Energy costs of chick rearing in Black-legged Kittiwakes (Rissa tridactyla)

Abstract

We studied energy expenditure in adult Black-legged Kittiwakes (Rissa tridoctyla) with doubly labeled water to measure energy costs of chick rearing. We removed eggs from randomly selected nests and compared energy expenditure late in the chick-rearing period between adults raising chicks and adults whose eggs had been removed. Adults raising chicks expended energy at a rate 21% higher than adults from manipulated nests, apparently owing to differences in activity patterns while away from the colony. No sex-specific differences were detected in energy costs of chick rearing or energy expenditure, although statistical power for these analyses was fairly low. Among the unmanipulated group, energy expenditure tended to be positively related to natural brood size. An ancillary goal of our study was to test hypotheses that describe how population-level field metabolic rates (FMRs) vary during chick rearing. We compared FMRs among kittiwakes raising chicks at a colony in Alaska (61°09'N) with those reported for a colony in Norway (76°30'N). FMRs of adults raising chicks were nearly identical at the two colonies, suggesting that adults may have preferred levels of energy expenditure during chick rearing that are relatively invariant with environmental conditions, and that are not adjusted according to adult survival probabilities.