Hibernation: how do squirrels go months without drinking?

Hibernation is a prolonged state of torpor in which some animals plunge during the winter. During this period, the body temperature is lowered and the metabolism is reduced. When the squirrel hibernates, its body temperature drops from 37 ° C to 4 ° C and its heart rate is lowered by 300 to 9 beats per minute. Conversely to other hibernating animals, such as bears, marmots or bat, the squirrel does not store food as fat, which can then be metabolized into energy or in water – which makes it possible to survive without drinking.

Every two weeks he wakes up briefly to dig into his reserve of hazelnuts and to go urinate. However, he does not even take the opportunity to drink! During the winter, the squirrel thus loses little by little water, by elimination and by evaporation. Despite this, he feels no feeling thirsty, which could force him to come out of his hiding place and potentially endanger him.

Suppress the feeling of thirst during hibernation

You might think that the squirrel stores water by drinking a lot before hibernating. In fact, it’s the opposite: he tends to drink less before going to sleep. So how does he go about suppressing the feeling of thirst? The latter is normally triggered by too high a concentration of serum blood and extracellular: when the external water supply is indifferent, the serum is not diluted enough, which sends to the brain the thirst signal.

Researchers discovered in 2019 that squirrels manage to keep a low serum concentration when they hibernate, despite the loss of water. For this, they reduce the electrolytes in the serum (sodium, potassium, urea …) by storing them elsewhere in the body while waiting (possibly in the bladder, suggests the study). When the squirrel comes out of its hibernation, theosmolarity normal is restored, which reactivates the physiological circuit of thirst.