Which Animals Hibernate And Why Do They Do So?

Many different animals hibernate or enter dormancy as a survival strategy to endure the challenges posed by seasonal changes in temperature, food availability, and other environmental factors. Hibernation allows them to conserve energy, lower their metabolic rate, and avoid the need to hunt for food during times when it is scarce or difficult to find. When spring arrives, they typically emerge from hibernation with renewed energy and can continue their life cycles.

Contents

1 Strategies for surviving the winter
2 What is hibernation
3 Types of hibernation
4 Which animals go into total hibernation?
5 Which animals go into partial hibernation?
6 Which forest animals don’t hibernate?
7 Animals that thicken their fur
8 Animals that migrate
9 What are the seasons of hibernation?
10 Which animals hibernate in autumn?
11 Which animals hibernate in winter?
12 How do they survive hibernation?
13 Animals that hibernate longer
14 More on this topic

Strategies for surviving the winter

In temperate climate regions, winters are long and cold, snow cover makes food scarce, so this season is a critical time for many species. To ensure their survival, different species have successfully developed different mechanisms.

Some animals migrate, such as birds, while others remain, but have developed strategies to resist the cold. Some mammals, generally ungulates and predators, can thicken their fur and increase the layer of subcutaneous fat to face the harshness of winter. Others take refuge in burrows with food reserves, such as squirrels, and others even allow themselves to freeze (amphibians, reptiles, insects).

What is hibernation

Animals have developed various techniques to survive the rigors of winter, but without a doubt hibernation is one of the most advanced strategies. In fact, it involves a behavioral adaptation that also involves significant physiological changes, aimed at reducing energy expenditure through a controlled and reversible lowering of body temperature and metabolism level.

The animal thus lives in slow motion for several months, consuming its fat reserves while waiting for the return of the hotter seasons. This strategy is found in many orders of mammals, including monotremes (echidnas), marsupials (Australian kultarr), insectivores (hedgehogs), chiroptera (bats), but it is the most common way to survive the rigors of winter in rodents (dormice, lemurs, herons, egrets, hamsters, squirrels and marmots).

Hibernation is not to be confused with dormancy, a state of quiescence, even very long, adopted by insects, reptiles and invertebrates, which go into a condition that resembles death more than deep sleep. The body temperature can approach zero and all metabolic activity is almost blocked. Thanks to the high concentration of substances present in the blood, the water present in the blood does not crystallize and the body’s cells are preserved.

In practice, during hibernation the body temperature of these animals lowers, in some species by up to 10° C / 50° F, and the heartbeat decelerates, even by 80%. During this time, digestion and breathing slow down, as do other physiological needs.

It is with the arrival of spring, the mating season, that animals that hibernate awaken, and also resume their metabolic activity.

In this long ‘sleep’ they lose a lot of weight and their energy will be low. In fact, once they emerge from the vegetative state, they will return to feeding vigorously, as before hibernation.

Types of hibernation

Hibernation is not a one-size-fits-all phenomenon: it can be total or partial, and there is a spectrum of dormancy states observed in animals. Let’s delve into these distinctions:

Total Hibernation (True Hibernation): This is what many mammals are known for. During total hibernation, animals experience a profound reduction in metabolic activity, body temperature, and physical activity. Their heart rate, breathing rate, and overall energy expenditure drop significantly. Some examples of animals that undergo total hibernation include ground squirrels, hedgehogs, and some species of bats. In this state, these animals are essentially “asleep” for extended periods of time, typically through the winter months.
Partial Hibernation (Torpor): Some animals enter a state of partial hibernation known as torpor. Torpor is characterized by a reduction in metabolic activity and a lowered body temperature, but it is not as deep or prolonged as true hibernation. Animals in torpor can periodically rouse themselves to eat, drink, and even move around, especially on warmer winter days. Black bears, for instance, undergo a form of torpor, not true hibernation. This state allows them to conserve energy but still remain somewhat responsive to their environment.
Daily Torpor: Some animals, particularly small mammals and birds, may enter a daily torpor, where they go into a temporary, short-term state of reduced metabolic activity and lower body temperature each day or night. This is often observed during cold nights, enabling them to conserve energy.
Seasonal Dormancy: Insects and other invertebrates often enter a form of seasonal dormancy in response to changes in environmental conditions. This dormancy can range from a temporary slowdown in activity to more extended states of reduced metabolic activity and inactivity, depending on the species and the severity of the environmental conditions.

Which animals go into total hibernation?

It’s generally warm-blooded animals, with some exceptions, as we will see that go into total hibernation, also known as true hibernation. True hibernation is characterized by a significant reduction in metabolic activity, a lowered body temperature, and a state of prolonged dormancy, during which the animal is essentially “asleep” for an extended period. Some examples of animals that undergo true hibernation include:

Ground Squirrels: Ground squirrels, such as the Arctic ground squirrel, groundhog, and thirteen-lined ground squirrel, are well-known hibernators. They enter a deep hibernation state during the winter, with body temperatures dropping close to freezing, and they do not eat or drink during this period.
Bats: Some species of bats hibernate during the winter months. They enter caves, mines, or other sheltered locations, where they experience a significant reduction in metabolic activity and body temperature to conserve energy.
Hedgehogs: European hedgehogs are known hibernators. They find sheltered locations and enter a state of hibernation to survive the winter when food is scarce.
Hamsters: Some species of hamsters, like the European hamster, hibernate during the winter months. They reduce their metabolic rate and spend long periods in burrows.
Turtles: Certain species of freshwater turtles, like the box turtle and the painted turtle, hibernate. They find shelter in bodies of water, allowing them to survive in an environment that would be lethal for other reptiles during the winter.
Amphibians: Certain species of frogs and salamanders hibernate. They may bury themselves in mud or find sheltered locations in ponds and streams to endure the cold months.

Which animals go into partial hibernation?

Partial hibernation, often referred to as torpor, is observed in various animals, and it represents a less deep or less prolonged state of dormancy compared to true hibernation. During partial hibernation, animals reduce their metabolic activity, body temperature, and physical activity but can occasionally rouse themselves to eat, drink, and move around. Here are some examples of animals that undergo partial hibernation (torpor):

Black Bears: Black bears exhibit a form of partial hibernation. While they do experience a reduction in metabolic activity and body temperature during the winter, it is not as deep as true hibernation. They can wake up and move around in response to changes in environmental conditions or to seek food.
Chipmunks: Chipmunks go into a state of torpor during the winter. They spend much of the winter in a deep sleep but occasionally wake up to eat from their stored food caches.
Bumblebees: Bumblebee queens are known to enter a state of torpor during the winter. They slow down their metabolic processes and remain quiescent but can become active during brief warm periods to forage for nectar and pollen.
Some Bird Species: Some bird species, particularly those living in cold climates, enter a state of torpor during extremely cold nights to conserve energy. They reduce their metabolic rate and lower their body temperature temporarily.
Hibernating Rodents: Some rodent species, like the golden-mantled ground squirrel, may enter a state of torpor during hibernation. While their hibernation is deep and extended, they can periodically wake up and move around within their burrows.
Lemurs: Some lemur species, like the fat-tailed dwarf lemur, enter a state of torpor during the dry season when food is scarce. They lower their metabolic rate and body temperature and may sleep for several months.
Bats: While some bats undergo true hibernation, others go into torpor. Torpid bats can occasionally rouse themselves and fly out of their roosts to feed during brief periods of milder weather.

These animals enter partial hibernation or torpor as an adaptation to conserve energy during challenging environmental conditions, such as cold temperatures and food scarcity. It allows them to endure winter or other unfavorable periods while maintaining some level of responsiveness to their surroundings.

FOCUS: Which animals are nocturnal?

Which forest animals don’t hibernate?

Many forest animals do not hibernate and remain active throughout the year. These animals are adapted to cope with seasonal changes and the availability of food in various ways. Here are some examples of forest animals that typically do not hibernate:

White-Tailed Deer: White-tailed deer are active year-round. They forage for food and adapt their diets based on seasonal changes, consuming leaves, twigs, and other vegetation in the forest.
Squirrels: While some squirrels, like ground squirrels, hibernate, many other squirrel species, such as gray squirrels and red squirrels, remain active and search for food throughout the year. They store nuts and seeds during the fall to sustain them through the winter.
Raccoons: Raccoons are known for their adaptability. They do not hibernate and continue to forage for food, including insects, fruits, and small mammals, in forests and urban areas.
Owls: Most owl species are active year-round and hunt for prey, such as rodents and other small animals, in forested areas during both day and night.
Foxes: Foxes, like red foxes, are active throughout the year. They are opportunistic predators that feed on small mammals, birds, insects, and vegetation as available.
Bobcats: These elusive felines are not hibernators and are active predators in forests, preying on small mammals, birds, and occasionally deer.
Wild Turkeys: Wild turkeys forage for food year-round, with their diet consisting of seeds, insects, and plant material found in forested areas.
Rabbits: Many rabbit species, like the Eastern cottontail, remain active in forests during the winter months. They feed on woody plant material and other available vegetation.
Woodpeckers: Woodpeckers are active year-round and forage for insects and larvae in tree bark within forested habitats.
Various Bird Species: Many bird species are non-migratory and can be found in forests throughout the year. They feed on a variety of foods, including seeds, insects, and berries.

However, it’s important to note that the specific behavior of these animals can vary based on factors such as geographic location, habitat, and the availability of food resources.

Animals that thicken their fur

Among the strategies adopted to resist the rigors of winter there are also adaptive ones. Some species do not hibernate, nor migrate to places further south, but remain in place and remain active, although less than in summer.

They also must accumulate fat during times when food is plentiful, but to stay warm during the winter they thicken their fur or develop denser plumage, like the wolf, bear, fox, and ermine or hare. Sometimes they change color to better integrate into the winter landscape.

Some even create a ‘pantry’ near the shelter, while others change their diet.

Animals that migrate

As we said, migration is another typical survival strategy. Then there are the animals that winter in warmer places and above all richer in available food, because they cannot survive the rigors of the cold season. Most migrations occur in groups, from a few tens to thousands of individuals together.

There are some cases of incredible migrations. For example, walruses, which migrate by drifting on blocks of ice detached from the pack, so as to reach new territories effortlessly. Or the Arctic terns, which have the record for the longest migration distance, 40,000 km in eight months!

Among the migratory animals we remember the swallow, the cuckoo, the penguin, the whale, the cricket, the stork.

Among the few insects to migrate for climatic reasons is the monarch butterfly, which travels thousands of kilometers in winter, forming clusters that can cover a tree.

What are the seasons of hibernation?

There are several periods in which animals can slip into this state of voluntary ‘hibernation’, not all necessarily in early autumn. Some can hibernate even in the dead of winter. Let’s see what the hibernation seasons are.

Which animals hibernate in autumn?

Mammals typically hibernate in autumn. But also snakes, crocodiles, lizards, and some species of earthworms. And then geckos, frogs, marmots, toads, hedgehogs, worms, skunks.

The earthworm does not stop feeding itself, but reduces this function to a minimum. Reptiles, on the other hand, go into brumation, a condition similar to hibernation, in which blood and other fluids experience a phase of sub-freezing. After awakening, they will feel the need to reproduce.

Which animals hibernate in winter?

Insects, such as the bumblebee, bee, some species of butterflies, ants and moths hibernate in winter.

But also bears, turtles, squirrels, rodents such as beavers, snails and bats, although theirs is partial hibernation. Actually, it is an alternating hibernation, with continuous awakenings. Bears, for example, interrupt their sleep to give birth and feed their cubs. Bats hibernate following food shortages for about 6 months; but they wake up approximately every 10 days to carry out their physiological needs or move to a better place.

How do they survive hibernation?

Since animals do not eat during hibernation, they prepare themselves a few weeks or days before by taking in more food than usual.

Once metabolic functions are slowed down, the animal will be able to rely on its fat reserves in order to survive. Furthermore, before hibernation, it will shed its fur and line its nest or den with insulating materials.

But here too there are many differences and specificities. For example, the oak mouse tends to warm up with its other peers, while the grass snake makes sure to hide in the narrowest cavities in the ground, like the toad. Female bumblebees, on the other hand, face pregnancy with a slowed metabolism.

Animals that hibernate longer

The dormouse is the best known of the animals that hibernate. Its hibernation lasts 6 months, except for short breaks dedicated to consuming a snack. Like the dormouse, the hedgehog will hide in its burrow from early October to May. Like marmots and salamanders, it will sleep 24 hours a day.

The bear also enters a period of hibernation which includes autumn and winter but is different from total hibernation. These animals can sleep from a minimum of 2 months to a maximum of 7: the warmer the location, the shorter the hibernation lasts. It’s called partial hibernation and is, more simply, a long sleep. In fact, its temperature only drops by a few degrees, since total sleep would actually constitute a large waste of energy, even dangerous, for such a large and heavy animal.