RED-LIGHT DISRUPTS MAGNETIC ORIENTATION OF MIGRATORY BIRDS

THE transduction mechanisms and the neurophysiological basis of magnet oreception in birds are still largely unexplained, even though the rol e of the magnetic compass in the orientation of birds is fairly well u nderstood1. The discussion on magnetoreception in birds and terrestria l vertebrates focuses mainly on two mechanisms: small particles of mag netite2,3 and biochemical bi-radical reactions of excited macromolecul es4,5. When the bi-radical hypothesis was first proposed, magnetic res onance phenomena in the retina were suggested as the primary processes 4, which led to the question of whether magnetoreception was light-dep endent. Homing experiments6 and electrophysiological evidence7 from pi geons have produced evidence consistent with such a mechanism. An effe ct of the spectral composition of light on magnetic compass orientatio n in amphibians has recently been described8: under blue light of 450 nm and below, newts oriented as they did under the full spectrum, wher eas they showed a roughly 90-degrees counter-clockwise shift when test ed under wavelengths at or above 500 nm. Here we report the first orie ntation tests on migratory birds under light of different wavelengths; the results suggest a light-dependent process that appears to differ from that reported in newts.