AGE AND SEX DETERMINATION OF MONOMORPHIC NON-BREEDING CHOUGHS - A LONG-TERM STUDY

We present criteria for sexing and aging non-breeding Choughs (Pyrrhoc orax pyrrhocorax) based on nine years of capture-recapture data. Shape of the rectrices, intensity of plumage colour and iridescent brightne ss, and the contrast between old flight feathers and Freshly molted on es allowed us to distinguish three age classes (first-year, second-yea r, and after-second-year). For sex determination we selected morpholog ical characters that (1) were independent of breeding status and (2) d id not change with age. Tarsus length and bill width, repeteable measu rements in both sexes, met both of these criteria. A discriminant anal ysis performed with these variables from breeding adults of known sex predicted with an accuracy of 100% the sex of non-breeding Choughs tha t were subsequently captured as breeding adults of known sex. This met hodology may be applicable to other species with delayed maturation wh ere monomorphic plumage precludes discrimination of age and sex.