Augst, Hans-Joachim, Bernd Hälterlein, and Katrin Fabricius. 2019. “From Stopover to Wintering: Bewick`s Swans Cygnus Columbianus Bewickii in Schleswig-Holstein, Northern Germany in Winters 2016 2017 and 2017 2018”. Wildfowl, November, 139-63. https://tidsskrift.dk/Wildfowl/article/view/154487.