Female plumage coloration in the bluethroat: No evidence for an indicator of maternal quality

Abstract

Sexual dimorphism in plumage coloration among passerines is believed to be largely the result of sexual selection, with males usually being more colorful than females. Yet in many species females also are brightly colored. Such 'ornaments' are traditionally viewed as nonfunctional byproducts of selection for the same trait in the male, i.e., as genetic correlation. Alternatively, female coloration may have a signaling function in contexts such as male mate choice or intrasexual competition. The Bluethroat (Luscinia svecica svecica) is a species exhibiting strong sexual dichromatism and large variation in plumage coloration of females. In a recent aviary experiment, males associated more with colorful females which were both larger and heavier than dull females. These results could be interpreted as evidence for male preference for high quality females. Here we present correlational data from a two-year field study on Bluethroats in which we tested whether female plumage coloration is an indicator of female reproductive quality. Female coloration was positively, although weakly, related to skeletal size, but was not related to body mass during the nestling period. Clutch size, hatching dates, feeding rates, and nestling growth gave no indication that more colorful females were of superior phenotypic quality. The results suggest that plumage coloration does not reflect parental abilities in female Bluethroats. We discuss the implications of our results for the understanding of processes of sexual selection in passerine birds.