Some animals change their lifestyle depending on seasonal conditions. This helps them survive. Who, when, how and why hibernates?
- Bears, bats, lemurs and other animals hibernate to survive in cold conditions and lack of food.
- During hibernation, animals’ vital processes slow down: their body temperature drops, their breathing and heartbeat slow down, which helps them save energy.
- The duration and nature of hibernation depend on the type of animal and the climate: for example, some species can sleep for up to 8 months, while others wake up periodically.
Bears
The classic image of animals hibernating is bears. But many other representatives of the fauna also save themselves from the cold, lack of food and water.
What is hibernation? The animal website The Dodo calls this state torpor (hibernation), when vital processes slow down so that the body spends a minimum of energy to maintain life. The publication about forest dwellers Tree Hugger considers this a remarkable adaptation that allows them to survive.
The most famous winter dormice are bears. But in Southeast Asia it is always warm, and there is food all year round, so the bears here remain active all year round, and do not hibernate.
During hibernation, the breathing and metabolism of bears slow down by 75%. Females are still able to feed a couple of cubs at this time using their own reserves.
Bats
The bat was added to the list of winter dormice. These animals live on almost all continents, in many climate zones, so their torpor is very different. When the temperature drops, some can sleep for a month, but most fall into a long seasonal hibernation of up to 8 months.
In this state, the metabolism and breathing rate decrease. The heart rate slows down from 200-300 during an active life to 10 per minute during hibernation. Another way to conserve energy is to hang upside down and rest with their claws clinging to something. When the weather gets warmer, the bats warm up in the sun.
Fat-tailed dwarf lemurs
On the island of Madagascar, three species of endemic lemurs hibernate, including the fat-tailed dwarf lemur. National Geographic magazine calls the lemur the only primate that has this feature.
The heat-loving animal falls into torpor in the tropics, where there is no harsh winter. They have their own reason for this – the onset of the dry season, when there is not enough water. The little lemur accumulates fat in its tail, for which it received the name fat-tailed. In the fall, it burrows into the foliage and sleeps from 3 to 7 months, surviving at the expense of its own reserves. But periodically, the sleeping animal experiences an increase in body temperature and an increase in heart rate.
Marmots
Marmots are considered hibernating animals. Marmots hibernate early — in August–September. They gather in wintering burrows of 2 to 24 individuals. The entrances are plugged with earth, stones, and branches, so the temperature in the burrow does not fall below 0 °C.
During hibernation, marmots’ body temperature drops, their breathing rate decreases from 16 to 2 per minute, and their heart rate decreases from 80–100 to 5–10 per minute. They wake up once every two weeks because they need to speed up their heartbeat and go to the toilet in a separate tunnel. During hibernation, the animals survive due to accumulated fat and water, but lose up to a quarter of their weight. Hibernation lasts from 5 to 6–8 months. If the winter is warm, they wake up in February.
Hedgehogs
Who hibernates in the forest in winter? In addition to bears, hedgehogs, raccoons, snakes, and wood frogs are distinguished by this.
Before hibernation, some hedgehogs gain more than 1 kg in weight, and then their hibernation can begin in August. Those that weigh less fall asleep in October. In pits and holes, bushes, under a porch, or in an old building, hedgehogs make nests of hay and leaves, in which they sleep curled up. But they wake up every 2–4 days or once a month, often moving to another nest.
The body temperature of a hedgehog can drop to 1.8 °C, but during short periods of awakening it rises by 30 °C. During the winter, they lose up to 38% of their weight. They wake up when it gets warmer to 15 °C.
Box turtles
Turtles hibernate in a special way, brumation, which is typical for cold-blooded animals. Like all reptiles, turtles do not produce their own heat, but take it from the environment. But when it gets cold, they cannot even digest food, so even though they do not sleep, they fall into torpor.
Better Planet Education writes that Central Asian turtles brumate for 1-2 months in the summer to survive the heat. In the fall, they begin their winter inactivity. They burrow into the silt at the bottom of bodies of water that do not freeze.
Frogs
Tree, forest, and grass frogs hibernate. Some hibernate in the forest litter, in the soil, while others hibernate in the silt at the bottom of bodies of water. The hibernation period usually lasts from September to March. Some species also hibernate to survive in very dry conditions.
During hibernation, frogs’ hearts stop beating, and up to 45% of their bodies can freeze. In this case, some of the water in their bodies is replaced by glycerol, which lowers the freezing point. During the winter, freeze-thaw cycles can be repeated several times. In Alaska, there have been cases of frogs surviving freezing to minus 16 °C.
Skunks
Skunks do not hibernate, but they can enter a state of special torpor. In cold climates, this lasts for several months, and in the south, it is much shorter.
Before the cold weather, skunks accumulate a significant layer of fat to survive the winter in their dens. Like all hibernating animals, their vital processes slow down: their body temperature drops, their breathing slows down, and their heart rate decreases. During the entire hibernation period, female skunks do not leave their dens, keeping their young warm. During warmer periods, males go out to look for food.
Raccoons
The duration of their hibernation depends on their habitat:
- In northern regions, it begins with the onset of cold weather and continues until the spring warmth, on average – 3-4 months.
- In the middle and southern climate zones, raccoons are often awake in winter, but not active, in a state of suspended animation.
- In tropical zones, they do not hibernate, but become lethargic, experiencing a light, superficial sleep.
- Domestic raccoons can sleep for up to two weeks in winter.
From summer, raccoons accumulate subcutaneous fat if they are going to hibernate. They hide for the winter in hollows, old burrows of other animals, in voids among stones or in old buildings.
Snakes
In winter, snakes fall into a state of inactivity without sleep – brumation. Its duration depends on the habitat. In northern latitudes it lasts several months, in the south – several weeks. But snakes can come out of this state to get a drink. If the winter is warm and thawed patches appear, reptiles crawl out to warm up.
A signal for hibernation is a drop in air temperature below 10 °C. Snakes hibernate in cracks in the ground, rodent burrows, under tree roots. Very often they curl up into one ball of up to hundreds of individuals of different species.
Conclusion
Hibernation helps many animals survive the time when there is not enough food or warmth. For this, nature gave them the opportunity to slow down the vital processes in the body to a minimum.