Orientation of night-migrating passerines kept and tested in an inverted magnetic field

Abstract

From 1992 tol999 more than 500 funnel experiments were car ried out with robins, redstarts, whitethroats, and pied flycatchers. The purpose was to elucidate the orientation of birds caged and tested for a prolonged time in an inverted magnetic field, i.e. a field where the vertical component was reversed (pointed up wards). Contrary to expectations, the results did not suggest that orientation was governed by a magnetic inclination compass; generally no differences were found between birds tested in the inverted field and those tested in the natural one. However, occa sional patterns of (bimodal) orientation at right angles appeared, probably elicited by the inverted field, and contradictions be tween stellar and magnetic information. Possibly, the significance and kind of magnetic orientation in passerine birds is less well understood than is normally supposed. © 2002 Taylor & Francis Group, LLC.