Zwarts L., Hulscher J.B., Koopman K. & Zegers P.M. (1996) Discriminating the sex of Oystercatchers Haematopus ostralegus. ARDEA 84 (A): 1-12

This paper presents methods to determine the sex of Oystercatchers of different age, using measurements of bill length, bill depth, shape of the bill tip, wing length and body weight. The bill length is the most important variable to differentiate between males and females. The shape of the bill tip, the bill depth, the wing length and the body weight consistently vary with sex, but since the overlap is large, it is less reliable to determine sex from these variables. The best segregation between the sexes is obtained by measuring bill length, bill depth, and determining the shape of the bill tip. The paper gives formulae to distinguish the sexes when different sets of variables have been measured.