Fig. 1. Orientation behaviour of European robins under monochromatic light of the following wavelengths: (A,E) 424 nm blue; (B,F) 510 nm turquoise; (C,G) 565 nm green; (D,H) 590 nm yellow. (A–D) Quantal flux of 7x10¹⁵ quanta s^–1 m^–2; (E–H) ‘bright’ lights, quantal flux of 43x10¹⁵ quanta s^–1 m^–2. The symbols at the periphery of the circle indicate the mean headings of individual birds. Filled symbols, unimodal means; open symbols, preferred end of an axis (E,G); triangles, data from 1999; circles, data from 2000. The arrow represents the grand mean vector proportional to the radius of the circle. The two inner circles mark the 5 % (broken line) and the 1 % (solid line) significance border of the Rayleigh test (Batschelet, 1981). For numerical data, see Table 2, Table 3 and Table 4. B, blue light; T, turquoise light; G, green light; Y, yellow light; X, bright light.

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