Molecular and Metabolic Aspects of Mammalian Hibernation

713eat seeds from cones and are toolarge to use the subnivian space; forthese animals, winter can be a longseason without foraging opportuni-ties, and they have therefore evolvedthe ability to pass winter by while ina torpid state of lethargy.A highly regulated sequence ofphysiological events beginningmonths in advance of winter coordi-nates entrance into the suspendedstate of animation known as hiber-nation. However, with the exceptionof bears, which become only moder-ately hypothermic, no hibernatingmammal remains deeply hypother-mic for longer than several weeks.Instead, for reasons that are not yetknown, they expend significantamounts of energy to periodicallyrewarm back to normal body tem-peratures for less than a day beforerecooling.The seasonal changes in body tem-perature that occur in an arctic groundsquirrel (