| Summary: | Dissertação de mestrado em Ecologia, apresentada ao Departamento de Ciências da Vida da Faculdade de Ciências e Tecnologia da Universidade de Coimbra Seabird populations are naturally regulated and their demographic fluctuations are explained by mainly two factors: the availability of suitable breeding habitats and the presence of foraging habitats with appropriate food resources. An important characteristic in determining suitability of breeding habitats for ground nesting seabirds is their vegetative cover. Suitable foraging habitats determine the availability of food resources, and are influenced by environmental variables, such as the climatic proxy, North Atlantic Oscillation (NAO) index. Environmental variables are known to affect the distribution of food resources in the marine environment which can cause declines in the availability of prey fish for seabirds. Little Terns (Sternula albifrons) are known to avoid nesting on densely vegetated areas to avoid predation, however the habitats with low vegetative cover preferred by these birds to nest are subjected to the overgrowth of vegetation which leads to the abandonment of the breeding site. Little Terns are also highly susceptible to fluctuations in food availability, especially during the breeding season, and abrupt changes in their diet can lead to variations in their breeding performance which will ultimately affect the breeding population size. This study aimed to first, evaluate if the fluctuations in Little Tern breeding population size in Ria Formosa, Algarve, could be explained by changes in vegetation cover. Secondly, it also intended to assess the role of the environmental variables and annual variations in diet, in Little Tern breeding parameters and in the number of breeding pairs in Ria Formosa, Algarve. The percentage of vegetation cover in each sandy beach was calculated from aerial pictures of Ria Formosa barrier islands from 1976 to 2012, and related with census data from the same period. A linear regression model was performed between ...
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