The ruddy shelduck grows to a length of 58 to 70 cm (23 to 28 in) and has a 110–135 cm (43–53 in) wingspan. The male has orange-brown body plumage and a paler, orange-brown head and neck, separated from the body by a narrow black collar. The rump, flight feathers, tail-coverts and tail feathers are black and there are iridescent green speculum feathers on the inner surfaces of the wings. Both upper and lower wing-coverts are white, this feature being particularly noticeable in flight but hardly visible when the bird is at rest. The bill is black and the legs are dark grey. The female is similar but has a rather pale, whitish head and neck and lacks the black collar, and in both sexes, the colouring is variable and fades as the feathers age. The birds moult at the end of the breeding season and the male loses the black collar, but a further partial moult between December and April restores it. Juveniles are similar to the female but are a darker shade of brown.