Comparison of Mallard, Black and Mottled Ducks
Female Mallards, Mottled and American Black Ducks are similar in appearance. Mottled Duck tends to be darker than the Mallard and lighter than the Black Duck. Ranges of the Mottled Duck (southern U.S.) and the American Black Duck do not overlap. Both species will cross with Mallards.
Bill color is a useful field mark. Female Mallard has an orangish bill with variable dark markings. Bills of the other two species range from yellow (male Mottled) to olive green on the American Black Duck and the female Mottled Duck.