Laubek, B.; Clausen, P.; Nilsson, L.; Wahl, J.; Wieloch, M.; Meissner, W.; Shimmings, P.; Larsen, B.-H.; Hornman, M.; Langendoen, T. Whooper Swan Cygnus Cygnus January Population Censuses for Northwest Mainland Europe, 1995–2015. Wildfowl 2019, 103-122.