HOATZIN

__Hoatzin (_Opisthocomus hoazin__) – The “Living Fossil” Bird

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Introduction
The *Hoatzin* (_Opisthocomus hoazin_) is a peculiar, medium‑sized bird native to the swampy lowland basins of the Amazon and Orinoco rivers in South America. Known locally as the *“Stinkbird”* because of its strong, herbivorous odor, it is often called a *“living fossil”* due to its unique, primitive characteristics that have survived for millions of years.

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Taxonomy & Naming
- *Scientific name:* _Opisthocomus hoazin_ (Müller, 1776)
- *Family:* Opisthocomidae (sometimes placed in its own order *Opisthocomiformes*)
- *Order:* Historically debated – once linked to Galliformes, Cuculiformes, now in its own clade near *Musophagiformes* (turacos).
- *Etymology:* _Opisthocomus_ = “rear‑long hair” (Greek _opistho‑_ = behind, _kome_ = hair), referring to its elongated crest; _hoazin_ from the Aztec word *“hoatzin”*, an onomatopoeic name for its call.

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Description
- *Size:* 62–70 cm (24–28 in) long; wingspan 90–100 cm (35–39 in).
- *Weight:* 700–900 g (1.5–2 lb).
- *Plumage:*
- *Head:* Small crest of brownish feathers, rufous face with a bare blue patch around the eye.
- *Upperparts:* Olive‑brown with white streaks on the neck and mantle.
- *Underparts:* Buff‑cream, faintly streaked.
- *Bill:* Short, stout, hooked, with a distinctive *red or orange cere*.
- *Wings:* Broad, rounded; *claws on the first and second digits* of juveniles (vestigial in adults).
- *Tail:* Long, graduated, brown with a rufous tip.

*Distinctive Traits:*
- *Clawed chicks:* Hatchlings have two functional claws on each wing, used to climb vegetation.
- *Foregut fermentation:* Similar to ruminants; a large crop ferments leaf material, giving the bird a musky, cow‑like smell.

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Habitat & Distribution
- *Range:* Amazon basin (Brazil, Peru, Colombia, Ecuador, Bolivia, Venezuela, Guyana, Suriname, French Guiana) and the Orinoco basin (Venezuela, Colombia).
- *Habitat:* Flooded forest, riverine swamps, black‑water “igapó” and “várzea” forests, often perched on low branches over water.
- *Elevation:* Sea level to ~ 500 m (1,600 ft).

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Behaviour & Ecology
Diet
- *Herbivore:* Primarily leaves, buds, flowers, and fruits of *aroids*, *Heliconia*, *Poulsenia*, and other soft vegetation.
- *Fermentation system:* The crop contains symbiotic bacteria that break down cellulose, converting plant matter into volatile fatty acids (similar to a ruminant’s rumen).

Social Structure
- *Gregarious:* Lives in small groups (3–10) called “clans”; often seen roosting together.
- *Territorial:* Defends feeding and nesting sites with low, croaking calls.

Breeding
- *Season:* Coincides with rainy/flooded periods (varies by region).
- *Nest:* Loose platform of twigs built in a low tree or shrub over water (1–5 m above surface).
- *Clutch:* 2–4 white or buff eggs with brown speckles.
- *Incubation:* 28–32 days, shared by both parents.
- *Chicks:* Hatch with *wing claws*, can climb out of the nest if threatened; claws disappear after ~ 2 months.

Vocalisations
- Harsh, guttural *“hiss”* or *“grunt”* calls; also a low, resonant *“hoo‑hoo”*.

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Conservation Status
- *IUCN Red List:* *Least Concern (2023)* – wide distribution and large population, though local declines noted.
- *Threats:*
- *Habitat loss:* Deforestation, conversion to agriculture, palm oil, and cattle ranching.
- *Flooding changes:* Dams and altered water regimes affect swamp habitats.
- *Protection:* Listed on *CITES Appendix II* (trade regulation). Several protected areas (e.g., Amazon National Park, Yasuní NP).

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Interesting Facts
- *“Living fossil”*: Morphologically unchanged for ~ 60 million years; retains primitive skeletal features (e.g., unfused sternum).
- *Climbing chicks*: The only bird species whose young use wing claws to climb back to the nest if dislodged.
- *Stinkbird*: The fermentation process produces methane and a strong odor, leading locals to call it “stinkbird”