Differential impacts of wind and waves on albatross flight performance in two ocean basins

Background: Albatrosses can commute long distances to feed during the breeding season by avoiding energetically costly flapping flight. Energy from both wind and waves can be used to sustain soaring and reduce flapping flight, yet most studies of albatross flight have focused solely on the influence of wind. Methods: To examine how wind and waves allow albatrosses to reduce energetic costs by limiting flapping flight, we analyzed how the flap rates of five albatross species (370 individuals) across two ocean basins varied with wind speed and swell height. Results: For all study species, soaring using both wind and waves resulted in an 89–93% reduction in the number of flaps per hour and thus more energetically efficient flight. We found notable differences in the relative importance of wind and waves for albatrosses breeding in the Southern Ocean and North Pacific. The flap rates of Southern Ocean species, black-browed (Thalassarche melanophris), grey-headed (T. chrysostoma), and wandering (Diomedea exulans) albatrosses, were better explained by variability in windspeed whereas those of North Pacific species, black-footed (Phoebastria nigripes) and Laysan (P. immutabilis) albatrosses, were better explained by variability in swell height. Conclusions: Our results suggest that Southern Ocean species relied more on dynamic soaring by exploiting winds whereas North Pacific species relied more on wave-slope soaring using swells. This divergence in behavior is likely the result of differences in the regional winds and swells between the two ocean basins. Although windspeeds experienced by albatrosses in both oceans were similar, North Pacific species experienced greater swell heights, likely allowing them to extract more wind energy from waves than albatrosses in the Southern Ocean. Our research highlights the importance of both wind and waves for albatross movement and the need to better understand environmental impacts on physiological drivers of foraging energetics to assess responses of seabirds to a rapidly changing climate.