[hoh-at-sin, waht-sin] 
| a blue-faced, crested bird, Opisthocomus hoazin, of the Amazon and Orinoco forests, having as a nestling a large, temporary claw on the second and third digits of the forelimb, for climbing among the tree branches. |
| hoat·zin (wät-sēn') n. A crested brownish bird (Opisthocomus hoazin) of tropical South America whose young have claws on the first and second digits of the wings. [American Spanish hoazín, from Nahuatl uatzin, pheasant or small game bird.] |
hoatzin
primitive chicken-sized bird of South American swamps, principally in the Amazon and Orinoco river basins. The young possess two large claws on each wing, a trait that has led some scientists to link the species with the fossil Archaeopteryx of the dinosaur era. The hoatzin is the only bird with a digestive system that ferments vegetation as a cow does, which enables it to eat leaves and buds exclusively. Hoatzins feed on swamp plants, grinding foliage in a greatly enlarged crop (not the gizzard, as in other birds). Adults can fly clumsily for short distances, but they spend most of their time perched, digesting their leafy food. A large rubbery callus on the bird's breastbone acts as a tripod to keep it from falling over when its stomach is distended.
Learn more about hoatzin with a free trial on Britannica.com.