KITAYSKY, A.S.*; SHULTZ, M.T.; BENOWITZ-FREDERICKS, M.Z.; KITAISKAIA, E.V.; IAB & Department of Biology and Wildlife, Univ. of Alaska, Fairbanks: Corticosterone levels link food availability and fitness in seabirds

The field endocrinology approach substantially enhances traditional methods used to assess food availability for seabirds. Traditional methods are indirect and have limited implementation on large spatial and temporal scales. The field endocrinology approach provides a direct measure of changes in recent food availability and foraging history integrated over periods of weeks. Specifically, temporal changes in food availability can be quantified by measuring concentrations of the stress hormone corticosterone (cort) in the blood of undisturbed individuals, and the rise in blood levels of cort in response to a standardized stressor: capture, handling and restraint. A long-term study of seabirds breeding in Cook Inlet, Alaska, has revealed that, in Common murres, baseline levels of cort were negatively correlated with current food abundance, whereas acute stress-induced levels of cort were negatively correlated with food abundance four weeks prior. Cort levels were also negatively correlated with reproductive performance, and baseline levels accurately predicted persistence of individuals affected by food shortages in a population. Using the field endocrinology approach, we currently investigate the relationships between climate and food web dynamics at several trophic levels and in several distinct oceanographic sites in the Bering Sea.