Today's Bird of the Week comes from an eminent source: Paul Crosbie, aka Jack Crosbie's dad, aka a whole professor of parasitology and evolution. That's right, the man has a full doctorate in being very brainy, so when he gets in touch with bird recommendations, I have to listen.

This brings me to today's bird, the hoatzin. Prof. Crosbie's full communiqué about this bird read as follows: "from an evolutionary perspective, an absolute trip." Which is exactly the kind of enigmatic intrigue that a professor interested in sending you on your own journey of knowledge would float your way. And wow, oh wow, was the prof right to point me in the direction of this bird, because the hoatzin is as thrilling, baffling, and amazing a bird as you will find, for a variety of reasons, including the aforementioned evolutionary ones which I promise we will get to. There are so many reasons, in fact, that I am going to have to throw out any semblance of "flow" and just do a list. Let's dive in.

The way it looks.

'Nuff said. Well, actually, I have to add this description from Cornell's eBird database, because it is so weirdly specific and cantankerous. Here it is: "Large, dumpy bird found around lake edges and slow-moving streams. Head looks too small for its large brown body. Its orange mohawk, blue facial skin, and stubby bill make this bird extremely distinctive." Rude. I love this bird no matter what.

The Flickr caption on the above picture reads, "the world's weirdest bird," which says so much—everyone who comes into contact with the hoatzin (which makes its home in swamps and rainforests across northern South America, especially the Amazon), turns into a version of the mind explosion emoji. Here's another picture.

And here's a good video showing the hoatzins in their full glory. About 2.5 minutes in there are six hoatzins sitting in a tree and it is very "rad" to me:

2. The way it eats (and smells).

Hoatzins are pretty literally like nothing else in the universe. They are definitely birds, but—twist number one!—they are also kind of like a cow? Here is the New York Times in 1995 (emphasis mine):

A TROPICAL bird with an unusual digestive system can process plant fiber just as efficiently as a cow, an ornithologist has found.
The scientist, Dr. Alejandro Grajal of the Wildlife Conservation Society, and his colleagues reported six years ago that the species, the hoatzin, was the only bird known to have a digestive system similar to a cow's. The hoatzin, also known as the stinkbird, has an enlarged crop and esophagus where bacteria break down the cellulose in plant cells into sugars that the bird can digest.
[...]"The surprising result is these animals have an incredible efficiency in digesting fiber, higher than anything measured in birds," he said. The hoatzins digested up to 70 percent of the plant fiber, he found in the study, published in the current issue of the journal Ibis.

A bird that eats like a cow! Bird! Cow! There are birds that are actually called cowbirds that do not eat like cows, but the hoatzin does. The digestive process takes up to 45 hours, by the way, so the hoatzin spends an inordinate amount of time just lounging around and getting its food through its system. In fact, its body is so devoted to this that its digestive area actually takes up space that would normally be occupied by bigger flight muscles, meaning that it can't fly that well.

Also you may have noticed that the hoatzin is also called a "stinkbird." This is related to the cow thing. Here's BBC Wildlife:

The hoatzin of the Amazon Basin is a folivore, or leaf-eater. This so-called ‘stink bird’ reeks of fresh cow manure or sweet-smelling hay, because of its unusual diet. The bird has a special digestive system to process the huge quantity of foliage it needs to provide enough energy.

It not only eats like a cow, it SMELLS like a cow. Brilliant.

3. The whole baby claw/crawling thing.

This is part of the evolutionary thing, but not the full part. But it's still wild, and—twist number two!—it's another thing that sets the hoatzin apart from l i t e r a l l y every other bird on the whole planet. Over to Inside Science (emphasis mine):

Hoatzins are the only living birds with functional claws on their wings, a trait they lose as adults. The chicks use their claws to climb back into trees after dropping in the water to escape predators. But, save for a description and sketch published in 1888, there has been hardly any research on the wing-claws or how chicks use them -- until now.
A paper published last week in the journal Science Advances reveals the muscles and tendons that allow the claws to grasp. The researchers also found that hoatzin chicks crawl in a familiar way, alternating movements of front and rear limbs on opposite sides of the body. This is the walking gait used by animals such as lizards and dogs, but it has never before been documented in birds, said Anick Abourachid, a functional anatomist at the National Museum of Natural History in Paris, France, and first author of the study.

Mind-explosion emoji! 🤯🤯🤯🤯🤯🤯🤯🤯

Here, courtesy of the GOAT David Attenborough (who, like Prof. Crosbie, is an Englishman, but unlike Prof. Crosbie, has NOT recommended any birds to me, which I find vaguely offensive), is a video of the little hoatzins with their little claws:

4. It is an evolutionary unicorn.

So now we are at the evolution part. You will have noticed that I keep saying "the hoatzin is the only bird to do this and that," so it should hopefully not surprise you that—twist number three!—its evolutionary history is as fantastical as everything else about it. Here's Audobon's Elizabeth Deatrick from 2015 to help me explain (emphasis, yes, mine):

The Hoatzin’s many anatomical anomalies have long made it a seductive research subject for scientists, who've been intent on solving one big mystery: Where the hell did this thing come from? For decades, anatomists were baffled.
[...] The latest twist of events, though, explains why scientists had such trouble: The Hoatzin is truly in a class (or, to be specific, a "sister group") of its own. Research published just this week estimates that the species branched off from the rest of the avian tree about 65 million years ago, and is the only species in its group today. Perhaps this shouldn't come as too much of a surprise—the Hoatzin always was the black sheep among birds. Every family has one; they're the ones who keep things interesting.

That's right: the hoatzin is in a bird group of exactly one. There's nothing related to it in the world!

That would be my favorite part but this next thing is my real favorite part: the hoatzin is so unique that a Christian creationist group has used it to argue that the theory of evolution has to be bunk. Here are some excerpts from the Answers in Genesis website (emphasis mine!):

Even ignoring the devastating blow hoatzin deals to Archaeopteryx as a transitional form, it causes evolutionists other significant problems, as evidenced by the trouble it gives to their cladistic models. They simply cannot determine what its ancestor was. However, if they would pause long enough to consider Genesis 1, they might recognize that hoatzin likely is its own created kind and thus its ancestor was a hoatzin.29 This also would explain the unique hoatzin digestive system, found in no other birds.30 Of course, that would require evolutionists to admit that there is a God, and since many refuse to even acknowledge a designer, this is unlikely. Sir Francis Crick summed up the attitude of the general science population towards any possibility of design. “Biologists must constantly keep in mind that what they see was not designed, but rather evolved.”31 In other words, evidence of design does not matter, scientists must embrace evolution, in spite of the evidence. Sadly, the hoatzin has not caused evolutionists to doubt their worldview, or even consider the possibility that hoatzin was made by God to do exactly what it does today.

I am going to go with the centuries of scientific theory on this one and not the group that runs the Creation Museum, but to each their own. (Also, pretty sure you can believe in both God and evolution.) It truly tickles me that there is a bird that is so weird that religious nutcases are using it as evidence that evolution has to be wrong. You can't say that about the pigeon!

OK, that's it. Drive on hoatzin! Prof. Crosbie, thank you!!!! (And please grade me on a curve, this is all the most science I have done in decades.)

A reminder: you can check out our complete Bird of the Week list here, and get in touch with your bird suggestions at hello@discourseblog.com.

Bird of the Week: Hoatzin