Production Of Melanin-Based Plumage Traits In Male House Sparrows: No Effect Of Dietary Copper

Abstract In many bird species, males possess conspicuous patches of black feathers on their head or breast, the size of which is often positively related to their success in intra- and intersexual interactions. The production of these plumage signals is presumed to depend upon one or more limiting factors which prevent low quality males developing large signals in order to gain the associated benefits. The coloration of these feathers is due to their infusion with the pigment melanin, which birds synthesize endogenously during a series of conversion steps beginning with the enzymatic oxidation of the amino acid tyrosine. Copper is the cofactor of the enzyme responsible for this process, and it is possible that copper level limits the activity of the enzyme and therefore limits melanin production. We tested this hypothesis by manipulating the level of dietary copper available to individually caged juvenile and adult house sparrows (Passer domesticus) throughout their moult. Birds were provided with artificial diets containing either 100%, 50% or 10% of the recommended level of copper. Dietary copper did not affect the size of the black breast patch, the most obvious melanin-based plumage trait in this species, nor did it affect the reflectance of the black feathers. In sum, we reject the hypothesis that dietary copper limits the size or blackness of the breast patch of the male house sparrow.