Orientation in migratory birds: time-associated relearning of celestial cues

Abstract

Migratory birds use the geomagnetic field and celestial cues to identify their migratory direction. In cue-conflict situations, when the two sets of cues give contradictory information, birds normally follow the direction indicated by the magnetic field and recalibrate celestial cues. To analyse the nature of these relearning processes, we repeatedly exposed Australian silvereyes, Zosterops l. lateralis, outdoors to conflicting magnetic and celestial cues at sunset by deflecting magnetic north anticlockwise to 240° west-southwest. The birds followed the altered magnetic cues, changing their preferred direction from south to east. During subsequent tests at sunset without magnetic information, the experimental birds continued to orient in the altered direction, confirming that they had recalibrated the celestial cues. Tested without magnetic information in the morning before sunrise, however, these birds preferred southerly directions that were not different from those of the control birds. This suggests that recalibration of celestial cues was specific for the time of the day when the birds had experienced the cue conflict. Relearning celestial compass mechanisms thus does not seem to be a generalizing process. The use of sunset cues is largely independent of the use of the corresponding cues at sunrise.