The importance of fish in the diet of the South Polar Skua (Stercorarius maccormicki) at the South Shetland Islands, Antarctica
Diego Montalti A B E , Ricardo Casaux A B , Néstor Coria A , Guillermo Soave A C and Maricel Graña Grilli DA Departamento de Biología, Aves, Instituto Antártico Argentino, Cerrito 1248, C1010AAZ-Buenos Aires, Argentina.
B Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Av. Rivadavia 1917, C1033AAJ-Buenos Aires, Argentina.
C Sección Ornitología, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque, B1900FWA-La Plata, Argentina.
D Departamento de Ciencias Básicas, Universidad Nacional de Luján, Rutas 5 y 7, B6700-Luján, Argentina.
E Corresponding author. Email: dmontalti@arnet.com.ar
Emu 109(4) 305-309 https://doi.org/10.1071/MU09042
Submitted: 21 May 2009 Accepted: 2 October 2009 Published: 4 December 2009
Abstract
Where South Polar Skuas (Stercorarius maccormicki) occur in the absence of Brown Skua (S. antarcticus), their main prey consists of other birds. In contrast, where the two species occur together, fish appears to dominate the diet of South Polar Skuas, probably because Brown Skuas monopolise the terrestrial resources. Twenty-eight stomach samples of South Polar Skuas were collected throughout the breeding season at Half Moon Island, South Shetland Islands, Antarctica. Fish were the most dominant prey item (100% frequency, 98% prey mass); their importance remained constant throughout the study period. Although there is a colony of Chinstrap Penguin (Pygoscelis antarctica) nearby the South Polar Skua population and there are very few Brown Skuas, the South Polar Skuas did not eat penguins. The result suggests fish are selected preferentially over terrestrial resources, at least in certain regions, and particularly when availability of terrestrial resources is limited. Thus, competitive exclusion by Brown Skuas may not fully explain dietary choice of South Polar Skuas.
Acknowledgements
We thank C. Garcia-Esponda for the field work. We are grateful to L. J. Marti and B. Wienecke for critically commenting on the manuscript and for improving the English. We are particularly grateful to the Editor and anonymous referees for their helpful comments on the manuscript.
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