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 info rmation, with the geomagnetic field and celestial rotation as references. T o test whether the direction of celestial rotation is of importance, hand-r aised pied flycatchers in Latvia were exposed during the premigratory perio d to a planetarium rotating in different directions. During autumn migratio n, when their orientation behaviour was recorded in the local geomagnetic f ield 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 so uth-westerly migratory direction. Birds that had been exposed to a sky rota ting in the reversed direction, in contrast, showed a bimodal preference of an axis south-west-north-east. Their behaviour was similar to that of pied flycatchers that had been raised without access to celestial cues. In Latv ia, the magnetic field alone allows only orientation along the migratory ax is, and celestial rotation enables birds to select the correct end of the a xis. Our findings show that the direction of rotation is of crucial importa nce: celestial rotation is effective only if the stars move in the natural.