Animal lists · 12 entries
Animals That Hibernate
True hibernators such as ground squirrels and marmots lower body temperature for months and cannot be easily roused, whereas bears enter torpor — a lighter sleep from which they can wake to defend cubs — and are often wrongly called hibernators.
Updated 25 July 2026
Hibernation is used loosely in everyday speech to mean any winter sleep, but biologists distinguish true hibernation from torpor and daily torpor. A true hibernator drops its body temperature close to ambient, slows its metabolism dramatically, and cannot be woken quickly. A bear in winter dens does none of these to the same degree.
This list includes both true hibernators and animals commonly described as hibernating, with the distinction stated for each. The point is not to exclude bears from winter ecology but to stop calling their torpor hibernation as though it were the same process as a ground squirrel's.
How this list was compiled
Entries are grouped by physiological state: true hibernation (multi-month, deep metabolic suppression, body temperature near ambient), torpor (shallower, shorter, easily reversed) and estivation (summer dormancy). Bears are listed under torpor, not hibernation. Species that merely reduce activity in winter without metabolic suppression are excluded. Duration and body temperature change are noted for each entry.
Animals That Hibernate
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Arctic ground squirrel
True hibernation; ~8 monthsBody temperature drops to around −2.9°C — below freezing — without forming ice in the blood.
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Marmot
True hibernation; ~7–8 monthsHeart rate falls from roughly 180 to 30 beats per minute. True hibernators of alpine and subalpine zones.
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European hedgehog
True hibernation; ~5–6 monthsBody temperature falls from 35°C to near ambient. Wakes periodically but cannot be roused quickly.
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Dormouse
True hibernation; ~6 monthsOne of the longest hibernators relative to active season among small mammals.
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Fat-tailed dwarf lemur
True hibernation; ~7 monthsThe only primate known to truly hibernate. Body temperature tracks ambient in tree hollows.
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Brown bear
Torpor, not true hibernationBody temperature drops only a few degrees. Mothers give birth and nurse cubs during winter dens — impossible for true hibernators.
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Black bear
Torpor, not true hibernationCan be roused quickly to defend cubs. Heart rate drops but not to true hibernator levels.
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Bats
True hibernation (many species)Hang in caves or trees with body temperature near ambient. Some species hibernate over six months.
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Wood frog
Freezing tolerance; ~65% body freezesNot hibernation in the metabolic sense — the frog freezes solid and thaws in spring using cryoprotectants.
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Common box turtle
Brumation; ~4–5 monthsReptiles enter brumation — a reptile-specific dormancy distinct from mammalian hibernation.
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Snail
Estivation and winter dormancySeals the shell opening with epiphragm and reduces metabolism. Can estivate in summer or overwinter.
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Bumblebee queen
Overwintering dormancyMated queens alone survive winter in burrows. Workers and males die. Metabolic rate drops sharply.
Key facts
- True hibernators drop body temperature near ambient and cannot be roused quickly — ground squirrels, marmots and hedgehogs qualify.
- Bears enter torpor, not true hibernation — body temperature falls only a few degrees and mothers nurse cubs through winter.
- The Arctic ground squirrel can supercool its body below 0°C without freezing — among the most extreme dormancy adaptations known.
- Reptiles brumate; insects and snails estivate — these are distinct from mammalian hibernation.
- Wood frogs freeze solid in winter using cryoprotectants — a different mechanism entirely from metabolic hibernation.
- Calling bears hibernators is common but biologically misleading; the distinction matters for understanding their winter physiology.
Animals That Hibernate: frequently asked questions
Do bears hibernate?
What is the difference between hibernation and torpor?
Which animals truly hibernate?
Can any animal survive being frozen?
Do bats hibernate?
What is estivation?
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Nocturnal Animals
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