OGILVIE, M A; ATKINSON-WILLES, G L; BEALE, C J. Wildfowl censuses and counts. Wildfowl, [S. l.], p. 152–153, 1969. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/155930. Acesso em: 13 feb. 2026.