Daily Energy expenditure by Adult Leach's Storm-Petrels during the Nesting Cycle

Abstract

We measured metabolic rates of adult Leach's storm-petrels on Kent Island, New Brunswick, in order to determine the energetic costs of reproductive activities in a small, pelagic seabird. Oxygen consumption of captive birds was determined volumetrically, and daily energy expenditure of free-living individuals was estimated by the doubly labeled water technique (DLW). Errors inherent in DLW gave rise to expected standard deviations in estimates of CO₂ production on the order of 20%-30% of the mean, which were similar in magnitude to the variation observed among individual measurements. Furthermore, when final concentrations of in body water were low, an apparent bias in the measurement of background consistently inflated estimates of CO₂ production. Minimum rate of oxygen consumption occurred at 36 C and averaged 90 cm³ h⁻¹ or 1.92 cm³ g⁻¹ h⁻¹. Rate of oxygen consumption increased gradually with decreasing temperature and more rapidly below 16 C, at which point thermal conductance plus evaporative heat loss was 2.6-2.9 J g⁻¹ C⁻¹ h⁻¹. CO₂ production of incubating adults averaged 80 cm³ h⁻¹. Analysis of individuals collected at the beginning and end of the incubation spell indicated that about twothirds of the energy for incubation was supplied by fat deposits and the rest by stomach oils and that the ratio of fat to water loss during incubation was about 1.55 by mass. Carbon dioxide production of adults away from the nest during the first half of the nestling period averaged 191 cm³ h⁻¹. Water turnover rates were 0.136 day⁻¹ in incubating adults and 1.01 day⁻¹ in adults away from the nest. Estimates of daily energy expenditure (DEE) are consistent with Leach's storm-petrels' spending considerable time resting on the water surface while at sea. Ratios of energy expenditure to water turnover suggest that adults assimilate a less energy-dense diet than that which they feed their chicks.