Changes in numbers and distribution of wintering waterbirds around Gotland 1969–2020

THE COASTAL AREAS of the island of Gotland in the center of the Baltic Sea is an important wintering site for water-birds in Sweden. Gotland offers extensive areas of shallow feeding grounds and, due to its location, some open waters remain available even during harsh winters. Wintering waterbirds have been counted annually on the island since the start of the international waterbird counts in 1967, with full coverage of all the inshore areas around the main island obtained during the years 1969–1978 and 2013–2020. Between these two periods, the mean total number of wintering waterbirds increased from 32,000 to 111,500. The most numerous species were Mallard Anas platyrhynchos, Tufted Duck Aythya fuligula, and Common Goldeneye Bucephala clangula. Some species such as Eurasian Wigeon Mareca penelope, Eurasian Teal Anas crecca, and Gadwall Mareca strepera started to winter during the second period. Marked increases were also found for Smew Mergellus albellus and Greater Scaup Aythya marila, likely related to progressively milder winters in recent years