THE ROLE OF DAYTIME CUES IN THE DEVELOPMENT OF MAGNETIC ORIENTATION IN A NIGHT-MIGRATING BIRD

To assess the role of celestial rotation during daytime in the develop ment of the magnetic compass course, pied flycatchers (Ficedula hypole uca Pallas, Muscicapidae) were handraised in Latvia under various cele stial and magnetic conditions. Tests were performed during autumn migr ation in the local geomagnetic field (50 000 nT, 73 degrees inclinatio n) in the absence of celestial cues. A group of birds that had never s een the sky showed a bimodal preference for the migratory southwest-no rtheast axis, whereas a second group that had been exposed to the natu ral sky from sunrise to sunset in the local geomagnetic field showed a unimodal preference for the seasonally appropriate southwesterly dire ction. A third group that had also been exposed to the daytime sky, bu t in the absence of magnetic compass information, also oriented bimoda lly along a southwest-northeast axis. These findings demonstrate that observing celestial rotation during daytime enables birds to choose th e right end of the migratory axis for autumn migration at the Latvian test location. This transformation of axial behavior into appropriate migratory orientation, however, requires the birds to have simultaneou s access to information on both celestial rotation and the geomagnetic field.