Sex determination and sexual size dimorphism in Southern Giant Petrels (Macronectes giganteus) from Patagonia, Argentina

COPELLO, S.; QUINTANA, F; SOMOZA, G

EMU Austral Ornithology

Csiro Publishing

Lugar: Collingwood, Australia; Año: 2006 vol. 106 p. 141 - 146

0158-4197

We used discriminant analysis of a series of external morphometric measurements, together with confirmation by genetic methods, to develop a simple method to determine the sex of fledgling and adult Southern Giant Petrels in colonies in northern Patagonia. We also described morphometric parameters (bill length, bill depth, tarsus and wing lengths, and weight) for different classes of age and sex and analyzed differences in size between male and female chicks over the growth period. The Southern Giant Petrel showed a conspicuous sexual size dimorphism, with males being significantly larger than females, with this being apparent within eight weeks of hatching. In adults, males were 40% heavier than females and consistently larger in all measurements (% sexual size dimorphism 5 to 15%). For fledglings, bill length was the most dimorphic variable (15.2%). The discriminant analysis of four external measurements correctly identified the sex of more than 90% of adults and fledglings. Bill length alone was sufficient to predict sex of adults and fledglings and can thus serve as a simple and effective tool for sexing Southern Giant Petrels.