Rees, Eileen C., Lei Cao, Preben Clausen, Jonathan T. Coleman, John Cornely, Olafur Einarsson, Craig R. Ely, et al. 2019. “Conservation Status of the world’s Swan Populations, Cygnus Sp. and Coscoroba sp.: A Review of Current Trends and Gaps in Knowledge”. Wildfowl, November, 35-72. https://tidsskrift.dk/Wildfowl/article/view/154486.