The German term for migratory restlessness in birds during migration season is Zugunruhe. It describes the restless, often highly active behavior that appears when a migratory bird is prevented from traveling.
In captivity, Zugunruhe can include hopping, fluttering, repeated perch changes and unusual activity after dusk. Researchers have recorded it in special cages, including Emlen funnels, to study the timing and direction of migration. The behavior commonly coincides with altered sleep patterns and increased nighttime movement.
The word combines German Zug, meaning movement or migration, with Unruhe, meaning restlessness or anxiety. It was published in 1707 in connection with the innate migratory urge of captive birds. Zugunruhe is not the same as torpor, which is a reduced-activity state, or imprinting, which concerns learned attachment and recognition. Scientists use it to investigate seasonal biological clocks, hormones, fattening and navigational mechanisms.