Long-Term Trends and Changes in Numbers and Distribution of some Wintering Waterfowl Species along the Swedish Baltic Coast

Abstract

Regular counts of wintering waterfowl have been undertaken as a part of the International Waterfowl Census (IWC) and the National Swedish Environmental Monitoring Program since 1964. After the first years, a network of annually surveyed sites was established for the calculation of annual indices. Country-wide surveys (also including aerial counts) were undertaken 1971–1974, 1987–1989, 1992–1993 (partial) and 2004. During the survey period, increasing trends were found in Mallard (Anas platyrhynchos), Tufted Duck (Aythya fuligula), Pochard (Aythya ferina), Goldeneye (Bucephala clangula), Red-breasted Merganser (Mergus serrator), Mute Swan (Cygnus olor) and Cormorant (Phalacrocorax carbo). Some of these trends reflect genuine population changes; others are related to changing winter conditions, e.g. the establishment of a new wintering tradition for Wigeon (Anas penelope). Tufted Duck and Goldeneye decreased in the south and increased in the northern part of the coast. Mallard, on the other hand, increased in some coastal sites but not in others, but this species is also common inland.