Age and food deprivation affects expression of the glucocorticosteriod stress response in Magellanic penguin (Spheniscus magellanicus) chicks

<p> We examined how the glucocortical stress response in free&hyphen;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&hyphen;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&hyphen;like levels. The larger sibling in broods of two showed a similar gradual stress&hyphen;response development pattern. In contrast, by day 45, when differences in body condition were well established between siblings, the smaller, food&hyphen;deprived chicks significantly increased baseline levels of corticosterone but showed normal stress&hyphen;induced levels. Near fledging, baseline levels had returned to normal, but stress&hyphen;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&hyphen;regulated earlier than expected. However, in cases of extended chronic stress, down&hyphen;regulation may ensue, thus avoiding the negative effects of chronically elevated levels of corticosterone.</p>