WILLIAMS, C.T.*; KITAYSKY, A.S.; BUCK, C.L.; Univ. of Alaska Fairbanks; Univ. of Alaska Fairbanks; Univ. of Alaska Fairbanks: Adrenocortical activity in tufted puffin nestlings varies with growth rates and fledging behavior

Birds modulate the hypothalamus-pituitary-adrenal axis (HPA) in response to changes in life and changes in nutritional status. Baseline levels of corticosterone (cort) and the adrenocortical response to acute stress in semi-precocial nestlings of some species negatively correlate with nutritional status. Conversely, species that are subjected to extended periods of chronic food restriction in their life histories may down-regulate the adrenocortical stress response to avoid the deleterious effects of long-term exposure to elevated levels of cort. Tufted puffin chicks routinely experience variable food availability; therefore, we hypothesized that the adrenocortical response of wild puffin chicks would negatively correlate with nutritional status. We also predicted puffin chicks would modulate plasma cort levels as they approached fledging, a major transitional period in the life of birds. We measured growth rates, baseline cort (<3 min post capture), and adrenocortical stress response (subsequent samples at 10, 30, and 50 min) of 30 and 40 day-old free-living puffin nestlings during a season with high reproductive success and above-average rates of growth. Plasma cort concentrations at 10 min. negatively correlated, whereas cort levels at <3, 30, and 50 min. rates were not significantly correlated with growth rates. Baseline levels of cort in puffin nestlings increased more than 3-fold as chicks approached fledging age. These results suggest that puffin nestlings modulate adrenal sensitivity but not capacity in response to changes in food intake. High levels of cort in fledging-age puffins likely acts to promote mobilization of stored energy reserves needed as chicks transition from the nest to the marine environment where they are completely self-reliant.