Sexing of adult Gentoo Penguins in Antarctica using morphometrics

Discriminant function analysis of morphometrics was used to develop a method for sexing Southern Gentoo Penguins (Pygoscelis papua ellsworthi) from Ardley Island, South Shetlands. A combination of five measurements was found to represent most of the differences between sexes: D-1 = 0.399 bill depth + 0.04 maximum gap + 0.0129 foot + 0.0589 head and bill + 1.096 mass - 38.64. Scores of D-1 greater than -0.09 indicated male sex, lower values female sex. Mass and bill depth had the greatest contribution to the discriminating power of this function. Because mass was subject to seasonal changes, a second function was calculated: D-2 = 0.753 bill depth + 0.066 maximum gap + 0.137 foot + 0.0791 head and bill -0.139 width of flipper -36.408. Values of D-2 above -0.086 indicated male sex. Misallocation rates were estimated by cross-validation to be 8.6 and 11.4% respectively. By comparing individual discriminant scores with critical values, more than 70% of all birds can be sexed with a confidence of >95%.