Energy Utilization by Wilson's Storm-Petrel (Oceanites oceanicus)

Abstract

Wilson's storm-petrels are the smallest endotherms (mean mass ca. 40 g) living and breeding in the cold climate of Antarctica and might therefore be expected to require unusually large amounts of food and energy. We studied the energetics of this species by measuring rates of oxygen consumption in captive birds and rates of CO₂ production in free-living storm-petrels (doubly labeled water method) during the breeding season. Basal metabolic rate (BMR) was 2.15 ± 0.09 cm³ O₂∙g⁻¹∙h⁻¹, equivalent to 37 ± 2 kJ∙day⁻¹, 25% higher than values predicted by allometric models. Thermal conductance, measured at ambient temperatures between 1 and 3 C, was 0.117 ± 0.011 cm³ O₂ ’g⁻¹ ∙h⁻¹∙C⁻¹, 15% below allometric predictions. The apparent lower critical temperature (∼ 16 C) was also well below predicted values (25-27 C). Mean CO₂ production by incubating birds in the field was 3.11 ± 0.82 cm³ ∙g⁻¹∙h⁻¹, equivalent to 81 kJ∙bird⁻¹ ∙day⁻¹. This is 2.2 x BMR and is the highest value yet published for metabolic rate during incubation in birds. Mean CO₂ production by storm-petrels away from the nest (free flight) was 5.77 ± 0.69 cm³∙ g⁻¹∙h⁻¹, equivalent to 157 kJ∙ bird⁻¹ ∙day⁻¹ or 4.2 x BMR. Flight is relatively economical in this species, and flight costs are comparable to those measured in other highly aerial birds. Integrated field metabolic rate (FMR) averaged about 119 kJ∙bird⁻¹ ∙day⁻¹ (3.2 x BMR) during the incubation and brooding stages, and 157 kJ∙bird⁻¹ ∙day⁻¹ (4.2 x BMR) during the chick-rearing period that follows. These are similar to values reported for tropical seabirds and birds in general. Rates of energy utilization were maximal late in the chick-rearing period, but estimated rates of energy capture required to meet the needs of the parent and its chick were probably greatest during the brooding period. Wilson's storm-petrels must consume between 120% and 154% of their body mass in krill per day of foraging to meet their energy requirements during their antarctic breeding season.