The masked duck (Nomonyx dominicus) is a tiny stiff-tailed duck ranging through the tropical Americas. They are found from Mexico to South America and also in the Caribbean. Primarily not migratory, masked ducks are reported as very uncommon vagrants in the southernmost United States, along the Mexican border and in Florida.
Breeding adult males have a rust-colored body with a black face and mottled wings. Adult females, winter males, and juveniles have a barred brownish gray body, with two horizontal, dark-colored stripes running through the buff-colored face.
The only member of the genus Nomonyx, it is intermediate between the rather primitive black-headed duck (Heteronetta) and the very apomorphic true stiff-tailed ducks. It is sometimes included with the latter in the genus Oxyura, but apparently the masked ducks now are the descendants of a missing link in the Oxyurini evolution, having changed but little for millions of years.
These ducks mainly feed on seeds, roots, stems, and leaves of aquatic plants. They also eat aquatic insects and crustaceans. They feed by diving. Masked ducks breed in any freshwater body with marsh vegetation and surrounded by heavy tree cover. They also occur in mangrove swamps. These ducks are usually very secretive.