Does food availability affect energy expenditure rates of nesting seabirds? A supplemental-feeding experiment with Black-legged Kittiwakes (Rissa tridactyla).

We used a supplemental-feeding experiment, the doubly labeled water technique, and a model-selection approach based upon the Akaike Information Criterion to examine effects of food availability on energy expenditure rates of Black-legged Kittiwakes, Rissa tridactyla, raising young in Middleton Island, Alaska. Energy expenditure rates of females were more responsive to fluctuations in food availability than those of males. Our objectives were to determine if the energy expenditure rates of parent kittiwakes provided with supplemental food, differed from those of control parents, and to determine the strength of the relationship between parental energy expenditure rates and a suite of extrinsic and intrinsic covariates and factors. Fed males likely expended more energy while off the nest than fed females, possibly because of nest defense. Energy expenditure rates of fed kittiwakes were similar to values reported for kittiwakes that were either not raising young or not foraging. Fed kittiwakes increased their reproductive output while simultaneously decreasing parental effort and increasing body condition. Parent kittiwakes, therefore, adjusted parental effort in response to variation in breeding conditions due to changes in food availability. Adjustments in reproductive effort in response to variable foraging conditions may have significant effects on the survival and productivity of individuals, and thus provide substantial fitness benefits for long-lived seabirds such as Black-legged Kittiwakes. Differences in survival rates between the sexes may occur if each sex experiences a different survival curve with respect to field metabolic rate or parental effort.