Sexual monomorphism in wing loading and wing aspect ratio in Black Vulture (Coragyps atratus) and Turkey Vulture (Cathartes aura)

Abstract Sexual dimorphism patterns in wing area, wing loading, and wing aspect ratio of Black Vulture (Coragyps atratus) and Turkey Vulture (Cathartes aura) are unknown but are of particular interest given the prevalence of these species in scavenging communities in the Western Hemisphere. I assessed these variables in sexed specimens from wintering populations in Nashville, Tennessee. Black Vultures exhibited higher wing loading and a lower wing aspect ratio than Turkey Vultures. Neither species exhibited significant age-related or sexual dimorphism in body weight, wing span, wing area, wing loading, or wing aspect ratio. The relatively low variance observed in the pooled sample of immatures (∼9–21 mo old) and adults suggests that definitive wing size and shape are acquired several years before individuals develop the bare rugose skin and head caruncles characteristic of adults. In a broader context, this study tentatively suggests that variance estimates for wing morphology obtained from unsexed vulture populations may not be unduly inflated by undetected sexual or age-related dimorphism.