Kitaysky, A. S. | Search bioRxiv

bioRxiv2025

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

Bidirectional relationships between hormones and behaviors are hypothesized: i.e. energetic consequences of behaviors may alter glucocorticoid levels, and elevated glucocorticoids may alter behavioral responses to stimuli in context-appropriate ways. We tested these relationships between the avian glucocorticoid corticosterone and behaviors related to food-acquisition in free-living seabird chicks (Black-legged kittiwakes, Rissa tridactyla) with robust HPA-axis activity. First, we tested the hypothesis that behavior affects HPA axis activity by quantifying chick behavior for 60 min, then taking a blood sample at baseline and 15-min post-restraint. Only feeding predicted subsequent corticosterone levels (fewer feeds = higher restraint-induced corticosterone). However, the hypothesis that increased corticosterone secretion alters behavior was supported: post-restraint corticosterone levels were positively correlated with increases in begging and aggression in the subsequent hour, primarily in males. In a second experiment, we isolated the role of corticosterone from other components of the stress response by administering exogenous topical corticosterone, which confirmed a positive relationship between subsequent corticosterone levels and changes in aggression, but not begging or feeding. Corticosterone:behavior relationships depended on nutritional context - they were eliminated in nests with experimental food supplementation. Finally, higher levels of corticosterone in response to restraint were associated with more rapid elimination of siblings, presumably increasing chick direct fitness by eliminating competition. We conclude that the magnitude of the endogenous corticosterone response to challenges is a) negatively correlated with recent feeding rates, b) subsequently associated with rapid, sex- and context-specific changes in chick behaviors, at least some of which are likely causally- driven by elevated corticosterone, and c) associated with fitness-relevant consequences.

animal behavior and cognition↗

bioRxiv2024

Corticosterone in very young seabird chicks (Rissa tridactyla) is sensitive to environmental variability and responds rapidly and robustly to external challenges

In birds, patterns of development of the adrenocortical response to stressors vary among individuals, types of stressors, and species. Since there are benefits and costs of exposure to elevated glucocorticoids, this variation is presumably a product of selection such that animals modulate glucocorticoid secretion in contexts where doing so increases their fitness. In this study, we evaluated hypothalamic-pituitary-adrenal (HPA) activity in first-hatched free-living seabird nestlings that engage in intense sibling competition and facultative siblicide (black-legged kittiwakes, Rissa tridactlya). We sampled 5 day old chicks (of the [~]45 day nestling period), a critical early age when food availability drives establishment of important parent-offspring and intra-brood dynamics. We experimentally supplemented parents with food ("supplemented") and measured chick baseline corticosterone secretion and capacity to rapidly increase corticosterone in response to an acute challenge (handling and a 15 min restraint in a bag). We also used topical administration of corticosterone to evaluate the ability of chicks to downregulate physiologically relevant corticosterone levels on a short (minutes) time scale. We found that 5 day old chicks are not hypo-responsive but release corticosterone in proportion to the magnitude of the challenge, showing differences in baseline between parental feeding treatments (supplemented vs non-supplemented), moderate increases in response to handling, and a larger response to restraint (comparable to adults) that also differed between chicks from supplemented and control nests. Topical application of exogenous corticosterone increased circulating levels nearly to restraint-induced levels and induced downregulation of HPA responsiveness to the acute challenge of handling. Parental supplemental feeding did not affect absorbance/clearance or negative feedback. Thus, while endogenous secretion of corticosterone in young chicks is sensitive to environmental context, other aspects of the HPA function, such as rapid negative feedback and/or the ability to clear acute elevations in corticosterone, are not. We conclude that 5 day old kittiwake chicks are capable of robust adrenocortical responses to novel challenges, and are sensitive to parental food availability, which may be transduced behaviorally, nutritionally, or via maternal effects. Questions remain about the function of such rapid, large acute stress-induced increases in corticosterone in very young chicks.

physiology↗