The Science of Birds - Random Bird Thursday: A Trans-Andean Ant-Follower with a Complex Social Life

Episode Date: April 9, 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 Bicolored Antbird (Gymnopithys bicolor).Sound Citations:Niels Krabbe, XC250916. Accessible at www.xeno-canto.org/250916.Johan Chaves, XC949385. Accessible at www.xeno-canto.org/949385.Niels Krabbe, XC248252. Accessible at www.xeno-canto.org/248252.Patricio Mena Valenzuela, XC275411. Accessible at www.xeno-canto.org/275411.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. And I'm happy to say today is a good day because it is Random Bird Thursday. Random Bird Thursday episodes are relatively short and sweet, and in each of them I spotlight a bird species, that I probably won't feature in a full-length episode. Because the thing is, there are over 11,000 bird species in the world. And Random Bird Thursday gives us an opportunity to put a dent in that number to cover some of these species on the podcast, and we can celebrate some of the ones that we might otherwise overlook.

So without further ado, let's figure out which species we're talking about today by hitting the Random Bird Selector button. Excellent. we have the bicolored antbird, gymnopithous bicolor. This is a small bird found in Central and South America. And this is great. This will be fun, and let's go ahead and get right into it. The bicolored antbird is a chunky, short-tailed bird. The wings, too, are relatively short and they're broad, and they're designed or adapted best for fluttering around rapidly in the forest,

over short distances rather than for high speed or for long sustained flights. That short tail is often held slightly fanned out and the bird regularly flicks its tail upward and then slowly lowers it. One thing that sticks out to me when I look at pictures of the bicolored ant bird right away is that it has really big eyes, these big dark brown eyes, and has kind of an astonished or shocked look. And those big eyes make it look pretty cute because, again, chunky little stocky bird with big eyes.

In terms of size, it's about five and a half to six inches long from beak to tail, which is 13.5 to 15 centimeters. So you can think of it as the size of a house finch or a house sparrow. The bill is relatively long, and it has a slightly swollen tip. The tip is kind of thick, and then it has a hooked tip as well. It's dark, kind of a dark gray. And that shape, that hooked bill, kind of the thick long bill, is really great for clamping down on invertebrate prey, for cutting them apart, pulling legs off and things. Okay, so that's the overall shape.

Now, in terms of the color patterning, well, first of all, both males and females are identical, so there's no sexual dichromatism or dimorphism. But adult bicolored ant birds have a brownish chestnut crown and also the nape is that. same color in the back and wings. So basically the upper part of the bird is a chestnut brown. But underneath, they have this snowy white throat and breast, and that is what contrasts with the dark back, giving the bird its common name of bi-colored, right? So two colors.

And that contrast is also highlighted because there's a black band that runs from the cheek along the flanks. So there's like a black line that divides the two colors, making even a starker contrast. The bicolored ant bird has a dark facial mask and black cheeks. And in terms of the bare skin, so around those big, cute, astonished-looking eyes, there's bare skin. So there's blue-gray skin, and that's around the eyes, but also the legs are that same kind of color. In terms of key behavioral traits, the bicolored ant bird is what we would call an obligate army ant follower.

It's hardly ever seen away from Army Ant Swarms. Now here's a thing. So Army Ant following or ant following is a really fascinating behavior among many different kinds of birds. And I absolutely plan to do an entire podcast episode on this phenomenon. It's really amazing and I look forward to doing that. So today we're just talking about this one species. I think it's the first time I've talked about an ant follower on the podcast. So in short, what happens is you have these large, aggressive,

swarms of army ants in the tropics, they radiate out across the forest floor and they are scaring off all kinds of things, right? Because they're really voracious. They eat a lot of things. So as the swarm moves through the forest, all kinds of little things are fleeing the ants, from invertebrates to small vertebrates. And so there's this entire suite of birds that have evolved to follow these ant swarms around and pick off those things that are running away from the ants. Because without the ants, a lot of those insects and arachnids and small vertebrates would be cryptic. They'd be hard to find, right? But because they're running for their lives, they come out into the open and they're more conspicuous. So all these birds just wait to pounce on them. It's a

crazy thing. And the bicolored ant bird is one of them. Now, this species is known for being kind of gymnastic while it's perching, it will kind of move around, you know, pitching forward and back and yawing to the left and right, swaying around as it's looking for things to pounce on or to sally out and snatch. Another interesting behavioral thing about the bicolored ant bird is that it has a complex social life. So there's a social hierarchy between this species and other birds that are following these ant swarms. So that begin, there's many different species. do this. And so this bird, the bicolored ant bird, is dominant over some of the smaller ant bird species, but it is subordinate to larger species like wood creepers and ground cuckus,

birds that aren't necessarily closely related, but have a similar lifestyle of being associated with the ants. So that's interspecies hierarchy, right? A social hierarchy between species, interspecies. Then we have intraspecies social dynamics. within the bicolored ant bird. And these can be really complex, the interactions between individual bicolored ant birds. And a lot of the heated action is happening in and around the ant swarms

because there's basically great places to forage from and not so great places. So the dominant birds are the ones that get the best foraging locations. There's a lot of competition. So when these birds are jockeying for people, position, they will literally supplant each other. So one bird might come in and knock another one off its perch to try to take that primo spot. And the highest ranking, most dominant birds are the ones that

are able to take those spots and maintain them and keep them. And the highest ranking birds are the ones that tend to find spots like right in the middle of the ant swarm, which again is the best place to be to get the most abundant food resources. And then on the other end of the social hierarchy, the more submissive birds. And so the subordinate birds will perform these cringing postures, you know, where they kind of make themselves small, they retract their heads, they even make kind of whimpering sounds, showing that they are subordinate. Now I mentioned sounds, so all of this, there's all these physical postures that the birds make as they're trying to sort out their social hierarchies, and a lot of those are accompanied with vocal sounds. So let's go ahead and talk about

the sounds that the bicolored ant bird make. First, let's talk about the song, though. So the song has a name. It's called the loud song. And this is a series of about 10 notes that last maybe two seconds or so. And the song begins with a long, slightly upslurred whistle. And then the notes tend to shorten and intensify, and they're spaced closer together. And at the end, the pitch drops and the intensity drops.

But good news, I actually have examples for you to listen to. So this is the loud song. The first one here was recorded in Ecuador, so give it a listen. And I've got another example of the bicolored ant birds loud song. This time, this one was recorded in Costa Rica. So that's the song. But there are also 14 different calls that this species makes. A lot of those have to do with the social hierarchy.

So for those subordinate individuals, they tend to be. make these faint peeping little whistle sounds that are called whimpering. But then when there's really intense battles and there's aggression between individuals, they tend to make these snarling or bugling calls. And then some calls are not associated necessarily with their social interaction, but just warning of predators. So there's a keening call, which is this kind of faint whistled key sound. And that's used when there's an aerial predator around and the bicolored ant birds want to warn each other, they use this faint keening sound. And then another warning call is called the Churring call, C-H-I-R-R-I-N-G. And that one is used when there is a large terrestrial animal in the

area, like a human or a chupacabra or a Sasquatch or something. And I actually have what I think are a couple examples of this cheering call. That's how I've interpreted these recordings. So the first one here is from Ecuador. Actually, both of them are from Ecuador. So take a listen to this. And again, I think this is the Churring call. And then one more example. Here again is what I think is the Churring call.

So here we go. Okay, now let's talk about the name of this bird. The common name is pretty straightforward. It's an ant bird. So it's really into the army ant swarms, right? And it's bicolored. It's dark on top, light underneath, which is a common pattern.

among birds, but also other animals, especially aquatic animals, you know, we could call an or a killer whale. Instead, we could call it a bicolored giant porpoise. Or the panda, we could call that instead a bicolored bamboo bear. And as I mentioned, you know, being bicolored among birds isn't necessarily a rare thing. You can probably picture many birds that are dark on top, light underneath, and in many ways that serves as camouflage, as it does for especially, you know, marine animals like killer whales, but also many terrestrial birds. They're dark on top, so when something is looking down on them, they blend in with the forest floor or some substrate, and then they're more brightly colored underneath. Now here's a little bit of a confusing thing

with bird names. So this is the bicolored ant bird, but believe it or not, there are two other species, one called bicolored ant virio, and the bicolored ant pitta. So yeah, You're trying to learn your bird name is a little confusing, but this is the ant bird. So let's look at the scientific name, Jimnopithus bicolor. By color, again, is pretty straightforward, the two colors, but Jimnopithus, what's the deal with that? Well, Jimno, G-Y-M-N-O, means naked. You see that turn up in a lot of scientific names. So Jimnopithis, naked pithis, P-I-T-Y-S.

What's that? Well, it's the genus of another type of ant bird, a relatively closely related bird. But when I looked up where Pythus itself came from originally, it seems that's a bit of a mystery. Like there doesn't seem to be an answer for where exactly that word came from. So, Jimnopithus, naked pithus, naked meaning the skin around the eye. That's the key part. That bluish-gray skin around the eye. That's naked.

It doesn't have any feathers. So the genus Gymnopithus has only three species, and that genus is in the family Thamnophilody. Thamnophilody is the family of what we call the typical antbirds, which would imply that somewhere out there there are bizarre ant birds, strange ant birds, abnormal antbirds, but these are just your vanilla typical ant birds. And in that family, Thamnophilody, there are 238 species. So this is a quite diverse family, and they're found all in the neotropics of the new world.

So as I mentioned, there are two other species in the genus Jimnopithus, the white-cheeked antbird, and the rufus-throated ant-bird. And those would be considered the closest relatives of our species of interest today. Once upon a time, the bicolored ant-bird was considered as the same species as the white-cheeked ant-bird. They were together as one. but eventually they were split because they do have plumage differences, vocal differences, and even some genetic difference in their genomes. So they're definitely different species, and interestingly, this pair of species, or these three birds, really,

follow an interesting pattern, which is common in the neotropics, where you have species that are separated by the Andes, right? The big mountains there in South America, long ago before the Andes existed, before those mountains rose up, There was some proto-population, some ancestral population of birds that then was split, was divided as the mountains rose up. They became isolated on either side, west and east. And over millions of years, that led to speciation, not just in these ant birds, but in many other groups that show a similar pattern. And in the case of our ant birds, the bicolored is on the trans-andian side, so basically the northern and western part.

Whereas its close relatives, those other two species are cis-andian, so they're on the other side, basically around the Amazon Basin, so on the eastern side of the mountains. Anyway, within the bicolored ant bird, there are five recognized subspecies, each of which occupies a different geographic area. And in terms of its range, its geographic extent, that is from Central America, so Honduras, Nicaragua, Costa Rica, Panama, down into northwestern South America. America, including Columbia and Western Ecuador. And its habitat is the deep shade of the understory in tropical lowland forests. But they also do get up into the foothills, into the evergreen forest there, and they'll also get into sort of second growth woodland as maybe a less than ideal habitat, but still suitable enough.

Mostly, the bicolored ant bird is found below 3,000 feet or 900 meters, but it can also get up to as high as about 5,700 feet or 1,750 meters in some regions. This is a non-migratory species, so it's resident or sedentary, does not move throughout the year, just stays in a relatively small area. The bicolored ant bird is categorized as least concern regarding conservation. So that's by the IUCN on the red list. It's least concern, which is great. however, the population trend is believed to be decreasing. So the bird is still widespread in common,

but it is decreasing. And the main threat is, of course, habitat loss and habitat fragmentation, and that's due to deforestation for human settlement, human agriculture, and those kind of shenanigans have caused at least some populations to completely disappear in parts of Honduras, Nicaragua, and Ecuador. So we've already talked a little bit about what these guys eat. Of course, they're eating insects and other arthropods that are flushed by army ants. So this is going to include spiders, cockroaches, crickets, and scorpions. They're particularly fond of orthopterans, right?

So crickets and grasshoppers, Katie Dids. And the bicolored antbird will also occasionally eat small frogs and lizards as those critters are fleeing the ants. So that strong hooked bill, again, is specialized for clamping down on these prey and cutting or tearing apart large prey that could be problematic. If they're thrashing around, they could injure the ant bird. So having that long bill keeps the prey at a little bit of a distance. I guess it's like if you had a crab or something in your hand. You know, if you held it close to your face, then you might get a nasty pinch. But if you hold it at arm's length, maybe that would save you from injury.

Earlier I introduced the idea of ant following, and the bicolored ant bird is what I said was an obligate follower of ants. And so the obligate part means that's what it pretty much does all the time. That is just the way it lives. It goes out every day, finds some army ants, and eats the things that are running away from the army ants. Now, as it's foraging, it tends to perch on vertical saplings or horizontal logs, and usually that's at about one meter above the ground. So a good place to be close to the army ants, not too close, because army ants can be really scary and dangerous, even to these birds. But one meter off the ground is a good vantage point to see all the things that are happening and running around on the forest floor.

The bicolored ant bird is going to make sallying forays where it's going to jump down from its perch onto the ground, grab a prey animal, and then try to return to its perch. And it basically he's just kind of bouncing down quickly to grab its prey because, again, it doesn't want to hang out there with that swarm of ants. It wants to get in and out relatively quickly. Another thing that the bicolored antbird does is it will toss leaves aside on the forest floor to uncover any hidden insects or other arthropods. And it also does something interesting that I just talked about in the last podcast episode, which was about the northern flicker. and that is that the bicolored ant bird does anting. It participates in the behavior of anting.

So if you listened to the last episode, you'll remember that this is where a bird lets ants crawl all over them or it might even actively pick up ants and rub the ants on its feathers before either tossing the ants aside or eating them. Now, there's different hypotheses about what the function of anting is. It could reduce skin irritation. It could combat feather mites or other parasites. and again, I want to do a whole episode on that as well.

So lots of ant-related podcast episodes coming eventually. Okay, our last thing to talk about is how these birds breed. The bicolored ant bird is a monogamous species. Pairs of ant birds maintain a territory all year long. And when they meet up and they fall in love, they go through courtship. And this involves the male feeding the female, so that's a, you know, ritualized courtship feeding. And he'll also do something called nest showing, where the male makes whistling calls, and he looks into a potential nest cavity to attract the female. He's like, hey, what about this?

What do you think? This looks pretty good. It's got an open floor plan. The kitchen was recently renovated. And then she hams and haws and thinks about it, and then they move in and life is good. So as I mentioned, the pair is going to maintain a territory. And it's fairly loose. As the ant birds are following the ant swarms around, they are going to stray into other ant bird territories. So there's a bit of overlap, but the resident pair is really dominant over all the other individual bicolored antbirds in their own nesting area. So there again is that social hierarchy. The nest is a simple cup, cup shape, and it's made of dead palm strips and leaves, and the ant birds will line it with fungal rhizomorphs. So these soft material,

from fungi that can make a nice lining. The nest is usually placed in a low cavity, such as the top of a hollow stump, and that's typically somewhere between, you know, just a little bit off the ground all the way up to seven or eight feet or 1.5 meters. The nest usually just has two eggs, and these are white or creamy,

and they've got a lot of streaks on them, sort of a dark reddish-brown streaking. And you're probably not surprised to know that both parents share in the responsibilities of raising their brood. They share an incubation with the female sitting on the eggs at night, and then they both alternate during the day. And they both bring food to the chicks. The incubation period is about two weeks long, and then the little guys are in the nestling stage for another two weeks or so. Then they fledge and they leave the nest, but they'll still remain dependent on mom and dad for another several

weeks. Their plumage transitions from being dark as juveniles to the adult bicolored pattern. And so there are some new bicolored antbirds in the world, they're just starting their lives, and how long are their lives typically? An estimate from one study has an annual survivor rate of 61% and the longest recorded lifespan was 11.5 years, which for a small bird isn't too bad, but that of course is the longest record. Many of them probably live much shorter lives, but we also just don't have a lot of data. I do just want to highlight one more thing, which is that there's this monograph about this species from 1967 by Edwin O. Willis. A monograph is just kind of like a really in-depth study of a particular thing, usually of one species.

And this was published by the University of California. And it's just really cool when you stumble across these things because it's just really in-depth study that was done in Central America by Edwin O. Willis. And just seeing the level of meticulous study that was done on these birds and how they live their daily lives, you know, I just imagine being a researcher back in the 60s trekking around in the rainforest,

looking at these birds and following individuals and taking all this data just on paper notebooks. Without computers, without smartphones, without any GPS tracking, none of that. There's kind of a romance to it in my mind. But I'm sure it was also really grueling, difficult work in hot and humid conditions. But yeah, that's where a lot of this information originally came from was the work of Edwin O'Willis in this monograph. So we are indebted to Edwin for his hard work. Now, have I seen this species?

No, I have not. I've not seen a bicolored ant bird. In fact, I don't think, well, no, I haven't seen, I don't think any ant birds. I've not seen this phenomenon of ant following. And that is a bucket list thing, I think, in the world of birding. It would be a spectacle, right, to go see multiple species of birds attending to an army ant swarm, plucking off little invertebrates and things as they're running away. That would just be really cool.

So I hope to see that someday. And maybe you have already. Have you had that experience? Have you seen a bicolored ant bird or any ant birds? Ant Viro's, Ant Shrikes. If so, let me know. My email address is Ivan at Science of Birds. And otherwise, that is it for today's random bird Thursday.

I hope you enjoyed learning about gymnopithous bicolor, the bicolored antbird, and I'll talk to you next time. Cheers.