We examined how the glucocortical stress response in free‐living Magellanic penguin (Spheniscus magellanicus) chicks changes with age and whether adrenocortical function of chicks within a brood varies in relation to food provisioned by adults. Chicks showed little corticosterone response to capture stress shortly after hatching, an intermediate response around 45‐d posthatch, and a robust stress response near fledging. However, in response to an adrenocorticotropic hormone (ACTH) challenge, hatchlings were capable of secreting corticosterone at adult‐like levels. The larger sibling in broods of two showed a similar gradual stress‐response development pattern. 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. Similar to altricial species, normally developing semialtricial Magellanic penguin chicks do not express a robust corticosterone stress response until near fledging. Chronic stressors such as food deprivation cause corticosterone use to be up‐regulated earlier than expected. However, in cases of extended chronic stress, down‐regulation may ensue, thus avoiding the negative effects of chronically elevated levels of corticosterone.
Physiological and Biochemical Zoology
Walker, Brian G.; Wingfield, John C.; and Boersma, P. Dee, "Age and food deprivation affects expression of the glucocorticosteriod stress response in Magellanic penguin (Spheniscus magellanicus) chicks" (2005). Biology Faculty Publications. 26.
Walker, BG, JC Wingfield, and PD Boersma. 2005. Age and food deprivation affects expression of the glucocorticosteriod stress response in Magellanic penguin (Spheniscus magellanicus) chicks. Physiological and Biochemical Zoology 78 (1):78-89.