MORPHOMETRIC TRAITS AND THEIR ASSOCIATION WITH SEX IN THE KEEL-BILLED TOUCAN RAMPHASTOS SULFURATUS

Abstract

Sexing monomorphic birds is essential for reproduction in conservation programs. In ramphastids (toucans) species, males have longer beaks than females, making beak morphometry potentially useful for sexing. In this study, we measured the following traits: curved beak length, total culmen length, straight beak length, curved and straight length of the ventral line of the gnathotheca, beak width, lateral area of the rhinotheca, and cloacal opening in 44 Keel-billed Toucans, as well as previously reported morphometric data from 17 additional individuals. Measurements were obtained using two methods (manual and image processing software), and the reliability between the two methods was assessed using the intraclass correlation coefficient (ICC). Individuals of unknown sex were sexed via PCR tests. The ICC showed poor reliability between the two measurement methods, so we only used manual measurements for comparisons between the sexes. We used GLMMs to determine whether the morphometric traits we measured could be used to determine sex in keel-billed toucans. In addition, we evaluated GLMMs to determine which morphometric trait was the strongest predictor of sex in this species. Beak length was longer in adult males than in females. The GLMMs indicated that beak traits associated with sex in this species are beak curved length, beak straight length, straight length of the ventral line of the gnathotheca, and total culmen length. The straight length of the ventral line of the gnathotheca was the strongest predictor of sex in the Keel-billed Toucan. Unlike previous research, the development of GLMMs allows us to determine the probability of a toucan’s sex based on continuous variables, facilitating sexing and allowing us to evaluate the reliability of the estimation of the sexing of each toucan. This method is an alternative for situations where other sexing methodologies cannot be performed.