The use of wing length for sexing Common Chiffchaffs Phylloscopus collybita in a local breeding population

ABSTRACT Common Chiffchaffs Phylloscopus collybita caught at Wicken Fen during the breeding season showed a strongly bimodal distribution of wing length, with females being typically shorter-winged than males. Studying wing length in a local population helped to control the effects of variables other than sex, and provided the opportunity to compare behavioural and other breeding-related sexing criteria with the sex indicated by the wing length. All records of brood patch and female-related behaviour were for short-winged birds, and all records of cloacal protuberance and male-related behaviour for long-winged birds. An overlap of wing length between the sexes existed at 58 mm.