Eumelanin levels in rufous feathers explains plasma testosterone levels and survival in swallows

Pigment-based plumage colouration and its physiological properties have attracted many researchers to explain the evolution of such ornamental traits. These studies, however, assume the functional importance of the predominant pigment while ignoring that of other minor pigments, and few studies have focused on the composition of these pigments. Using the pheomelanin based plumage in two swallow species, we studied the allocation of two pigments (the predominant pigment, pheomelanin, and the minor pigment, eumelanin) in relation to physiological properties and viability in populations under a natural and sexual selection. This is indispensable for studying the evolution of pheomelanin-based plumage colouration. Pheomelanin and eumelanin share the same pathway only during their initial stages of development, which can be a key to unravel the functional importance of pigment allocation and thus of plumage colouration. Using the barn swallow, Hirundo rustica, a migratory species, we found t...