Hoatzin

The Opisthocomidae family, under the order Opisthocomiformes, is represented today solely by the hoatzin (Opisthocomus hoazin), a distinctive bird found in the Amazon and Orinoco delta regions of South America. Although this family includes several identified fossil species from different parts of the world, the living hoatzin is notable for its colorful plumage, prominent crest, and sociable nature, often forming large groups. Hoatzins are unique in their digestive system, which relies on bacteria in their crop to ferment leaves—this is a rare trait among birds known as foregut fermentation. They are highly adapted to their arboreal, folivorous lifestyle in tropical forested wetlands, feeding on a restricted diet of leaves, flowers, and fruit, which negates the need for frequent drinking. Juvenile hoatzins are remarkable for their clawed wings, which aid in climbing. Once thought to be related to fowl, recent phylogenetic studies suggest that they belong to the Neoaves. The noisy and gregarious birds are sedentary and can be found in elevations between 200 to 500 meters, where they build flat nests in bushes or trees over water, and their semi-precocial chicks are known to swim to evade predators.