Biometrics and sex determination of Black-faced Ibis in Captivity

PROSDOCIMI, LAURA; DALIA, ANALIA; ANGULO-FERNANDEZ, CLAUDI; GUNTIN, EUGENIA; GATTINONI VIVIANA

Congreso; IX Congreso de Ornitología Neotropical y VIII Congreso Peruano de Ornitología; 2011

Sex determination is essential in different kinds of ecological studies. Many bird species are not obviously dimorphic in size or plumage, and sex cannot be distinguished by plumage characteristics, but by exhibiting sexual size dimorphism in certain body measurements. Black-faced Ibis, Theristicus melanopis, is sexually monomorphic in plumage so that plumage characteristics cannot be used to distinguish sex.  Six measurements were taken from a sample of 37 known-sex adults. Comparison of the measurements of males and females showed significant differences in curved beak length, height of gluttony, over tarsus and weight, although this results showed a high overlap in the ranges of both sexes. An improved classification of sexes was achieved by applying stepwise discriminant analysis, indicating that curved beak length and height of gluttony were the most accurate variables in a discriminant function model, predicting the sex of adults with about 86% accuracy. Cross-validation using jackknife analysis accurately assigned the sex of 85.7% of males, 77.8% of females.  Black-faced Ibis showed size dimorphism, males are larger than females for most tested variables. We propose a simple and inexpensive method to sex Black-faced Ibis, using only two variables easily measured in the field, which provides classification with a high level of accuracy.