Hoatzin (Opisthocomus hoatzin), or chicken bird/stinkbird/Canje pheasant, is a crested bird of tropical South American swamps, principally in the Amazon and Orinoco river basins. It is roughly pheasant size. A distinguishing physical feature of the Hoatzin is its clawed wings. While these are indistinguishable in an adult bird, the Hoatzin chick has prominent dual claws on each wing, which helps it to grip and pull itself up onto branches. No other avian species has such a physical trait. The presence of such digits indicates that these birds would perhaps climb trees and then use their wings to fly from an elevated point. The Hoatzin bears an uncanny resemblance to the the prehistoric dinosaur Archaeopteryx, the first known bird (though it was a blend between a lizard and a bird). Since that bird no longer exists, the Hoatzin remains in a unique scientific class of its own, as the sole member of the genus Opisthocomus. The Hoatzin emits deep and hoarse cries, grunts and groans as well as hissing vibrantly. This distinctive audio presence, unlike other birds, is often likened to a smoker's wheezing cough. Hoatzins in a group can be very disturbingly noisy, often emitting such cries in unison to communicate and to warn off threats and invaders. Hoatzins are one of the rare birds that are exclusively herbivores. They eat different kind of green plants such as leaves of arum, legume trees and other succulent plants.