Age and sex determination of monomorphic non-breeding choughs: a long-term study

We present criteria for sexing and aging non-breeding Choughs( Pyrrhocorax py rrhocorax) based on nine years of capture-recapture data. Shape of the rectrices, intensity of plumage colour and iridescent brightness , and the contrast between old flight feathers and freshly molted ones allowed us to distinguish three age classes( first-year,second-year, and after-second-year). For sex determination we selected morphological characters that (1) were independent of breeding status and (2) did not change with age. Tarsus length and bill width, repeteable measurementsin both sexes,met both of these criteria. A discriminant analysis performed with these variables from breeding adults of known sex predicted with an accuracy of 100% the sex of non-breeding Choughs that were subsequently captured as breeding adults of known sex. This methodology may be applicable to other species with delayed maturation where monomorphic plumage precludes discrimination of age and sex

Blanco, G., Tella, J. & Torre, I., J. Field Ornithol., 67(3):428-433