Cosmetic Coloration in Birds: Occurrence, Function, and Evolution

Abstract

Colorful plumages are conspicuous social signals in birds, and the expression of these colors often reflects the quality of their bearers. Since mature feathers are dead structures, plumage color is often considered a static signal that does not change after molt. Feathers, however, can and do deteriorate between molts, and birds need to invest heavily in plumage maintenance. Here we argue that this need for preserving plumage condition and hence signaling content might have given rise to a novel type of sexual signal: cosmetic coloration. Cosmetic coloration occurs when the substances used for plumage maintenance change the color of the feathers, thereby becoming a signal themselves. Our review of cosmetic coloration in birds demonstrates that it is more widespread than currently realized, occurring in at least 13 bird families. Cosmetics have varied origins: they can be produced by the bird itself (uropygial and skin secretions, feather powder) or obtained from the environment (soil, iron oxide). Intraspecific patterns of cosmetic use (sex, age, and seasonal dimorphism) suggest that in many cases it may act as a sexual signal. However, more information is required on function, mechanisms, and costs to understand the evolution of cosmetic coloration and to confirm its signaling role.

Seasonal Changes in Colour: A Comparison of Structural, Melanin- and Carotenoid-Based Plumage Colours

“…Indeed, plumage is exposed to a variety of biotic and abiotic factors that could alter coloration. Colour expression could change due to microbial activity [3], ectoparasites [4], accumulation of dirt particles [5], feather abrasion [2], [6]–[8], application of cosmetics [9], [10] or exposure to ultraviolet (UV) light [11], [12]. These effects can in turn be modulated through investment in plumage maintenance [13].…”

Natural soiling has a small effect on structurally-based plumage coloration

“…Condition-dependent coloration supports the hypothesis that birds trade off investing energy in developing brilliant plumage coloration and maintaining other important biological functions. Recently, another mechanism has been proposed to modify pigment-and structurally-based feather coloration (Piersma et al, 1999;Mongomerie, 2006a;Delhey et al, 2007). The color of fully-grown feathers could change due to external factors produced by birds themselves, like preen waxes (Delhey et al, , 2008, or originating from the surrounding environment, like UV radiation (Surmacki, 2008) or ectoparasites (Shawkey et al, 2007).…”

Evaluation of a glossmeter for studying the surface appearance of avian eggs

“…Gloss plays an important role in determining the appearance of avian structures such as eggs and feathers (Delhey et al 2007;Wilson et al 1958;Spottiswoode and ColebrookRobjent 2007;Toomey et al 2010). In this study, we define gloss solely as specular reflectance of white light, i.e.…”

“…In feathers, glossiness decreases when they are preened less or when they cannot be preened at all because of their position on the bird (e.g. crest feathers), and this decrease of gloss may serve as an honest signal to potential mates and competitors of the bearer's weak condition (Delhey et al 2007). Accordingly, feather gloss has been found to be correlated with other measures of male quality in species with visibly glossy plumages (Toomey et al 2010).…”