Denning chronology in an Arctic brown bear population

Abstract

Denning is a critical behavioral adaptation for brown bears Ursus arctos to cope with winter, a period of extended resource scarcity. Bears reduce their body temperature, heart rate, and metabolism during this time to minimize energy expenditures. The Arctic has among the most pronounced and longest period of resource scarcity. Thus, we predicted bears in the region would respond by having among the longest recorded denning periods. We used GPS data from brown bears to determine the den entry, den exit, and denning duration for a population living primarily above the Arctic Circle. On average, brown bears in the region denned for 206 days, the longest duration reported using GPS data of which we are aware. The longest denning duration for any individual bear was a remarkable 233 days (64% of the year), which is near the theoretical maximum of 241 days. We found that food availability in fall delayed den entrance, with bears that appeared to consume more salmon entering their dens later. Bears showed greater synchrony in den exiting than den entrance, and female bears with cubs exited their dens more than a week after other bears. Later snow melt out in spring was also associated with later den exits. Climate change has the potential to affect the denning ecology of Arctic brown bears by altering the availability of food, ambient temperature, and precipitation, all of which can alter the costs and benefits of hibernation for brown bears.