Hoatzins live in flocks along slow-moving rivers and flooded forest edges in Guyana. They are not very good fliers — they tend to flap awkwardly from branch to branch and crash-land rather than glide elegantly. But what they lack in flying grace they make up for in character. They are noisy, social birds that grunt, hiss and wheeze at each other all day long.
The hoatzin's digestive system is extraordinary. Leaves are not very nutritious, so to get enough energy from them, hoatzins have a huge crop (a special pouch in their throat) that ferments the leaves — a bit like how a cow has multiple stomachs. This fermentation process is what causes the distinctive smell. Some people say it is like smelling a cow farm. Others say it is worse.
Hoatzin chicks are one of the most remarkable things in the bird world. They hatch with tiny claws on their wings — like miniature dinosaur arms. If a predator comes near, the chick dives into the river below the nest and swims to safety underwater. When the danger has passed, it climbs back up the bank and into the tree, using those wing claws to grip.
The wing claws disappear as the chick grows up, which is one reason scientists find hoatzins so fascinating — they seem to be a living link to very ancient birds. Fossils show that early prehistoric birds had similar claws on their wings. The hoatzin is sometimes called 'a dinosaur bird' because of this connection.