Coloration of spotless starling nestlings shows genetic and environmentally determined characteristics while begging for food

Similar to other signals, coloration of traits expressed by nestlings while they are begging for food are assumed to reflect their phenotypic conditions, and, therefore, they should be environmentally determined. However, these colorations are also species specifics and, thus, a genetic component explaining the evolution of nestling coloration should exist; a possibility rarely explored in the literature. Cross‐fostering experiments allowed us to quantify genetic and environmental components of coloration of mouth, flanges and skin in a spotless starling Sturnus unicolor population. In addition, by supplementing some nestlings within each brood with non‐pigmented antioxidants (Vitamin E or Vitamin complex), we explored the effects of food supplementation on coloration of begging‐related traits and plasma carotenoid concentration. We detected significant genetic components of colorations of skin and mouth, but not of flanges or plasma carotenoid concentration. Moreover, experimental supplementation with Vitamin E affected UV coloration of mouth, flanges and skin, while vitamin‐complex supplementation exclusively affected flange coloration. Furthermore, coloration of flanges, but not that of other traits, predicted plasma carotenoid concentration suggesting a direct link between these two traits. All these results suggest that coloration of begging‐related traits is a multifaceted signal informing parents about genetic characteristics, and of short‐term needs of nestlings, including antioxidative capacity, that parents could use to adjust feeding efforts, and deciding which chick to feed. Future research should focus on the parents' perspective, taking into account their feeding effort and feeding preferences in relation to genetically and/or environmentally determined coloration of begging‐related traits. A free Plain Language Summary can be found within the Supporting Information of this article Resumen Como ocurre con otras señales, se asume que la coloración de los rasgos relacionados con el comportamiento petitorio refleja las condiciones fenotípicas de los pollos y, por tanto, debe estar determinada por el ambiente. Sin embargo, al ser esta coloración específica de cada especie, debería de existir un componente genético que explique su evolución; una posibilidad que ha sido poco explorada en la literatura. Un experimento de intercambio de pollos entre nidos nos permitió cuantificar el componente genético y el ambiental de la coloración de la boca, boqu