Female Mallards may have much darker plumage and no apparent speculum. It is usually difficult, however, to distinguish individual variation from influences of hybridization or domestic duck crosses, so identification must remain tentative. The ducks in Figures 4 to 11 probably include examples of both domestic blood and natural variation, but the remainder of this discussion will focus on the more easily identifiable traits of domestic ducks. The common domestic strains of Mallard raised in Greater Vancouver and the Fraser Valley currently include the Pekin, Rouen, Khaki Campbell, and Indian Runner, and there are also many minor and ornamental breeds. Domestication has resulted in several major changes from the wild Mallard that can serve as clues when identifying these ducks in the wild.
Domestic ducks are generally bulkier, with larger, rounder heads and shorter bills.
They have increased fertility and tend to be promiscuous rather than monogamous. Ducks bred for egg-laying tend to have longer bodies, and the legs of many domestic ducks are set farther back on the body, necessitating a more upright stance. Some domestic varieties look very unlike Mallards, such as the large, all-white Pekin and Aylesbury ducks. Pekins are the typical barnyard duck, while the less common Aylesbury is a very heavy-breasted bird. The ancestry of the Cayuga duck is controversial.