ALLEN, R H; RUTTER, G E. The Shelduck population of the Mersey area in summer, 1957-1963. Wildfowl, [S. l.], v. 15, p. 2, 1964. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/155189. Acesso em: 5 apr. 2026.