Sarkidiornis melanotos sylvicola The comb duck or American comb duck (Sarkidiornis sylvicola), is an unusual duck, found in tropical wetlands in continental South America south to the Paraguay River region in eastern Paraguay, southeastern Brazil and extreme northeastern Argentina,[2] and as a vagrant on Trinidad.

[3] Analysis of mtDNA sequences of the cytochrome b and NADH dehydrogenase subunit 2 genes, however, suggests that it is a quite basal member of the Anatidae, vindicating the earliest placement, but its closest living relatives cannot be resolved to satisfaction without further study.

The male is much larger than the female, and has a large black knob on the bill.

However, knob-billed ducks in immature plumage are rarely seen without adults nearby and thus they are usually easily identified, too.

[3] This duck feeds on vegetation by grazing or dabbling[3] and to a lesser extent on small fish, invertebrates, and seeds.

[8] Comb ducks nest mainly in tree holes,[3] also in tall grass.