アメリカコブガモ Sarkidiornis sylvicola

Large bicolored waterbird. Both sexes are iridescent purplish-green above with a white breast. Males have a large black lump on the bill, dark flanks and whitish belly, whereas females have a plain bill and gray flanks. Note all dark wings. Occurs throughout much of South America, rarely straying north to Costa Rica. Found in freshwater rivers, lakes, and marshes where it is usually uncommon. Normally silent.