The species has a total length of 80-93 cm, and weighs on average 3.5 kg. There is sexual dimorphism in plumage and size, with the males being larger. Both sexes present a black head, neck, breast, back, wings and tail. Males have white belly and underparts, while in females these areas are cinnamon-brown. Both sexes have a black crest formed by curled feathers, but in the females the crest is barred with black and white. Males also have a red cere, which may be so well developed in older males that it appears to form a knob. Females have a black cere, and never have a bill knob (IBAMA 204).
Crax blumenbachii is morphologically similar to Wattled Curassow (Crax globulosa). The distributions of these two species do not overlap, however, because Crax globulosa inhabits flooded forests of Amazonia and does not naturally occur in the Atlantic rainforest. In addition, the bill knobs of C. globulosa are more developed than are those of C. blumenbachii, and females of C. globulosa also show a red, not black, cere.
Sexes differ. The following description is based on Blake (1977):
Adult male: Feathers of crown and nape elongated, with recurved tips, forming a well-developed, curly crest. Head (including crest), neck, back, rump, wings, tail, and breast black, glossed with greenish. Belly, undertail coverts, and a long tuft at the base of the tibial feathers white. Brightly colored skin (cere) at base of bill, usually with knob and wattles (see Bare Parts).
Adult female: Similar in pattern to male. Crest black, with prominent white bars. Plumage mostly black, as in the male, but the belly, undertail coverts, and tufts on the tibial feathers cinnamon-brown or ochraceous, rather than white; and the wings are variably marked with rufous to chestnut wavy bars. Colored skin (cere) at base of bill, dull in color (see Bare Parts).
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Iris: Dark brown (male) or light brown (female). Narrow area of bare skin around eyes purplish brown.
Bill: Dark brown with black tip (male) or dull blackish (female). Cere and wattles bright lacquer red or orange-red in male; cere dull blackish (female).
Tarsi and toes: Blackish (male) or dull flesh to dull orange-rose (female)
Data from Delacour and Amadon (1973).
Total length: 80-93 cm
Linear measurements (data from Vaurie 1968: 157):
wing, male: mean 391 mm (range 390-393 mm, n=3); wing, female: mean 371 mm (range 350-385 mm, n=3)
tail, male: mean 340 mm (range 330-351 mm, n=3); tail, female: mean 316.7 mm (range 310-325 mm, n=3)
tarsus, male: mean 110.3 (range 105-115 mm, n=3); tarsus, female: 102.3 mm (range 98-107 mm, n=3)
culmen (exposed), male: mean 43.7 mm (range 41-45 mm, n=3); culmen (exposed), female: mean 42 mm (range 39-45 mm, n=3)
Mass: mean 3-3.5 kg