Dirksen S, Beekman JH. Population size, breeding success and distribution of Bewick’s Swans Cygnus columbianus bewickii wintering in Europe in 1986-87. Wildfowl [Internet]. 2013 Apr. 16 [cited 2025 Dec. 17];:120-4. Available from: https://tidsskrift.dk/Wildfowl/article/view/155000