Corticosterone elevation is associated with rapid, sex-specific increases in food-acquisition behaviors in free-living seabird chicks

The energetic consequences of behaviors may rapidly alter glucocorticoid levels, and glucocorticoids are assumed to redirect behavioral responses to stimuli in ways that increase fitness. We investigated these relationships in young seabirds (Black-legged kittiwakes, Rissa tridactyla ) with facultative siblicide and robust HPA-axis activity, considering environmental context and genetic sex. First, we assessed potential impacts of behavior on corticosterone by quantifying behavior of first-hatched chicks in nests containing two chicks for 60 min before taking a baseline blood sample, restraining for 15 min, then bleeding again. The only behavior that predicted subsequent corticosterone levels was feeding (fewer feeds = higher restraint-induced corticosterone). However, there was evidence for consequences of increased corticosterone secretion on behavior: post-restraint corticosterone levels were positively correlated with increases in begging and aggression in the subsequent hour, primarily in males. Larger corticosterone response to restraint was also associated with more rapid brood reduction. Corticosterone:behavior relationships were eliminated in chicks from food-supplemented nests. To evaluate potential causality of corticosterone in redirecting behavior, we isolated it from other components of the endogenous stress response using minimally-disruptive exogenous topical treatments, and confirmed a positive relationship between corticosterone and aggression (stronger in males), but not begging or feeding. We conclude that elevation of endogenous corticosterone is negatively correlated with recent feeding rates, and is subsequently associated with rapid, sex- and context-specific changes in kittiwake chick behaviors, at least some of which are causally driven by elevated corticosterone and associated with fitness-relevant consequences.