Livezey, Bradley C. “Comparative Morphometrics of Anas Ducks, With Particular Reference to the Hawaiian Duck Anas Wyvilliana, Laysan Duck A. Laysanensis, and Eaton’s Pintail A. Eatoni”. Wildfowl, Jan. 1993, pp. 75-100, https://tidsskrift.dk/Wildfowl/article/view/154693.