Fig. 2. T_b data from four echidnas early in the 2000 hibernation season, illustrating how during hibernation T_b tracks T_ref (solid black line). One echidna (male 4572, down-triangles) enters hibernation for the first time in the season on April 21, while another (female 006F, squares) shows her first periodic arousal on April 27. Echidnas 006F and 1E7C (male, circles) entered hibernation on February 12, while 2753 (female, up-triangles) entered hibernation on March 7. All echidnas were hibernating in different locations up to 2 km apart.