Colour schemes for birds: structural coloration and signals of quality in feathers

Abstract

Plumage coloration may signal individual quality through carotenoid and melanin colour patterns; novel mechanisms by which structural coloration in feathers could signal individual quality are proposed here. Uniformity of structural colour is suggested to signal developmental stability during feather growth, the colour constituting an amplifier. For structural coloration produced by coloured portions of barbules which are susceptible to loss by abrasion, the intensity of colour is suggested to signal feather quality and abrasion-resistance, the structural colour constituting an amplifying handicap. In both cases, large areas of structural coloured plumage may be more revealing of quality than small areas. Predictions as to the extent, position and combinations of these structural colours relative to carotenoid and melanin coloration were derived from these mechanisms and supported by comparative tests. Structural coloration may thus be a component in multiple messages of individual quality in plumage coloration.