A little-studied, diminutive, tropical relative of the Ruddy Duck (Oxyura jamaicensis), the Masked Duck inhabits ponds and small lakes covered with emergent vegetation from northern Argentina north through South and Central America (east of the Andes) to south Texas. This species was first documented in the United States (in Wisconsin, well outside its usual tropical and subtropical range; perhaps an escaped captive) in 1870; by 1905 it had been collected in Massachusetts, Maryland, and Texas. Currently it is considered an irregular visitor to Louisiana and Florida and a resident of Texas, the only state where nesting has been documented.
As with other members of the tribe Oxyurini, the Masked Duck has elongated and pointed tail feathers with stiffened shafts. It is distinguished from other stifftails by its large white wing-patch. Grebelike and secretive in its behavior, it is sighted only rarely, usually as it slips into dense reeds or below water. Often only the tip of its tail and head are visible, as it sinks noiselessly beneath the surface.
This species has a long breeding season: Nests are found from October until August. The nest is a deep cup usually near water, sometimes roofed over (basketball-like), containing 4 to 8 eggs. Males are believed to play a minor role in rearing the young. In Texas, Masked Duck numbers increase following wet cycles that create new ponds with emergent vegetation. Despite its small Texas population, estimated at 3,800, the species is legally hunted.
Johnsgard and Carbonell's (Johnsgard and Carbonell 1996) treatise on the stiff-tailed ducks, the most thorough treatment to date of this group, points out how little is known of the Masked Duck compared to other stifftails.
Details from captive populations are particularly lacking. Informed conservation of this species will depend on filling these gaps in knowledge.