Hibernation has been a key area of research for several decades, essentially in small mammals in the laboratory, yet we know very little about what triggers or ends it in the wild. Do climatic factors, an internal biological clock, or physiological processes dominate? Using state-of-the-art tracking and monitoring technology on fourteen free-ranging brown bears over three winters, researchers recorded movement, heart rate, heart rate variability, body temperature, physical activity, ambient temperature, and snow depth to identify the drivers of the start and end of hibernation. Studies revealed that brown bear hibernation was initiated primarily by environmental cues, but terminated by physiological cues.

More information: Evans, A. L., N. J. Singh, A. Friebe, J. M. Arnemo, T. G. Laske, O. Fröbert,  J. E. Swenson, and S. Blanc.  2016.  Drivers of hibernation in the brown bear. Frontiers in Zoology 13:7, DOI: 10.1186/s12983-016-0140-6.