Multiple structural colors of the plumage reflect age, sex, and territory ownership in the Eurasian Magpie Pica pica

The role of structural coloration, which is produced by the optical interactions among micro- and nanostructures in the feather barb or barbules, is still unclear in the context of sexual or social signaling, because the mechanism of color production is complex and the factors affecting it are not fully documented. We investigated whether structural colors represent class signals related to age, sex, and territory ownership in a social, sexually monochromatic species, the Eurasian Magpie Pica pica. We examined the reflectance spectra from white scapulars, bluish iridescent secondary and greenish iridescent tail plumage, as well as size of white scapular patch. Significant color differences between age classes were found in all measured plumage parts, with adults having plumage with higher color score, that is brighter, shorter wavelength- directed, and more saturated color, than young magpies. Color differences between males and females and between breeding adults (territorial owners) and non- breeding adults were only detected in the tail plumage. Size of white scapular patch did not differ between age and sex classes. Color differences among individuals belonging to different social classes may lessen agonistic confrontations. Sex differences in coloration may enable prompt sex recognition and thus facilitate pair formation. Higher tail color scores of adults, particularly males, support previous suggestions that the tail characteristics of avian species with relatively long tails represent a visual signal of the bearer's quality.