The Science of Birds - Random Bird Thursday: An Orange and Black Species With Females That Like to Sing

Episode Date: August 22, 2025

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 Streak-backed Oriole (Icterus pustulatus).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 that it is random bird. Thursday. In this short and mostly unscripted episode, I'll be spotlighting a bird species that probably won't get featured in a full-length normal episode.

There are over 11,000 bird species in the world, and so Random Bird Thursday is our opportunity to celebrate one of those species that we might otherwise overlook. So let me just reach over here and push the Random Bird Thursday. selector button, and let's see who we're talking about today. Okay, very cool. We have the streak-backed oriole. Icturus Pustulatus, the streak-backed Oriole. And how about we just get right on into it? Let's learn about this bird.

So, starting with what it looks like. This is a medium-sized, Passerine bird, a songbird. It's about seven and a half to eight and a half inches long from beak to tail, and that's 19 to 21 centimeters. And your impression, if you see one, is that it is overall a orange and black bird, or yellowish and black. The head is a bit more orange, whereas the body kind of leans towards yellow. The wings are black, the tail is black. There's a sort of a black mask, the lores in front of the eye are black, and the chin leading down into the upper breast is black. The bill is blackish, kind of bluish-gray in parts, as well as the feet. Those are also

bluish-gray. And I should say that the wings have white edges to the feathers, which kind of highlights each feather, which is really cool. And the name of this species is the streak-backed oriole, so yes, it does have streaks running down the back. The back is yellowish-orange, and the streaks are black. This is a very striking, beautiful bird. Now, that's just kind of the basic male plumage, but there's variation within this species. So is northern most populations

look a bit different from those in the south? Northern males tend to have a more reddish-orange head, and that's actually kind of an unusual color for orioles in this group. An earlier name, an old-school name for the streak-backed oriole was the flame-headed oriole because of that reddish-orange color on the males. And northern populations of this species

have pretty fine and small black streaks on the back. And in the north, the females are similar in pattern, but their plumage coloration is much duller. The females are more kind of olive green or yellowish, just not as contrasty as the males.

But they still have that dark streaking. Now, as you move south, you get into these populations where the males and females actually look very similar. They're monochromatic rather than dichromatic, right? So dichromatic in the north, monochromatic more so in the south. Now in many bird species, when we have monochromatic plumage between males and females, that tends to mean that both sexes are relatively dull in plumage. So as you move south, the females become increasingly more like males.

Also, in some of the southern populations, that streaking on the back is much wider. So the bird's back starts to look almost black because the streaks are blending together. And I'm saying north and south, and we'll talk about the distribution in just a minute here. But first, let's talk about the voice of this bird. So the streak-backed aureole has a variety of different calls and a few different versions of its song. So let's listen to a call. This is a type of chatter call. Then you can hear that that is a sort of short, harsh sound with that rapid succession.

This type of chatter call is common throughout the year, and it's typically associated with territorial defense or aggressiveness, dominance between birds. And apparently the females make more of these chattering calls during the breeding season than the males. This next recording I'm going to play for you is a streak-backed Oriole in Mexico, making its Dawn song. Regarding vocalizations, one of the coolest things about the streak-backed oriole is that, unusually for songbirds, the females sing more frequently than the males, both during the breeding

and post-breeding seasons. And the females make pretty complex songs that are similar to what the males make. We often think of it being the reverse, right? Where males sing more often and they have more complex songs. But not so in the streak back to Oriole. Now, it's important to note that this is only true for the southern populations that live in more tropical habitats. In those areas, and I'll just give it away, we're talking about like southern Mexico, Central America, in those regions, these birds maintain year-round territories. And so the idea is that it might be useful for a female to expend greater effort to help the male defend the territory in those places where the territory persists throughout the year.

In the north, in contrast, the females don't sing as much, if at all, and these birds defend a territory only during the breeding season. So that's just a really cool thing about the streak-backed Oriole, is this propensity for the females in the south to sing a lot. Okay, so let's talk now about the name, the scientific name, Icturus Pustulatus. Icturus, the genus, comes from Icturos, which is a Greek word for yellow bird. But what that refers to are the Old World Orioles, which are also yellow and orange. Old World Orioles are not closely related to Orioles in the New World, in North and South America.

But in any case, that word got applied to these New World species. And then we have the specific epithet, the second part of the scientific name, Pustulatus. What does that mean? That means blistered or pimply, like a pus, right? and I don't know why this bird has that name. I didn't dig super deeply, but I did not figure out where that came from. I mean, like, when I look at pictures of the bird,

I don't see any sort of acne apparent, like on a self-conscious teenager or something. But, yeah, if you know the answer, give me a shout and let me know why you think this bird is called Icteros postulatus. Right, so the family is Icturidy. and if you look on eBird or Birds of the World, anything from the Cornell Lab, they tend to call this the family of the troupeals and allies.

But others will call it the New World Oriole family. And yeah, I think that's what I prefer, the New World Oriole family. That's my preference for the colloquial name. But that's just me. My opinions on matters, however, are of no consequence. I am nothing and I am no one. Anyway, the family Icturidae has 106 species distributed across North and South America. And in case you're wondering, yes, I will definitely do an episode on the family Icturity.

It is coming. So far, the only other podcast episode that focused on birds in this family was episode 85, which was all about metal larks. And those are the birds in the genera sternella and lysties, but within the family Icturity. Now, the genus of our bird today, Icturus, is the most diverse of the genera in Icturity, with 32 species. And among those 32, the streak-backed Orioles closest relative is Icturus Bolochiae. And if you know a little bit about North American birds, you might know that that is Bullock's Oriole. Icturus Bolochiae, Bullock's Oriole. That species breeds in the western U.S. and southwestern Canada, and it spends its winters primarily in

Mexico. That's Bullock's Oriole. And I should just go ahead and tell you the distribution for the streak-backed Oriole is from northern Sonora in Mexico, south to Costa Rica, and it's concentrated mostly along the Pacific slope, so on the sort of western parts of Mexico and Central America. But some of these birds do occasionally end up in the U.S., in Arizona, California, and Texas. But it is a rare bird in the southwestern U.S., and so it's an exciting one to see for birders. There are eight subspecies in the streak bactorial, and these show various differences in plumage and appearance. But interestingly, there was research done on the streak factorial looking at mitochondrial DNA, so looking at genetic data, and that study didn't find any major genetic differences in these subspecies.

then really across the entire species range, there were no deep divergences in populations. So you have these physical differences that don't necessarily show up at the deep genetic level, at least when you look at mitochondrial DNA. And what that suggests is that this species has had a relatively recent population expansion, that those differences are relatively recent things that have evolved. Now, I said there aren't any deep genetic divergences or differences. However, one population stands out from the rest, and that is the population on the Tres Marias Islands off the west coast of Mexico, west of Puerto Vallarda.

So males on those islands are a bit more yellowish rather than orange, and they tend to lack the streaks on their back. They only have just a few little streaks on their scapular feathers. And the females are more pale than their counterparts on the mainland, and again, they kind of lack that streaking on the back, so they don't really live. up to their namesake. Now, in that study, that mitochondrial DNA study, the researchers actually found that the Tresmarias population is actually so different genetically that they, the researchers, proposed

that it should be a separate species. So rather than a subspecies, it should be Icturus gracenii, a full-blown species. And that species, that isolated population, whatever you call it, subspecies or species, is very small and it's vulnerable and so if it were a species we would almost certainly consider it being somewhat endangered. Another thing that's interesting about the evolution of this species ties back to the vocalizations. Remember I said that females in the south sing a lot and they sing maybe even more than the males and they have complex songs. Whereas northern populations in this species are more typical for songbirds where the females don't sing so much. Well there's been research on

other New World Orioles, and including this species, that shows that the southern species of orioles tend to have females that vocalize more and sing more, whereas the northern species don't. There was a study in 2009 where they looked at these losses of female song over evolutionary time as species expanded to the north. So it seems like the ancestral situation for these birds as a group is that females looked similar to males, and that they sang more. But as the species colonized North America, the females became distinctly different

in terms of their plumage and they stopped singing so much. Which is really interesting, isn't it? And I suppose for the explanation or the hypothesis for why that would be, it ties back again to having year-round territories when you're in the tropics and being non-migratory,

whereas in the north, you have this relatively short breeding season, a short time of the year where you're defending a territory, and you're probably migratory. You're not going to stick around on the same area, the same patch of land throughout the year. In terms of conservation, yes, the Tres Maria's population might be in trouble potentially, but in general, this species, the streaked bacterial, is considered least concern by the IUCN. So at the global level, it's not considered an endangered species in any way. And that's because it seems to have a large, apparently stable population. One very rough estimate from 2016 gives its global population at between 5 and 50 million. That's a pretty broad range,

but we could say at least that there are millions of these birds. And I just want to take a moment to say that if you enjoy the Science of Birds podcast, Random Bird Thursdays and all the other episodes, if you've been enjoying it, learning from it, then please consider supporting the show There's a couple ways you can do that. One is you can become a member of my Patreon community. That's where you give a little monthly contribution and that gives some financial support to what I'm doing here.

And you get some perks. So check that out. That's at patreon.com slash science of birds. There's also a support the show link in your podcast app in the show notes. And then the other way you can support what I'm doing is to buy some t-shirts at birdmerch.com. That's a little side business I've started

as an artistic outlet for me creating fun t-shirt designs for you so you can strut around looking good and showing off how cool you are and how much you love birds so check out the shirts at birdmerch.com and I am actively working on new designs so stay tuned for those. All right so moving on with the streak-backed oriole. Let's look at its diet and the way it forages. This is an omnivorous bird. so its primary diet we would probably say is arthropods like insects and arachnids thing in terms of arthropods

these birds are going to glean those from leaves right so they're going to pluck them off of leaves on trees or maybe inside rolled leaves or from the flowers on a tree and the birds will even extract beetle larva from rotten wood and what i should have pointed out earlier is that the beak shape is very conical but comes to a very sharp point and that's pretty typical for birds in the family ecturidae, especially the Orioles. So that pointy bill is great for use as sort of forceps for picking little insects off of leaves, but also for pecking around into wood and plucking out larvae. But as an omnivore, this bird also consumes plant material.

It likes to eat fruit, as well as seeds, and some nectar. One of the streak-backed orioles' favorite sources of fruit is the pitaia cactus, which actually there are multiple species in the genus, stinocerius. These are large calumner cactus that grow throughout Mexico and Central America. And pitaia is actually a cactus fruit that people eat. So streakbacked orioles love them too. And then as I said, these birds also sip nectar from flowers

off of a variety of tropical plants. And they'll come and take nectar from human-made sources, so from, you know, a feeder or something. Streak-backed orials typically forage in pears or in small groups, sometimes with other Oriole species like Baltimore Oriole or spot-breasted Oriole. And they use those pointy bills to do something called gaping. We talked about that before. That's where they insert the closed bill into a flower or fruit or rotten wood or something,

and then they open the bill to access the food. The bill sort of pries the thing open, right? The flower or fruit or whatever. And they have specialized muscles that allow for that strong opening of the bill to pry something open. Now let's talk about breeding. The streak-backed oriole is pretty much a monogamous species, although I guess there have been some cases of polygyny

that have been documented by scientists. As far as I know, there isn't much elaborate courtship behavior that has been documented anyway, but they use vocalizations, their songs and something called a wine call, W-H-I-N-E, and those vocalizations help establish the pair bond and maintain the bond. And so those would be in the category of courtship.

And these bonded pairs will maintain their year-round territories, at least in those southern, more tropical latitudes. And vocalizations, again, become important because they use those vocalizations to defend the territory against other orioles or other birds. Now, how about the nest? The nest of the streak-backed oriole is pendulous. It's a hanging bag, sometimes described as penjul.

Pencil, it's another word, pendulous or pencil. It's teardrop shaped. And this is kind of typical for many birds in the family Icturidae. Not all, but many. In this species, the length of the nest is somewhere between 10 and 20 inches or 25 to 50 centimeters. It's made out of plant fibers and something called fungal rhizomorphs. These are black fibers. And so the nest, if it has a lot of these fungal rhizomorphs, looks very dark or black. And those rhizomorphs, come from fungus that's found around the roots of trees or on decaying logs. I want to make a little sidebar here because fungal rhizomorphs, right? This is an interesting thing.

Let's talk about them for a sec. Another name for them is mycelial cords. And what they are is, if you know anything about fungi, a fungus is made up of these little microscopic fibers called mycelia. And in the case of these cords, there are a bunch of parallel-oriented hyphy, or mycelia, that creates something large enough that's kind of substantial that we can see pretty easily. The word rhizomorph means root-like form or root-shaped. And in fact, these do look similar to plant roots, although of course fungi and plants are totally different critters, but mycelial cords

or fungal rhizomorphs have some similar function. They spread out and they allow the fungus to absorb water and nutrients. They spread out through the soil or rotting wood to help the fungus spread or again to absorb material. And in some of these, in some species, these mycelial cords or fungal rhizomorphs are so persistent that they can actually bore their way through bricks, masonry, over a long time, of course, but still, that's pretty impressive. You know, if you've ever seen the HBO show The Last of Us, which is based on the video game The Last of Us, the sort of zombie apocalypse thing. The whole premise there is that there's this corticeps fungus

that has infected humans and caused people to become these mindless fungus-infected zombies. Well, in that TV show, they show these fibers kind of spreading out and moving around, and so to me, that's very much like a mycelio cord or a rhizomorph. So I just did this little sidebar because this is the kind of stuff I love, right? You're learning about a bird, and then some interesting term comes up,

and you're like, well, what's that? What's a fungal rhizomorph? and then you go down the rabbit hole and you learn about that and it's just another example of learning about how everything is connected and there's even more to the story because the streakbacked oriole builds its nest in high trees that tend to have thorns so think trees like acacia with these big gnarly spike-like thorns so that helps to protect the nest but there's more because those trees are symbiotic typically with stinging ants the ants are just swarming on the tree And sometimes the orio nests are also built near wasp nest in those trees. So you got the thorns, you've got ants, you got wasps. All of that helps to protect the nest from nest predators. Things like snakes, other birds, mammals. But you'd think that maybe the ants could get into the orio nest and cause some havoc, right?

Maybe to attack the nestlings or something. But dig this. There's more connections, right? There was a study in the journal Animal Behavior in 2024 that showed that those Those fungal rhizomorphs actually seem to repel and actually intoxicate the ants. So maybe the ants are coming up to the nest and be like, hey, what's this? And then they're like, hey, I don't feel so good. I feel kind of crazy.

You know what I'm saying? And then the ant just like passes out and falls off the tree rather than attacking the Oriole nestlings. So by using those fungal rhizomorphs to construct the nest, that may help to deter the ants from getting inside the nest. So it's the circle of life. Everything is connected. I love it. I love it. So that's the nest. And then inside the nest we have three or four eggs per clutch. That's pretty typical. And unfortunately for the streak-backed Oriole, it is one of the more common hosts of the bronzed cowbird. The bronze cowbird is another member of the Icturity family, but it is a brood parasite. Do you remember brood parasitism from way back in episode 12? This is where one species of bird, a female, drops her eggs in the nest of another species and that second species raises the chick as its own even though it's a different species. It gets fooled. It's a victim.

Well, that happens to streakbacked orioles. Now remember how I said that streakbacked orioles are rare in the southwest in the U.S., so there's very few cases of that species breeding in the U.S. But in one example, there was a nest, if I believe in Arizona, and it was parasitized by a bronzed cowbird. so that didn't work out brood parasitism aside

incubation is performed exclusively by females in the streaked bacterial and incubation lasts maybe a couple weeks and then once the little guys hatch then you have mom and dad and they both feed the chicks and the time in that pendulous nest made out of fungul fibers

and other fun things that is about another two weeks and then the little guys fledge and I don't have a lot of data on this but presumably mom and dad feed them for a bit longer, and then they're off on their own. They fly off into the uncertainty of life on planet Earth. And that, my friends, is the story of the streak-backed Oriole, a beautiful, colorful bird that's maybe a bit more complex than we might expect. That's probably true for most

bird species. They've got something interesting about them that sets them apart. But this one has a few outstanding unusual traits, right? From the striking plumage differences that we see across its range, including the fact that females are monomorphic in the south, but dimorphic or dichromatic in the north. And then there's the apparent lack of strong genetic divisions among those eight subspecies. And we have the unusual situation where the females often sing as much or more than the males in the southern populations. So if you're lucky enough to spot one of these birds on its rare appearance in the southwest, in the U.S., Or you run into them where the species is more common in Mexico or Central America, you'll probably agree with me that the Streak-backed Oriole, Icturus, Pustulatus,

is a beautiful and interesting bird, one that's definitely worth appreciating. And that's what you just did. You took a few minutes out of your busy day to appreciate the streaked aureole. Good on you! I hope you enjoyed this edition of Random Bird Thursday. I'm Ivan Philipson and I'll catch you next time. Peace. I don't know.