van der Wal, R. J. and Zomerdijk, P. J. (1979) “The moulting of Tufted Duck and Pochard on the IJsselmeer in relation to moult concentrations in Europe”, Wildfowl, pp. 99–108. Available at: https://tidsskrift.dk/Wildfowl/article/view/154135 (Accessed: 18 December 2025).