Autumn is a crucial season for bearsduring which they accumulate the resources necessary to survive the winter. The hibernation of bears, which usually lasts from November to March, is not a real hibernation, but more of a period of generalized torpor and reduced activity, during which the animal slowly consumes the resources stored in the fall in its own body fat and does not produce excrement. The autumn process of resource accumulation is accompanied by a obsessive hunger: The hormones that signal the body to be full are suppressed, and the bear can spend up to 20 hours a day feeding. Bears prefer acorns during this phase, due to their high fat and protein content. Due to their increased activity in the fall, it is therefore easier to meet them also near population centers during this period.
Not all bears hibernate
The species that live in tropical areas (such as the panda, the sun bear and the spectacled bear), where food resources are available all year round and the seasonal temperature range is not severe, they don’t hibernate at allas well as the polar bears in which only the female reduces activities in a comparable manner when preparing for birth. Hibernation is therefore a prerogative of the bear species that live in the temperate zones with cold winterssuch as the brown bear or the American grizzly. This is an evolutionary survival strategy: rather than spending resources searching for the rare food available in winter, the animal prefers it eat as much as possible when this is still found.
The difference between hibernation and torpor during hibernation
In bears there is no real hibernation, but rather a sort of torpor. THE’hibernation is characterized by a drastic drop in metabolism, heat and body weight: the animal falls asleep for months in its den without never wake upsometimes even if disturbed. Typical mammals that hibernate during the winter are the hedgehog and the dormouse. The winter torpor of bears, however, it is more similar to a period of prolonged drowsiness: the animals never fall asleep completely and alternate rest with short periods of activity. In brown bears present on Italian territory, hibernation usually lasts from November to March.
What happens to the bear’s body during winter torpor
To go months without eating or drinking, bears must rely on significant reserves of body fat. To accumulate enough, in the autumn the bears experiment with the so-called hyperphagia: they eat up to 20 hours every dayputting on almost two kilos of weight daily. There leptin, the hormone produced by adipose tissue that regulates appetite e signals to the body when we are fullis reduced and so bears are able to eat for hours without ever feeling full. Since they are omnivorous animals, a bear in hyperphagia does not disdain any food, but has a predilection for acorns, going so far as to neglect other food sources if these are present. Acorns, in fact, are rich in fats and proteins compared to their carbohydrate content, a food therefore very suitable for hibernation.
As the cold months arrive, the bear enters one state of torpor and can rely throughout the winter only on the resources accumulated in the autumn. During torpor, in fact, bears they do not eat, do not drink and do not produce excrement – they do not urinate or defecate; their body metabolizes fat very slowly, transforming it into water and calories necessary for survival. Despite the prolonged period of inactivity, bears maintain good muscle tone and reduce inflammation: this is because they are able to recycle waste nitrogen metabolic processes and transform it into other proteins. As temperatures rise in early spring, the bear’s metabolism slowly accelerates, causing a progressive awakening and a resumption of normal activities.
The increase in activities during the autumn
Because they have to eat so much for so long, bears are particularly active in the fall and this can lead to a increase in encounters with human beings during this period. Meetings that are not always pleasant: this year in Japan there was in fact the record of attacks by the brown bear and the Japanese black bear. In 2025, there were over 100 people injured by bears in Japan, to the point of pushing the government to involve the army to protect rural areas where bears venture more and more frequently.
In addition to climate change which increasingly reduces the duration of the cold months, this phenomenon could be caused by destruction of natural habitat of bears. According to the Japan Bear and Forest Associationbears approach inhabited centers in search of food because their forests are poor in foods suitable for them, especially acorns. 67% of Japanese territory is in fact covered by forests, but these are mostly forests conifers planted for lumber during post-World War II reforestation. Only 7% of Japanese forests have food sources suitable for bears, pushing more and more bears to find food in rural areas and multiplying the likelihood of attacks.
