The hoatzin (pronounced "hwat-zin") is a tropical bird native to the rivers of South America. About the same size as chickens, hoatzins have blue faces, red eyes, golden throats and crests. Their bodies are reddish-brown, and they have long black-and-white wing feathers and tails. Hoatzins are sometimes known as “stink birds” because of their foul-smelling scent, caused by a special bacteria they use to digest their food. Hoatzins were once thought to be related to cuckoos or turacos, but it is possible they have no close living relatives at all.

Chicks

Hoatzins live in small groups alongside rainforest rivers and marshes, where they nest in trees above the water. This is so that hoatzin chicks, if threatened by predators, can drop into the water below and swim away from danger. They can later climb back to the nest using the claws at the tips of their wings. The claws are lost when the birds reach adulthood and learn to fly. This escape route is crucial, as chicks are preyed upon by capuchin monkeys, which track the birds by their distinctive smell.

"Stink birds"

Hoatzins are among the few small birds that eat broad leaves. They digest their food in the crop (a part of the oesophagus, in their throats) rather than in their stomachs. Special bacteria in the crop ferments the leaves, breaking them down. The bacteria gives the hoatzins a bad smell—like cow manure—and makes them burp, earning them the nickname “stink birds”. While digestion is happening, hoatzins have to rest: they spend most of their time resting on tree branches. A knobbly bump on their fronts helps them to balance on the branch while their crops are full.