Animals that Hibernate

Hibernation is a strategy adopted by animals to survive during harsh weather and food scarcity.

What do animals do when they hibernate: They undergo several physiological changes, including lowered body temperature, reduced metabolic rate, slow heart rate, and slow breathing.

Mammals display two kinds of hibernating behavior. Some, like hedgehogs and ground squirrels, are obligate hibernators, entering into a state of inactivity in the colder months, irrespective of the temperature changes and availability of food. A few, like prairie dogs, are facultative, hibernating when food-deprived or stressed because of cold.

Why do animals hibernate : Animals hibernate to cope with the cold winters when food becomes scarce, making foraging almost impossible.

Hibernation can be of three types:

True hibernation: This is the most traditional type of hibernation, where animals become completely inactive in winter, going into a deep sleep. Their body, temperature, heart rate, breathing, and metabolism lowers. E.g., groundhogs, bats, woodchucks
Brumation: It is not truly hibernation but a state of inactivity or torpor seen in amphibians and reptiles. They don’t sleep through that period, unlike true hibernators but wake to drink water between their periods of inactivity.
Torpor: Torpor is the time of inactivity when the hibernator maintains a low metabolism and body temperature. It could go on for weeks or even months or last for less than 24 hrs (daily torpor). In the case of daily torpor, animals have normal metabolic rates and body temperature during the time of the day they are active. However, when they are inactive, which happens mostly at night, there is a drop in metabolic rate and body temperature.

Aestivation is not a kind of hibernation but an equivalent to it. While hibernation is winter sleep, aestivation is summer sleep.

List of Hibernating Animals

Animals that Hibernate in Winter

Name of the animal	Class	Description
Bear	Mammal	Bears are a classic example of true hibernators. Researchers thought their deep sleep to be torpor and not hibernation until studies conducted in 2011 and 2016. Contrary to the belief, they don’t sleep continually through the period they hibernate but wake up in intervals and move around in their dens. They don’t eat, drink or defecate during hibernation.
Bumblebee	Insect	All bumblebees save the queen die in winter. The queen sleeps through the colder months and wakes up in spring to set up a new colony.
Ground Squirrel	Mammal	They hibernate underneath burrows for 5-8 months. During hibernation, the squirrels enter into torpor (inactivity) where their metabolism drops to 1% and their body temperature almost reach a freezing point.
Chipmunk	Mammal	Most chipmunk species hibernate when the temperatures go beyond the freezing point. They take shelter in their burrows but don’t sleep through that time. Instead, they try maintaining a normal body temperature and feed on the food they have stored rather than entirely relying on fat reserves. They even urinate and defecate during that period.
Bat	Mammal	Bats hibernate during November and don’t come out until March or April. They become fully active by May. Some bats hibernate solitarily, while a few form colonies. Their favorable spots include buildings, hollow trees, and barns. However, some bat species may also migrate to warmer regions in winter instead of becoming inactive.
Common Poorwill	Bird	They choose leaf piles or hollow logs as their hibernation spots. These birds remain asleep or in torpor for a couple of weeks or even months. One individual was recorded to hibernate for 85 days during the 1947-1948 season.
Snake	Reptile	They don’t hibernate but, like other cold-blooded animals, enter into brumation during winter. During this time, their metabolism slows, and they stop eating.
Woodchuck	Mammal	They hibernate from October to March. During this time, their temperature falls from 99°F to 38°F. Their heartbeat drops to as low as 4 beats/ minute from 100 beats/minute.
Wood Frog	Amphibian	They nestle in leaf litter, and their body temperature lowers to such an extent that they almost freeze.
Marmot	Mammal	They hibernate in groups for as long as eight months. The marmots lower their body temperature during this time and survive on the fat and water stored by their body. They even lower their heartbeat to 3-4 beats/per minute and take not more than 2 to 3 breaths per minute.
Skunk	Mammal	They get into sleep mode between December and March. They shed around 30% of their weight then and search for gardens, sheds, and patios to hide till spring.
Groundhog	Mammal	Groundhogs hibernate between October and April for not more than three months. They are true hibernators, with their heart rate and body temperature dipping drastically. Their sleep is so deep that they wouldn’t wake up to any loud noise or even if touched or disturbed.
Hazel Dormouse	Mammal	They hibernate throughout the colder months to survive. If food is scarce, they preserve their energy by entering into torpor and also reduce their body temperature.
American Bullfrog	Amphibian	They hibernate underwater, with some individuals moving quite slowly in this period.
Salamander	Amphibian	They cannot live when it is freezing and burrow under leaf litters.
Hermit Crab	Invertebrate	These crabs hibernate when the temperature falls below 68 °F. They remain in the soil during this time for 4-6 weeks. Some crabs may hibernate for a little longer.

Animals that Hibernate (or Aestivate) in Summer

Name of the animal	Class	Description
Snail	Invertebrate	Snails can withstand the harsh winter but not the intense summer heat. They dig holes underground and hide within leaf litter. Their shells serve as a protective covering, helping them remain cool. The mucus that seals the entrance helps to retain moisture.
Hedgehog	Mammal	When the temperature is above 86°F, hedgehogs lower their metabolism and survive on the fat stored in their body for as long as 6 weeks. During this time, they remain curled into a ball.
Frog	Amphibian	Frogs sleep through summer and remain active in winter. They can be found near water drains and moist soil pits during the hotter months.
Lungfish	Fish	They aestivate when it is too hot in water beds and may stay in that way for as long as 4 years. A mucus coating secreted by the lungfish prevents them from dehydration.
Tortoise	Reptile	They aestivate in summer for a few days to a couple of weeks. During this period of inactivity, their metabolic rate lowers.
Crocodile	Reptile	To escape the prolonged droughts in summer, crocodiles dig burrows near lakes or riverbanks and sleep till the time the rains are back.
Earthworm	Invertebrate	They become inactive when the soil gets too dry or hot. However, the earthworms hibernate too. Before the soil freezes, they make burrows to depths of as much as 6 feet. Since they have a mucous coating, it is easy for them to go without moisture for a long.
Ladybug	Insect	When it is too hot and food is scarce, they enter into a state of dormancy.

FAQs

Q. How many animals hibernate?

A. Though the exact number remains unknown, a variety of animals, primarily those from the mammalian class, hibernate. Amphibians and cold-blooded reptiles do not hibernate but go into brumation.

Q. Where do animals hibernate?

A. They may hibernate in dens or tunnels or even make burrows underground.

Q. Do animals sleep when they hibernate?

A. While some sleep throughout hibernation, certain animals wake up in intervals.