Sexes similar. Elongated crest of stiff-shafted feathers. Sides of head naked. Tail of ten feathers. Fifth secondary quill present. Hind toe very long. The young are hatched naked. The thumb and first finger being provided with claws, enables them to climb and grasp the branches soon after they are hatched; the bill as well as the legs and wings being used for a similar purpose. They are able to swim and dive with facility. Eggs are double-spotted like those of a Rail and are laid in a nest of loose twigs built high up over water or soft mud. Only one genus from S. America.
O. hoazin. 23". Plumage dark brown, glossed olive. (O.G. ii. 259.)