Polar bear body temperatures and behavior in the changing Arctic summer

Background/Question/Methods

In the Arctic summer, extent and duration of sea ice melt is increasing, displacing Alaskan polar bears from ice in productive near-shore waters to deep-water ice or to land. In these habitats, seal prey is likely at low availability. Additionally, extensive open water may increase long-distance swimming. It is unknown how these changes affect metabolic rates and thermoregulation of polar bears. We recorded body temperature (T_b) with loggers implanted adjacent to the abdominal peritoneum, ventral to the linea alba, in 4 bears on deep-water ice (May–Oct) and 5 bears on shore (Aug–Oct) in the Beaufort Sea.  

Results/Conclusions

T_b of ice bears declined from a weekly mean of 37.2–37.5°C (May 23–Jun 03) to 34.7–36.6°C (Sep 21–Oct 09). We propose this reflects a gradual reduction in metabolic rate in response to limited seal availability. Bears had unexpected, rapid bouts of T_b decline and recovery. In Aug–Oct, ice bears averaged 0.65 bouts per day (95% were ≤ 12 hours) that reached a mean minimum T_b of 33.6°C; shore bears averaged 1.06 bouts per day (94% were ≤ 12 hours) that reached a mean minimum T_b of 28.6°C. The cause of these bouts and why they were more frequent and reached a lower T_b for bears on shore is not clear. Pending analyses explore relationships between gradual T_b decline and energetics; relationships between bouts of low T_b and swimming behavior; and implications of these patterns for polar bears in the changing Arctic summer.