Use of external biometrics to sex Carrion Crow Corvus corone, Rook C. frugilegus and Western Jackdaw C. monedula in northern England.

Abstract

Carrion Crow Corvus corone, Rook C. frugilegus and Western Jackdaw C. monedula culled as part of a predator control study in Northern England were sexed by inspecting internal reproductive organs and measured to determine whether external biometrics (wing, head-plus-bill and tarsus length) could be used to identify the sex of live birds. Tarsus length was found to vary between observers measuring the same bird so was not considered further. Due to considerable size overlap between the sexes it was not possible to sex all individuals correctly, particularly those less than a year old. The larger males and smaller females could be sexed with 85-93% accuracy, in adult birds using wing length of Carrion Crows of male >327 mm, female <309 mm; Rook male >320mm, female <307 mm; and Western Jackdaw male >246 mm, female <233 mm. Head-plus-bill length improved the number of birds sexed when used in combination with wing length for Carrion Crow and Rook.