A Technique for Recording Migratory Orientation of Captive Birds

CERTAIN birds when held in small cages during the migration seasons exhibit a nocturnal restlessness which has been interpreted as an expression of migratory condition and termed Zugunruhe. In 1949 the late Gustav Kramer demonstrated that Red-backed Shrikes (Lanius collurio) and blackcaps (Sylvia atricapilla), placed in cages under the night sky, often tended to orient their Zugunruhe toward the side of the cage corresponding to the normal migration direction. This observation suggested a new approach to the elusive problem of migratory orientation, an approach which has since been exploited by several investigators under a variety of conditions.