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Like all corvids, the Azure-winged Magpie Cyanopica cyanus is sexually monomorphic in plumage, makingit difficult to distinguish between males and females in the field. We examined sexual size dimorphismin a population of Iberian Azure-winged Magpies C.c. cooki and used a discriminant function analysisbased on five morphological characters to determine the sex of first-year and adult individuals. Females were significantly smaller than males for all tested variables within each age class except for keel length of first-year individuals. In both sexes, wing length of adults was greater than that of yearlings, but only males showed significant differences in tail length between age classes (longer in first-year birds). Stepwise discriminant analysis indicated that tail length and head plus bill length were the most accurate variables in a discriminant function model, predicting the sex of yearlings with about 90% accuracy. Adding wing length to the model yielded the same level of accuracy for adults. We propose a simple system to sex Iberian Azure-winged Magpies, using only two or three variables easily measured in the field, which provides classification with a high level of accuracy.

http://www.avibirds.com/pdf/B/Blauwe%20Ekster1.pdf

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