Hoatzin

The Hoatzin is one of the most unusual birds alive, a large, ungainly-looking species with a small head topped by a ragged, spiky crest, a bare patch of striking blue skin around the eye, and deep red eyes. The body is mostly dark brown above with buff streaking, a chestnut-brown belly, and long, loosely arranged tail feathers, giving the bird an almost dinosaur-like silhouette that has long fascinated ornithologists.

What truly sets the Hoatzin apart is its digestive system: unlike almost all other birds, it is primarily a leaf-eater, and it digests its tough, fibrous diet through foregut fermentation in an enlarged crop and esophagus, a process more typical of cows than birds, that produces a distinctive, sometimes described as manure-like, odor responsible for its colloquial nickname of "stinkbird." Young Hoatzin chicks possess functional claws on their wings, used to clamber through branches near the nest, a striking echo of ancient feathered dinosaurs that is lost as the birds mature.

Key field marks

• Ragged, spiky crest atop a small head
• Bare, bright blue facial skin and red eyes
• Dark brown upperparts with buff streaking, chestnut belly
• Long, loose tail and a heavy, ungainly flight

Similar species

• No other bird in its range resembles the Hoatzin; its unique combination of spiky crest, blue face, and prehistoric silhouette make it unmistakable.
• Chicks with functional wing claws are unique among living birds, further distinguishing the species even at the nestling stage.

Habitat

Inhabits riverine forest, swamp forest, and flooded vegetation along slow-moving rivers, lakes, and oxbows.

Range

Found throughout the Amazon and Orinoco river basins of South America, including Venezuela, the Guianas, Brazil, Colombia, Ecuador, Peru, and Bolivia.

Migration

Non-migratory and highly sedentary, remaining closely tied to riverside vegetation.

Behavior

Gregarious, living in small social groups that cooperatively defend a territory and help raise young; a weak, clumsy flier that relies on gliding short distances between branches over water.

Voice

Harsh, grunting, hissing, and croaking calls, along with wheezing sounds, quite unlike the calls of typical songbirds.

Feeding

Feeds almost entirely on leaves, along with some buds, flowers, and fruit, digested through bacterial fermentation in an enlarged crop, similar in principle to a cow's rumen.

Nesting

Builds a stick platform nest over water; chicks possess functional claws on the bend of the wing, allowing them to climb through branches and even swim if they fall into the water, a trait unique among living birds.