Hoatzin

The hoatzin is a leaf-eating bird of the Amazon and Orinoco basins. Its foregut ferments foliage, and its chicks have claws on their wings.

Foregut fermentation: A digestive strategy in which microbes ferment food in chambers before it reaches the stomach. Hoatzins ferment leaves in an enlarged crop and lower esophagus before digestion continues.
Galliformes: An order of mostly ground-dwelling birds that includes chickens, turkeys, and pheasants. Hoatzins were once grouped with galliform birds, but modern evidence places them elsewhere.
Amazon rainforest: The vast tropical forest system of the Amazon Basin in South America. Much of the hoatzin's range lies in this forest and its river-edge vegetation.
Ruminant: A mammal that regurgitates and rechews food and ferments it in a specialized stomach. Ruminants also ferment foliage, but use a stomach-based system rather than the hoatzin's foregut crop.
Crop (anatomy): An expandable pouch in the esophagus that stores food before digestion. The hoatzin's enlarged crop is the main chamber where foliage undergoes microbial fermentation.
Opisthocomiformes: The bird order containing the hoatzin as its sole living species. The hoatzin's unusual anatomy and uncertain affinities leave it alone in this order.
Orinoco River: A major river system in northern South America flowing through Venezuela and Colombia. The Orinoco basin is another core region of hoatzin distribution.
Cecal fermentation: Microbial digestion of plant material in the cecum or colon after it passes through the stomach and small intestine. This is the hindgut strategy that contrasts with fermentation in the hoatzin's foregut.
Rumen: The largest chamber of a ruminant stomach, where microbes ferment plant material. Like a rumen, the hoatzin's crop supports fermentation, but the bird has no multi-chambered stomach.
Herbivory: A mode of feeding in which animals consume plant material. The hoatzin is unusual among birds for relying heavily on leaves.

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