Stiff-tailed ducks are part of the Oxyurinae subfamily of ducks. All have, as their name implies, long stiff tailfeathers, which are erected when the bird is at rest. All have relatively large swollen bills.
These are freshwater diving ducks. Their legs are set far back, making them awkward on land, so they rarely leave the water.
Their unusual displays involve drumming noises from inflatable throat-sacs, head throwing, and erecting short crests.
Plumage sequences are complicated, and aging difficult. Plumage is vital for survival because of this animals tendency to spend time in the water. Without plumage this duck would die of hypothermia because of an inability to regulate its body temperature.
A fossil species from the Late Pliocene or Early Pleistocene of Jalisco (Mexico) was described as Oxyura zapatanima. It resembled a small ruddy duck or, even more, Argentine blue-bill. A larger Middle Pleistocene fossil form from the southwestern USA was described as Oxyura bessomi; it was probably quite close to the ruddy duck.