The Weak Iridescent Feather Color in the Jungle Crow<i>Corvus macrorhynchos</i>

Abstract

We investigated the origin of the iridescent violet-bluish feathers of the adult Jungle Crow, Corvus macrorhynchos, using microscopic and optical techniques. A single layer of melanin granules was found below the surface of the barbules in the feathers of male crows. Although the barbule microstructure was clearly sexually dimorphic, neither the appearance nor the optical measurements were notably different between the sexes, which indicated that the single layer of melanin granules did not contribute to the iridescent color of the feathers. We also found a thin layer, which we refer to as the epicuticle, at the surfaces of the barbules of both male and female feathers, indicating thin-film interference as the most likely cause of the iridescent color. We investigated this possibility by measuring reflection patterns and spectra. Our results suggest that the weak violet-bluish feather color of the feathers of the Jungle Crow is caused by thin-film interface due to the presence of an epicuticle on the feather barbules.