Fig. 1. T_b of male echidna 4572 during the 2000 hibernation season (solid line) and reference soil temperature (T_ref; circles). T_b was measured at 96 min intervals by an implanted data logger. T_ref data were measured at a depth of 20 cm at a Bureau of Meteorology station about 4.5 km from the centre of the field site, and recorded daily at 09:00 h. Note the changes in relationship between T_b and T_ref that occur at arousals 4, 6 and 8. The location of the hibernating echidna was checked at the times marked by the arrows; it had moved 120 m between the first and second observations, and 430 m between the second and third.