Gender Determination from Morphometrics in Migrating Magellanic Penguins Spheniscus Magellanicus

Abstract

Magellanic Penguins Spheniscus magellanicus are sexually dimorphic while breeding, but in winter the difference is not always sufficiently evident for visual determination of gender.We examined published discriminant functions and produced additional discriminant functions using morphometric data from 408 beachcast Magellanic Penguins from the Centro de Recuperao de Animais Marinhos on the most southerly point of the Brazilian coast (3115'38"S to 3345'03"S), for which gender was determined by post mortem examination or polymerase chain reaction.The discriminant functions correctly determined the gender of 70-90% of these penguins.However, an important gender-associated bias was detected, as previously published discriminant functions developed for animals in breeding colonies were systematically misclassifying males as females.A method is proposed to adjust the functions and correct this gender bias.While other methods may be more accurate, gender determination from morphometric data still offers reasonably reliable results and is an accessible, rapid, inexpensive and non-invasive method for determining the gender of Magellanic Penguins.