Odd Creatures is a recurring column about the World’s Weirdest Animals written by award-winning science writer and author Bec Crew, and illustrated by the super-talented Aiyana Udesen
Dinosaurs are birds and birds are dinosaurs, and nowhere is this more evident than in the Hoatzin, a mighty bird with claws on its wings, stomachs in its oesophagus, and the lingering scent of freshly laid cow manure.
Found in the swamps, marshy forests, and mangroves of South America, the Hoatzin (Opisthocomus hoazin) cuts a striking figure as it hops through the canopy. Its smoky black, chestnut, and gold plumage is capped off by an elaborate black-tipped crest, and its face is a featherless smear of bright blue flesh.
Growing to around 70 cm long and weighing half a kilo, these birds are about the size of an Archaeopteryx. But unlike their long-dead doppelgänger, Hoatzins are staunch vegetarians. They’ll occasionally eat flowers and fruit, but what they really love is leaves. More than eighty percent of their diet is made up of them, which means they’ve had to evolve a specialized digestive system to cope with all that noxious ruffage.
No vertebrate can produce the amount of enzymes needed to break down and digest large amounts of vegetation on their own. So heavy-duty herbivores like cows, sheep, sloths, and kangaroos house enlarged and highly modified chambers in their guts where scores of microbes accumulate and produce these enzymes for them. This form of digestion is known as ‘foregut fermentation’ and the Hoatzin is the only bird on Earth that can do it. It’s even got structures in its oesophagus that act as extra fermentation chambers.
Life in the wild is a relentless and all-consuming struggle to keep yourself safe and fed, so the ability to live off something as abundant and easily obtained as vegetation is a real boon for the Hoatzin. But it comes at a price. Because the Hoatzin’s chest area is filled with digestive organs, there’s little room for their wing muscles to develop, which means they’re pretty useless at flying. Plus all that fermenting activity makes them emit a strong, musky stench, which is how they got their nickname – the Stinkbird. It’s not very dignified by our standards, but being stinky has ended up being a blessing in disguise for these near-flightless birds – locals assume they taste as bad as they smell, so for the most part they leave them well alone.
Like many of the world’s herbivores, Hoatzins are highly social and tend to congregate in large groups. They can often be found in tight, noisy groups of up to 100 individuals, these breaking off into smaller family groups when it’s time to breed.
The Hoatzin might look badass as an adult, but it’s even more badass as a baby. Hoatzins breed during the rainy season, which means there’s a good chance their nests will be sitting directly above flooded rivers and creeks. To give them the best chance at survival, young Hoatzins hatch from their eggs with a pair of claws on each wing, which they use to keep a tight grip on their surroundings. Not that they can’t swim though – if Hoatzin nests are attacked, often by larger hawks and vultures, the chicks will drop into the water below and submerge themselves while their parents create a flappy diversion. Once the coast is clear the chicks will use their hooked wing-claws to climb back up to the safety of the nest.
—Bec Crew / @BecCrew