The hoatzin is an Amazonian forest bird known for fermenting leaves in a specialized digestive system.
Hoatzins live in swamps and river-edge vegetation across northern South America. Their diet is unusually dominated by leaves, which are fermented by microbes in an enlarged crop and foregut. This digestive arrangement resembles the fermentation systems of some mammals more than those of most birds.
Fermentation makes the hoatzin smell distinctive and limits how efficiently it can fly. The species has also attracted attention because young hoatzins possess claws on two wing digits, a feature used for climbing branches. That juvenile trait is the subject of a separate well-known fact and is not the reason for the adult bird’s leaf-fermentation reputation.
The hoatzin’s classification has been debated, but its scientific name is Opisthocomus hoazin.