During winters 1990-1992, we manipulated food availability 5%-20% less than that of ad libitum feeding for captive groups of wild-strain North American wood ducks (Aix sponsa) to test effects of increasing levels of food restriction on prebasic molt of females. Birds fed ad libitum and 5%-15% restricted diets exhibited a protracted molt (>90 days) of low intensity. Most females fed a 20%-restricted diet did not initiate molt until resumption of ad libitum food availability. We hypothesize that a 20% restriction exceeds a threshold in food availability and possibly body condition needed by captive female wood ducks to meet nutritional demands of maintenance and prebasic molt. A lower threshold may exist for free-living wood ducks, implying the importance of adequate food availability and quality during winter to minimize negative effects on within- and cross-seasonal life-cycle functions. We encourage continued conservation of bottomland hardwood forests in southeastern United States because of their intrinsic values to sustaining populations of wood ducks in North America.