Using interpubic distance for sexing manakins in the field

Abstract

Field methods for determining the sex of birds are often limited due to morphometric overlap between sexes, intermediate plumages, seasonality, and reliance on subjective age classification. Interpubic distance, characterized in birds as the distance between the distal ends of the pubic bones, has not been formally tested as a method for determining the sex of birds, despite references among parrot breeders and the frequent use of analogous measurements in mammals. We developed a harmless and easily performed field method for measuring interpubic distance in studies involving bird capture, and compared the interpubic distances of known sex Whiteruffed Manakins (Corapipo altera), Orange-collared Manakins (Manacus aurantiacus), and Blue-crowned Manakins (Lepidothrix coronata) to evaluate the possible use of this measurement to determine sex. Using interpubic distance ranges based on 85% confidence intervals where overlap existed between sexes, the sex of 92.8-100% of all manakins in our study was accurately determined with no misclassification. Interpubic distance performed better than plumage-based methods that sexed 74.0% of all individuals and misclassified 1.5%. Using linear discriminant analysis, we developed classification equations that allowed us to accurately determine the sex of all individuals with 100% accuracy using mass and interpubic distance. Additionally, we compared the interpubic distances of female White-ruffed Manakins to evaluate the potential to determine age and reproductive status. Despite an apparent relationship between interpubic distance, age and reproductive status, we concluded that interpubic distance has limited use for determining age and reproductive status due to extensive overlap (31.6-100%), but shows potential in other applications. Based on these results, we endorse the use of interpubic distance to determine the sex of manakins. We encourage further study to develop additional classification equations using different morphometric measurements and to test the efficacy of interpubic distance to determine sex in other bird species.

Molecular sex determination of 20 bird species protected in the Republic of Serbia

“…Traditional methods of avian sex determination are based on the observation of sex-specific behaviour and comparison of different morphological entities (Tella and Torre, 1993;Baker and Piersma, 1999;Jodice et al, 2000;Mendenhall et al, 2010). Alternatives are aggressive surgical methods (Griffiths and Phil, 2000) and ultrasonography (Hildebrandt et al, 1995), which can be difficult due to the presence of air sacks (Jensen and Durrant, 2006).…”

Sex Determination in 58 Bird Species and Evaluation of CHD Gene as a Universal Molecular Marker in Bird Sexing

“…Accordingly, a number of recent studies have focused on the development of efficient molecular methods for sex identification, which are gaining undivided attention as an aid in research and conservation of many bird species [Cerit and Avanus, ]. Other methods of avian sex determination are based on the observation of sex‐specific behavior and the comparison of different morphological entities [Baker and Piersma, , Jodice et al, , Mendenhall et al, , Tella and Torre, ]. Surgical methods (laparoscopy and laparotomy), which enable the direct observation of gonads, although successful in most cases, are aggressive [Griffiths and Phil, ].…”

Dancing drives evolution of sexual size dimorphism in manakins

“…This study leveraged a large, field-collected morphological dataset and detailed behavioural information from a charismatic group of Neotropical birds to understand the evolution of sexual size dimorphism. We advance on the previous understanding of size dimorphism in manakins by incorporating a phylogenetic comparative framework, considering multiple axes of size dimorphism, and testing whether variation in environment constrains evolution of sexual sizedimorphism [96,97]. The alternative-hypothesis-testing framework demonstrates that although associations between courtship displays and sexual dimorphism in mass reveal the importance of sexual selection in the morphological evolution of this clade, other aspects of morphology have been more strongly shaped by environmental constraints.…”