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Fig. 3. Photographs of feathers indicating how colours alter with varying surface orientation (O) and illumination elevation (E). The feathers are aligned vertically (Fig. 1); see Materials and methods for details. (A) Magnificent hummingbird cap. (i) O=0°, E=5°; the feather is black; (ii) O=45°, E=5°; (iii) O=0°, E=-75°. (B) Feral pigeon. (i) O=0°, E=5°; (ii) O=30°, E=80°; (iii) O=45°, E=100°. (C) European jay. (i) O=0°, E=5°; (ii) O=5°, E=5°; the feather shows a specular highlight; (iii) O=45°, E=70°. (D) Common kingfisher. (i) O=30°, E=5°; (ii) O=30°, E=45°; (iii) O=30°, E=90°. (E) Indian roller. (i) O=0°, E=5°; (ii) O=45°, E=5°; (iii) O=45°, E=90°.