Corticosterone levels in feathers and blood of rhinoceros auklets Cerorhinca monocerata are affected by variation in environmental conditions

Abstract

In order to fully understand factors that affect animals during their annual cycle, it is important to measure physiological and behavioral responses to environmental conditions in multiple seasons. We tested the hypothesis that corticosterone levels (CORT) are affected by spatial and temporal variations in marine environmental conditions by measuring levels in the feathers (grown outside of the breeding season) and blood (collected during the breeding season) of an abundant North Pacific seabird, the rhinoceros auklet Cerorhinca monocerata. Birds involved in our study bred on three widely dispersed colonies in three years in which oceanographic conditions differed markedly. Combined nitrogen (δ 15N) and carbon (δ 13C) stable isotope values in blood differed among colonies, while values in feathers did not, suggesting that individuals from the three colonies were segregated during the breeding season (as expected from foraging range around breeding colonies), but not during the nonbreeding period (as expected from genetic homogeneity). CORT showed the same pattern of dichotomy; of particular note, but contrary to our a priori prediction, blood CORT levels were higher in auklets that bred on a colony in which early chlorophyll-a bloom in local waters suggested good feeding conditions, than in auklets that bred on a colony with later local chlorophyll-a bloom. Also contrary to prediction, feather CORT was higher in a year featuring favorable, cold-water La Nina conditions than in a year of unfavorable, warm-water El Nino conditions; values in a third, moderate year were intermediate. We conclude that CORT levels are affected by spatiotemporal variation in marine environmental conditions, but relationships appear to depend heavily on context and thus require careful interpretation and more study.