Nutritional stress affects corticosterone deposition in feathers of Caspian tern chicks

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The article was published by John Wiley & Sons Ltd. and is in the public domain. The published article can be found at: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291600-048X.Stressful environmental conditions affect the adrenocortical function of developing animals, which can have consequences\ud for their fitness. Discovery of the avian stress hormone corticosterone (CORT) in feathers has the potential to broaden the\ud application of endocrine research in ecological and evolutionary studies of wild birds by providing a long-term measure\ud of CORT secretion. Mechanisms of CORT deposition in feathers are not well known and few studies have related feather\ud CORT to circulating plasma CORT during feather growth. Our objective was to experimentally test the validity of\ud using feather CORT as a measure of CORT secretion in developing birds experiencing nutritional stress. Caspian tern\ud Hydroprogne caspia chicks were fed ad libitum or restricted (35% less than ad libitum) diets for four weeks. We measured\ud CORT in feathers from these chicks to examine the relationship between feather CORT concentrations and nutritional\ud limitation, circulating plasma CORT, and feather development. We found that feather CORT was higher in controls fed\ud ad libitum than in restricted individuals, despite higher levels of plasma CORT in restricted chicks compared to controls.\ud Feather mass and growth rates were strongly and positively related to feather CORT concentrations in both treatments.\ud This is the first experimental study to show that feather CORT concentrations can be lower in response to nutritional\ud stress, even when plasma CORT concentrations are elevated. Our results indicate that CORT deposition in feathers may be\ud confounded when feather mass and growth rates are compromised by nutritional stress. We conclude that feather CORT\ud can be used for assessing nutritional stress in growing birds, but the direction of response depends on how strongly stress\ud affects feather development