Snow as a factor in animal hibernation and dormancy

Hibernation in its broadest sense is a strategy employed by both endothermic and ectothermic animals in cold environments which enables them to reduce energy demands in a sheltered refuge (hibernaculum) over winter. Hibernation in endotherms involves a sequence of torpor periods interspersed with short normothermic periods. Body temperature (Tb) during torpor becomes readjusted to new, lower levels. Hibernation is most efficient when torpor bouts are long and arousal periods are short and infrequent. This is achieved when the ambient temperature (Ta) in the hibernaculum is constant at or slightly below the species specific minimum Tb. Two endotherms hibernate in the Australian snow country. Minimum Tb in the only endemic species, the endangered mountain pygmy-possum (Burramys parvus), is approximately 2?C. This temperature closely reflects the environmental temperatures typically experienced during winter in boulderfields which have a good cover of snow. Ectothermic hibernators have variable Tbs derived from heat acquired from the environment. Hibernation in these animals involves a retreat to a winter hibernaculum and a prolonged period of dormancy at Tbs which follow the Ta of the hibernaculum. Ectotherms hibernating in the Australian snow country include arthropods and a number of endemic herpetofauna (frogs and lizards). The major strategy used by most species to survive the cold, is avoiding sub-zero temperatures by choice of sheltered hibernacula. A deep snow cover provides insulation for both endothermic and ectothermic hibernators. Surface temperatures are often well below 0?C and fluctuate dramatically during winter in the Australian snow country, but remain stable above 0?C beneath the snow. If there is a reduction in, or loss of snow cover in the Australian snow country, hibernators are likely to suffer high mortality rates due to extremes and wide fluctuations in temperatures.