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    Niggeler, E. & V. Keller (2007)

    Winterbestände der Wasservögel am Aare-Stausee Niederried 1951/52-2005/06.

    Further information

    Ornithol. Beob. 104: 279–300

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    verena.keller@vogelwarte.ch

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    Abstract

    Since 1951, waterbirds on the Niederried reservoir along the Aare river near Berne, Switzerland, have been counted once every month from September to April. The paper documents the results of the counts, which since 1959/60 have been carried out without gaps, up to 2005/06. 13 species were observed regularly and with a sum of monthly counts over 100: Gadwall Anas strepera, Eurasian Teal A. crecca, Mallard A. platyrhynchos, Northern Shoveler A. clypeata, Common Pochard Aythya ferina, Tufted Duck A. fuligula, Common Goldeneye Bucephala clangula, Common Merganser Mergus merganser, Little Grebe Tachybaptus ruficollis, Great Crested Grebe Podiceps cristatus, Great Cormorant Phalacrocorax carbo, Eurasian Coot Fulica atra and Common Black-headed Gull Larus ridibundus. 21 species with small numbers occurred in over a third of all winters, another 17 species only in a few years. The total number of waterbirds increased from the 1950s to the 1980s and decreased subsequently. Diving ducks were mainly responsible for this pattern. Species composition changed over the decades. Diving ducks dominated the waterbird community for the first decades, whereas dabbling ducks increased in importance at a later stage, a pattern which has been observed at other reservoirs along rivers in central Europe. Numbers of Gadwalls in particular showed a marked increase in the 1990s but decreased again in recent years. The Niederried reservoir reached quantitative Ramsar criteria for international importance for Common Pochard in the 1960s and 1970s, and for Gadwall in the 1990s. Silting up of the reservoir and massive changes in nutrient loads seem to be the main causes for the changes in the waterbird community.