Avian orientation at steep angles of inclination: experiments with migratory white-crowned sparrows at the magnetic North Pole

The Earths magnetic field and celestial cues provide animals with compass information during migration.Inherited magnetic compass courses are selected based on the angle of inclination, making itdifficult to orient in the near vertical fields found at high geomagnetic latitudes. Orientation cage experimentswere performed at different sites in high Arctic Canada with adult and young white-crownedsparrows (Zonotrichia leucophrys gambelii) in order to investigate birds ability to use the Earths magneticfield and celestial cues for orientation in naturally very steep magnetic fields at and close to the magneticNorth Pole. Experiments were performed during the natural period of migration at night in the localgeomagnetic field under natural clear skies and under simulated total overcast conditions. The experimentalbirds failed to select a meaningful magnetic compass course under overcast conditions at themagnetic North Pole, but could do so in geomagnetic fields deviating less than 38 from the vertical.Migratory orientation was successful at all sites when celestial cues were available.