Card #037 · Birds
Hoatzin
Opisthocomus hoazin
Common LC · Least Concern
Field notes
- Classification
- Order Opisthocomiformes · Family Opisthocomidae
- Range
- Amazon & Orinoco basins, South America
- Size
- ~65 cm (26 in)
- Weight
- ~700 g (1.5 lb)
- Lifespan
- Not established
- Diet
- Leaves, some flowers
Most Notable
The only bird known to digest like a cow. Bacteria ferment leaves in its huge crop, and in 1989 Grajal and colleagues found the chemistry there matches a ruminant's stomach.
Chicks hatch with two claws on each wing, on the thumb and first finger. Nests hang over water, and when a predator comes, a chick drops in, swims away under the surface, then climbs back up to the nest using its wing claws. The claws are gone by adulthood.
It is not a living link to Archaeopteryx, whatever the wing claws suggest. Ostriches and several other living birds have wing claws too, and the hoatzin is a fully modern bird whose chick claws are a specialisation of its own. Its line goes back to Protoazin, a fossil from France about 34 million years old, and genetics put its split from every other living bird at about 64 million years.
The crop is so big it has pushed aside the flight muscles and shrunk the keel of the breastbone, which is why hoatzins fly clumsily, in short flapping hops between riverside branches.
Locals call it the stinkbird. The fermenting leaves in its crop give it a smell like fresh manure.
It is the only species in its genus, its family and its entire order, Opisthocomiformes.
Range: Riverside forest of the Amazon and Orinoco basins.