Dynamics of food availability, body condition and physiological stress response in breeding Black-legged Kittiwakes

1. The seasonal dynamics of body condition (BC), circulating corticosterone levels (baseline, BL) and the adrenocortical response to acute stress (SR) were examined in long-lived Black-legged Kittiwakes, Rissa tridactyla, bre eding at Duck (food-poor colony) and Cull (food-rich colony) Islands in low er Cook Inlet, Alaska. It was tested whether the dynamics of corticosterone levels reflect a seasonal change in bird physiological condition due to re production and/or variation in foraging conditions. 2. BC declined seasonally, and the decline was more pronounced in birds at the food-poor colony. BL and SR levels of corticosterone rose steadily thro ugh the reproductive season, and BL levels were significantly higher in bir ds on Duck Island compared with those on Cull Island. During the egg-laying and chick-rearing stages, birds had lower SR on Duck Island than on Cull I sland. 3. The results suggest that, in addition to a seasonal change in bird physi ology during reproduction, local ecological factors such as food availabili ty affect circulating levels of corticosterone and adrenal response to acut e stress.