Activity‐Specific Metabolic Rates of Free‐Living Northern Gannets and Other Seabirds

Abstract

Field and activity—specific metabolic rates of 20 free—living Northern Gannets (Sula bassanus; mean mass = 3.21 kg) rearing chicks at Funk Island, Newfoundland, were measured using doubly labeled water and activity timers. Field metabolism (FMR) averaged 4865 kJ/d or 6.6 x basal metabolism (BMR). Regression analyses indicated a metabolic rate of 144 kJ/h while at the nest or on water, 349 kJ/h during flight, and 250 kJ/h during diurnal time at sea. These metabolic rates are high, probably because of costs of thermoregulation and flapping flight. BMR was slightly lower than predicted. Statistical analyses of metabolic rates of free—living seabirds indicated that rates are elevated in seabirds in cold—water regions and in seabirds that use flapping flight, but do not vary with phylogenetic order. FMR was correlated strongly with both BMR and metabolism at the nest. Population energy models may gain accuracy if metabolic rates are either expressed as multiples of metabolism at the nest or calculated from allometric equations appropriate for the species' activity pattern, oceanographic regime, and foraging mode.