Sex discrimination in the Savi’s Warbler (Locustella luscinioides) using morphometric traits

Abstract

Determining an individual's sex is often difficult in species with monomorphc plumage. but it is important in many ecological studies. This study proposes a logistic function for sexing the Savi's Warbler, Locustella luscinioides, based on standard body measurements. Nine measurements (wing length, tail length, head to bill length, bill length, bill width, billheight, tarsus width in two dimensions and hind-claw length) were selected via logistic regression using AIC (Akaike's information criterion for small sample size). with sex (determined by molecular analysis) as the dependent variable. In total, 224 Savi's Warblers (161 immatures and 64 adults) caught in northern Poland during autumn migration in 2010 and 2011 were examined. The function applied to immatures identified wing length, bill length, head to bill length and hind-claw length as the best measurements for sexing, with 91% of birds correctly classified (90% of females and 92% of males). A second function, applied to adults, included only wing length and bill length as the best predictor variables to identify sex, and it correctly classified 94% of individual (93% of females and 94% of males).