Field studies of avian nocturnal migratory orientation I. interaction of sun,wind and stars as directional cues

Tracking radar and visual observation techniques were used to observe the orientation of free-flying passerine nocturnal migrants in situations in which potentially usable directional cues were absent or gave conflicting information. When migrants had seen the sun near the time of sunset and/or the stars, they oriented in appropriate migratory directions even when winds were opposed. Under solid overcast skies that prevented a view of both sun and stars, the birds headed downwind in opposing winds and thus moved in seasonally inappropriate directions. The data point to the primacy of visual cues over wind direction, with either sun or stars being sufficient to allow the birds to determine the appropriate migration direction.