Isotopic homogeneity of breath CO 2 from fasting and berry-eating polar bears: implications for tracing reliance on terrestrial foods in a changing Arctic

• Published in: Canadian Journal of Zoology
• Main Authors: Hobson, K. A., Stirling, I., Andriashek, D. S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 2009
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; Arctic; Hudson Bay; Hudson; Ursus maritimus
• Online Access: http://dx.doi.org/10.1139/z08-137; http://www.nrcresearchpress.com/doi/full-xml/10.1139/Z08-137; http://www.nrcresearchpress.com/doi/pdf/10.1139/Z08-137

With a changing Arctic climate, it is important to know whether polar bears ( Ursus maritimus Phipps, 1774) can supplement their stored fat reserves by intake of terrestrial berries. Although polar bears are known to consume berries while on land, it has been difficult to quantify their relative dependence on stored adipose tissue and berry carbohydrates to meet their energy needs. We sampled breath CO 2 from 300 bears fasting on land in western Hudson Bay during the open-water seasons of 1997 and 1998 and analyzed this breath for stable carbon isotope (δ 13 C) values. We found no difference in the bear breath δ 13 C values for bears known to have recently fed on berries and those that had not. The distribution of δ 13 C values was remarkably tight with average values ranging from –24.2‰ to –24.8‰ with no effect of age, sex, or year of capture. This result was counter to our simple isotopic discrimination model that predicted bears metabolizing adipose tissue derived from seals would have breath δ 13 C values close to –24.7‰ and those metabolizing berries exclusively would have values close to –32.6‰. If correct, our results suggests that the bears which had fed on berries while fasting on land received an insignificant amount of energetic benefit.