Age composition and sexual size dimorphism of albatrosses and petrels off Brazil

Abstract

We present data on age composition and sexual size dimorphism (SSD) of albatrosses, petrels and shearwaters in southern Brazil for 301 birds of 14 species captured live at sea. The pelagic community of seabirds off Brazil comprises birds of different ages and breeding status according to species. Although juveniles of some species such as Black-browed Albatross Thalassarche melanophris and Southern Giant Petrel Macronectes giganteus predominated, all age classes (including breeding birds) were recorded for Atlantic Yellow-nosed T. chlororhynchos and Wandering Diomedea exulans albatrosses. For this heterogeneous community composed of individuals from different colonies, with adults and immature birds pooled, the SSD was more pronounced in bill measurements than in other traits (confirming previous studies) and more conspicuous in giant petrels and Diomedea albatrosses. Closely related species pairs of Thalassarche albatrosses and Procellaria petrels had differing levels of sexual dimorphism. All linear external traits measured within Thalassarche and Procellaria overlapped considerably and, despite being significantly different, were not adequate for species determination or sexing.