Figure 6.

Peak rates of rewarming from hibernation in marmots (Marmota marmota) and echidnas (Tachyglossus aculeatus) as a function of body temperature. Peak rewarming rates were calculated from the first derivative of a sigmoid curve fitted to the rewarming data, and each point represents one rewarming. Because rewarming rate is inversely related to body mass (Geiser and Baudinette, 1990) the figure compares data from hibernators of the same mass (10 marmots, mass 3.39 ± 0.46 kg, mean ± SD and 10 echidnas 3.71 ± 0.75 kg). In marmots, which possess BAT, the highest rewarming rates occur at lower T_b than in echidnas, although active T_b in marmots is 38°C and in echidnas 32°C. The contrasting relationships between peak warming rates and T_b reflect a difference between BAT and muscle thermogenesis. Redrawn from Nicol et al. (2009).