REES, Eileen C; BOWLER, Jonathan M; BUTLER, Linda. Bewick’s and Whooper Swans Cygnus columbianus bewickii and C. cygnus: the 1990-91 season. Wildfowl, [S. l.], p. 169–175, 1991. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/154066. Acesso em: 17 dec. 2025.