Stiff-tailed ducks (Oxyurini) are reputed to be unique among waterfowl in having two complete wing and tail molts annually. We examined molt patterns in wild Ruddy Ducks (Oxyura jamaicensis) and in captives of known age. Adults of both groups underwent a complete wing molt in early autumn. A spring wing molt was very rare in wild Ruddy Ducks, but occurred more often in captives, especially in adult females. Ruddy Ducks replace rectrices twice annually. These molts are complete but unusual in that feathers are typically replaced in two waves, in which (1) every other rectrix is lost and largely re-grown before (2) the intervening feathers are molted. As a result, the molt is protracted and the tail plumage, at times, includes feathers of two generations. The pattern ensures that a functional tail is maintained at all times.