Plumage color manipulation has no effect on social dominance or fitness in zebra finches

Colorful plumage ornaments may evolve because they play a role in mate choice or in intrasexual competition, acting as signals of species identity or of individual quality. The zebra finch (Taeniopygia guttata) is a model organism for the study of mate choice and its colorful plumage ornaments are thought to be used in both of these contexts. Numerous genetic color variants have been described for this species, but they are rare in the wild. This raises the question whether discrimination against deviant phenotypes maintains the species' uniform plumage color (rare-mate disadvantage). Furthermore, comparison to closely related species suggests that the lack of colorful ornaments in female zebra finches is a derived condition. Male preferences for less-ornamented females may have led to sexual dichromatism in the zebra finch. Here, we test the role of plumage ornaments experimentally by altering male and female coloration to mimic 2 types of naturally occurring genetic color variants. We estimated effects on social dominance and reproductive success in large breeding aviaries in one domesticated and 2 recently wild-derived populations. Hypotheses, methods, and analyses were preregistered to ensure maximal objectivity of the results presented. Despite a fairly drastic manipulation and a powerful experimental design, we found no effect of the treatment on social dominance or on reproductive success. Our results suggest that mate choice is not the mechanism that maintains homogeneity of zebra finch plumage coloration, or that can explain the loss of ornaments in females.