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

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 chlorophylla bloom. Also contrary to prediction, feather CORT was higher in a year featuring favorable, cold-water La Niña conditions than in a year of unfavorable, warm-water El Niño 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.