How do bears know when to hibernate?

Bears do not actually enter a state of hibernation in the traditional sense, but rather they experience a period of deep sleep called torpor. Torpor is a dormant state characterised by a decreased metabolism and heart rate, and a drop in body temperature. Torpor is triggered by a combination of factors, including the availability of food, changes in day length, and cold weather. Bears enter torpor when their food sources become scarce in the winter, and come out when the conditions are more favourable. The timing of torpor varies by species and region, with some bears, such as the American black bear, experiencing multiple periods of torpor throughout the winter, while others, such as the grizzly bear, may stay in torpor for several months at a time.