The Wing Length as a Sexing Criterion of Cettia diphone cantans in Autumn Routine Ringing

Abstract

For the one form, Cettia diphone cantans, of Bush Warbler, it is well known that the colouration of the sexes is identical and that the general size is considerably different between them, though the numerical data of wing length have not been published sufficiently. An aim of this paper is to find a sexing criterion of cantans in autumn routine ringing. The data of this paper were obtained at Otayama Bird Observatory during autumn ringing from 1974 to 1981. One hundred and twenty birds were composed of 92 first winter juveniles and 28 adults. The measurements of wing and tail lengths of these birds are given in Table 1, and Figs. 1-4. Both wing and tail lengths were apparently bimodal. Based on the frequency distribution of wing length, these birds were divided into two groups; Group-A, birds have wings shorter than 61mm, and Group-B have wings longer than 60mm. It seems that these two groups are females and males, respectively. The separation point of the sexes as a criterion was proposed: the birds have wings (1) shorter than 61mm are females, (2) longer than 62mm are males, and it is safe to write (3) 61mm or 62mm are not decidable.