During winter sleep (or hibernation) in bears, metabolism is greatly reduced and all metabolic processes are slowed down, so that they do not consume energy for metabolism and movement. However, their metabolism does not slow down completely, as during the hibernation of ground squirrels or other rodents, which is why the bears call it winter sleep. They consume the accumulated fat reserves, which are accumulated during the goad period, and in the spring they get out of the winter sleep much thinner: they lose up to 30% of the body weight during the winter. The level of basal metabolism decreases drastically, protein metabolism decreases, all processes, including pulse and respiration, slow down. Bears, naturally, do not eat during the winter sleep, they do not have urination, and only in the spring, when they begin to leave the den, they gradually start these processes step by step.
At the same time during the winter sleep, bears continue to grow bones, fur grows. Bears survive in winter without food, because it is due to their nature. During the winter sleep they have a very different physiology, and after, in the spring, they come out of the den and for a long time come to their senses - this period is called walking hibernation. At the first exits, they almost do not eat, they have a departure from the cork, that is, all the remains of vegetation accumulated in the intestine, which they ate before sleeping.
Bears are experiencing the winter period in a state of hibernation because in winter there is no plant food they need. Their diet is approximately 80% of plant foods. Bears consume a little animal food, including small mammals, occasionally ungulates, birds and their eggs, insects and carrion. Unlike other subspecies, the main nutritional feed of Kamchatka brown bear is the fish of the family of salmonids.
Sleeping bears of months on 5-6 and leave from a den in the spring when there is a first grass. Leave the lairs all at different times: first adult males, then single females and young individuals, and last - lactating females with cubs (around April-May). In Kamchatka, some large males do not sleep at all, because there the fish spawns in winter, too, all year round, so they can afford not to sleep, but to continue to feed.
In winter, an important event takes place in the life of bears: bear cubs are born during the winter sleep of the mother, who sleeps with a weak sleep and immediately begins to lactify and lick the cubs immediately after birth. Usually they are born in January-February, rarely at the end of December. When there is a hunt for a den and hunters kill a bear, the female is often killed, next to which are found tiny newborn cubs weighing 300-400 grams. Hunters often take them to themselves, somehow groom, feed with human food, and then these orphan cubs often grow into huge brazen uncontrollable bears, and the masters have to kill them.