USE OF MORPHOMETRIC PARAMETERS FOR THE DETERMINATION OF SEX OF ADELIE PENGUINS

The sex of Adelie penguins, Pygoscelis adeliae, may be determined by cloacal examination during the early part of the breeding season. Later in the season it becomes increasingly difficult to determine the sex of penguins by this method as the structures used for identification regress. Discriminant analysis of morphometric characters has been suggested as an alternative. This technique was examined for breeding birds of known sex near Mawson Station, Antarctica. The sex of 89% of breeding birds could be correctly determined by comparing the discriminant score D=0.582 B(L)+1.118 B(D)+0-219 F(W), where B(L) is bill length, B(D) is bill depth and F(W) is flipper width, with a mean discriminant score (MDS) of 55-39. In all, the sexes of 87% were correctly determined by means of length and depth only (D=0.601 B(L)+1.154 B(D), MDS=44.96). The sex of juvenile birds could not be determined. Determination of sex by discriminant analysis is shown to give acceptable estimates of morphometric characters divided by sex where only the mean and variance of these variables but not the sexual identity of individual birds is required. Where absolute accuracy in sex determination is required, 80% of the birds in our samples would have to be discarded to be 90% confident of the sex of the remainder.