Sexing adult Cory's Shearwater by discriminant analysis of body measurements on Linosa Island (Sicilian Channel), Italy

Abstract

Males and females of many avian species may show no plumage dimorphism, but often can be sexed by differences in body measurements. Sex determination of many Cory's Shearwaters Calonetris diomedea, was possible by multiplying bill length by bill depth. In this study, discriminant analysis of six measurements (bill length, bill depth, wing, tail, tarsus and mass) was performed on Cory's Shearwaters breeding on Linosa Island (Sicilian Channel), Italy and the efficiency of sex determination was compared with the univariate method. Results show the advantages of the discriminant functions. Bill depth is the best parameter (up to 92% correct classification), followed by mass (84% correct classification); using mass is simple and causes less disturbance to the birds. Received 10 August 2000, accepted 2 February 2001.