The hoatzin is the Amazonian bird known for its foul-smelling fermented-leaf diet.
Hoatzins live in swampy forests and river-edge vegetation across northern South America. They eat mainly leaves, along with some flowers and fruit. Their digestive system is unusual among birds: an enlarged crop and foregut ferment plant material with the help of microorganisms, producing a manure-like odor.
Hoatzin chicks are famous for another unusual feature: they have functional claws on two wing digits. These claws help young birds climb through branches and escape into water when threatened. The claws are lost or become reduced as the birds mature.
The hoatzin’s scientific name is Opisthocomus hoazin, and it is the only living species in its family, Opisthocomidae. Its evolutionary relationships have long puzzled scientists, and its classification has changed as anatomical and genetic evidence improved. The smell is not evidence that the bird is poisonous; it is a consequence of its specialized plant-fermentation system.