20.1 Wednesday, Jan. 4 Polar bears may depress body temperature and metabolic rate during summer WHITEMAN, John P.*; HARLOW, Henry J.; BEN-DAVID, Merav; DURNER, George M.; University of Wyoming; University of Wyoming; University of Wyoming; US Geological Survey email@example.com
In the Arctic summer, extent and duration of sea ice melt is increasing. This displaces Alaskan polar bears from ice in productive near-shore waters to deep-water ice or to land; both areas where seal prey is likely not as available. Also, extensive open water may increase long-distance swimming. Whether bears adjust metabolic rates and thermoregulation to accommodate these changes is unknown. We recorded body temperature (Tb) 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. Tb 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. Shore bears did not show a decline over time in weekly mean Tb, perhaps reflecting a more constant metabolic rate enabled by human-provided food on shore. Bears also had unexpected, rapid bouts of Tb decline and recovery. In Aug–Oct, ice bears averaged 0.65 bouts per day (95% were ≤ 12 hours) that reached a mean minimum Tb of 33.6°C; shore bears averaged 1.06 bouts per day (94% were ≤ 12 hours) that reached a mean minimum Tb of 28.6°C. The cause of these bouts and why they were more frequent and reached a lower Tb for bears on shore is not clear. We propose bouts do not reflect reduced whole-animal metabolic rate and temperature, but regional heterothermy similar to diving penguins. Data on location, ambient conditions, and blood and muscle chemistry may clarify causes and advantages of these bouts in both groups, as well as the gradual Tb decline in ice bears.