Carotenoids and Skin Coloration in a Social Raptor

Abstract

Abstract The outcome of social and sexual competition in animals is typically mediated through the expression of body traits. Conspicuous characters such as yellow, orange, and red colorations in skin, scales, and feathers are often posited as quality-dependent signals, because such colors are made of dietary carotenoids and their use for signaling conflicts with health functions. Raptors often lack brightly colored feathers but most diurnal species display intense orange and yellow hues in the cere and legs. Here we test the hypothesis that integument coloration functions as a signal of status in wild raptors, revealing availability of carotenoid pigments. As study model we used the Black Kite (Milvus migrans), a highly social, long-lived, and sexually monogamous Accipitriform. Regular trapping of adults throughout the breeding season revealed that circulating carotenoid levels were highest in breeding males, whereas breeding females and floaters showed moderate and statistically similar carotenoid titer...