Resonance effects indicate a radical-pair mechanism for avian magnetic compass
Thorsten Ritz1, Peter Thalau2, John B. Phillips3, Roswitha Wiltschko2 & Wolfgang Wiltschko2
Department of Physics and Astronomy, University of California, Irvine, California 92697-4575, USA
Zoologisches Institut, Fachbereich Biologie und Informatik, J.W. Goethe-Universität, Siesmayerstrasse 70, D-60054 Frankfurt am Main, Germany
Department of Biology, 2119 Derring Hall, Virginia Tech, Blacksburg, Virginia 24061, USA
Correspondence to: Thorsten Ritz1 Correspondence and requests for materials should be addressed to T.R. (Email: tritz@uci.edu).
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Abstract
Migratory birds are known to use the geomagnetic field as a source of compass information1, 2. There are two competing hypotheses for the primary process underlying the avian magnetic compass, one involving magnetite3, 4, 5, the other a magnetically sensitive chemical reaction6, 7, 8. Here we show that oscillating magnetic fields disrupt the magnetic orientation behaviour of migratory birds. Robins were disoriented when exposed to a vertically aligned broadband (0.1–10 MHz) or a single-frequency (7-MHz) field in addition to the geomagnetic field. Moreover, in the 7-MHz oscillating field, this effect depended on the angle between the oscillating and the geomagnetic fields. The birds exhibited seasonally appropriate migratory orientation when the oscillating field was parallel to the geomagnetic field, but were disoriented when it was presented at a 24° or 48° angle. These results are consistent with a resonance effect on singlet–triplet transitions and suggest a magnetic compass based on a radical-pair mechanism7, 8.
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