Hoatzin Birds: the Strangest Bird in the Amazon?

Hoatzin Birds born with claws on their wings, bear a striking resemblance to a late Jurassic era dinosaur

Having sailed and explored the Pacaya-Samiria National Reserve for over a decade, we’ve seen some astounding wildlife. Out of everything we’ve witnessed, we feel that the hoatzin (pronounced wat-sin) might just be the strangest bird of all in the Peruvian Amazon.

We’re not alone in thinking this. Just last month in May 2019, French biologists have joined numerous other scientists in associating the hoatzin (scientific name: Opisthocomus hoazin) with the Archaeopteryx, a dinosaur species with strikingly similar characteristics that was believed to have existed from 150 to 125 million years ago and widely considered to be the first bird to exist.

The late Jurassic archaeopteryx (left) and the hoatzin (right)

Hoatzin Birds: A truly unique species

In truth, studies of the hoatzin have shown that it has no close relatives. Biologists have been debating its heritage since the species was first described by the German zoologist Statius Muller in 1776.

Genetic research published back in 2015 concluded that the hoatzin is the last surviving member of a genus of birds that branched off and evolved separately about 64 million years ago, around the time the dinosaurs became extinct.

Such conclusions, along with the fact that hoatzin chicks are born with claws on their wings like the long-extinct Archaeopteryx, have led some to proclaim this species as a “living fossil”. In other words, one of the most primitive forms of still-existing wildlife.

Illustation of hoatzin adult with juvenile. Note the wing-claws on the latter.

Like the nearly flightless dinosaur species, hoatzin birds can barely fly as an adult despite losing the ability of their unique wing-claw as they mature.

Mysterious origins

Interestingly, while today geographically restricted to South America, ancestors of hoatzins are believed to have emerged in Europe and Africa. Because the continents had already begun to drift apart by the time hoatzin ancestors emerged, and because hoatzins are weak flyers, evolutionary biologists have theorized that these birds reached the western world by means of rafting.

This may sound like the plot line of a cartoon, but experts believe that when large chunks of floating soil and vegetation were washed out to sea by ancient rain and floods, the early hoatzins had went along for the ride across the Atlantic, eventually setting up permanent residence in the lush Amazon rainforest.

Today in the Peruvian Amazon, we have the unique opportunity to observe these intriguing birds, sometimes together with their young. With their wing-claws, young hoatzin chicks can crawl by alternating movements of front and rear limbs on opposite sides of their body ⁠— just like common mammals. No other living bird species has the ability to execute this crawling motion!

A canny defense strategy

Be it from a jungle trail or aboard a skiff that’s sailing close to the shore, you can spot hoatzin birds hanging around trees near wet areas in the Peruvian Amazon’s Pacaya-Samiria National Reserve, such as still water, slow-moving creeks, flooded forests, swamps and oxbow lakes.

An adult hoatzin, on average, is about the size of a pheasant, about two feet long and typically weighing nearly 1kg (which is heavy for a bird). Not only is its spiky, unkempt crest, lumpish body, blue face and bright red eyes easily spotted from afar, the hoatzin also often makes its presence known by making chuffing and grunting noises as a human explorer gently approaches.

Male and female hoatzins look alike. Both parents, along with older siblings, work together to raise two to five young. Eggs hatch after four weeks of incubation, and adults feed the chicks a regurgitated leaf paste.

To defend themselves and their young, adult hoatzins hiss, hoot, and yelp at predators, which include tayras and capuchin monkeys. Nests are built over water, and if danger threatens, the young hoatzin birds instinctively hurl themselves out of their nest, plunging into the waters below. Don’t worry; they are excellent swimmers!

This is when the wing-claws come in handy. Drenched but safe, the chicks return to shore and use their claws to climb back up to their nest. How’s that for independence?

A stinky and clumsy reputation

Nicknamed the stink bird or the skunk bird, the hoatzin is also unique in being the only avian species with a digestive system that ferments vegetation in the stomach (same as a cow), enabling it to eat leaves and buds exclusively. Hoatzins commonly feed on swamp plants, grinding foliage in their stomach and not the gizzard as other birds do. Only rarely do they eat insects.

Inside the hoatzin’s stomach, the bacterial fermentation process breaks down the vegetable matter it consumes and detoxifies certain leaves. Even though it doesn’t regurgitate food in the manner cows do, the hoatzin’s unusual foregut ruminant digestive system gives the bird an odor so unpleasant that it’s rarely ⁠— if ever ⁠— hunted by humans for food.

Perhaps precisely because of this, the hoatzin usually doesn’t appear flustered in the least whenever we pass close to their habitat. Rather than taking flight as our tenders sail near to their perching spots, the most the hoatzins would and could do is flap their wings and, somewhat clumsily, clamber to a branch a couple of feet away.

Hoatzins might spread their wings, but they can’t fly far!

Not that they’re lazy or truly fearless; the hoatzin’s unique, double-chamber digestive tract takes up so much space in its sternum that its muscles have been either displaced or reduced, meaning that the bird flies extremely poorly and are highly sedentary. Some even call the hoatzin a ‘flying cow’!

Looks-wise, the hoatzin might not be the prettiest bird to spot while on an Amazon river cruise, but it is no doubt one of the most fascinating species of wildlife to discover for travelers venturing into this biodiverse evolutionary wonderland.
 

Amazon River Cruises:

Sail with us and see the hoatzin and other Amazonian wildlife up-close in the company of experienced naturalist guides with Aqua Expeditions, on board the five-star Aria Amazon and Aqua Nera river cruise ships.