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

We studied energy expenditure in adult Black-legged Kittiwakes (Rissa tridoctyla) with doubly labeled waterto measure energy costs of chick rearing. We removed eggs from randomly selected nests and compared energy expenditurelate in the chick-rearing period between adults raising chicks and adults whose eggs had been removed. Adultsraising chicks expended energy at a rate 21% higher than adults from manipulated nests, apparently owing to differencesin activity patterns while away from the colony. No sex-specific differences were detected in energy costs ofchick rearing or energy expenditure, although statistical power for these analyses was fairly low. Among theunmanipulated group, energy expenditure tended to be positively related to natural brood size. An ancillary goal of ourstudy 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 deg 09