The Science of Birds - Random Bird Thursday: A Large Fat-eater from Patagonia

Episode Date: March 5, 2026

In each Random Bird Thursday (RBT) episode, the goal is to highlight a bird species that probably isn't going to get featured in a full-length podcast episode. These are birds we might overlook, even though they certainly deserve some appreciation and attention. ~~~~~~~~~~~~~~~~~⚠️ SPOILER ALERT!The featured species in this episode is the White-throated Treerunner (Pygarrhychus albogularis).White-throated Treerunner sounds (Xeno Canto recording XC49939 and XC52238)Support the show

Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted exploration of bird biology for lifelong learners. In case you hadn't noticed, it's Random Bird Thursday. Random Bird Thursday episodes are relatively short and sweet. In each, I spotlight a bird species that probably won't get featured in a full, length episode. With over 11,000 bird species in the world, Random Bird Thursday gives us a chance

to celebrate one that we might otherwise overlook. Now, Random Bird Thursday is truly random. We don't know what species we're going to get unless we push the Random Bird Selector button. So let's do that right now. Okay, the Random Bird Generator gave us the White Throated Tree Runner, Pygaricus Albo Gular Pygaricus albulgularis. Now, I'm not sure of the best pronunciation of that scientific name. I'm going to go with pygagicus for the genus, but I think it'd be okay to pronounce it pigerichus or pigericus. Take your pick. In any case, it's the white-throated tree runner. This is a bird from the new world from South America, and let's go ahead and get into it. The white-throated tree runner is a medium-sized songbird.

It's about six inches long from beak to tail, which is 15 to 16 centimeters. And if you're looking at its body shape, it is reminiscent of a nut hatch, if you're familiar with nut hatches. It's not a nut hatch, but it kind of looks like one. It has short, broad wings that are adapted for high maneuverability in the dense forests where it lives. The tail is somewhat rounded, and the shafts on the rectercese, the tail feathers, the end in these little spines. So for these tail feathers, there's the central rachis, right? That's the central shaft. And there are the barbs that come out to the side. Well, the tips of these feathers don't have barbs. So for about 0.35 inches or so, or 9 millimeters,

at the end, there's just this kind of protruding spine, which is just the bare, empty, rakeas. And the bird uses this tail with these stiff feathers to brace itself on tree trunks when it's climbing vertically, very much like what we see with woodpeckers. The bill of the white-throated tree runner is pointed, and it has a chisel-like shape. But if you think of a nut hatch, again, this is not a nut hatch, but if you think of a nut hatch, it has this straight Coleman, so the upper bill is straight, and the bottom curves upward, so the lower mandible curves upward. And that's what's going on with the tree runner as well. In adult tree runners, the bill is bicolored. The upper part is dark and the lower part is pale, more whitish. The white-throated tree runner is overall a brown

bird, but indeed it does have a white throat. So the throat and breast are bright white. And that contrasts sharply with this chestnut brown back and cap that the bird has. So on the top of the head and the front of the head, it's this darker brown. And then as it fades to the back of the body, it becomes more of a chestnut color, so a little bit more roof-y-or-chestnut, towards. the rump. And then if you look at the belly and the sides, there's this irregular scalloped look or scaly look, and it's quite pretty, where there are basically white spots surrounded by brown. The bird has dark eyes with a dark brown iris, and the feet are gray or brown. What does the white-throated tree runner sound like? Well, it has a relatively

simple repertoire. It makes these short little metallic notes, either as single notes or little galloping couplets. It can also make a high-pitched trill or a loud pete-peat call. But luckily, I do have some recordings to share with you. So these are from the east slope of the Andes in Argentina. And the first one was recorded in the National Park Lanin, so Parque Nacional Lanin. And here we go. This next recording was made a little further north in Argentina from around Lago-Kien, which is also again on the east lobe of the Andes. So that gives you a little taste of what these birds sound like.

This is a strictly arboreal species. So that means it hangs out in trees. It doesn't fly long distances. Typically it just moves from one tree to the next. And if you're observing one, it kind of spirals vertically up the trunk. And as it goes, it moves its head first. and it uses its rigid tail as a brace. It's been described as a confident bird

that often ignores people, and rather than flying away or freaking out, it just moves to the other side of the tree trunk and goes about its business. You often see white-throated tree runners in pairs, especially during the breeding season. But in the austral winter, so we're talking June, July, August,

this bird often joins mixed species foraging flocks, and two species that it's often in the company of are the thorn-tailed rayadito, Raiadito, great bird, and the striped woodpecker. So at least in the austral winter, if you see some thorn-tailed rioditos, those are fairly common birds, and they tend to move around in flocks,

and keep your eyes open because you might also find a white-throated tree runner. Okay, so let's move on to look at where the name of this bird came from, its scientific name anyway. Let's talk about its family, habitat distribution, all that good stuff. The species was first formally described in 1831 by a British explorer named Philip Parker King. And the first scientific name that was assigned by him was Dendro Calaptis Albo-Gularis. All right, so Albo-Gularis means white throat. And then in 1839, John Gould independently described the same species as Dendro-Draindrae. Lucas Sternus.

And that was based on some specimens collected on the voyage of the Beagle, D. HMS Beagle, Darwin's famous ship. So Dendro Dramus. Dendro Dramus translates literally as tree runner. Pretty cool. It's a great genus name.

However, that's not the current genus name for this bird or any other bird. There are no bird species out there with the genus name Dendro Dramus. So, the name we do have, the genus we do have is Pygarekis, right? P-Y-G-A-R-R-H-I-C-H-A-S, P-G-G-A-S, Pygurikas.

This is derived from Greek words, P-Y-G-E, not sure exactly how to pronounce that. That means rump, and then Arikos, A-R-R-H-I-K-H-O-S, which means wicker. You know, like a wicker basket. So, P-Garicus is referring to the stiffness of this bird's tail. wicker rump. And then Albo-Gularis again means white-throated. Now because this bird is in South America,

the people there are speaking, or where this bird lives, the people speak Spanish, so it has some some fun Spanish names. One is Comesebo Grande, commisibo grande, literally meaning large fat eater, large tallow eater or large fat eater. Now the question is, why, why is it called this? I don't know. If you live in that part of the world in Argentina or Chile and you know why, that would be great. Let me know. Maybe because it's poking around in the trees pulling out like grubs that are kind of fatty. I don't know.

Or maybe it's based on some kind of old wife's tail or something. But anyway, come a sebo grande. And in Chile, another name is Carmelita, carmelita, meaning essentially the brown one or the tawny one. which doesn't really narrow it down. There's a lot of brown birds, but hey, sure, whatever, Carmelita. And then one more local name in Argentina this time is Picolesna Patagonico. Picolesna Patagonico.

Picolessna literally means something like all beak or all build. All being AWL. So something that's thin, sharp, and pointed. You know, a tool used for piercing leather or other material. Most kids today are familiar with the common tool, the all, AWL. You know, you can use it for piercing leather or piercing your enemies. Just a good thing to carry around in your backpack. Just kidding, kids, do not pierce your enemies or your friends.

Okay, so that's Pygaricus Albulgularis, the scientific name. Now, this bird is in the family Fernariety. And this is the family of the oven birds and animals. wood creepers. It's a mega-diverse family in Latin America in the neotropics with 320 species, more or less, across Mexico, Central and South America. We'll do an entire episode, of course, on this family at some point. It's really fascinating. There's all this diversity within the family with the different tail shapes and bill shapes that are adapted to all kinds of different niches. This is an amazing example of an adaptive radiation in a family. And one of the things I love about it, which I'll talk

about when I do the episode, is that most of these birds are some shade of brown or Rufus or chestnut or that kind of thing. So it's really interesting kind of the uniformity of color among the birds in this family. Okay, so the white-throated tree runner is in the family, Fernarie Adi. Now within that family, who are the closest relatives of this bird? So it's in its own genus. It's in a genus of one, there are two other genera that are relatively close to pygaricus. Now, you'd think that the four species of tree runner, other species, also in this family, would be the closest relatives. They are in the genus Margarornis, and it turns out those other tree runners are not the closest

relatives. Within the family Fernariadi, there are a bunch of these birds that are bark gleaners, right? They're running around like nut hatches on the trunks and branches, probing for small things in the bark, and you'd think that our white-throated tree-runner would be closely related to those. But molecular genetic studies, using DNA, have revealed that nope,

Pygarecus, our lone little white-throated tree-runner, is in its own genus, and its similarity to those other bark gleaners in the family is due to convergent evolution. They look and behave similarly because they live a similar lifestyle. natural selection has acted similarly on them. And we could say that for nut hatches as well, right?

Nut hatches are in an entirely different family, not at all closely related to these guys, but there is some similarity because they live a similar lifestyle, lifestyle. Convergent evolution. One key difference, though, is that nut hatches don't use their tails to brace themselves as they move around on tree trunks or branches. The tree runner does. But anyway, the actual closest relatives to the white-throated tree runner are the Rufus-tailed Xenops,

and that's one species in its own genus, and then there are four species in the genus Okotorinkus, and those are generally called Earth Creepers. So those are the closest relatives of our Tree Runner. And what we learned from the molecular genetic data, considering the molecular clock, looking back in time, is an estimate for the split from those Earth creepers, the genus Okotorinkus and our Pygarekis genus, that split occurred seemingly about 10 million years ago. Now also considering the evolution of the white-throated tree runner, some might call this a living fossil because it is the only living species within its genus.

Whatever other really close relatives it had, other species in that genus, well, they're all gone. They've gone extinct. And it could be that the divergence of this species or the emerging, the emerging, of this species or this lineage happened when dry habitats opened up in the Miocene epoch as the Andes were uplifted, as the Andes mountains rose and created dry environments, causing fragmentation in the forest habitats of these birds. And speaking of forest habitats, this species is found in forests across Chile and Argentina, from sea level all the way up to the tree limit, approximately 7,200 feet or 2,200 meters. but it depends highly on old-growth native forests, primarily of trees in the genus Nothophagus. And in those old-growth forests, the trees ideally would be large

and provide habitat for nesting and foraging for our tree runners. So these are forests in the southern parts of Chile and Argentina. They're temperate, relatively cool, with lots of moss and ferns. And I should mention that those Nothophagus trees, are called in common English southern beaches. They're not related to northern beaches so much, but they're called southern beaches.

And we see Nothelagus species in various southern parts of the world, like New Zealand and Tasmania, places like that. Places that used to all be part of Gondwana, the supercontinent many millions of years ago. But regarding habitat, these white-throated tree runners, they want there to be some large, old trees, that are dead or dying, that provides the maximum amount of nesting and foraging habitats, or microhabitats. And as soon as you get out of the forest into shrub lands or open habitats,

you're not going to find white-throated tree runners. This species doesn't really migrate. It's thought to be resident, so it just hangs out in its forest all year long. And that brings us to the question of conservation. How are these birds doing? Well, at least according to the International Union for the Conservatives, of nature, the IUCN, this species is in the least concern category. And that's good news. These birds are seemingly doing okay. Nevertheless, they face some threats, as many birds do. They do, there has been habitat degradation through the removal of dead trees, the proliferation of exotic plantations, as well as forest fires, and as usual, there's predation by invasive species

like feral dogs, rats, and domestic cats. Okay, so I mentioned that these birds are foraging on tree trunks, right? They're climbing around vertically, and they're bracing themselves with their tails, scooting around on tree trunks. What are they eating? They're primarily insectivorous. So they're looking for arthropods like insects and spiders, both adults and larvae and maybe even eggs,

of things like beetles and flies, caterpillars, anything that might be tucked in the crevices of the bark. Now, although they're primarily insectivorous, they are also known to eat some fruit and some seeds, and there's even some documentation of the white-throated tree runner eating a small lizard, the blue-green smooth-throated lizard. And that lizard tends to hang out on tree trunks. Surprise, surprise. So remember that the white-throated tree runner has this chisel-like bill,

and that is an adaptation for pecking at wood and pulling on. off pieces of bark, and also for just reaching into crevices in the bark. This bird also has a specialized tongue, kind of like what we see in woodpeckers. The white throat of tree runner has a barbed tongue that it can reach into crevices and folds to pull out prey that might be unreachable otherwise. So if you watch one of these birds, it'll fly down to sort of the base of a tree and then spiral its way around the trunk as it moves upwards. And it's going to be flipping off little pieces of bark.

dead wood, maybe some moss, and it's reaching with its bill and that little spiky tongue into crevices. When it comes to breeding, this is thought to be a monogamous species, where both pairs take care of the chicks. We don't know much about courtship. There may be some, but ornithologists don't really know much about its territorial vocalizations or the function of its vocalizations in general. But what we do know is that this is a primary cavity excavator. And that's an important distinction because there are a lot of birds that nest in cavities, but they are not primary excavators. They don't make their own nest cavities. They aren't necessarily capable. And that would be something like chickadees, right, or maybe bluebirds.

Those species depend on primary cavity excavators to make the holes in the first place. So the white-throated tree runner is capable of making its own nest cavity, but that's going to be typically in wood that is relatively soft that has been decaying. That's why this bird needs there to be some large old senescent or old and dying trees. The nest cavity is kind of rounded or spherical. It's lined with sawdust, some dry sticks and grass and pieces of bark. The opening is circular or kind of oval shaped and the entrance hole is maybe one to two point seven inches wide or two point five to seven centimeters. The cavity itself is 10 to 16 inches deep, or 25 to 40 centimeters. And the whole thing is located maybe 10 to 25 feet off the ground or 3 to 8 meters. And again, this is going to be in kind of an

old decaying tree or a fire damage tree. Now, even though this species can and does excavate its own nests, it will also sometimes use pre-existing cavities made by other species, typically the striped woodpecker or the Magellanic woodpecker. White-throated tree runners have strong fidelity to their nests, it seems, so they've been documented coming back at least for a couple years to the same nest, maybe for longer. And as far as I can understand, they do have a bit of a territory around their nest, a territory of about maybe one kilometer in radius that they protect and defend. And when it comes time to lay eggs, there are three to four little white eggs with a range

from one to eight. And those are going to get incubated for maybe about 17 days. Again, with both parents taking care of the chicks, I'm not sure they both incubate, but they certainly help provision the chicks once they're hatched. And after about three weeks, the chicks are going to fledge, and they might stay with their parents for even up to a year, which is pretty remarkable. And as far as we know, these little buggers can live for up to five years, perhaps longer, but at least five years. It turns out that the white-throated tree runner is culturally significant. It shows up in the traditional stories of the Yagana people in South America,

and they call it Tata J-Jurge. T-A-T-A-J-U-R-J. I'm sure I'm not pronouncing that right, Tata-Jurge. And this is a bird that accompanies women as they collect fungi from trees. So it's just hanging out with these ladies as they're collecting fungi. And so this bird has a long association with, humans in southern South America for many, many thousands of years. And so what these women were doing is they're collecting Katron, which is a type of fungus,

a fungus in the genus Cittaria, or Cytaria, C-Y-T-A-R-I-A. And that fungus grows on those southern beech trees, the Nothophagus trees. And if you've never seen one of these funguses, these fungi, they're really wild-looking. They grow as this big, woody mass. they create this kind of big burl or whatever on the tree trunk or tree branch, this dark spherical mass, and then out of that grows these fruiting bodies of the fungus that are pale yellow or orange and they're spherical,

and the whole thing just looks like something from an alien planet. It's really wild. So I'm trying to paint this picture. So you've got this large, maybe like soccer ball-shaped canker, this woody spherical mass, and out of that you have these bright orange or yellow spherical. fungai, these escoma, technically. And they're kind of like a morale, or they've been described as like a deeply dimpled golf ball. So these individual fruiting bodies have these little dimples all over them.

So again, very alien. And the native people call this one, or one name for it is Yao Yao, I believe that's how it's pronounced, L-L-A-O-L-A-O, Yow. And people eat these things. They have for thousands of years, and they still do. It's part of the indigenous cuisine. Another common name for it is Indian bread. And if you eat these things straight up, my understanding is they're kind of gelatinous on the inside, maybe with a little bit of sweetness, but very watery, kind of rubbery. One of the species of Cittaria is Cittaria Darwinia, named after Charles Darwin. And he described the species on the voyage of the beagle. He said it contains a lot of fluid and is relatively tasteless. So you've got this fungus, it is associated with these nothophagus trees, and of course,

the white-throated tree runner is also closely associated with these trees. So it's really cool that you have this ethno-botanical, ethno-ornithological relationship that the native people have been involved with for a long, long time. And then you have to wonder if there is an ecological association with the bird and the fungus, right? because if the bird requires old trees that are partially rotten that have soft wood that's decaying, well, if the fungus has a role in that decay, then the bird would depend on the fungus to play a role to create nesting habitat. So there you go. That's why I went on and on about the fungus, because one, I just think it's cool because I've seen them. And I just remember thinking like,

what is this thing? And I love all of these connections, right? This is one of the things. This is one of the things that's great about learning about birds is that how they are connected to so many other things in nature, everything is connected. And I have a connection to this species. I have seen it. I led a tour in Patagonia, I guess it was last year, a birding tour. And yeah, this was a really exciting bird to see. I saw it in several different locations, but certainly down in Tierra del Fuego, right at the southern tip of South America in the southern beach forests. And I also saw it in Torres del Paine,

National Park in Chile, Torres del Paine. And actually in one of my walks, I had a little free time, so I went on a birding walk by myself while my group was doing something else. And, you know, I saw these thorn-tailed riotitos, so I saw a bunch of them, great bird. And I got to see several white-throated tree runners.

So we're talking about this mixed flock, mixed foraging flock phenomenon, right? So just some lovely birds from South America. And yeah, I hope to see this bird species again. I have a soft place in my heart for any of these bark foraging species, bark gleaners. I do love nut hatches. We will definitely do an episode on nut hatches at some point. And yeah, that is the white-throated tree runner, Pygaricus Albuoyuleris.

I hope you really enjoyed learning about this little guy, this little species. And if you happen to have seen it yourself, you should let me know. tell me your story, send an email to Ivan at scienceofbirds.com. And that, my friends, is all for Random Bird Thursday for this time. Catch you later.