Bowler JM, Butler L, Rees EC. Bewick’s and Whooper Swans Cygnus columbianus bewickii and C. cygnus: the 1992-93 season. Wildfowl [Internet]. 1993 Nov. 1 [cited 2026 Apr. 15];44:191-9. Available from: https://tidsskrift.dk/Wildfowl/article/view/154692