By no stretch of the imagination could hoatzins (Opisthocomus hoazin) be described as beautiful.
Regarded as one of the weirdest birds in the world they have a few a few assorted features to be sure, but the sum total of these parts almost borders on grotesque.
What do hoatzins look like?
A funky mohican crest and neon-blue facial skin surrounding a beady red eye are accessorised by dramatic, cape-like wings and an extravagant fan-shaped tail – used to keep balance when scrambling around in vegetation.
They weigh 700-900g and grow to 62-70cm in length. They are big and pheasant-like, with a long, bristly crest.
The black, russet and cream plumage has a hint of the Georgian gentleman. But the elegance stops there. It looks ungainly due to its seemingly oversized wings and tail, and has a characteristic startled expression.
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Can the hoatzin fly?
Hoatzins are awkward birds. Their flight is laboured, with many a comical crash-landing, and their flouncing gait probably ray rise to one of their local Brazilian names: cigana, meaning gypsy.
Where does the hoatzin live?
The hoatzin principally lives in South American swamps in the Amazon and Orinoco river basins. It nests in waterside trees and bushes beside bodies of water.
What do hoatzins eat?
Whatever the truth about the hoatzins' past, their diet makes them unique. They are the only birds known to possess a foregut fermentation system. This highly specialised arrangement equips them to process the huge quantity of foliage needed to provide enough energy (leaves are low in nutrients).
The hoatzins' oesophagus and enlarged crop serve as fermentation chambers. Inside are anaerobic bacteria that secrete enzymes able to break down the otherwise indigestible cellulose present in plant tissue.
The birds chew leaves before swallowing, and ridges inside their crops help to break down the leaf bulk further so that it can be processed more easily. In digestive matters, hoatzins have more in common with cattle and sheep than with their feathered relatives.
Hoatzins digest their food very, very slowly. A meal takes up to 45 hours to pass from bill to baca. This is why these birds loaf around for up to 80 per cent of the time – they are effectively chewing the cud.
Hoatzins consume leaves and buds of more than 50 plant species, including several toxic to other birds. It also eats fruit.
There is a downside to having a supersized crop, however: Hoatzins only have enough space left inside their bodies for a simple, reduced sternum (breast bone) and puny fight muscles. Small wonder then that they are such weak flyers.
Very much creatures of habit, hoatzins are almost always to be found feeding in trees or shrubs, but they can still spring surprise. One of the entries into BBC Wildlife camera-trap photo competition revealed a group feeding on the ground in a dry river – unusual behaviour possibly explained by presence of fallen fruit.
Why does the hoatzin stink?
The hoatzin, also known as the stink bird, reeks of fresh cow manure or sweet-smelling hay, because of its unusual diet.
Like cows, it produces rather foul-smelling methane and particularly fragrant droppings.
Are hoatzins social?
Besides their reputed perfume, hoatzins are endowed with another typically bovine characteristic: they are highly social. The birds form family groups (or should that be herds?) of up to a dozen or so individuals. Flocks of 40 or more birds have even been recorded.
An entire family may engage in the hoatzin equivalent of cattle lowing – a cacophony of grunts, squawks and hisses, often delivered in unison. Usually the birds are set off by one particularly enthusiastic individual, who leads the rest of the ensemble in a bizarre chorus.
What does the hoatzin sound like?
Listen to a hoatzin's call in the BBC's Tweet of the Day.
When were hoatzins discovered?
Hoatzins have intrigued and befuddled scientists ever since they were first described by German zoologist Statius Müller in 1776.
Taxonomists later spent decades bickering over their origins, originally lumping these oddities with pheasants, then moving them around the avian family tree from pigeons to cuckoos and rails to turacos. Today, they have their own family, the Opisthocomidae (from the Greek for those with long hair behind').
Is the hoatzin related to reptiles?
Hoatzins split from other bird groups a very long time ago, though precisely how and when remains unclear since only one fossil hoatzin has ever been found.
The species has been seen as living evidence of the transition between reptiles and birds – the wing claws of young hoatzins are frequently cited as proof of ancient ancestry. But the trait probably evolved separately in hoatzins rather than being inherited directly from Archaeopteryx and other early birds.
How many eggs does a hoatzin lay?
The hoatzin breeds during the rainy season, often with several pairs nesting in close proximity. Females lays two to four eggs on a simple twig platform in a tree overhanging water; usually only one chick fledges, at about 60 days old.
A co-operative breeder, it has up to six 'helpers', including previous years' offspring.
How long to hoatzins live?
These dramatic-looking birds can live up to about 10 years in the wild.
What threats do they face?
The chief threats to the species are deforestation and disturbance, including from uncontrolled tourism.
Researchers who placed microphones in hoatzin nests at Cuyabeno in Ecuador discovered that, while the owners did not flee straight away, their heart rates and stress levels soared. Repeated visits from tourists may therefore adversely affect hoatzin populations near lodges and camps.
Their conservation status is common, but has a patchy distribution across its large range. The flesh of hoatzins is reputed to be disgusting, so they are rarely hunted.
Main image: Getty Images