<P> Also, the paucity of morphological differences between the Old World mallards and the New World mallard demonstrates the extent to which the genome is shared among them such that birds like the Chinese spot - billed duck are highly similar to the Old World mallard, and birds such as the Hawaiian duck are highly similar to the New World mallard . </P> <P> The size of the mallard varies clinally; for example, birds from Greenland, though larger, have smaller bills, paler plumage, and stockier bodies than birds further south, and are sometimes classified as a separate subspecies, the Greenland mallard (A. p. conboschas). </P> <P> The mallard is a medium - sized waterfowl species that is often slightly heavier than most other dabbling ducks . It is 50--65 cm (20--26 in) long--of which the body makes up around two - thirds--has a wingspan of 81--98 cm (32--39 in), and weighs 0.72--1.58 kg (1.6--3.5 lb). Among standard measurements, the wing chord is 25.7 to 30.6 cm (10.1 to 12.0 in), the bill is 4.4 to 6.1 cm (1.7 to 2.4 in), and the tarsus is 4.1 to 4.8 cm (1.6 to 1.9 in). </P> <P> The breeding male mallard is unmistakable, with a glossy bottle - green head and a white collar that demarcates the head from the purple - tinged brown breast, grey - brown wings, and a pale grey belly . The rear of the male is black, with white - bordered dark tail feathers . The bill of the male is a yellowish - orange tipped with black, with that of the female generally darker and ranging from black to mottled orange and brown . The female mallard is predominantly mottled, with each individual feather showing sharp contrast from buff to very dark brown, a coloration shared by most female dabbling ducks, and has buff cheeks, eyebrow, throat, and neck, with a darker crown and eye - stripe . </P>

When does a male mallards head turn green