Figure 1.

The studied duck species. Male and female of each of the studied duck species: a) Anas platyrhynchos (mallard), b) Anas acuta (northern pintail), c) Anas crecca (teal), d) Anas penelope (Eurasian wigeon), e) Anas strepera (gadwall), f) Aythya fuligula (tufted duck). Except for c) the more colourful male is in the front. Evidently, plumage ornamentation in these ducks is very distinctive among species. Drawings are from the artwork stocks of the WWT, Slimbridge, UK, and used with permission.