WALKER, B.G.*; WINGFIELD, J.C.; BOERSMA, P.D.; Univ. of Washington, Seattle; Univ. of Washington, Seattle; Univ. of Washington, Seattle: Developmental and nutritional aspects of the adrenocortical stress response in free-living Magellanic penguin chicks

In nest-bound chicks that are unable to defend themselves or avoid noxious stimuli, a robust adrenocortical stress response shortly after hatching may be costly due to detrimental affects of a prolonged secretion of corticosterone. Thus, nest-bound chicks may delay the development of the adrenocortical stress response until near fledging. As well, the development of the stress response may be affected by dietary restriction (i.e. quantity or quality of food). Here, we report the development of the stress response in free-living Magellanic penguin (Spheniscus magellanicus) chicks, and the adrenocortical function of chicks within a brood in relation to body condition. Healthy, normally developing penguin chicks showed little glucocortical response to capture stress shortly after hatching, an intermediate response around 45-days post hatch, and a robust adult-like stress response near fledging. The larger sibling in broods of two showed the same pattern, as expected for healthy chicks. In contrast, by day 45, when differences in body condition were well established between siblings, the smaller, food deprived chicks significantly increased baseline levels of corticosterone, but showed normal stress induced levels. Near fledging, baseline levels had returned to normal, but stress-induced levels were lower than expected. These results show that Magellanic penguin chicks do not develop a robust glucocortical stress response until near fledging. However, food deprived chicks appear to increase the rate of development early on, but down-regulate their stress response late in the season. For food deprived chicks, this may be a mechanism to avoid the effects of long-term elevation of glucocorticoids.