Hibernation ecology of brown bears in Sweden

Abstract

Hibernation is an adaptive strategy to cope with unfavourable environmental conditions. Bears are the only large mammal that use this strategy during winter. They reduce their body temperature by several degrees and their metabolism by 20-50 % during hibernation. However, bears have an exceptional position among hibernators, because they are the only mammal with delayed implantation, gestation, parturition, and lactation during hibernation. Bears do not consume food but must rely on fat reserves during winter and give birth to one to three cubs during hibernation. In general, the length of hibernation is shorter at more southern latitudes and increases towards the north, and bears lose 20-45 % of their body weight during this time. Three types of winter dens are used by brown bears in Scandinavia: excavated anthill and soil dens (74 % of all dens), natural cavity dens (11 %), and open nest dens (15 %). Reproductive success in female brown bears is affected by the choice of den type, and females hibernating in better insulated dens have a higher probability of producing offspring. Brown bears prefer to den in forested areas that provide shelter from wind and cold temperatures, as well as at higher altitudes and areas with steeper slopes. Bears are especially sensitive to human disturbances during hibernation and prefer to den far from human infrastructure and settlements.