Résumé
Ocean environments and associated biota are affected by wind. Expected future changes in wind conditions could impact seabirds because they influence flight energetics. Seabird morphological characteristics influence their wing loading and other aspects of flight, and hence their responses to varying wind conditions. Foraging efficiency of seabirds can also be affected by the presence of conspecifics, with formation flight potentially reducing energetic costs. Using data obtained from bird-borne video cameras and GPS loggers in conjunction with concurrent wind data, we studied the effects of wind, wing loading and conspecifics on the flight dynamics of Cape gannets Morus capensis . Overall, gannets spent more time flapping than gliding, with the latter used increasingly as wind speed strengthened. Wind direction (relative to direction of flight) influenced the ground speed, which was lower in head- than in tailwinds. We found no significant effect of wing loading on flight dynamics. Instead, the presence of conspecifics was the most influential predictor, showing positive relationships with the duration of time spent in a flight bout, the distance travelled within the bout and flying behaviour (proportion of time spend flapping and gliding, and the number of switches between the 2 states). These results suggest that Cape gannets may benefit from flight formation with conspecifics by reducing the energetic costs of flight (reduced proportion of time spent flapping), which would ultimately result in an increased distance travelled in a single flight bout.