BOWLER, J; BUTLER, L; HESKETH, R; LIGGETT, C; REES, E C. Bewick’s and Whooper Swans Cygnus columbianus bewickii and C. cygnus: the 1994-95 season. Wildfowl, [S. l.], p. 176–186, 1995. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/154654. Acesso em: 17 dec. 2025.