Changes in prey species availability can present energetic challenges to wintering western North American harlequin ducks (Histrionicus histrionicus). The goal of this study was to examine the feeding behavior of captive harlequins and compare energy and nutrient contents of native crab, Hemigrapsus oregonensis to invasive exotic crab, Carcinus maenas. Intake rate, gut retention time, and assimilation efficiency did not differ between crab species. Green crabs had significantly larger (P=0.0034) meat-to-carapace ratio, 79% greater (P=0.0168) fat, and 15% greater (P=0.0058) energy than yellow shore crabs. Yellow shore crabs required 130% more (P=0.0301) force for carapace failure. Gross energy intake rate and assimilable energy intake rate did not differ between crab species. Therefore, energetically and nutritionally, green crabs provide a viable food option to harlequins, if yellow shore crabs are not available. However, the potential impacts of green crabs as an invasive species must be considered within an overall ecological context.