Which bird has claws on its wings?

The little-known hoatzin which lives in the mangrove swamps of Venezuela. Young hoatzins have two small claws on their wings, and they use these to help grip the branches as they clamber about the trees.

They are poor fliers even when adult. When the chicks grow up the claws drop from their wings. Watching a hoatzin chick clambering through the branches is like going back in time, millions of years, to when the first known bird appeared. This bird was called Archaeopteryx and it, too, had claws on its wings, and quite possibly also clambered about the branches in the same way as the young hoatzins.