Diet of the common tern (Sterna hirundo) during the nonbreeding season in Mar Chiquita Lagoon, Buenos Aires, Argentina

The Common Tern breeds widely across the Northern Hemisphere in colonies all along North America, Europe and Asia. Common terns breeding in the Atlantic coast of North America migrate during the boreal winter to the Southern Hemisphere, showing a wide nonbreeding distribution that includes the Atlantic coasts of Argentina and Brazil. The coast of Buenos Aires Province (Argentina) constitutes the main wintering area of the species in South America. In Mar Chiquita Lagoon, their diet was assessed by the analysis of regurgitated casts collected on nonbreeding grounds. A total of 538 pellets were analyzed, containing 1092 prey. About 88% by number of prey were fish, 11.4% were adult insects and 0.5% were crustaceans. Adult Coleoptera, Odonata, Orthoptera, Hemipthera and Lepidoptera was the main insects found in the diet. A total of nine fish species were identified. Argentine anchovy (Engraulis anchoita) represented 70% by number and 51% of the consumed biomass of fish. The average length of fish prey was 80.1 +/- 17.0 mm. With respect to habitat, 78% of the prey came from marine foraging habitats while the other 22% were from estuarine environments. Forthcoming studies will include the development of additional methods in order to analyze to a finer scale the temporal variations in the diet and environmental variables involved in such changes.