Hibernation: seasonal dormancy and reduced metabolism in animals

Physiology and behavior

During hibernation an animal suppresses its metabolism, lowers its core temperature and slows respiration and heart rate. Energy for maintenance comes largely from stored fat reserves that are accumulated during active seasons like summer and autumn. Many species enter repeated bouts of deep torpor interrupted by brief arousals; others remain in prolonged sleep-like states. The timing, depth and duration of those torpor bouts vary widely among species and with environmental conditions.

Which animals hibernate?

Hibernation is most commonly observed among mammals and appears in several groups of small and medium-sized species as well as some larger ones. Examples include:

• Bats
• Ground squirrels and marmots
• Hedgehogs (which may sleep for one to several weeks)
• Certain marsupials
• The fat dormouse, noted for long uninterrupted bouts of torpor
• Large carnivores such as bears, though their winter sleep is physiologically shallower than classic hibernation
• Some birds, for instance certain hummingbirds, may enter brief torpor resembling hibernation

Variation, distinctions and related terms

Not all dormancy is identical: "true" hibernation implies a profound, prolonged metabolic depression and low body temperature. Bears undergo a lighter winter dormancy that preserves more normal physiology and allows them to wake more readily. Cold-blooded animals undergo brumation, a similar slowing of activity tied to external temperatures rather than internal regulation. Researchers also distinguish daily torpor (short, regular drops in metabolism) from multi-week hibernation.

Ecological role and scientific interest

Hibernation helps animals survive winters by conserving energy when food is unavailable and by reducing exposure to severe weather. It influences seasonal patterns of reproduction, migration and predator–prey interactions. Because hibernating animals tolerate low blood flow, low body temperature and altered metabolic states, the phenomenon attracts medical and space-science interest for potential applications in organ preservation, trauma care and long-duration human spaceflight.

Notable facts

Duration and depth of hibernation vary with species, climate and individual condition: some small mammals enter torpor for hours or days, while others may remain dormant for weeks. Successful hibernators rely on timely fattening and suitable shelter; disturbances during hibernation can deplete energy reserves and reduce survival.