Bowler JM, Butler L, Rees EC. Bewick’s and Whooper Swans Cygnus columbianus bewickii and C. cygnus: the 1992-93 season. Wildfowl [Internet]. 1993 Jan. 1 [cited 2025 Dec. 16];:191-9. Available from: https://tidsskrift.dk/Wildfowl/article/view/154692