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

The Earth's magnetic field and celestial cues provide animals with compass information during migration. Inherited magnetic compass courses are select ed based on the angle of inclination, making it difficult to orient in the near vertical fields found at high geomagnetic latitudes. Orientation cage experiments were performed at different sites in high Arctic Canada with ad ult and young white-crowned sparrows (Zonotrichia leucophrys gambelii) in o rder to investigate birds' ability to use the Earth's magnetic field and ce lestial cues for orientation in naturally,,cry steep magnetic fields at and close to the magnetic North Pole. Experiments were performed during the na tural period of migration at night in the local geomagnetic field under nat ural clear skies and under simulated total overcast conditions. The experim ental birds failed to select a meaningful magnetic compass course under ove rcast conditions at the magnetic North Pole, but could do so in gcomagnetic fields deviating less than 3 degrees from the vertical. Migratory orientat ion was successful at all sites when celestial cues were available.