Sexual and social functions of ornamental wing feathers in Black Swans (Cygnus atratus)

Studies on the evolution of ornamentation have traditionally focused on sexual selection, although ornaments may also signal an individual's quality in non‐sexual contexts. Using wild‐captured Black Swans Cygnus atratus , we conducted two‐way association trials to study how a putative mutual ornament (curled wing feathers) influenced swans' intersexual and intrasexual preferences. When allowed to freely associate with two candidate birds matched for size and condition, focal males preferentially associated with the candidate with the higher number of curled wing feathers whereas focal females showed no consistent preference. Males preferred the more ornamented bird during both sexual trials (where both candidates were female) and social trials (where both candidates were male), supporting the hypothesis that monomorphic ornaments can function in both sexual and social interactions.