The white-winged duck or white-winged wood duck (Asarcornis scutulata) is a large species of duck, formerly placed in the genus Cairina with the Muscovy duck (Cairina moschata) and allied with the dabbling ducks. However, mtDNA cytochrome b and NADH dehydrogenase subunit 2 sequence analysis indicate that the anatomical similarity to the Muscovy duck is deceiving and that the species is appropriately placed in a monotypic genus, as Asarcornis scutulata, which is evolutionarily closer to the redhead (Aythya americana, one of the diving ducks). This is one of the largest living species of duck next only to the steamer ducks which are heavier. The Muscovy duck also attains sizes that nearly rival the white-winged duck, but may average a bit smaller in a wild state. Length is 66–81 cm and wingspan is 116–153 cm. The most noticeable feature on adult birds, is the dark body contrasting with a whitish head and neck. Males have mostly dull yellowish bill, blackish mottling on the head and upper neck, white lesser median coverts and inner edges of tertials and bluish-grey secondaries. In flight, white wing-coverts contrast with the rest of the wings. Females are smaller and usually have more densely mottled head and upper neck. The juvenile is duller and browner. This secretive species is only known to feed at night. Its diet consists of seeds, aquatic plants, grain, rice, snails, small fish and insects. It inhabits stagnant or slow-flowing natural and artificial wetlands, within or adjacent to evergreen, deciduous or swamp forests, on which it depends for roosting and nesting, usually in tree holes. Although lowlands (below c.200 m) provide optimum habitat, it occurs up to 1,400 m of altitude, especially on plateaus supporting sluggish perennial rivers and pools.