regulate its body temperature by creating its own heat. When we think of ‘cold-blooded’ animals, we usually think of lizards or snakes and we think of birds and mammals as ‘warm-blooded’ animals; however, some species of fish, insects, and reptiles are actually warm-blooded. Being ectothermic means less energy is used to regulate body temperature, meaning they rely more on environmental conditions. However, endotherms need to produce heat for the regulation of their body temperature, which rough weather might impact their capability to find food sources.

Many endothermic animals enter a state called ‘torpor’ which causes physiological processes to slow down. Animals with the ability to adjust their metabolism and base body temperature are called heterothermic endotherms. Hibernation is a series of periods of torpor that each lasts for multiple days. Some animals go into daily torpor and wake up to forage and feed while other animals in hibernation feed off stored food or body fat. Animals that enter daily torpor consume large amounts of energy during the day and being able to conserve that energy even for just a few hours a day can increase chances of survival on colder nights. Some birds who migrate in the winter will also enter a state of torpor to save energy before they take off. Hibernation is more common than torpor in smaller animals. In fact, small animals who hibernate have a 15% higher survival rate and 50% longer lifespan than other animals their size who don’t hibernate. This is because animals in hibernation are more difficult to see, hear, and smell.

“Deep” hibernators are endotherms that are so incapacitated by the metabolic changes that they are nearly impossible to awaken during the winter months. During hibernation, animals who stored food will wake up now and then to eat and drink, or else they will not have enough energy reserve. Because they eat and drink, these animals will also need to go to the bathroom. Animals who hibernate can lose about one-quarter of their body weight over the winter and because of their unconscious state, they are more prone to predation. Animals will be weak when they wake up and they have to recover quickly to survive. If they do not have enough energy stored, they might not even wake up at all.

Although hibernation is seasonal, not all animals hibernate sleep in the winter and wake up in the spring. Hibernation is not only for animals living in very cold climates, but rather it occurs in a wide range of animals living from arctic as well as tropical regions. Aestivation is essentially what hibernation in the summer is called. Animals aestivate when the weather gets too hot or dry. Since coldblooded species can’t regulate their body temperature the way mammals and other endotherms can, reptiles brumate instead of hibernating. Brumation is when animals like frogs, snakes, and turtles burrow underground to stay warm. Humans, although we are endotherms, don’t need to hibernate. This is because of our technology and biology that keep us comfortable year-round. However, scientists have looked into the possible benefits of human hibernation.



Novacurious. “Not Just Sleep: All about Hibernation.” Curious, 19 Sept. 2019,

Scholl, Juliann. “Hibernation 101: Facts and Myths.”, 16 Mar. 2021,

“Why Do Animals Hibernate?” Teatown, 7 Nov. 2018,'s


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