Adrenal responsiveness of black-legged kittiwake chicks (Rissa tridactyla): interannual variation and the effects of nestling status, brood size and investigator disturbance

Abstract

The adrenal response to stress in birds is characterized by the release of the hormone corticosterone. Measurement of corticosterone of individuals is increasingly being promoted as a means to gauge the effects of environmental change or human disturbance on populations. However, species respond differently to stressors based upon their natural history, individual life history stage and the context of the stressor; thus, the collection of baseline data from individuals in their natural environment has been advocated. We measured baseline and stress-induced corticosterone levels of 12-15 day-old black-legged kittiwake (BLKI) chicks from 2002-2005 in Chiniak Bay, Alaska. The goals of the study were to explore the relationships between the adrenal responsiveness of BLKI chicks and 1) BLKI colony productivity; 2) brood size and nestling status; and 3) investigator disturbance. Adrenal responsiveness of chicks negatively correlated with colony productivity, implicating corticosterone concentration as an accurate indicator of colony productivity in poor years. Neither brood size nor nestling status affected the adrenal responsiveness of chicks in both natural broods and broods manipulated to control for maternal hormone deposition. Lastly, two levels of investigator disturbance analogous to that of a growth rate study on chicks did not significantly affect the adrenal responsiveness of chicks.