Energy Expenditure in Adult Least Auklets and Diving Petrels during the Chick-Rearing Period

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Abstract
Energy expenditure rates of three high-latitude seabirds (least auklet [Aethia pusilla], common diving petrel [Pelecanoides urinatrix], and South Georgia diving petrel [P. georgicus]) were measured during the chick-rearing period to test the hypothesis that power requirements for reproduction in pursuit divers are high relative to other seabirds. Oxygen consumption of resting adults was measured volumetrically using a temperature-controlled, closed system. Carbon dioxide production in free-ranging adults during the chick-rearing period was measured using the doubly labeled water (DLW) method. Standard metabolic rates (SMR) were 1.5 to 1.9 times predictions of allometric equations relating SMR to body mass in nonpasserine birds. Mass-specific CO₂ production and fractional water-turnover rates in free-ranging adults were similar in the three study species. The daily energy expenditure (DEE)/SMR ratio ranged from 3.1 to 4.2. Among values of DEE for breeding birds measured by the DLW method, those obtained in this study were relatively high. Energy expenditure is apparently elevated in pursuit divers by high power requirements for flight and foraging, as surface-feeding seabirds had lower relative energy expenditures. The low gross foraging efficiency and high DEEs of the auklet and diving petrels suggest that the high energetic cost of foraging and food delivery to the nest constrains brood size.