| I investigated the comparative foraging behavior and energetics of albatrosses to evaluate how interannual variability in the marine environment, reproductive constraints, and location of the breeding colony influence the foraging strategies of these pelagic seabirds. First, I studied the foraging behavior and marine habitats used by Laysan (Phoebastria immutabilis) and black-footed (P. nigripes) albatrosses, to examine whether these marine predators changed habitat preferences, foraging distributions, or both, in accordance with natural interannual variability in the marine environment. Despite interannual differences in foraging distribution, sea surface temperature was the most important environmental variable in habitat use models, suggesting that both species use similar, consistent environmental cues when searching for prey. I then studied the foraging behavior and marine habitat selection of Laysan and black-footed albatrosses, during different reproductive stages. Habitat selection was again correlated with sea surface temperature for both species, with a preference for cooler water temperatures during incubation and chick-rearing; distance to colony and wind conditions were also important predictors of habitat preference. Individuals ranged significantly further and for longer durations during incubation and chick-rearing as compared to the brooding period, resulting in a narrower range of thermal environments available during brooding. Last, I compared the foraging behavior and energetics of Laysan and black-footed albatrosses to Indian yellow-nosed albatrosses (Thalassarche carteri) breeding on Amsterdam Island, Southern Indian Ocean, to evaluate how proximity to preferred marine habitats during breeding has shaped the foraging strategies of these species. During the incubation period, all three species traveled to subtropical-subpolar transition zones, where marine productivity is high. However, Hawaiian albatrosses traveled further, and for longer durations, to reach these habitats due to the low-latitude location of the breeding colony. During the brooding period, all species retracted their foraging ranges and reduced time at sea. As a consequence, Hawaiian albatrosses foraged in a warm, oligotrophic environment during this stage. Field metabolic rates were significantly lower for Laysan and black-footed albatrosses compared to yellow-nosed albatrosses, and may reflect an adaptation to foraging in a low-productivity environment. |
