Cortex Thickness Is Key for the Colors of Iridescent Starling Feather Barbules With a Single, Organized Melanosome Layer

The iridescent plumage of many birds is structurally colored due to an orderly arrangement melanosomes in their feather barbules. Here, we investigated the blue- purple-colored feathers European starling ( Sturnus vulgaris ) and blue green Cape Lamprotornis nitens ). In both cases, barbules contain essentially a single layer melanosomes, but S. they are solid rod-shaped, L. hollow rod- as well platelet-shaped. We analyzed coloration by applying imaging scatterometry, bifurcated-probe- micro-spectrophotometry. reflectance spectra showed multiple peaks distinct, peak for feathers. Assuming that two species simple multilayer, consisting locally only cortex plus interpret experimental data effective-medium-multilayer modeling. optical modeling provides quantitative insight into function keratin thickness, being principal factor determine wavelength bands; melanosome plays minor role. air cavity creates strongly enhanced refractive index contrast, thus very effectively causing high reflectance.