The lowest recorded body temperature in a hibernating mammal is −2.9 °C, measured in the abdomen of an Arctic ground squirrel. This remarkable temperature was observed during deep hibernation, when the animal’s metabolism and physiological activity are drastically reduced.
Arctic ground squirrels live across the far north, including Alaska, Canada, and parts of Siberia. They spend winter in underground burrows, where they alternate between extended torpor and brief periods of warming called arousals. During torpor, abdominal temperatures can remain below freezing for more than three weeks.
The squirrel does not freeze solid because its tissues use specialised freeze-avoidance strategies. Importantly, the head and neck remain at or above 0 °C, helping protect the brain. The −2.9 °C figure therefore refers specifically to an internal abdominal measurement, not a uniform temperature throughout the animal.
This fact is often misunderstood as proof that all hibernating mammals become frozen. Most do not. Arctic ground squirrels are exceptional because they can safely tolerate subzero body temperatures while preserving vital organs and later returning to normal activity.