Opisthocomus hoazin The young of this crow-sized bird from the rainforest of South America have talons on their wings, allowing them to climb around trees “on all fours”. The talons later disappear as the bird matures. The hoatzin survives on a diet of tree leaves, which are rolled into balls and swallowed into its enormous crop, or pouched gullet. Distinctive for its spiked head plumage and tail of ten feathers, the hoatzin is not hunted because of its foul odour.