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(wätsēn`) [Aztec], common name for a peculiar marsh bird, Opisthocomus hoatzin. The hoatzin is a slender bird with a brownish plumage spotted with white above and reddish-yellow to rust below. It may reach up to 25 in. (64 cm) in length, but weighs no more than 1 3-4 lb (810 grams). It has a long tail of 10 loosely bound feathers, and a large, bristly crest mounted on a tiny skull. Its young are good swimmers and are peculiar in having claws on their first and second wing digits, which they use along with their short curved bills and weak toes for climbing trees. In this respect the hoatzin is reminiscent of the extinct lizard-bird Archaeopteryx. As the young mature and begin to fly (though never especially well), the claws dwindle. Hoatzins are sometimes called reptile-birds because of their crocodilian odor and harsh, monotonous call. In yet another respect, they are the most advanced of avians. In other birds, food is broken up in the gizzard, but the hoatzin accomplishes this in its well-developed, muscular, horny-walled crop, and its gizzard is much reduced. The hoatzin's specialized diet consists of certain marsh plants, including the mangrove, and the bird is thus restricted to the riverine forests centering around the Amazon Basin where it lives in small colonies of 10 to 50 birds. Both sexes participate in the building of loosely entwined stick nests, 5 to 20 ft (1.5–6.1 m) over the water, in the forks of riverbank trees. The female lays two to four small eggs per clutch, which are yellowish in color with pink or brown spots. Little is known of the incubation period or of parental responsibilities. Hoatzins are classified in the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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, subphylum Vertebrata, class Aves, order Galliformes, family Opisthocomidae.



(Opisthocamus hoazin), a bird, the only species of the suborder Opisthocomi of the order Galliformes. Body length, approximately 60 cm. The plumage on top is olive with white spots, and the abdomen is reddish. Hoatzins are distributed in South America from Colombia to Bolivia. They keep to flooded river thickets. Hoatzins are barely able to fly and spend a large portion of their time in trees. They nest from December through July. There are two to four eggs in a clutch. In the young, claws develop on the first and second digits of the wing. The claws help the young birds to creep along branches, but they disappear in the adult hoatzin. The diet is vegetarian. The hoatzin has an unpleasant odor, and its meat is inedible.

References in periodicals archive ?
But hoatzins have an unusually big crop (food-storage pouch) and esophagus (tube leading from the mouth to the stomach), explains Alejandro Grajal, an ornithologist (bird scientist).
Hoatzins have leaves all around them in their lush, tropical habitat.
Since describing the bird, Opisthocomos hoazin, in 1776, ornithologists have had problems pinpointing its closest kin, as the hoatzin looks and acts so unlike other birds.
They found that hoatzin DNA most closely resembles cuckoo DNA.
The scientists conclude, however, that the hoatzin belongs next to the cuckoo's nest, not in it, because the species' DNA and structural differences.
Paul DeBenedictis of the State University of New York Health Science Center at Syracuse says that Hedges and his colleagues should have compared the hoatzin with a wider variety of birds.
While performing autopsy studies on the red-eyed, foul-smelling jungle birds in their native Venezuela, Rodriguez discovered that the adult hoatzin harbors remarkably few parasites or disease-causing bacteria.
Strahl discovered that the hoatzin (Opisthocomus hoazin) is the only bird known to digest food in the same way as cows, sheep and other ruminants--using bacteria to break down fibrous plant material in a special foregut chamber above its stomach.
With flying not an option, Grajal says, a baby hoatzin pursued by predators must use other traits to escape, such as its agility underwater and its clawed wingtips, which enable the chick to clamber up trees like a monkey.
Like an overstuffed hen, the adult hoatzin can flutter clumsily for several hundred yards, but that short range is all it needs to find the seven plant species that make up more than half its leafy diet.
Why did the hoatzin develop a foregut in the first place?
Seuss, turkey-like, claw-winged hoatzins vie for attention with azure gallinules; macaws, parrots, and troupials call out overhead.