Tissue structure contributes to the production of a coloured skin display in the Common Myna

Conspicuous coloured displays from ultraviolet to bright red have been documented in many species throughout the animal kingdom. These colours often occur as sexual signals and can be incorporated into different types of integuments (e.g. scales, feathers, skin). Two main mechanisms are known to produce coloured integuments: pigmentation and tissue structure. Although pigmental and structural coloration are separate mechanisms and can occur independently, some coloured displays might emerge from a combination of both. Here, we demonstrate, using biochemical, optical and morphological methodologies, that the yellow coloration of the skin located around the eye of Common (Indian) Mynas (Acridotheres tristis) is produced by both light-reflecting nanostructures and light-absorbing carotenoid pigments. Our analysis confirms that nanostructured collagen in the avian dermis work in combination with carotenoid pigments to produce vivid integumentary colours. Identifying the mechanisms behind the production of a coloured signal provides a basis for predicting how a signal's function might be influenced by environmental factors such as fledgling nutrition.