Sexual size dimorphism and sex determination by external measurements in the Redshank Tringa totanus

Abstract

The Redshank is a wader species that shows no sexual dimorphism in plumage, but some dimorphism in size. To propose a method for sexing birds of this species by linear measurements, a discriminant function analysis was applied to a set of morphometric traits in birds captured during the spring migration in southern Belarus. In total, 113 males and 75 females were measured and sexed molecularly. On average, females were larger in all measurements than males. The most sexually dimorphic trait was wing length, which was included in the discriminant function analysis. Jackknife cross-validation showed that the provided equation allowed the correct sexing of 67% of birds (81% of males and 52% of females). When identifying birds with this discriminant function, values lower than -0.96 indicated males, while those larger than 1.17 indicated females. This allowed the correct sexing of 95% of birds of each sex. The presented discriminant equation may be successfully used for sexing Redshanks when blood sampling is not possible, and could be applied to samples collected in the past, providing the opportunity to re-examine results of previous analyses.