Interannual variability of Black-legged Kittiwake productivity is reflected in baseline plasma corticosterone.

Seabird productivity is shaped by marine resource availability. We examined the link between seabird productivity and an indirect measure of food availability: baseline plasma corticosterone. We predicted low productivity would coincide with elevated baseline corticosterone levels in Black-legged Kittiwakes (Rissa tridactyla). During a 5-year period of declining Kittiwake productivity in Chiniak Bay, Kodiak Island, Alaska, we found increasing baseline corticosterone levels during both incubation and chick-rearing. Significantly lower baseline corticosterone levels were observed in the years with the highest Kittiwake productivity and the least productive years exhibited the greatest baseline corticosterone levels in Kittiwakes. Although we did not measure food availability, declining Kittiwake productivity was consistent with warming ocean temperatures and decreased availability of forage fishes to apex predators. Baseline corticosterone measurements may help researchers assess how Kittiwakes are responding to variations in the marine environment.