Smith, Cyndi, Fred Cooke, and R Ian Goudie. “Ageing Harlequin Duck Histrionicus Histrionicus Drakes Using Plumage Characteristics”. Wildfowl (January 1, 1998): 245–248. Accessed February 13, 2026. https://tidsskrift.dk/Wildfowl/article/view/154601.