American Black Ducks (Anas rubripes) molt some tertials and tertial coverts during their first fall and winter, but descriptions are incongruous and the timing, extent and sex-specific differences in molt patterns are largely unknown. We studied molt of these feathers from fall to spring using captive, harvested, and trapped wild birds, as well as specimen wings. During their first fall and winter, males molted earlier and replaced more tertials and tertial coverts than females, but all birds retained some juvenile tertial coverts until the end of April. We attribute these differences to their primary mating system of annual monogamy, with females being the limiting sex. The early acquisition of adult tertials and tertial coverts are likely selectively advantageous for males because these feathers are prominently displayed during courtship and pair bond formation. Young birds that have acquired adult-like feathers may exhibit a higher degree of fitness, facilitating breeding in the first year. This knowledge of wing feather replacement is useful for determining the age of Black Ducks as either second year or after second year and can also be used in dual feather isotope analysis to link natal and wintering areas.