CAROTENOIDS AND SEXUAL DICHROMATISM IN NORTH-AMERICAN PASSERINE BIRDS

Sexual dichromatism and the extent of male carotenoid-derived plumage coloration in breeding season North American passerine birds was analy zed by phylogenetic statistical methods. Passerines as a whole and fiv e passerine subclades were analyzed by both independent contrasts and simulation methods. In passerines as a whole, carotenoids and sexual d ichromatism are positively correlated irrespective of analysis method. In three of the subclades, the correlations are significant by a clea r majority of analysis methods. Neither melanin nor structurally deriv ed colors show similar significant increases with dichromatism. Carote noids are obtained by animals solely through the diet, whereas both me lanins and structurally derived colors can be synthesized. The relatio nship between sexual dichromatism and the use of carotenoids in plumag e suggests that sexual selection may have promoted the expression of a condition-dependent honest indicator of phenotypic quality.