Ferns, P N, J P Reed, E D Gregg, C O’Hara, A Lang, and G R Sinkowski. “Bill Knob Size and Reproductive Effort in Common Shelducks Tadorna Tadorna”. Wildfowl 55 (April 16, 2013): 47–58. Accessed April 15, 2026. https://tidsskrift.dk/Wildfowl/article/view/153938.