Physiological dynamics of body temperature and heart rate during hibernation periods in male Japanese black bears ( <i>Ursus thibetanus japonicus</i> )

The Tb of male bears decreased gradually from the pre-hibernation period to the hibernation-induction period, experienced a predicted mean Tb of 35.2 °C (95% confidence interval (CI) [35.00-35.38]) during the hibernation period, and subsequently increased gradually during the post-hibernation period. The HR decreased rapidly at the end of the pre-hibernation and hibernation-induction periods, stabilized at a predicted mean of 44.76 bpm (95% CI [34.54-54.98]) bpm during the hibernation period, and subsequently increased rapidly at the beginning of the post-hibernation period. Tb and HR followed ~24-h cycles during the pre-and post-hibernation periods. Conversely, Tb and HR fluctuations exhibited synchronization with multi-day cycles during the hibernation periods. These results suggest that Japanese black bears exhibit a daily (24-h) rhythm of Tb and HR during the pre- and post-hibernation periods, while autonomic nervous system regulation predominates during hibernation period. We observed a difference between changes in Tb and HR, Tb decreased only moderately by approximately 4% from the pre-hibernation level, whereas HR dropped dramatically by approximately 38%, with rapid changes in HR and gradual changes in Tb. Our findings enhance the understanding of hibernation physiology and highlight synchronized subcutaneous Tb and HR as key biomarkers in large hibernators.