The bright plumage of male ducks in sexually dichromatic species is thought to have evolved through intense sexual selection. This study examined the relationship between the timing and speed of moult into this bright plumage and subsequent mating success of male Harlequin Ducks (Histrionicus histrionicus). Males which molted relatively slowly had a lower chance of establishing a pair bond than others. The timing of molt was unrelated to whether a male obtained a mate. Molt speed and timing were not correlated within individual males. Both molt speed and molt timing were significantly repeatable in individual males over two years. Molt speed probably reflects the condition of males, whereas timing of molt is more likely related to the distance to an individual's breeding area, which determines the timing of arrival to the molting grounds. In waterfowl species that have been studied, males usually form dominance hierarchies before pairing and females tend to chose dominant males. We suggest that male Harlequin Ducks which molted slowly are poor quality individuals and, as such, were relegated to subordinate status and unable to attract a mate the following fall.