THE DIRECTION OF CELESTIAL ROTATION INFLUENCES THE DEVELOPMENT OF STELLAR ORIENTATION IN YOUNG GARDEN WARBLERS (SYLVIA BORIN)

The study presented here was conducted in order to analyze the role of the direction of celestial rotation in the development of stellar ori entation in young migratory birds, The test birds were garden warblers , Sylvla borin, which leave their breeding ground on a southwesterly c ompass course, The birds were hand-raised and, during the premigratory period, exposed to an artificial 'sky' in the local geomagnetic field , For the control group C, the star pattern was rotating in the natura l direction, with the centre of rotation and magnetic North coinciding , For the three experimental groups, the star pattern was rotating in the opposite direction; for group E-1, the centre of rotation coincide d with magnetic North, for group E-2 the centre of rotation was at mag netic West and for group E-3 it was at magnetic East. During autumn mi gration, the birds were tested without magnetic information under the same, now stationary, sky, All four groups were able to use stellar in formation for orientation, but only the control group preferred the no rmal southwesterly course, The three experimental groups, in contrast, all oriented towards a significantly different direction, preferring due south, The results for group E-1 showed less scatter than those fo r the other two experimental groups. These results indicate that the d irection of celestial rotation is crucial for the development of the n ormal migratory course with respect to the stars in young garden warbl ers. Establishing the species-specific southwesterly migratory course requires an interaction between celestial rotation and magnetic cues; this interaction appears to depend on the natural direction of celesti al rotation, Rotation in the reverse direction allowed the birds to re spond only in a manner that oriented them away from the centre of rota tion.