Reproductive Energetics and Prey Harvest of Leach's Storm‐Petrels in the Northwest Atlantic

Abstract

Leach's Storm—Petrels (Oceanodroma leucorhoa), the smallest and most abundant seabirds that breed in the northwest Atlantic, are not usually included in avian energetics models. To round out an energy analysis of seabirds spanning the full range of body sizes in the northwest Atlantic, the field metabolic rates (FMRs) of breeding Leach's Storm—Petrels were measured using doubly labeled water techniques (DLW). Metabolic, dietary and, demographic data were used as inputs in a populations energetics model to estimate the energy requirements and prey harvests of the Leach's Storm—Petrel population of eastern North America. FMRs of storm—petrels that remained in burrows averaged 83.3 ± 19.4 KJ/d. FMRs increased significantly with time (i.e., x in hours per day) at sea (y = [85.8 ± 6.5] + [3.13 ± 0.48]x), and metabolism at sea was estimated to be 161 ± 18 KJ/d. FMRs integrated over activity on land and activity at sea averaged 124 KJ/d during incubation and 142 KJ/d during chick rearing. Incubating adults weighed significantly more than adults rearing chicks, although adult mass did not vary with age of chick. Basal metabolic rate (BMR, measured as O2 flux) averaged 2.02 ± 1.01 cm3°g—1°h—1, equivalent to 45.4 ± 30.4 KJ/d, very similar to values obtained for breeding conspecifics in the Bay of Fundy and in the Bering Sea. Thermal conductance averaged 0.124 ± 0.065 cm3°g—1°h—1°°C—1. FMR/BMR ratios averaged 2.73 for incubating birds and 3.13 for birds rearing young. Population energetics modelling indicated that during a 7—mo breeding period Leach's Storm—Petrels at colonies in the northwest Atlantic Ocean consume >74 000 Mg of prey, mostly myctophids and amphipods (mostly Hyperia galba), as wall as euphausiids (mostly Meganyctiphanes norvegica) and other prey (decapods, copepods, isopods). Leach's Storm—Petrels make up °80% of the breeding seabird population in eastern Canada, but owing to small body size and metabolic efficiency, they account for comparatively little of the energy that flows through the avian assemblage of the northwest Atlantic. An intra—specific, inter—colony difference in FMR is suggested: FMRs measured in a Newfoundland colony were significantly higher than those determined with the same DLW procedure in the Bay of Fundy near the southern limit of the species' breeding range in the northwest Atlantic. Differences in ambient temperatures and wind speed associated with different oceanographic regimes may generate energetic differences. Like inter—colony differences in feeding ecology, inter—colony differences in FMR need to be considered in population and community energetics models and in meso— and mega—scale extrapolations.