Figure 7.

Photoreceptor spectral sensitivities and feather reflectance spectra. (a) Normalized spectral sensitivities of the four cone photoreceptors with oil droplets having average absorbances (dashed curves; from figure 5) and spectral sensitivities for cones of the blue tit (solid curves). (b) Reflectance spectra (normalized) measured from the distal ends of single breast feathers of a siskin (left inset), and a male bullfinch (right inset). (c) Reflectance spectra of different feather areas of a European goldfinch. The numbers near the spectra correspond to the numbered areas in the inset. The low reflectance for wavelengths <350 nm, even in the unpigmented white feathers (curve 2) is due to far-UV absorption by the main component of the feathers, keratin. The black (5) and brown (3) feather parts presumably contain mainly broadband absorbing eumelanin and phaeomelanin, respectively. The yellow feathers (1) have blue-absorbing carotenes and/or zeaxanthin and lutein, and the red head feathers (4) contain predominantly concentrated astaxanthin.