SEASONAL FASTING BY POLAR BEARS IS MORE COSTLY THAN HIBERNATION
Polar bears in some regions are forced on land during the summer-fall months when sea ice melts. While waiting for the ice to re-freeze in the fall, these bears typically go without significant food sources for months at a time. This period has been referred to as “walking hibernation.” However, researchers were skeptical of whether a fasting bear’s metabolism is similar to hibernating bears. This is of special concern because the amount of time polar bears have been spending on land fasting has lengthened over time, and it is projected to continue to expand. This increases the amount of energy bears need to store as body fat to sustain them through the fast, and it also leaves less time during the year for bears to hunt and obtain those energy stores. Our research showed that the energy expenditure of fasting polar bears was higher than hibernating bears, with fasting polar bears losing 2.4-3.2 times the mass of equal-sized hibernating brown bears. Therefore, the idea that polar bears are able to enter “walking hibernation” implies greater energy and protein conservation than actually occurs. This information helps researchers better predict the energy stores necessary for fasting, as well as whether bears will survive during longer fasts.