(Today I Learned) About The Hoatzin aka Stinkbird

The Hoatzin (Opisthocomus hoazin), also known as the Hoactzin, Stinkbird, or Canje Pheasant, is an unusual species of tropical bird found in swamps, riverine forest and mangrove of the Amazon and the Orinoco delta in South America. It is notable for having chicks which possess claws on two of their wing digits.

It is the only member of the genus Opisthocomus (Ancient Greek: "wearing long hair behind", referring to its large crest, which in turn is the only extant genus in the family Opisthocomidae. The taxonomic position of this family has been greatly debated, and is still far from clear.

It is a roughly pheasant-sized bird some 26 in. long, with a long neck and small head. It is brown in color, with paler underparts and has an unfeathered blue face with maroon eyes, and its head is topped by a spiky, rufous crest. The Hoatzin is herbivorous, it eats leaves and fruit, and has an unusual digestive system with an enlarged crop used for fermentation of vegetable matter, in a manner broadly analogous to the digestive system of mammalian ruminants.

The name Stinkbird is related to a strong smell produced by this bird, perhaps due to the consumption and fermentation of leaves. The alternative name of "stinkbird" is derived from the bird's manure-like odor, caused by their digestive system.

The Hoatzin was originally described by German zoologist Statius Müller in 1776.

This is a noisy species, with a variety of hoarse calls, including groans, croaks, hissing and grunts. These calls are often associated with body movements such as wing spreading. Calls are used to maintain contact between individuals in groups, warn off threats and intruders and by chicks begging for food.

Feeding

The Hoatzin eats the leaves and to a lesser degree fruits and flowers of the plants which grow in the marshy and riverine habitats where it lives. It clambers around clumsily among the branches, and being quite tame (though they become stressed by frequent visits), often allows close approach and is reluctant to flush. The Hoatzin uses a leathery bump on the bottom of its crop to help balance itself on the branches. It was once thought that the species could only eat the leaves of arums and mangroves, but the species is now known to consume the leaves of over fifty species. One study undertaken in Venezuela found that the Hoatzins diet was 82% leaves, 10% flowers and 8% fruit.

One of this species' many peculiarities is that it has a digestive system unique amongst birds. Hoatzins use bacterial fermentation in the front part of the gut to break down the vegetable material they consume, much like cattle and other ruminants. Unlike ruminants, however, which possess the rumen (a specialized stomach for bacterial fermentation) in the Hoatzin this is the function of the crop (an enlargement of the esophagus). The crop of the Hoatzin is so large as to displace the flight muscles and keel of the sternum, much to the detriment of their flight capacity. Because of aromatic compounds in the leaves they consume and the bacterial fermentation, the bird has a disagreeable, manure-like odor and is only hunted for food in times of dire need. Any feeding of insects or other animal matter is purely accidental.

Relationship with humans

Though conspicuous, even attractive, at close range due to its bizarre shape and striking colors, unwary and a poor flier, it is not considered endangered. In fact, its survival seems to be more assured than that of many other endemics of its range. In Brazil, tribal people sometimes collect the eggs for food, and the adults are occasionally hunted, but in general this is rare, as it is reputed to have a bad taste. While its preferred habitats, mangrove and riverine forest, are disappearing quickly in some regions, it is less threatened than terra firme forest, which is the primary target for deforestation in the Amazon. The Hoatzin therefore remains fairly common in a large part of its range. The Hoatzin is the national bird of Guyana.

Genetics

The Hoatzin is arguably the most enigmatic living bird in regard to its phylogenetic relationships. No satisfying evolutionary hypothesis has been proposed, and the situation has actually become worse with the availability of DNA sequence data.