REES, Eileen C; BOWLER, Jonathan M; BUTLER, Linda. Bewick’s and Whooper Swans: the 1989-90 season. Wildfowl, [S. l.], p. 176–181, 1990. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/154035. Acesso em: 17 dec. 2025.