Fig. 2. Orientation behaviour of robins pre-exposed to red light and to total darkness tested under red and green light in spring 2000. C, control tests under `white' light. Upper row: tests under low-intensity red light; R, normal tests; RpeR, after pre-exposure to red light; DpeR, after pre-exposure to total darkness. Lower row: tests under low-intensity green light; G, normal tests; RpeG, after pre-exposure to red light, with open symbols indicating data from 1999; DpeG, after pre-exposure to total darkness. Symbols as in Fig. 1.