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2. Beason, R. C., Semm, P., in: Orientation in Birds (P. Berthold, ed.). Basel: Birkhäuser 1991
3. Wiltschko, W., Wiltschko, R., in: Effects of Atmospheric and Geophysical Variables in Biology and Medicine (H. Lieth, ed.). Den Haag: SPB 1991
4. Larkin, R. P., Sutherland, P. J.: Science195, 777 (1977)
5. Southern, W. E.: ibid.189, 143 (1975)