Meeting Abstract
Most seabirds are sexually monomorphic and do not display conspicuous differences in plumage or size. Two sexually monomorphic seabird species, Royal Tern (Thalasseus maximus) and Sandwich Tern (Thalasseus sandvicensis), have been intensely studied on the Isles Dernieres Barrier Island Refuge (IDBIR) in Louisiana. However, sex-bias of parameters, such as natal recruits, survivorship, foraging movements, parental care, and site fidelity, have not been addressed due to the difficulty of sexing individuals. The goal of this study was to determine if morphometric measurements are a reliable method of sex determination for Royal and Sandwich Terns. During the 2014 and 2015 breeding seasons, we captured adult Royal and Sandwich Terns, measured morphometric attributes (mass, wing chord, bill length, head+bill length, and tarsus) and collected blood samples to determine sex using molecular techniques. Analysis of blood samples identified the sex of 82 Royal Terns (57 males and 25 females) and 84 Sandwich Terns (40 males and 44 females). Discriminant function analysis (DFA) was used to determine if morphometric measurements were effective in determining sex of each species. DFA resulted in a correct classification rate of 75.6% for Royal Terns based on wing chord and head+bill length and 79.8% for Sandwich Tern based on mass and head+bill length. The ability to determine sex of monomorphic seabirds using morphometric measurements will allow for rapid sexing and enhance ecological investigation of these species.
