Nighty Night, Sleep Tight! Hibernation, Brumation and Torpor Explained

Rest and Relaxation. Catching some ZZZ’s. Hibernation, Brumation, and Torpor are all animal responses to dealing with the need to conserve energy and slow down.

Animals use energy all day. Things like walking, digestion, heating and cooling their bodies, all of these things use energy. Even thinking uses energy.

Energy is produced when animals eat. Just like putting gas in a car to make it go. However, food sources aren't necessarily available all year long.

Animals slow down their body’s need to produce energy and become inactive. But their level of inactivity goes much deeper than you slumping out on the couch binge-watching Grey’s Anatomy.

Hibernation, Brumation, and Torpor are actually biological reactions to the environment. By slowing down their metabolic rate animals can conserve energy, have less need for food, and survive lower temperatures.

Grab a warm blanket and curl up by the wood stove. Let’s break it all down and look at each one.


Many of us think of bears when we hear the word hibernation. However, many animals hibernate including bats,  groundhogs, bees, and rodents.

Hibernation is the winter term for lowering metabolism – aestivation is what animals do in summer when they slow down their body functions.  

Heterothermy is the term scientists use to describe an animal’s ability to lower its body temperature to match the surrounding air temperature. This is an active metabolic response which means the animal can control when it happens.

So a bear will receive clues from the surrounding environment and have the urge to store up fat (eat lots) and find an area of the shelter. Scientists actually like to argue about whether bears truly hibernate since their body temperature only drops a few degrees. Some wildlife biologists use the term denning. But we won’t go there today.

Depending on the animal, and the climate they may hibernate for weeks or months. This depends on the severity of the climate and the local food supply.

Little Brown Bat

Little Brown Bat

The bat species located in Kentucky all eat insects. In the winter insects are not an available food source so our bats either migrate south or hibernate during cold months.

Some animals cycle through hibernation and intermittingly wake up. The groundhog does this.

Some animals hibernate through gestation and give birth. I wish I knew about that when I had my children!


Hibernation is not as easy as just going off to a nice warm cave. It is directed by the endocrine system. Glands in the body regulate hormones that are released at key times. They control the physiological reactions of hibernation.

  • The thyroid gland controls metabolism and activity levels.

  • The pineal gland secretes melatonin the hormone that controls growing winter coats

  • Pituitary gland that regulates metabolic functions, storing fat, heart, and breathing rate

  • The pancreas produces insulin the hormone that regulates glucose and energy levels


There are actually several different types of hibernation.

Obligate Hibernation

These are animals that hibernate seasonally. Bears and ground squirrels hibernate every winter and are obligate hibernators.

Facultative hibernation

Some animals hibernate in response to environmental stressors such as lack of food or draught. This may often overlap with what we call torpor because these animals may wake up during winter and go look for food.

Difference Between Sleep and Hibernation

Hibernation is much more than sleep. In fact, animals who come out of hibernation may be tired and cranky and need more sleep.

In hibernation, the animal undergoes physiological changes that can be quite dramatic. Temperatures may drop sixty degrees. A hibernating animal does not awaken easily and loses consciousness. Waking up a hibernating animal may actually harm it and cause death.

Sleeping is a period of rest that has a slower heart and breathing rate but nothing drastic. The brain is quite busy when we sleep. Not only does it continue to give commands to our bodies such as “repair these tissues” and “we need to grow” it is also very active dreaming.


Reptiles brumate. The difference in brumation and hibernation is simple. Reptiles can not control their metabolic response. As an ectotherm, their body temperature is based on the environment.

When the nights get colder and the days shorter it lets our reptile friends know that it is time to get underground. Turtles and snakes typically go underground where the temperatures are more stable. In Kentucky, our friends the box turtles typically go down about twelve inches.

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Reptiles often brumate together. In fact, some cohabitate. In the south gopher tortoises dig holes to brumate and are often joined by the Eastern diamondback rattler who cant dig very well.

Gardner snakes often brumate in groups. On warm days they may come out to sun themselves and get a drink. Read our article on Kentucky snakes.


Torpor can be a confusing term because it can refer to a short or long period and can happen at any time of year. Torpor is a period of “decreased physiological activity” such as reducing their body temperature and metabolism.

Birds undergo torpor as well as marsupial mammals like our opossums, bats, skunks, and rodents. Sometimes torpor occurs at night after a day of looking for food. This nighttime rest allows the animal to conserve energy and deal with the colder weather.

Torpor has been observed in hummingbirds as they migrate. The hummingbird needs immense amounts of energy to reach the southern climates. They depend on the fat they have stored from summer pollen. During migration, the hummingbird flies during the day and enters torpor during the night. This allows them to conserve energy needed for flight.

In Kentucky, we have several species of chickadees that overwinter. These high energy little birds are fun to watch during the cold winter months. They are also a good example of a bird that practices torpor.

Chickadees feed on dormant insects, berries and cone seeds of evergreens during the cold winter months. A study in the Journal of Comparative Physiology showed that the Black-capped Chickadee, Parus atricapillus, was able to lower their body temperature by about ten degrees below normal. This saved them up to twenty-three percent of their metabolic expenditure.

Torpor has a survival advantage. Out of the sixty-one mammals to have gone extinct only four have been animals that utilized torpor.

Author, Ame Vanorio has 25+ years of experience living off-grid and as an organic farmer. She is the director of Fox Run Environmental Education Center and a licensed wildlife rehabilitator. In addition, she is a content creator and writes on a variety of environmental issues. Ame recently moved to Wisconsin where she is involved in a prairie restoration project and cant wait to try snowshoeing.

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