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Resonance effects indicate a radical-pair mechanism for avian magnetic compass


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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Figure 1: Experimental set-up.
Figure 2: Effects of oscillating magnetic fields on magnetic orientation behaviour of European robins.

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We thank the Deutsche Telekom AG, especially H. Küpper, T. Loppnow and B. Marx for technical assistance, and F. Galera, S. Hilmer, C. Koschella and S. Münzner for their help with conducting the experiments. J.B.P. acknowledges the National Science Foundation for financial support. Our work was supported by the Deutsche Forschungsgemeinschaft (W.W.) and the Fetzer Institute (T.R.).

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Correspondence to Thorsten Ritz.

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Ritz, T., Thalau, P., Phillips, J. et al. Resonance effects indicate a radical-pair mechanism for avian magnetic compass. Nature 429, 177–180 (2004).

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