3 Characteristics of hibernation behaviour
The animal kingdom reveals a bewildering variety of regulated hypothermic behaviours, which are characterized by sustained hibernation at one extreme and regular short bouts of shallow torpor at the other. The many patterns observed and the variety of animal groups that exhibit these behaviours have not made it any easier to work out why different animals adopt their own strategies. Elephant shrews (Elephantulus myurus), which live in the relatively moderate climate of southern Africa for example, reduce their T b to one of the lowest levels seen in mammals in which frequent torpor bouts are observed. Torpor occurs with complete recovery about five times a day over the winter months, with the T b falling to as low as 7.5° C at a T a of 2.5° C. It seems that elephant shrews, whose body temperature fluctuates closely with environmental temperature cycles, are budgeting their energy by using – as heterotherms do – passive heating to assist their return to normal T b levels in the spring. In Section 3 we will consider the physiology of ‘typical’ hibernators, but there are new extremes of behaviour still to be explained, and no doubt yet to be discovered.