Rewarming rates and thermogenesis in hibernating echidnas

We measured body temperatures (Tb) in 14 free-ranging echidnas (Tachyglossus aculeatus) using implanted data-loggers. An average of 1020 ± 744 days of Tb data was recorded from each animal. The average maximum Tb was 35.3 ± 0.7 °C (n = 14), and the lowest Tb was 4.7 °C. Detailed analysis of rewarming events from four echidnas showed rewarming time to be dependent on initial Tb (rewarming time in hours = 15.6 − 0.41Tinitial, n = 31) with an average rewarming rate of 1.9 ± 0.4 °C h− 1. Based on an hourly sampling rate, the peak rewarming rate was found to be 7.2 ± 0.8 °C h− 1 (n = 12), which was measured at a mean Tb of 26.2 ± 2.4 °C. This rate of heating was calculated to be equivalent to a peak oxygen consumption rate of 1.4 ± 0.2 ml O2 g h− 1, approximately 9 times the basal metabolic rate. We found that a plot of rate of change of Tb against Tb for the entire data set from an individual echidna provided a useful summary and analytical tool.