Freeze Avoidance in a Mammal: Body Temperatures Below 0°C in an Arctic Hibernator

Hibernating arctic ground squirrels, Spermophilus parryii , were able to adopt and spontaneously arouse from core body temperatures as low as -2.9°C without freezing. Abdominal body temperatures of ground squirrels hibernating in outdoor burrows were recorded with temperature-sensitive radiotransmitter implants. Body temperatures and soil temperatures at hibernaculum depth reached average minima during February of -1.9° and -6°C, respectively. Laboratory-housed ground squirrels hibernating in ambient temperatures of -4.3°C maintained above 0°C thoracic temperatures but decreased colonic temperatures to as low as -1.3°C. Plasma sampled from animals with below 0°C body temperatures had normal solute concentrations and showed no evidence of containing antifreeze molecules.