BOWLER, Jonathan M; REES, Eileen C; BUTLER, Linda. Bewick’s and Whooper Swans Cygnus columbianus bewickii and C. cygnus: the 1991-92 season. Wildfowl, [S. l.], p. 225–231, 1992. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/155925. Acesso em: 17 dec. 2025.