Natural History Wanderings

All Birds Wiki writes about the Hoatzin a bird that is difficult to classify and doesn’t cleanly fit taxonomic classification.

The Hoatzin (Opisthocomus hoazin), is a species of tropical bird found in swamps, riparian forests, and mangroves of the Amazon and the Orinoco basins in South America. It is notable for having chicks that have claws on two of their wing digits.Large, dumpy bird found around lake edges and slow-moving streams. Head looks too small for its large brown body. Its orange mohawk, blue facial skin, and stubby bill make this bird extremely distinctive. Usually found in groups or pairs. Moves clumsily around waterside vegetation, making loud huffing noises.

For decades ornithologists have debated the relationships of this unique South American bird: at various times the Hoatzin has been thought to be related to Galliformes (cracids and relatives) or to Cuculiformes (cuckoos and relatives), but to date the Hoatzin has defied easy classification.

Read more about Hoatzin at  Hoatzin | All Birds Wiki | Fandom