Contrary to phylogenetic predictions, crown coloration of the Eared Dove is not regulated by sex hormones

The mechanisms regulating plumage coloration appear to be phylogenetically conserved in avian species: the plesiomorphic character state is estrogen-dependent regulation while testosterone, luteinizing hormone and non-hormonal control are derived states. Limited data exist on the underlying regulatory processes of sexual dichromatism in the Eared Dove (Zenaida auriculata des Murs, 1847). Since the Columbiformes order is close to basal branches, we hypothesised that estrogen and testosterone play a central role in the regulation of crown plumage coloration in the Eared Dove. To test this, we subjected adult males to a forced molt accompanied by an exogenous increase of estradiol and testosterone to determine whether the presence of these hormones during molting modified the spectrophotometric characteristics of the plumage. No significant differences were found between treatments and controls in the colorimetric variables hue, ultraviolet saturation and brightness. Similarly, the avian visual model showed no perceptible changes in chromatic and achromatic signals in the individual male adults. We also analysed the effects of estrogen and testosterone on the growth speed of the new feathers. The hormone-treated groups increased in the speed of molting compared to the control group. These results suggest that the Eared Dove is an exception to basal branch models: rather than regulating coloration, sex hormones speed up the growth of the new feathers.