Size: L: 60cm. Wt: Males: 1260 g. Females: 1080 g. Sexually dimorphic in size and colour. Males of this species exhibit eclipse plumage. Mallards are known to hybridize with the American Black Duck (Anas rubripes); hybrids show intermediate, patchy plumage characters.

Male: metallic green head; yellow bill; chestnut breast, separated from head by white line; back and flanks grey; blue speculum bordered in white; black central tail feathers curled; outer tail feathers white; legs orange.

Female: head brown; bill orange, marked with black; body mottled dark brown; central tail feathers not curled.

Eclipse Male: similar to female, but with greenish bill, more chestnut on breast.

Juvenile: as eclipse male, but less chestnut on breast.

Duckling: dark greenish-brown above, with a dark line through the eye; face, edge of wing, and breast deep yellow; yellow spots on rump; bill flesh-colored; legs dark grey.

Note: American Black Duck-Mallard hybrids are common in some regions; they typically show characteristics of both species; males often have green and brown patches on heads.