Chagas, Anna L. J. (2016) Foraging behavior of Avocets (Recurvirostra avosetta) in the northern coast of the Wadden Sea (Schleswig-Holstein, Germany). (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 48 pp.

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Abstract

The Wadden Sea is an important breeding area for many bird species. Among these, 12.000 pairs of Pied Avocets (Recurvirostra avosetta) have been recorded breeding on its salt marshes and coastal wetlands. Monitoring data show that the population size of Pied Avocets, both in the Wadden Sea, as well as regionally, in Schleswig-Holstein, is decreasing. Declines in population size of Avocets have been observed before and were mostly linked with lack of suitable habitats, adverse weather conditions, nest loss or failure, presence of predators and food availability. By combining GPS-tracking data and stable isotopes analysis, key foraging areas and the contribution of several prey species to the diet of Avocets were investigated across two consecutive breeding seasons. A total of 24 birds were caught on their nests in two different breeding areas in Nordfriesland, Schleswig-Holstein, Germany. Blood and feather samples were collected for stable isotope analysis and sex determination, respectively. Dropping samples were collected as an additional method for diet analysis. A total of 11 birds were equipped with small GPSdata loggers which logged date, time, position and speed for 7-8 days. After the successful recapture of 4 birds from Hamburger Hallig, data were retrieved and important foraging areas could be recognized. Later, water samples, sediment, and potential prey items were collected from these areas to characterize feeding grounds chosen by the birds. Results suggest that the visited areas provide different habitats and are used differently. Stable isotopes mixing models indicated that the sites with “marine-like” features were the most important for feeding, providing high-profitable prey items that were found to be better assimilated by Avocets. Sites with brackish features seemed to be important for other activities, such as resting and breeding. Results from this study additionally suggest that sites located close to the breeding areas were sub-optimal for feeding, since they did not provide ideal conditions for important prey items as identified by the diet analyses.

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