Reflectance spectra of a European jay wing covert, which had diffuse coloration with a specular highlight. Reflectance spectra of a European jay wing covert, which had diffuse coloration with a specular highlight. (A) Reflectance under localised illumination for three viewing geometries: (i) E=5°; O=0°; (ii) E=5°; O=5°; (iii) E=90°; O=45°. Curve ii is elevated across the spectrum, consistent with a specular highlight. Curves i and iii are alike, implying that the structural colour (rather than the highlight) was insensitive to viewing geometry. (B) Reflectance under diffuse illumination for two orientations: (i) O=0°; (ii) O=60°. At O=30°, reflectance resembled that at O=0°. These reflectance curves had narrower peaks than for localised illumination, probably because they were recorded from different locations on the blue coloration band (this feather grades from white through black and is most saturated at an intermediate location). Otherwise the reflectance was unaffected by the difference in lighting. O, surface orientation; E, illumination elevation. D. Osorio, and A. D. Ham J Exp Biol 2002;205:2017-2027 © The Company of Biologists Limited 2002