1. Zoologisches Institut, Fachbereich Biologie und Informatik, J.W. Goethe-Universität, Siesmayerstrasse 70, D-60054 Frankfurt am Main, Germany
2. AE Biopsychologie, Fakultät für Psychologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany

Correspondence to: Wolfgang Wiltschko¹ Correspondence and requests for materials should be addressed to W.W. (e-mail: Email: wiltschko@zoology.uni-frankfurt.de).

Lateralization of brain functions, once believed to be a human characteristic, has now been found to be widespread among vertebrates^{1, 2, 3}. In birds, asymmetries of visual functions are well studied, with each hemisphere being specialized for different tasks^{4, 5, 6, 7, 8}. Here we report lateralized functions of the birds' visual system associated with magnetoperception, resulting in an extreme asymmetry of sensing the direction of the magnetic field. We found that captive migrants tested in cages with the magnetic field as the only available orientation cue were well oriented in their appropriate migratory direction when using their right eye only, but failed to show a significant directional preference when using their left eye. This implies that magnetoreception for compass orientation, assumed to take place in the eyes alongside the visual processes^{9, 10, 11}, is strongly lateralized, with a marked dominance of the right eye/left brain hemisphere.