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Hibernation makes animals become inactive

On some mornings, you might not feel like getting up. On cold mornings, you might want to stay snuggled warmly in bed. You might say, “I’m just going to hibernate today.” You mean that you are not going out. When animals hibernate, it means something very different. Hibernation is a deep sleep that helps them to save energy and survive the winter without eating much. During hibernation the animal’s body temperature drops, and its heartbeat and its breathing slow down so that it does not use much energy.

A hibernating dormouse curled up asleep in its nest next to hazelnuts


An animal hibernates by becoming inactive. It enters a kind of sleep. Many changes take place in the animal’s body. Most of the animals that hibernate are mammals. Mammals hibernate in winter, when it’s cold.

Animals first must get ready to hibernate. They eat a lot of food. The food gets stored in their bodies as fat. Then the animal goes into a cave, underground burrow, or some other shelter. It needs to be safe from cold weather and enemies when it hibernates.

The hibernating animal’s body makes less and less energy. It makes very little body heat. The animal’s body temperature drops.

The animal’s heartbeat slows down. It breathes slowly. Animals without much energy go into a kind of very deep sleep.


Animals usually hibernate in winter. It is cold outside during the winter. The animals could freeze to death.

There is not much food around to eat in winter. The animals could starve to death. Animals need food to make energy. A hibernating animal makes less energy, so it does not have to eat. A hibernating animal can live off of fat stored in its body.

Some animals that live in deserts—including some squirrels and insects—go into a kind of deep sleep during summer. This sleep is called estivation. They sleep underground during the blazing heat. Their bodies slow down so that they do not need to drink water. There is not much water in a desert in the summer.
For most animals finding enough food in winter can be difficult when the main source of food like insects or green plants is in short supply.  Some animals solve this problem by hibernating. Hibernation is a deep sleep that helps them to save energy and survive the winter without eating much.  During hibernation the animal’s body temperature drops, and its heartbeat and its breathing slow down so that it does not use much energy.  Hibernating animals get ready for their winter sleep by eating extra food and storing it as body fat which they then use as energy while sleeping.  There are two types of fat – regular white fat and brown fat.  The brown fat forms patches near the animal’s brain, heart and lungs. It sends a quick burst of energy to warm these organs first when it is time to wake up.  Some of the hibernating animals include fish, frogs and turtles, which have no way to keep warm during winter. They shelter under logs, rocks and fallen leaves in the water. When the weather gets cold, they move down to the bottom of lakes and ponds and some even burrow into the mud.  Some insects also hibernate and to keep warm they find holes in the ground, under tree bark or in rotting logs. Can you name some of the animals that hibernate in the winter?  Some hibernators go into such a deep sleep that it is almost impossible to wake them, and they appear to be dead.  If the temperature falls too low some animals will awaken slightly and shiver to warm up a bit.  Even when the weather is severe, hibernators may wake up for a short period every few weeks to use their ‘toilet rooms’ and eat a little food if it is available.
Hibernation refers to a season of heterothermy that is characterized by low body temperature, slow breathing and heart rate, and low metabolic rate. Although traditionally reserved for “deep” hibernators such as rodents, the term has been redefined to include animals such as bears and is now applied based on active metabolic suppression rather than based on absolute body temperature decline. Many experts believe that the processes of daily torpor and hibernation form a continuum and utilize similar mechanisms.

he equivalent during the summer months is known as aestivation. Some reptile species (ectotherms) are said to brumate, or undergo brumation, but any possible similarities between brumation and hibernation are not firmly established. Some insects, such as the wasp Polistes exclamans, hibernate by aggregating together in groups in protected places called hibernacula.  Often associated with low temperatures, the function of hibernation is to conserve energy during a period when sufficient food is unavailable. To achieve this energy saving, an endotherm will first decrease its metabolic rate, which then decreases body temperature. Hibernation may last several days, weeks, or months depending on the species, ambient temperature, time of year, and individual’s body condition.  Before entering hibernation, animals need to store enough energy to last through the entire winter. Larger species become hyperphagic and eat a large amount of food and store the energy in fat deposits. In many small species, food caching replaces eating and becoming fat. Some species of mammals hibernate while gestating young, which are either born while the mother hibernates or shortly afterwards. For example, the female polar bear goes into hibernation during the cold winter months to give birth to her offspring. She loses 15–27% of her pre-hibernation weight and uses stored fats for energy during times of food scarcity, or hibernation. It is evident that pregnant female polar bears significantly increase body mass prior to hibernation, and this increase is further reflected in the weight of their offspring. The fat accumulation prior to hibernation in female polar bears enables them to provide a sufficient and warm, nurturing environment for their newborns.


A number of warm-blooded animals hibernate. Warm-blooded animals make their own body heat from food energy. Chipmunks, ground squirrels, hamsters, and hedgehogs are warm-blooded animals that hibernate. The common poorwill is the only bird that hibernates all winter.

Some cold-blooded animals hibernate, too. Cold-blooded animals cannot make body heat. Their bodies are the same temperature as the air or water around them. Frogs, toads, and other amphibians are cold-blooded animals that hibernate. Lizards, snakes, turtles, and other reptiles also are cold-blooded and hibernate.

Some animals spend part of their day in a deep sleep like hibernation. This deep sleep is called dormancy. Bats and some kinds of birds go dormant each day.
Hibernation is a state of inactivity and metabolic depression in endotherms.

Bears spend several months during the winter sleeping in dens. They do not eat. Scientists do not know whether bears really hibernate. Some scientists say that the body temperature of bears does not drop low enough for true hibernation.


Animals hibernate for several months. Every once in a while, the animal wakes up. Chipmunks and squirrels eat nuts and other food they have stored in their burrows. Then they go back to sleep again.

Hibernating animals wake up when their bodies get warm again. The bodies of cold-blooded animals do not warm up until the outdoor temperature gets warm. Warm-blooded animals may start shivering. This motion helps their bodies warm up. Small animals warm up and come out of hibernation much faster than large animals.