Carotenoid and melanin coloration are correlated in Black-bellied Whistling-Ducks ( Dendrocygna autumnalis )

The function of multiple patches of color in the plumage of a bird remains poorly understood and most studies of multiple color elements have focused on songbirds. We took advantage of a huge gathering of Black-bellied Whistling-Ducks (Dendrocygna autumnalis) in Costa Rica to capture images of large numbers of ducks under identical lighting conditions. From these images we quantified the saturation of red bills and the brightness of dark neck plumage of 156 adult ducks. We found a significant relationship between bill color and neck color—ducks with redder bills tended to have darker neck plumage. These observations are consistent with predictions of both the redundant signal hypothesis and the shared pathway hypothesis. However, only 12% of variation in one color trait was explained by the other color trait, so even though the darkness of neck plumage and the saturation of bill coloration are correlated, each might still convey distinct information about individual condition.