Zugunruhe

Zugunruhe or migratory restlessness is determined by the circadian clock in response to the annual cycle. In a study of the orientation of Zugunruhe in Common Starlings, the birds were placed in cages in a room where they could see the sun, including its change of position as the day progressed. As long as they could see the sun, they focused their attention towards the northeast, the correct direction for spring migration. On overcast days, however, the starlings showed no directional tendency.