Visual but not trigeminal mediation of magnetic compass information in a migratory bird.

How do birds find their way home? Magnetic compass information is known to have a key role in bird orientation, but how birds are able to sense the Earth's magnetic field remains unresolved, although two hypotheses have been proposed — the iron-mineral-based hypothesis and the light-dependent hypothesis. Here, reported data from European robins strongly suggest that a vision-mediated mechanism underlies the magnetic compass in this migratory songbird.