Browsing by Subject "saaristolinnut"

Small and medium-size gulls typically breed in colonies, which helps them to defend their breeding area more effectively than separately nesting gulls. Other bird species nest in association with aggressive colonial gulls to reduce nest predation. According to previous studies, especially Aythya duck species and Common Eider (Somateria mollissima) benefit from gull colonies. Seperately nesting Aythya ducks are more exposed to nest predation than individuals nesting with gulls. By understanding the relationship between gulls and waterfowls, conservation measures can be targeted more effectively. It is important since population trends of many waterfowl species have been declining since the 1990s. Previous studies on the interactions between gulls and ducks have been focusing on a single species and are mainly based on short-term monitoring data. The aim of this study is to demonstrate the impact of gull colonies on the choice of nesting sites of ducks, geese and swans (Anatidae) in islands at both family and species level using a 19 year long bird survey data. In addition, other possible factors affecting the breeding site selection of the waterfowl are identified. Those studied factors were chosen based on previous studies and on available information. The explanatory variables are the number of breeding small and big gulls, the presence of predator bird, crow (Corvus corone corvix), the area of the island and the distance to the nearest island or the mainland. Model selection was made with Akaike´s Information Criterion. The study data included bird surveys made in the archipelago of Helsinki during 1995–2013. Of the 149 monitored islands, islets or quarries in the study, 118 island bird calculations were used. All gull species were considered in the study. The waterfowl birds included mute swan (Cygnys olor), Canada goose (Branta canadensis), Barnacle goose (B. leucopsis), Eurasian Wigeon (Mareca penelope), Mallard (Anas platyrhynchos), Northern Shoveler (Spatula clypeata) ja Tufted Duck (Aythya fuligula), Common Eider, Common Goldeneye (Bucephala clangula), Red-breasted Merganser (Mergus serrator) and Common Merganser (M. merganser). The results indicate that at both family and species level the gull colonies have a positive effect on the selection of the breeding site of the waterfowl. Ecological models used in the study showed that the best predictors to explain nesting site selection were the number of small and big gulls, the presence of the crow and the area of the island. A similar model explained also the breeding of the Barnacle Goose and Common Eider. The best models for other species had more dispersion. With a large-sized mute swan the number of small colonial gulls were left out from the statistical model. Same was made with Common Goldeneye and Common Merganser because they nests exclusively in nest boxes or tree cavities. There was little uncertainty in the choice of models because the difference between Akaike –values were low. This study shows that the gull colonies have a positive influence on the selection of breeding site of the waterfowl. The results support the earlier observations of the aggregation of waterfowl breeding on the vicinity of gull colonies. The results can be applied to the management of waterfowl birds and in conservation biology.