Molt and migration can coincide in Arctic nesting waterfowl because they have little time between fledging and the severe weather that precipitates migration. Objectives were to observe how patterns in autumn and winter molt by Long-tailed Ducks (Clangula hyemalis) were influenced by nutrient reserves or seasonal life-cycle events. Molt scores and nutrient reserves were determined for birds salvaged during autumn 2011 (n = 79) and collected during winter 2002–2004 (n = 255). Differences in molt among sex-age classes and correlation between molt and nutrient reserves were determined. It was predicted that adult females and juveniles of both sexes suspended molt during autumn migration to limit energetic overlap; however, greater molt in juveniles during autumn than winter was detected. Correlation between molt and nutrient reserves were not detected. Molt was less in adult males than females and juveniles during winter, which may suggest that the effects of reproduction (females) and growth (juveniles) extended their molt into winter. Observed molt patterns are consistent with fixed cues associated with the timing of seasonal life-cycle events of this species. This could have important implications in understanding the life-cycle events of Long-tailed Ducks and provide novel explanations of seasonal molt.