Hibernation, Winter Rest and Cold Torpor

In short: Many animals survive the food-scarce winter by sharply reducing their energy use. Depending on the species, this happens as hibernation, as a lighter winter rest or as cold torpor.

In more detail: True hibernators such as hedgehogs and bats lower their body temperature drastically, while animals in winter rest such as the squirrel lower it only a little. Cold-blooded animals such as frogs and lizards, on the other hand, fall into cold torpor because their body temperature follows their surroundings.

In detail

• True hibernation: Hedgehogs, edible dormice, marmots and many bats sharply reduce body temperature, heartbeat and breathing and live off their fat reserves for months (fledermaeuse-grundlagen).
• Waking phases: Even hibernators wake up briefly from time to time; warming up costs a lot of energy, which is why frequent disturbances can dangerously use up their reserves.
• Brown fat: A special type of fatty tissue can produce heat and helps many hibernators warm themselves up again when they wake.
• Winter rest: Squirrels and badgers sleep a great deal but lower their body temperature only slightly, wake up more often and then eat, for example, from food stores they have made.
• Bears: Bears spend the winter in a den and often eat nothing for months; however, their body temperature drops much less than that of small hibernators.
• Cold torpor: Amphibians, reptiles and insects cannot produce their own body heat and become rigid in the cold; they therefore spend the winter in frost-protected places, such as in the soil or in mud (amphibien-und-reptilien-ueberblick).
• Triggers: Shorter days, falling temperatures and lack of food act through the hormone system to control when animals prepare and go into hibernation.
• Preparation: In autumn many animals build up fat reserves, look for sheltered places and line them with leaves, moss or hair.
• Other strategies: Not every animal sleeps through the winter: some migrate to warmer regions, while others stay active and protect themselves with a thick winter coat (zugvoegel-und-ihre-navigation, polartiere-und-anpassung-an-kaelte).