Hibernation is a state of inactivity with decrease in metabolic processes, body temperature, slower than usual breathing and heart rates. It refers to endotherms – warm blooded animals.
Hibernation is a way of conserving the energy by the animals when there are low temperatures, and the food is scarce. Depending on species, body condition, time of the year or the temperature of the surrounding environment, hibernation may last from several days to several months.
Although polar bears remain active throughout the year, pregnant females enter the state similar to hibernation in the snow den for a few winter months before they give birth to their cubs.