RAVKIN, Yu S. Number and distribution of Mute Swans, Cygnus olor, Bewick’s Swans, C. bewickii, and Whooper Swans C. cygnus in the West Siberian plain. Wildfowl, [S. l.], p. 68–72, 2013. Disponível em: https://tidsskrift.dk/Wildfowl/article/view/155005. Acesso em: 17 dec. 2025.