Sexual Size Dimorphism and Sex Discrimination in the Wood Sandpiper (Tringa glareola)

The possibility of sex identification in birds is of substantial importance for studies on various aspects of their ecology and behaviour. Discriminant functions have become increasingly popular in studies of bird species that are monomorphic in plumage characteristics because these methods are inexpensive and non-invasive. In this paper, we provide the first discriminant function that could potentially aid in determining sex in a common wader species, the Wood Sandpiper, based on external body measurements. Females were larger than males in all linear body measurements; however, no single measurement can be used to determine sex due to the high degree of overlap between the sexes. Discriminant equation with the most commonly used linear measurements, wing length and bill length, was provided. Identifying birds with discriminant function values D3 < –0.409 as males and those with D3 > 0.217 as females would lead to sex misclassification of only 5% of individuals of each sex, but it would leave as many as 83% of the individuals unsexed. Allowing for a misclassification of 10% would shift the cut-off values to −0.509 for males and 0.633 for females and reduce the number of unsexed birds to 66%. The method presented here allows us to account for sex-specific patterns in future ecological studies of the Wood Sandpiper and can be applied to past data.