Razor-billed Curassows are large chicken-like birds, with a long tail and a large, laterally compressed, bright red bill. They also have a short crest. The plumage is mostly black, except for a white tip to the tail, and a chestnut belly and undertail coverts.
Razor-billed Curassow is the only curassow present in most of its range, and so field identification usually is straightforward. Its distribution is parapatric, however, with that of the similar Salvin's Curassow (Mitu salvini) in northeastern Peru and southeastern Colombia. Salvin's Curassow is slightly smaller than Razor-billed, and has a smaller bill. The most striking difference between the two species is the color of the lower belly and undertail coverts, which are white in Salvin's rather than chestnut as in Razor-billed. North of the Amazon in Brazil, the distribution of Razor-billed Curassow is parapatric with that of Crestless Curassow (Mitu tomentosum). Crestless Curassow has chestnut, not white, tips to the rectrices; the bill also is smaller (lacking the casque that is typical of the bill of Razor-billed), and lacks the short crest of Razor-billed. The female Wattled Curassow (Crax globulosa) also is large and black with brown lower belly and undertail coverts, but, among other differences, Wattled Curassow has an entirely black tail (lacking the white tip of the tail of Razor-billed Curassow) and has a much smaller black bill, with an orange cere. Wattled Curassow also is limited to varzea forest, and is more arboreal than Razor-billed Curassow.
The following description is based on Blake (1977), except where noted otherwise:
Adult: Sexes similar. Large and long-tailed, with large, laterally compressed bill. Feathers of crown elongated, forming a ragged crest; this crest "is composed of flat, well-integrated, and glossy feathers, which broaden out distally to end in a well-rounded tip ... the longest feathers average about 45 mm. in length" (Vaurie 1967). Plumage mostly black, strongly glossed with purplish blue. Tips of rectrices white. Lower belly and undertail coverts chestnut.
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Iris: brown or reddish brown
Bill: bright red
Tarsi and toes: red or reddish
Bare parts color data from Delacour and Amadon (1973) and Blake (1977).
Total length: 83-89 cm (Blake 1977)
Linear measurements (mm) of Razor-billed Curassow (from Vaurie 1967, Blake 1977):
| measurement|| sex|| n|| mean|| range|
| wing (flat)|| male|| 41|| 398.7|| 376-435|
| || female|| 30|| 368.3|| 348-385|
| tail|| male|| 41|| 333.7|| 315-355|
| || female|| 30|| 313.7|| 290-340|
| culmen (from posterior base of swelling)|| male|| 41|| 62.6|| 57-69|
| || female|| 30|| 58.3|| 52-65|
| tarsus|| male|| 41|| 110.5|| 102-122|
| || female|| 30|| 103|| 94-112|
Mass: 3860 g (male, n = ?; Delacour and Amadon 1973)