Avian Magnetoreception: A Radical Pair and a Magnetite-Based Mechanism

Wolfgang Wiltschko and Roswitha Wiltschko

Abstract:	Birds use two kinds of information from the geomagnetic field: directional information and positional information. The avian magnetic compass is an 'inclination compass', deriving directions from the axial course of the field lines and their inclination; it is narrowly tuned to the local field intensity, but can adjust to other intensities. Magnetic intensity and/or inclination are involved in the navigational 'map' and can serve as 'sign posts' or triggers that elicit specific responses. For magnetoreception, two hypotheses are discussed, one proposing magnetite-based mechanisms, the other a radical pair mechanism involving photopigments. Attempt to test the two models with migratory birds and homing pigeons produced evidence for both. Birds responded to a short, strong magnetic pulse designed to change the magnetization of magnetite particles with a marked shift in direction; this effect, however, was observed only in experienced birds. Tested under various light regimes, old experienced birds as well as young, inexperienced birds showed oriented behavior in the presence of light from the blue-green part of the spectrum, while they were disoriented under long wavelengths beyond 590 nm. High frequency magnetic fields in the MHz-range interfered with orientation when they were presented at an angle to the static geomagnetic field. Together, these findings suggest that a radical pair mechanism provides directional information for a compass, while a magnetite-based mechanism provides positional information used as part of the navigational 'map' or as 'sign posts' to indicate specific locations.
Published in:	Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004) June 7 - 9, 2004 Dayton Marriott Hotel Dayton, OH
Pages:	138 - 147
Cite this article:	Wiltschko, Wolfgang, Wiltschko, Roswitha, "Avian Magnetoreception: A Radical Pair and a Magnetite-Based Mechanism," Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004), Dayton, OH, June 2004, pp. 138-147.
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