Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

How does hibernation work?

ScienceLesson on requestFree to read

Quick answer

Hibernation is a survival state in which an animal slows its metabolism to a small fraction of normal. Its body temperature, heart rate and breathing drop dramatically, so stored fat can fuel it through months without food. Cues like shorter days trigger the process, and brief rewarming episodes powered by brown fat interrupt it.

Hibernation works by sharply slowing an animal's metabolism so that its body temperature, heart rate and breathing fall far below normal, letting it survive cold months on stored fat. Shortening days and falling temperatures trigger the change, and the animal rewarms periodically using heat from special brown fat.

Step by step

  1. Through late summer and autumn, the animal eats heavily and builds up thick reserves of white and brown fat.
  2. Shortening days and falling temperatures trigger hormonal changes, and the animal retreats to a sheltered den or burrow.
  3. Metabolism slows sharply, so heart rate, breathing rate and body temperature fall far below their active levels.
  4. The animal survives for weeks by slowly burning stored fat, interrupted by short rewarming bouts fuelled by brown fat.
  5. As days lengthen and temperatures rise in spring, the animal rewarms fully, leaves its shelter and starts feeding again.

Key things to understand

  1. In late summer and autumn, hibernators eat heavily and store energy as body fat, including heat-producing brown fat.
  2. Shorter days, cooler weather and hormonal changes signal the body to prepare for a long period of inactivity.
  3. During hibernation, metabolic rate can drop to just a few percent of normal, so stored fat lasts for months.
  4. Small hibernators such as ground squirrels let body temperature fall close to that of their surroundings, sometimes near 0 °C.
  5. Every week or two, many hibernators burn brown fat and shiver to rewarm briefly before sinking back into deep torpor.

Labelled diagram

  1. Autumn feeding

    Heavy eating builds fat reserves, including heat-producing brown fat.

  2. Entry

    Day-length cues and hormones slow metabolism as the animal enters its den.

  3. Deep torpor

    Body temperature, heart rate and breathing fall far below normal levels.

  4. Arousals

    Brown fat and shivering briefly rewarm the body every week or two.

  5. Spring exit

    Longer days and warmth end hibernation and feeding begins again.

A hibernator's body through the winter

Real-world examples

  • Himalayan marmots in Ladakh hibernate in burrows through the long, freezing high-altitude winter.
  • Arctic ground squirrels in Alaska can let their body temperature drop below 0 °C without freezing.
  • Brown bears in Canada and Russia spend several months in dens without eating or drinking.
  • Hedgehogs in Britain hibernate in leaf nests under hedges and log piles.

Common mistake

✗ Myth: Hibernating animals are simply in a long, deep sleep the whole winter.

✓ Fact: Hibernation is a controlled drop in metabolism, not ordinary sleep. Many hibernators rewarm repeatedly through winter, and some even appear to need to sleep during those warm intervals.

People also ask

How do animals survive hibernation without eating?
They live on body fat stored before winter. By slowing metabolism to a small fraction of normal, a hibernator uses energy very slowly, so its fat lasts for months. Bears also recycle nitrogen from urea back into proteins, which helps them keep muscle and avoid producing waste during their long fast.
What triggers hibernation in animals?
The main triggers are shortening day length, falling temperatures and declining food supply. These cues change hormone levels and the animal's internal seasonal clock, prompting it to fatten up and then seek a den. Some species, such as ground squirrels, follow an internal annual rhythm that persists even under constant laboratory conditions.
Do hibernating animals wake up?
Yes, many do. Small hibernators such as ground squirrels and bats rewarm to near-normal body temperature every week or two for less than a day, then return to torpor. These arousals use much of their winter energy, and scientists are still studying exactly why they are necessary.
Do bears truly hibernate?
Yes, by the modern definition. Their body temperature falls only a few degrees, but their metabolism drops sharply and they can go months without eating, drinking, urinating or defecating. Older textbooks called this a lighter 'winter sleep'.
What is the difference between hibernation and sleep?
Sleep is a nightly brain state with a nearly normal body temperature. Hibernation is a prolonged state of deep metabolic suppression, with body temperature and heart rate held far lower for days or weeks at a time.
What is torpor?
Torpor is a short-term drop in metabolism and body temperature, often lasting hours. Hibernation is a series of long torpor bouts across a season, while hummingbirds use nightly torpor to save energy.
Do animals hibernate in hot places?
A related state called aestivation helps animals survive heat and drought. Some frogs, snails and lungfish seal themselves in mud or burrows during dry seasons and become active again when rains return.

Part of the guide: Nature & Earth: Living Things and Rocks →