The Alpine marmot hibernates to survive months when herbaceous food disappears under the snow: it actively lowers its body temperature close to that of the burrow (often 4 to 6°C) and its heart, which beats at rest around 80 to 100 beats per minute, drops to only 3 to 10 beats per minute for several days in a row.
A metabolism put on standby, but not turned off
Contrary to simple drowsiness, the true hibernation of the marmot alternates long phases of deep torpor, from several days to around two weeks, with brief periodic awakenings where the animal raises its body temperature to normal within a few hours. These awakenings, although short, consume a significant part of the fat reserves accumulated before winter: researchers estimate that they represent the majority of the total energy expenditure of the season, while they occupy only a fraction of the time spent underground.
During torpor, the respiratory rate also drops drastically, sometimes to a handful of breaths per minute, and brain activity is greatly reduced. This profound lethargy clearly distinguishes the marmot from the bear, whose winter state — often called hibernation or dormancy — maintains a body temperature close to normal (drop of only a few degrees) and an almost immediate awakening in the event of disturbance, without the costly cycles of awakenings observed in strict hibernators.
The trigger is not just the cold
Entry into hibernation is not a simple reaction to the thermometer: it is programmed in advance by the shortening of the photoperiod at the end of summer, which acts on an internal seasonal biological clock. This endogenous clock prepares the body, notably via hormonal changes, several weeks before the first frost, which explains why marmots kept in controlled conditions can initiate a hibernal cycle even without a sudden drop in ambient temperature. The cold then modulates the depth and duration of the torpor phases, but the internal clock remains the main conductor of the phenomenon.
