Sexual Size Dimorphism in the Antarctic Shag

Abstract

-Analysis of the morphology of 141 Antarctic Shags (Phalacrocorax bransfieldensis) breeding at Harmony Point (62017'S, 59014'W), South Shetland Islands, and 85 at Danco Coast (64009'S, 60057'W), Antarctic Peninsula, indicated that males are significantly heavier and larger than females. However, there are overlaps in the morphometric variables (mass, culmen, bill, tarsus and wing length, and bill depth and width) between sexes. Two discriminant functions correctly classified 97.8% and 97.6% of the males and females considered to generate them. When the validity of the discriminant functions was checked on other Antarctic Shags breeding at Harmony Point and at Danco Coast, the rate of correct classification remained high. These discriminant functions could be used to sex chicks older than 45-50 days and juveniles. Received 17 November 1999, resubmitted 4 May 2000, accepted 8 May 2000.