| Summary: | Dissertação de Mestrado em Biologia apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra. Seabirds are top predators, and can be used as sentinels of changes in marine environments. Estuarine small seabirds such as Little Terns (Sternula albifrons) are particularly sensitive to alterations in prey availability because they need to feed regularly and closer to their breeding sites. Changes in prey availability influence the seabirds’ breeding parameters and success, and other factors such as breeding habitat type, human pressure and presence of predators have a strong influence on breeding success. In this study we analysed the influence of the selection of natural (sandy beaches) and man-made (salt-pans) habitats on reproductive parameters and breeding success of Little Terns breeding in Ria Formosa, Algarve, Portugal. We identified the diet of Little Tern during 2013, 2014 and 2015 breeding seasons, comparing the identification of otoliths and the identification of scales, both found in pellets dropped in the colonies. Also the predators of Little Tern clutches were identified based on footprints and photographs. Finally, we tested the possible relations between a large scale climatic index (the North Atlantic Oscillation index, NAO) and Little Tern diet, breeding parameters (e.g. clutch size, egg size) and breeding success. Overall, breeding parameters were not influenced by habitat type or colony location. Breeding success was influenced by colony location but not by habitat type, suggesting that the characteristics of the breeding site are more important than habitat type explaining breeding success. The diet of Little Tern was dominated by sand-smelts (Atherina spp.) during all breeding seasons according with both identification methods, reflecting the opportunistic feeding behaviour of Little Tern, because this is the most common fish species in Ria Formosa. There were significant differences in secondary prey items between the two identification methods. In general more prey items ...
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