The Direction of Celestial Rotation Affects the Development of Migratory Orientation in Pied Flycatchers,Ficedula hypoleuca

The migratory direction in young passerine migrants is based on innate information, with the geomagnetic field and celestial rotation as references. To test whether the direction of celestial rotation is of importance, hand-raised pied flycatchers in Latvia were exposed during the premigratory period to a planetarium rotating in different directions. During autumn migration, when their orientation behavior was recorded in the local geomagnetic field in the absence of celestial cues, birds that had been exposed to a sky rotating in the natural direction showed a unimodal preference of their south-westerly migratory direction. Birds that had been exposed to a sky rotating in the reversed direction, in contrast, showed a bimodal preference of an axis south-west-north-east. Their behavior was similar to that of pied flycatchers that had been raised without access to celestial cues. In Latvia, the magnetic field alone allows only orientation along the migratory axis, and celestial rotation enables birds to select the correct end of this axis. Our findings show that the direction of rotation is of crucial importance: celestial rotation is effective only if the stars move in the natural direction.