The Horned Screamer is a large bird, easily recognizable by its size, the white spiny appendage on its head, its carpal spurs, and its large grey legs. Its plumage is mainly black with white feathers on its head, a white belly, white/tan splotches on its wings, and white feathers around its neck. The iris is yellow to orange and the bill is deep black.
The Horned Screamer is most similar to the two other species of screamer, the Northern (or Black-necked) Screamer (Chauna chavaria) and the Southern (or Crested) Screamer (Chauna torquata), but easily is recognizable by the 'horn,' dull-colored face and tarsi, and plumage coloration. The two species of Chauna have bare red skin on the face, and their tarsi are reddish. The body plumage of Chauna is mostly gray in color, not black, and both species have a contrasting black band around the neck.
The following description is based primarily on Blake (1977), except where noted otherwise:
Adult: A large, heavily-bodied bird, with a long spine-like appendage on the forecrown. Mostly black. The top of the head is speckled white. The feathers of the lower neck and upper breast are white or whitish, tipped black. Lower breast, belly, and underwing coverts white. Carpal edge of the wing is pale brownish or white. Its most notable characteristic is the spiny "horn" protruding forward from the forecrown, up to 150 mm in length (Kear 2005). There also are two spurs on the manus (fused metacarpals); the more proximal spur is the larger, and can be up to 60 mm long (Rand 1954). Sexes similar.
Juvenile: Duller in color and often have a shorter horn (Kear 2005).
Downy young: Yellow above and white below (Kear 2005).
Little information. Feathers are molted in a gradual way, so they do not go through an annual flightless period as ducks, geese and swans (Anatidae; Kears 2005). In the inner primaries, Horned Screamers molt in a descending order, but in the middle and outer primaries, there seems to be no regular order (Haffer 1968). There is also no regular order in the molt of the rectrices (Haffer 1968).
Bill brownish or black.
Tarsi grayish brown, brown or ash gray.
The crown "horn" and the spurs are pale yellow to white.
(Data from Herklotts 1961, Blake 1977, and Kear 2005.)
Males (n=10; Blake 1977):
Wing length (flat): mean 545.1 mm (range 482-585 mm)
Tail length: mean 256.4 mm (range 214-293 mm)
Culmen: mean 52.2 mm (range 49-55 mm)
Proximal spur: 58-61 mm; distal spur: 15-16 mm (Rand 1954)
Females (n=9; Blake 1977)
Wing length (flat): mean 548.7 mm (range 504-590 mm)
Tail length: mean 260.4 mm (range 216-305 mm)
Culmen: mean 51.7 mm (range 49-55 mm)
Proximal spur: 50-55 mm; distal spur: 11-17 mm (Rand 1954)
3000-3150 g (Carboneras 1992, Kear 2005); 3150 g (Sick 1993)