Thermal Relations Of Free-Living Echidnas During Activity And In Hibernation In A Cold Climate

All twelve echidnas studied by radiotelemetric techniques in Kosciusko National Park 1987-1989 entered hibernation in early winter and woke in early or late spring. During hibernation, body temperatures fell close to those in the hibernaculum, as low as 3.7 degrees C. Each individual's hibernation season was characterised by brief , periodic arousals to approximately 32 degrees C. The frequency of arousals was proportional to body temperatures during the period of torpor, implying a possible correlation between metabolite accumulation and the function of arousals. Adults above 1300m hibernated for an average of 4.4 months, those at 1000 m for 3. 1 months, although the statistical signiflcance was marginal. Echidnas gained weight at the rate of 7-13% per month in the active season and all animals for which there is adequate data also showed 'test ' (sensu Strumwasser 1960) prior to entering hibernation. Weight losses of 2-3% per month were typical in the hibernation season. During the active season, echidnas in this region were conspicuously diurna1, emerging mid-morning from their overnight retreats and remaining active until evening. Body temperatures showed a conspicuous daily cycle in every individual, the modal temperature of 32 degrees C being reached during the daily active period. Overnight, body temperatures fell, commonly to 29 degrees C but frequently lower. The daily cycling of body temperature was remarkably consistent from day to day and throughout the active season, both within and between echidnas. All individuals defended successfully against body temperatures above about 34 degrees C, presumably relying particularly on behavioural rather than physiological means, and shade-seeking and water bathing are identified as being important in this context. Neither daily minimum nor maximum body temperatures correlated with minimum or maximum ambient temperatures, implying good control over the daily temperature cycle. Nevertheless, occasional low temperatures were observed during the active season, either during test drops or when, in response to particularly foul weather, an individual might remain all day in its retreat, entering shallow torpor as body temperatures continued to fall until the onset of the following day's activity period. Heat produced as a correlate of muscular work appears to be the main source of the daily increase in body temperature to about 32 degrees C.