This strange bird climbs trees using claws on its wings
The hoatzin, a bizarre pheasant-sized bird native to the Amazon rainforest, is a living throwback. Hoatzin chicks are born with two prominent, functional claws on each wing, reminiscent of ancient theropod dinosaurs like Archaeopteryx. If a predator approaches, the chick leaps out of its nest into the water below, swims to safety, and then uses its wing claws to climb back up the tree.
An Escape Hatch with Claws
In the flooded forests and riverbanks of the Amazon and Orinoco river basins, the hoatzin nests in branches that hang directly over the water. This nesting location is not accidental; it provides a specialized escape route for vulnerable chicks. When a predatory hawk, snake, or monkey approaches the nest, a young hoatzin chick will intentionally drop out of the branches and plunge into the river below. Submerging completely, the chick swims underwater to evade danger and waits out the threat near the sheltered vegetation of the riverbank.
What happens next is unique among living birds. Once the danger passes, the chick must return to its nest high above the waterline. To scale the tangled vegetation and tree trunks, the chick relies on two sharp, functional claws located on the first and second digits of each wing. Using these wing claws in tandem with its oversized feet and beak, the chick climbs the rough bark and lianas, hauling itself back up to the canopy. As the bird matures, the wing claws are lost or become non-functional, and the wing anatomy reorganizes to support adult plumage.
Echoes of Deep Avian History
The wing claws of the hoatzin chick have fascinated evolutionary biologists since their discovery, often prompting comparisons to fossil theropod dinosaurs and early transitional birds such as Archaeopteryx. Early naturalists wondered whether the hoatzin represented an ancient, direct relict lineage that had simply retained primitive ancestral avian claws unchanged across tens of millions of years.
Modern anatomical and genetic assessments offer a more nuanced view. While the hoatzin belongs to an exceptionally ancient and isolated avian lineage, researchers generally consider the functional wing claws of the chick to be a specialized developmental feature rather than a simple, unevolved holdover. Many modern bird embryos still exhibit latent genetic pathways for digit formation on their forelimbs, but the hoatzin is one of the very few species in which these digits fully develop into active, usable juvenile climbing tools before receding in adulthood.