The head of the hoactzin is ornamented with a semipendent crest composed of rather long, loose, yellowish feathers, as shown in the figure below. Below, the body is of a dull chestnut, while above it is olive splashed with white. Its large tail is conspicuously tipped with yellow, while its wings are short and rounded.
These birds congregate in loose companies in the undergrowth found upon the banks of streams and sloughs. Here they are
easily approached, inasmuch as they are weak fliers and seldom take to wing. They are believed to be polygamous, and it is known that in the manner of their nesting and the appearance of their eggs they strongly remind us of the gallinules and rails. This is a curious circumstance, for it falls into line with another gallinuline character. The claws on the indicial digits of young gallinules are pretty well developed—so much so that they can use them to help crawl out of their nests with, by catching on to twigs, and so forth, in their way and neighborhood. These claw joints are even better developed in the hoactzin, where in the young they are more or less functional. Opisthocomus lives upon fruits, leaves, etc. "Its voice is a harsh, grating hiss, and it makes the noise when alarmed, all the individuals sibilating as they fly heavily away from tree to tree when disturbed by passing canoes" (Bates), In British Guiana it is called the "stink bird," from the disagreeable odor it has, and which, according to Newton, Deville likens to that of a cow house. No fossil forms of opisthocoraine birds are known.