Clock-Shift Experiments with Migratory Yellow-Faced Honeyeaters, Lichenostomus Chrysops (Meliphagidae), an Australian Day-Migrating Bird

Abstract

ABSTRACT The behaviour of an Australian day migrant, the yellow-faced honeyeater Lichenostomus chrysops, was studied in order to assess the role of the sun in migratory orientation. During autumn migration, all tests took place under a sunny sky; birds were tested while living in the natural photoperiod (control) and with their internal clock shifted 4h fast and 4h slow. In spring, all birds were shifted 3h fast; tests in overcast conditions, with the birds relying on their magnetic compass, served as controls. In control tests in both seasons, the birds preferred directions corresponding to those observed in the wild. When tested under sunny conditions with their internal clock shifted, the birds changed their directional tendencies. However, their preferred directions were different from those expected if a time-compensating sun compass was being used. After about 6 days, the shifted birds’ directions were no longer different from the control direction. This behaviour argues against a major role of the sun compass in the orientation of day migrants. The dramatic changes of the sun’s arc with geographic latitute might cause day-migrating birds to prefer a more constant orientation cue, such as the geomagnetic field. The initial response to the clock-shift might have occurred because the birds were confused by the conflicting information from solar and magnetic cues. This suggests that the sun is usually used as a secondary cue in combination with the magnetic field.