Are morphometric traits cryptic indicators of sexual size dimorphism in ‘monomorphic’ species? Evidence from the King Vulture ( <i>Sarcoramphus papa</i> )

Understanding sexual dimorphism is essential for ecological and evolutionary research, as it can influence species adaptation, population dynamics and the development of effective conservation strategies. Evidence suggests that sexual size dimorphism is absent or subtle in over 50% of bird species – including most New World vultures (Cathartiformes). We employed a molecular sexing and morphometric analysis approach to assess whether this pattern is present in the King Vulture Sarcoramphus papa and to determine whether males and females can be distinguished morphometrically. We present evidence of moderate male‐biased sexual size dimorphism in the King Vulture, showing that head and bill measurements – and to a lesser extent, wing traits – can be used to discriminate between sexes based on extreme values, thus challenging the traditional view of monomorphism in cathartids and highlighting the value of morphometric analyses in detecting cryptic sexual differences in species considered monomorphic.