Worden, Jenny, Peter A Cranswick, Olivia Crowe, Graham McElwaine, and Eileen C Rees. 2013. “Numbers and Distribution of Bewick’s Swan Cygnus Columbianus Bewickii Wintering in Britain and Ireland: Results of International Censuses, January 1995, 2000 and 2005”. Wildfowl 56 (April):3-22. https://tidsskrift.dk/Wildfowl/article/view/153969.