Female choice for age-specific plumage in the orchard oriole: implications for delayed plumage maturation

Subadult orchard orioles, Icterus spurius, are sexually mature yearlings that have a distinctive non-definitive (immature) plumage. Field data indicate that subadults remain unmated significantly more often that adult males. In addition, subadults that do obtain mates do so after most adult males have mated. In mate choice trials using both live and stuffed males as stimulus birds, females preferred males with adult plumage over those with subadult plumage, indicating that subadult plumage may be costly in the context of female mate choice. These results, in conjunction with previously reported findings that failed to find a benefit to subadult plumage, suggest that subadult plumage may be the non-adaptive result of age-specific constraints on plumage development. In addition, female preference for adult over subadult plumage suggests a role for epigamic selection in the evolution of delayed plumage maturation.