Sexing juvenile Goldfinches Carduelis carduelis by plumage colour. Revista Catalana d’Ornitologia 19

Sexing juvenile birds can be very valuable for ringers and researchers, and of critical importance in ecological studies about sexual differences in mortality, dispersal strategies or sex-ratio variation at nests. However, juveniles of many passerine species are typically not sexed by ringers and researchers, often because they have a rather dull plumage colour that shows little individual variation. This paper suggests an easy method of identifying the sex of juvenile Goldfinches by measuring maximum wing length and the number of rectrices with an oval white spot; the method has proved accurate in 91 % of the cases studied. Furthermore, we have validated the classification function provided here with a data set of Swiss birds, of which 96 % of individuals were correctly classified using this system