10 Animal Hibernators: What Is Hibernation and How Do Animals Do It?

Brown Bear Family | Via Getty Images

When winter rolls around, many animals vanish from sight, not because they’ve migrated, but because they’ve entered one of nature’s most remarkable survival strategies: hibernation. From bears and bats to frogs and even microscopic tardigrades, hibernation is more than just a long nap, it’s a physiological marvel. Bears hibernate in dens during the winter, significantly reducing their metabolism to save energy.

The hibernation period is a crucial phase for various animals, marked by significant physiological changes such as drastic reductions in heart rate and body temperature. For example, groundhogs and bears adapt their behaviors and bodily functions to survive extended periods without food or activity.

In this article, we’ll explore what hibernation is, the types of hibernation that exist in the animal kingdom, and highlight 10 amazing examples of hibernating creatures. Whether you’re curious about how animals survive harsh winters or just love cool biology facts, this guide will answer your questions.

What Is Hibernation?

Hibernation is a state of dormancy that allows animals to conserve energy by significantly slowing down their metabolism, heart rate, breathing, and body temperature. Contrary to the idea of a deep sleep, deep hibernation is a state where animals, such as hedgehogs, undergo significant physiological changes that distinguish it from regular sleep. During this phase, their body temperature drops to match the external environment, and their metabolic and respiratory rates decrease drastically, leading to long periods without breathing, showcasing the complexity and mystery of the hibernation process. By doing so, they conserve energy and can endure long periods without food. Many animal species, including bears, bats, and ground squirrels, hibernate during the winter months to survive the cold temperatures and lack of food. T

Hibernation is not limited to winter—it can also help animals cope with extreme heat and drought. While winter hibernation is common in cold climates, some animals in arid regions enter similar states during hot, dry periods.

Why Do Animals Hibernate?

Animals hibernate primarily to survive seasons when resources are scarce. Most animals utilize hibernation or similar strategies to endure periods of extreme environmental conditions. Cold temperatures and food shortages in winter drive many animals into this energy-saving state. During hibernation, animals can lose a significant percentage of their body weight as a survival adaptation to endure harsh conditions. By reducing physiological functions to a bare minimum, animals can survive for weeks or even months without eating.

Animals hibernate primarily to survive seasons when resources are scarce | Photo by Sasha Fox Walters

Types of Hibernation

Not all hibernation is the same. Cold-blooded animals, such as reptiles, undergo brumation, a process similar to hibernation, to survive winter by relying on external temperatures for their metabolic functions. In fact, scientists categorize it into several distinct types depending on the environmental trigger and physiological process.

1. True Hibernation

This is the most well-known form. Animals enter a state of deep unconsciousness, characterized by a deep, prolonged dormancy with significantly lowered body temperature, heart rate, and breathing. During this phase, their body temperature drops to match the external environment. As temperatures drop, these animals enter a state of deep unconsciousness to conserve energy. For example, arctic ground squirrels can lower their body temperature below freezing without damage.

• Examples: Ground squirrels, hedgehogs, and bats.

2. Torpor

Torpor is a short-term, lighter form of hibernation. It can last from a few hours to a few days and allows animals to conserve energy during brief periods of cold or food scarcity. Torpor helps animals conserve energy during cold nights by significantly reducing their metabolic rate and body temperature. Some animals can remain active during brief periods of torpor if food sources are available.

• Examples: Hummingbirds use torpor overnight to conserve energy. Some small marsupials use daily torpor.

3. Brumation

Brumation is the reptilian equivalent of hibernation. Reptiles, being ectothermic (cold-blooded), become less active and rely on environmental heat sources.

• Examples: Turtles, snakes, and lizards brumate in underground burrows or underwater.

4. Aestivation (Estivation)

This is the hot-weather version of hibernation. Animals aestivate to escape extreme heat or drought by entering a state of dormancy. Land snails, for example, utilize aestivation by climbing trees and sealing themselves in their shells with dried mucus to protect against drought conditions.

• Examples: Lungfish in Africa can aestivate for up to 4 years in dried mud. Snails and crocodiles may also aestivate. Other animals, such as certain amphibians and reptiles, also aestivate to survive extreme heat and drought.

5. Diapause

Diapause is a suspended developmental stage often seen in insects, embryos, or microscopic animals. Worker bees, for instance, play a crucial role during diapause by ensuring the hive’s survival and productivity through seasonal changes.

• Examples: Monarch butterfly eggs enter diapause during winter. Mosquito larvae and tardigrades also exhibit this behavior. When temperatures drop, worker bees die off while the queen survives by hibernating, ensuring the hive's survival through seasonal changes.

6. Cryptobiosis

An extreme form of dormancy where metabolism nearly stops. Animals in cryptobiosis can survive desiccation, freezing, radiation, and even space travel. Other insects, such as certain butterflies and ladybirds, also enter cryptobiosis to survive harsh conditions.

• Examples: Tardigrades (“water bears”) are champions of cryptobiosis, able to endure for decades in suspended animation.

Animal Hibernators | Infographic by Wildlife Nomads

10 Incredible Animals That Hibernate

1. Brown Bear (Ursus arctos) - 2 to 5 months

Bears are the poster animals for hibernation, although what they experience is more accurately termed torpor. Unlike true hibernators, bears can wake more easily and occasionally rouse if disturbed. During torpor, their metabolic rate drops dramatically, heart rates slow to as low as 8–10 beats per minute, and body temperature decreases slightly. They don’t eat, drink, urinate, or defecate during this period, surviving entirely on fat reserves accumulated in the months prior. One of the most remarkable aspects of bear hibernation is that females can give birth and care for their cubs, all while in this dormant state. Cubs nurse and grow while their mother remains immobile, waking only when spring arrives. Scientists continue to study bear torpor for insights into muscle preservation, kidney function, and even applications for space travel and medical care.

Brown Bear | via Getty Images

2. Ground Squirrel - Up to 8 to 9 months

One of the best examples of true hibernators. Arctic ground squirrels can drop their body temperatures below freezing—without freezing themselves. During hibernation, their heart rates decrease significantly from 80 to 100 beats per minute to as low as five or ten beats per minute. They wake briefly between torpor cycles but remain underground for up to 8 months.

Baby Ground Squirrel | Via Getty Images

3. Common Poorwill (Phalaenoptilus nuttallii) - Weeks to months

The common poorwill holds a unique title in the bird world, it's the only known avian species that truly hibernates. Native to arid and semi-arid regions of western North America, this nocturnal bird belongs to the nightjar family. During colder months, when its insect prey becomes scarce, the poorwill enters a prolonged state of torpor that can last for several weeks or even months. Its body temperature, heart rate, and metabolic rate all drop dramatically, conserving energy and allowing it to survive without food. Remarkably, this bird can remain motionless in rock crevices or shaded ground cover, blending perfectly with its surroundings. Its ability to hibernate has fascinated scientists and birders alike, offering rare insight into how warm-blooded animals can temporarily shut down in extreme environments.

Common Poorwill | Photo by Adria Bates

4. European Hedgehog - 4 to 6 months

Hedgehogs curl up in leaf piles or burrows during winter, entering deep hibernation, a state where they undergo significant physiological changes. Their body temperatures fall close to ambient temperatures, and their metabolic and respiratory rates decrease drastically.

European hedgehog | Photo by Dieter Meyrl

5. Little Brown Bat - 5 to 7 months

These bats hibernate in caves and mine shafts. Similarly, big brown bats hibernate in locations such as caves, buildings, and tree cavities, relying on stored fat during this period. They enter torpor for weeks at a time but may briefly wake to drink. Disturbing hibernating bats can be fatal, as waking depletes their limited energy stores.

Little Brown Bat | Via Getty Images

6. Wood Frog (Lithobates sylvaticus) - Weeks to months

The wood frog is one of nature’s most impressive cold-weather survivalists. Found in North America, even as far north as the Arctic Circle, this small amphibian doesn’t flee the frost—instead, it embraces it. As temperatures drop, the wood frog burrows into leaf litter and enters a remarkable state of suspended animation. Up to 70% of its body water can freeze solid, and its heart stops beating entirely. What saves it from ice damage are special antifreeze-like compounds—mainly glucose and urea—that flood its cells and protect tissues from crystallization. Come spring, the frog thaws out and returns to life, hopping away as if nothing happened. This adaptation not only allows it to survive extreme winters but has also made it a subject of intense scientific research into cryopreservation and organ freezing.

Wood Frog | Photo by Steve Byland

7. Box Turtle - 3 to 6 months

Box turtles, like many reptiles, enter a state of brumation rather than true hibernation. As ectotherms, they rely on external temperatures to regulate their body heat, so when winter approaches, they burrow into soft soil, leaf litter, or beneath logs to escape the cold. Their metabolism slows dramatically, allowing them to survive for months without food. Unlike mammals in hibernation, brumating box turtles may wake briefly during warm spells, sometimes even shifting position or rehydrating slightly before returning to dormancy. This flexibility helps them cope with fluctuating winter temperatures, especially in temperate climates. Their ability to survive freezing conditions and low oxygen levels has fascinated researchers, as it reveals the incredible adaptability of reptiles in harsh seasonal environments.

Box Turtle | Photo by Bernhard J Mueller

8. Fat-Tailed Dwarf Lemur (Cheirogaleus medius) - Up to 7 months

One of the iconic animals of Madagascar. The fat-tailed dwarf lemur isn’t just cute, it’s also the only known primate that hibernates. Endemic to Madagascar, this small, nocturnal lemur spends up to seven months in hibernation, typically nestled in the hollows of trees. What makes it especially fascinating is how it relies on the fat stored in its tail, hence the name, to sustain itself during dormancy. Instead of remaining in a static sleep-like state the whole time, it cycles between deep torpor and brief periods of arousal, likely triggered by external temperature shifts. Its ability to enter such a prolonged metabolic shutdown is a rare trait among primates and offers scientists valuable insights into evolutionary adaptations and the potential for human medical applications, like long-term space travel or critical care medicine.

Fat-Tailed Dwarf Lemur | Photo by Neil Bowman

9. Tardigrade (Water Bear) - Potentially decades

Tardigrades might be microscopic, but when it comes to survival skills, they’re absolute legends. These tiny, water-dwelling invertebrates can survive conditions that would kill nearly any other form of life. When faced with extreme environmental stress—like desiccation, freezing, high radiation, or lack of oxygen—they enter a state called cryptobiosis. In this phase, they dry out completely, curl into a protective tun, and essentially hit the pause button on life. In this glass-like state, tardigrades can remain dormant for decades—possibly even longer—and reanimate when conditions improve. They’ve survived in outer space, inside boiling hot springs, and deep under polar ice. Tardigrades aren’t just tough—they redefine what it means to be resilient.

Tardigrade enter a state called cryptobiosis | Via Get Images

10. Gila Monster - 2 to 4 months

Native to the arid deserts of the American Southwest and northern Mexico, the Gila monster is one of the few venomous lizards in the world, and one of the most fascinating hibernators. During the cooler months, it enters a state of brumation, retreating into rocky crevices or underground burrows to avoid temperature extremes. While in this state, its metabolism slows dramatically, conserving energy until warmer conditions return. Gila monsters may emerge briefly during mild winter days, but they remain largely inactive, feeding off stored body fat. Like rattlesnakes and other desert reptiles, this seasonal dormancy is essential for surviving the harsh desert winters when food and warmth are scarce.

Gila Monster | Via Getty Images

Extreme Hibernation in Harsh Environments

Some animals take hibernation to the next level to survive the most inhospitable conditions on Earth. Extreme hibernation helps these animals save energy by significantly reducing their metabolic rates during periods when food is scarce and temperatures are extreme. Ectothermic animals, such as reptiles, do not generate their own body heat and rely on external temperatures to survive these harsh conditions.

• Wood Frogs in Alaska: Survive being frozen for 7 months each year.

• Lungfish: Survive years of drought thanks to aestivation.

• Tardigrades: Survive in outer space, volcanic vents, and frozen tundra.

• Painted Turtles: Survive months with no access to air by using anaerobic respiration and absorbing oxygen through their skin.

These adaptations show just how flexible and resilient nature can be.

Climate Change Impact

Climate change is having a significant impact on hibernating animals, as changes in temperature and precipitation patterns are altering the duration and timing of hibernation. For example, warmer temperatures are causing some hibernating animals to wake up too early, while changes in precipitation patterns are affecting the availability of food and water for hibernating animals. This can have significant consequences for hibernating animals, as it can affect their ability to survive the winter and reproduce in the spring.

A study on little brown bats found that climate change is causing them to wake up from hibernation too early, which can lead to a lack of food and water, and ultimately, to the death of the bats. Similarly, a study on fat-tailed dwarf lemurs found that climate change is affecting their hibernation patterns, causing them to hibernate for shorter periods of time. These changes can have significant consequences for their survival and reproduction. As climate change continues to alter seasonal patterns, it poses new challenges for hibernating species, highlighting the need for conservation efforts to protect these vulnerable animals.

Physiological Changes

Hibernation involves a range of physiological changes that help animals conserve energy and survive the winter. These changes include a decrease in body temperature, reduced heart rate and breathing rate, and a slower metabolic rate. Cold-blooded animals, such as reptiles, cannot generate their own body heat and rely on external temperatures to regulate their metabolic processes during hibernation. These adaptations are crucial for hibernating animals to endure the harsh conditions of winter.

Decrease in Body Temperature

During hibernation, an animal’s body temperature drops significantly to conserve energy. This decrease in body temperature is a key physiological change that occurs in hibernating animals, allowing them to reduce their energy expenditure and survive the winter. For example, the body temperature of hibernating arctic ground squirrels can drop as low as -2.9°C, while the body temperature of big brown bats can drop to around 10°C. This drastic reduction in body temperature helps these animals conserve their stored energy and survive the cold months when food is scarce. For example, a bear's body temperature only drops a few degrees during its winter denning.

Reduced Heart Rate and Breathing Rate

Hibernating animals also experience a significant reduction in heart rate and breathing rate. This reduction helps to conserve energy by minimizing the amount of oxygen and nutrients the animal needs to survive. For instance, the heart rate of a hibernating wood frog can drop from 60 beats per minute to just 4 beats per minute, while the breathing rate of a hibernating bear can drop from 40 breaths per minute to just 8 breaths per minute. These changes are essential for hibernating animals to endure the long winter months without depleting their energy reserves.

Hibernation Preparation and Behavior

Before hibernation, animals prepare by eating more food to build up their fat reserves, which will help them survive the winter months. This period of increased food intake is crucial for hibernating animals, as the stored fat provides the necessary energy to sustain them during their dormant period. Hibernating animals, such as big brown bats, will often find a safe and cozy place to hibernate, like a den or a burrow, to protect themselves from cold temperatures and predators.

During hibernation, an animal’s heart rate and breathing rate slow down, and their body temperature drops, allowing them to conserve energy and survive the cold weather. Some hibernating animals, like bears, can wake up periodically during the winter to drink water or eat food, while others, like the wood frog, will remain in a state of deep hibernation until spring arrives. Hibernation is a complex process that involves changes in an animal’s physiology, behavior, and ecology, and is an important adaptation that helps many species survive and thrive in challenging environments.

Hibernating animals, such as the fat-tailed dwarf lemur, can survive for extended periods without food or water, relying on their stored fat reserves to sustain them until the weather begins to warm up. The duration of hibernation varies among species, with some animals, like the little brown bat, hibernating for only a few weeks, while others, like the bear, can hibernate for up to five months. Hibernation is not just a state of inactivity; it is a highly regulated process that involves changes in an animal’s metabolism, body temperature, and behavior, and is essential for the survival of many species during the winter months.

FAQs About Hibernation

What animal actually hibernates?

True hibernators include ground squirrels, hedgehogs, and certain bat species. These animals enter a state of deep unconsciousness, a profound state of dormancy that is more intense than ordinary sleep, with significantly slowed bodily functions.

Which animal hibernates for 3 years?

The African lungfish can aestivate (a summer equivalent of hibernation) for up to five months to 3 or 4 years when water sources dry up, surviving by creating a mucous cocoon underground.

What is the longest animal to hibernate?

The edible dormouse holds the record for longest known mammalian hibernation—up to 11 months in harsh conditions. Among small species, the common poorwill, a type of nightjar, is a unique bird known for its long hibernation during winter. Some frogs and snakes also hibernate for over half the year.

Is hibernation actually sleeping?

Not exactly. While it may look like sleep, hibernation is a distinct physiological state where metabolism slows significantly, body temperature drops, and other vital functions are drastically reduced. Unlike sleep, animals don’t experience REM cycles and can stay in hibernation for weeks or months.

Hibernation is not a one-size-fits-all phenomenon. From bears taking winter naps to frogs freezing solid, the diversity of strategies is as wild as the creatures themselves. Warmer weather acts as a cue for many hibernating animals to wake from their dormancy and become active. Understanding these survival techniques not only showcases the adaptability of life but also underscores the fragility of ecosystems where these animals live.

As climate change threatens seasonal patterns, many hibernating species face new challenges. By learning more about hibernation and supporting conservation efforts, we can help preserve the delicate balance of life that allows these amazing survival stories to continue.