Wikipedia
Zugunruhe (pronounced ) is a German compound word consisting of Zug (move, migration) and Unruhe (anxiety, restlessness).
In ethology it describes anxious behavior in migratory animals, especially in birds during the normal migration period. When these animals are enclosed, such as in an Emlen funnel, Zugunruhe serves to study the seasonal cycles of the migratory syndrome. Zugunruhe involves increased activity towards and after dusk with changes in the normal sleep pattern. Researchers have been able to study the endocrine controls and navigational mechanisms associated with migration by studying Zugunruhe.
Zugunruhe has been artificially induced in experiments by simulating long days. Some studies on White-crowned Sparrows have suggested that prolactin is involved in the pre-migratory hyperphagia (feeding), fattening and Zugunruhe however others have found that prolactin may merely be associated with lipogenesis (fat accumulation).
The phenomenon of Zugunruhe was generally believed to be found only in migratory species; however, a study of a resident species has shown low-level Zugunruhe, including oriented activity, suggesting that the endogenous mechanisms for migratory behaviour may be present even in a resident species. Further suggestions for endogenous programs are provided by observations that the number of nights on which Zugunruhe is exhibited by caged migrants appears related to the distance of migration involved.