The Comb Duck is named because of the male’s distinctive knob on top of its beak. There are two sub-species of this duck: the Old World Knob-billed Duck (Sarkidiornis Melanotos Melanotos) and the Comb Duck (Sarkidiornis Melanotos Sylvicola) from South America which is smaller with darker flanks. This duck nests in tree cavities or in tall grass near to water. Despite the wide range of this duck it is declining in numbers due to habitat loss, and hunting.