Bird orientation: displacement experiments with young autumn migrating wheatears,Oenanthe oenanthe, along the Arctic coast of Russia

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Abstract
Migratory naive birds are thought to find the migration route from their natal site to a specific wintering area by either clock-and-compass orientation or goal area navigation. These two alternative hypotheses were tested by extensive longitudinal displacements of juvenile wheatears, hatched in northeastern Siberia, on their first autumn migration towards the wintering area in East Africa. Orientation of individual birds was repeatedly recorded in circular orientation cages, under natural clear and overcast conditions in the local geomagnetic field, during the westward displacement. During the initial part of the migration period (no stars visible), the wheatears oriented towards geographic NW-NNW under both clear and overcast skies. At the last test site, when the birds got access to directional information from the stars, their orientation changed and became bimodal with the majority of headings towards south. These results fail to support both clock-and-compass orientation and goal area navigation, and show that additional factors, not yet understood, affect the birds' orientation in field tests.