Consistent effect of an attached magnet on the initial orientation of homing pigeons, Columba livia

There is ongoing debate about which sensory mechanisms are critical for animal navigation over long distances. We tested whether magnetoreception associated with the front of the head is involved in navigation by homing pigeons. We attached small, but strong, rare-earth magnets atop the ceres of experienced homing pigeons and released the birds under sunny conditions. In releases distributed over a wide range of distances and directions, the mean vanishing directions of birds carrying magnets were consistently (91% of releases) shifted to the right of controls carrying brass weights. The right shift appeared within a few minutes after release and was reproducible over consecutive years. The magnetʹs effect was sustained (82%) in birds released repeatedly at one site and was larger (73%) for a North-up than for a South-up orientation of the magnet in releases (88%), where the North-up and South-up groups of experimental birds were right-shifted relative to their controls. We discuss several possible nonnavigational and navigational explanations for the magnetʹs effect on the pigeonsʹ vanishing direction.