Bowler JM, Rees EC, Butler L. Bewick’s and Whooper Swans Cygnus columbianus bewickii and C. cygnus: the 1991-92 season. Wildfowl [Internet]. 1992 Jan. 1 [cited 2025 Dec. 17];:225-31. Available from: https://tidsskrift.dk/Wildfowl/article/view/155925