Evolutionary biologists struggled for a long time to categorize the hoatzin, perhaps the strangest bird in the Amazon basin.
Studies of the hoatzin (Opisthocomus hoazin) have shown that it has no close relatives, and biologists have been debating its heritage since the species was first described by the German zoologist Statius Muller in 1776. While the taxonomic status of the hoatzin remains disputed, genetic research published in 2015 concluded that the hoatzin is the last surviving member of a genus of birds that branched off and evolved separately some 64 million years ago, around the time the dinosaurs were wiped out. Such conclusions, together with the fact that hoatzin chicks possess claws on their wings, have led some observers to describe this species as a “living fossil”. In fact, the claws its young are born with appear to be a quite recent adaptation. The hoatzin is practically flightless even as an adult and the young use their claws to hold onto the tree branches they roost in.
The hoatzin inhabits wetland areas of the Amazon basin and the Orinoco basin in Venezuela. In Peru’s Tambopata National Reserve, it can be seen roosting in the low trees that grow around the many oxbow lakes common to this part of South America’s tropical forests. It is one of the forest’s noisiest birds, producing a quite un-birdlike grunting sound as it hops among branches, snapping off the leaves it feeds on. Unusually among the birds of the Amazon, the hoatzin is primarily an herbivore, and only very rarely will it eat insects.
The hoatzin’s unusual herbivorous digestive system has led to it also being known as the “stink bird”. Uniquely among birds, the hoatzin employs a bacterial fermentation process to break down the vegetable matter it consumes, in the same way that ruminants such as cattle digest their food. This unusual digestive system gives the bird such a foul odor that it is rarely –if ever- hunted by humans for food. Perhaps precisely because it has never been hunted, the hoatzin appears barely disturbed by human visitors to its wetland habitat. It hardly bothers to flap and clamber a few meters away when visitors’ boats approach. In fact, the hoatzin’s unique, double-chamber digestive tract takes up so much space in its sternum that its muscles have been displaced, meaning that the bird flies extremely poorly.
While certainly not as beautiful as macaws or toucans, the hoatzin is not an unattractive bird. About the size of a turkey, its face is maroon and topped by an unusually large crest, while its plumage ranges from dark, almost black on its flanks and the underside of its wings, to a rich, reddish-brown color. However, thanks to its terrible smell and the reportedly bad taste of its flesh, the hoatzin is not endangered, and most visitors to the wetlands of Tambopata National Reserve will spot it among lakeshore vegetation.