The red-collared widowbird has one of the highest measured plumage carotenoid concentrations in birds. There is a high presence of lutein and zeaxanthin in the feathers, which is consistent with their high dietary consumption of grass seeds. There is a carotenoid basis of ‘redness’ observed in the bird, and studies suggest that its color production is due to enzymatic conversion of dietary pigments into red keto-carotenoids, a costly process. The red collar functions as a dominance signal, which was supported experimentally through manipulation of the badges. The experiment showed that red-collared males dominated orange males, which in turn dominated brown and blue collared males. Furthermore, with additional manipulation of badges, males with enlarged red, enlarged orange, and reduced red collars obtained territories, while those with reduced orange and blackened or removed collars failed to establish or maintain territories. Lastly, males with reduced signals defended smaller territories, had more intruders, and spent more time, thus increased cost, on aggressive interactions. Collectively, these observations led to the conclusion that redness, and to a lesser degree size, indicate dominance status and fighting ability in male contests.