The hoatzin is the rainforest bird whose chicks have claws on two wing digits.
Hoatzins live in swampy forests and river-edge vegetation across northern South America. Newly hatched chicks use their clawed wings to climb through branches and escape predators. As they mature, the claws are lost or become greatly reduced, and the birds rely on their feet and wings like other adult birds.
Hoatzins are unusual for another reason: their digestive system ferments leafy food in an enlarged crop. This gives them a distinctive fermented odor and has led to the informal nickname “stinkbird.” Their diet is mainly leaves, with some flowers and fruit.
The hoatzin’s exact evolutionary relationships were debated for many years. Modern genetic studies place it on a very isolated branch of the bird family tree, making it one of the most distinctive birds of the Amazon and Orinoco regions.