A recent paper in Science deals with flexibility in birds magnetic sense. Cochran et al (Science 304,405) claim that a kind of thushes they study recalibrate their magnetic compass on a daily basis. Abstract as follows:
Night migratory songbirds can use stars, sun, geomagnetic field, and polarized light for orientation when tested in captivity. We studied the interaction of magnetic, stellar, and twilight orientation cues in free-flying songbirds. We exposed Catharus thrushes to eastward-turned magnetic fields during the twilight period before takeoff and then followed them for up to 1100 kilometers. Instead of heading north, experimental birds flew westward. On subsequent nights, the same individuals migrated northward again. We suggest that birds orient with a magnetic compass calibrated daily from twilight cues. This could explain how birds cross the magnetic equator and deal with declination.
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Night migratory songbirds can use stars, sun, geomagnetic field, and polarized
light for orientation when tested in captivity. We studied the interaction of
magnetic, stellar, and twilight orientation cues in free-flying songbirds. We
exposed Catharus thrushes to eastward-turned magnetic fields during the twilight
period before takeoff and then followed them for up to 1100 kilometers.
Instead of heading north, experimental birds flew westward. On subsequent
nights, the same individuals migrated northward again. We suggest that birds
orient with a magnetic compass calibrated daily from twilight cues. This could
explain how birds cross the magnetic equator and deal with declination.