Magnetic Orientation Of Migratory Wheatears (Oenanthe Oenanthe) In Sweden And Greenland

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Abstract
Orientation experiments were performed with wheatears (Oenanthe oenanthe) subjected to artificially manipulated magnetic fields, in Sweden and Western Greenland, during the autumn migration period. The objective was to compare responses by birds exposed to widely different geomagnetic conditions and, specifically, to clarify if birds are able to use magnetic cues for orientation at high geomagnetic latitudes, as in Western Greenland. Orientation experiments were run under clear sunset skies and under simulated total overcast. Clear-sky tests did not reveal any clearcut orientation responses by wheatears in deflected and vertical magnetic fields. There was a tendency, however, for previous experience of the relationship between geomagnetic cues and visual information to affect the birds' orientation in a vertical magnetic field. Under simulated overcast, the birds closely followed a 90° shift in magnetic direction in both study areas, and both samples failed to exhibit statistically significant mean directions when tested in vertical magnetic fields. The results clearly demonstrate that wheatears possess a magnetic compass. Furthermore, the birds are able to detect and use local geomagnetic information even at high magnetic latitudes in Western Greenland, notwithstanding the steep inclination (+81°) and large declination (−46°). A persistent attraction towards magnetic northwesterly headings, under both clear and overcast skies, is not consistent with migratory directions according to ringing recoveries and warrants further investigation.