Flocking behaviour in the twilight ascents of Common Swifts Apus apus
Among the many unique flight behaviours of Common Swifts Apus apus, the most puzzling may be their ascents to high altitudes during both dusk and dawn. Twilight ascents have been hypothesized to be functionally related to information acquisition, including integration of celestial orientation cues, high-altitude visual landmarks and sampling of weather conditions. However, their exact purpose rema