The Science of Birds - Swallows and Martins

Episode Date: December 23, 2021

This episode is all about birds in the family Hirundinidae. These are the swallows and martins.Other than when they’re nesting, swallows are in the air almost all day long. This aerial lifestyle and that high-speed, erratic flight pattern can make it hard for us earthbound primates to get close looks at swallows. But these flappy little birds definitely deserve our attention. They have many charms and talents that—with a little patience—we can learn about and see for ourselves.~~ Leave me a review using Podchaser ~~Support the show

Have you ever found yourself surrounded by dozens of swooping swallows? I'm guessing you have. Maybe it was tree swallows or cliff swallows in North America or barn swallows in Europe. Birds like these zip through the air like little fighter jets. They're so fast that it's hard to get a good look at one. Binoculars feel sort of useless in these moments. I mean, good luck getting focused on a swallow in flight for anything more than a millisecond. The little buggers keep zigging and zagging unpredictably, and they stay airborne for what seems like forever.

If you're trying to identify swallow species in flight, it might be better to just use your naked eyes to glimpse some of their field marks. I once heard a professional wildlife photographer give this advice. If you want to learn how to focus your camera on a moving target, practice getting sharp photos of swallows in flight. Now, I fancy myself something of a photographer, so I recently tried this with some cliff swallows in Alaska. They were flying around over a river north of Gnome. There were tons of swallows, and I snapped lots of photos. Did I come home with any photos of cliff swallows worth keeping? No, I did not. Even with my fancy camera and fancy lens, I couldn't get a shot of a swallow that was in focus. The birds were not cooperative, and honestly, I was a bit impatient that day.

But of course, patience is important when photographing birds. Oh well, maybe I'll have better luck next time. Other than when they're nesting, swallows are in the air almost all day long. This aerial lifestyle and that high-speed erratic flight pattern can make it hard for us earthbound primates to get close looks at swallows, or to get good photos. But these flappy, seemingly out-of-focus birds definitely deserve our attention. They have many charms and talents that, with a little patience, we can learn about and see for ourselves. Hello and welcome. This is the science of birds.

I am your host. host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners. This is episode number 41, which is all about birds in the family, Hyrondinidae. These are the Swallows and Martins. My supporters over on Patreon helped me choose which bird family this episode would focus on. That's one of the fun perks my patrons get, the ability to vote in polls. I sent out a poll about a month ago with three options for this episode. Swallows, wrens, or nut hatches. The swallow family, Hyrondinity, won by a narrow margin. And that's how we got here. I'll definitely cover wrens and nut hatches at some

point, but today it's swallows. These are wonderful little birds, and there is much to discuss, so let's jump right in. We'll start by looking at what distinguishes swallows and martins from other birds. What makes them special? What's their deal? First off, the body and wing shapes of swallows are highly conserved across all the species in the family. By conserved, I mean, these guys pretty much all have the same general shape. Their bodies are cylindrical, kind of elongated and sleek. Body lengths across the species range from 4 to 7 inches from beak to tail, which is 10 to 20 centimeters.

The heaviest species is, well, it's a tie between the Purple Martin, Progni-Subis, and the Southern Martin, Progni elegans. Those beefy birds weigh in at about 1.7 ounces or 50 grams. The smallest species is the fante saw wing, solidoprochny obscurea, which weighs only about 10 grams. Swallows and Martins have long pointed wings. Episode 37 of the podcast was about how birds fly. In that episode, I talked about the four primary wing shapes we see in birds. Swallows have the so-called high-speed wing shape.

Other birds with high-speed wings include falcons, sandpipers, swifts, and turns. Many swallow species have shortish, square tails, but others have V-shaped forked tails with longer feathers on the outside edges. That's the case for the familiar barn swallow, for example. A deeply forked tail is so strongly associated with swallows that we have the word swallowtail in the dictionary.

There are swallow-tail butterflies, swallow-tail coats, and even something called a swallow-tail catastrophe. The latter is a complex concept from the world of math, and I have no idea what it means. But it sounds cool. Swallow-tail catastrophe. Let me just get my notebook here.

And I'll put that swallow-tail catastrophe as one of my possible band names. Now, perhaps the most extreme tale among birds in the family Hyrendenity belongs to the Montane Blue Swallow, Hyrundo Atrocerulia of Africa. The male of this species has two long tail streamers that can be as long as his entire body. That's a common theme among swallows. For species with forked tails, the male usually has longer tail streamers than the female.

Biologists have done a lot of research over the last few decades into why there's this wide range of forkiness or forkedness. Forkitude? Whatever you call it, among swallow species. And into why the differences exist between males and females. There are two primary explanations. First is that a long forked tail makes a male look super sexy to females. So this would mean sexual selection is driving the evolution of tail shape and length in swallows. Be sure to check out episode 27 of the podcast to learn more about sexual selection in birds. The fact that males have longer tails in forked-tailed swallows supports this idea. The second explanation, the other hypothesis, is that tail shape in these birds has more to do with aerodynamics and agility in flight. Biologists have conducted experiments which showed how a bird's

maneuverability in flight is enhanced by a deeply forked tail. There's scientific evidence supporting both the sexual selection hypothesis and the aerodynamics hypothesis. It seems there's a good chance that, in reality, these forces are operating at the same time, interacting over the generations to give us the variety of tail shapes we find in the Swallows and Martins. So what else? Besides the body and wing shapes, we have the legs, which are small and kind of stubby in these birds. But get this. As I was researching this episode, I stumbled across some photos of common house martens that revealed something amazing. This species, and its two close relatives, also in the genus Delican, the legs of these guys are

completely covered in fuzzy white feathers, all the way to the tips of the toes. It's friggin' adorable. They look like miniature tarmigan or snowy owl legs. I love it. Anyway, the neck on swallows is also short, and the head is round or sort. sort of flat. The bill, too, is short, but it's also flat and very wide. When a swallow opens its bill, it has a shockingly large mouth. We say that these birds have a wide gap. With these enormous pie holes, swallows can catch and swallow insects more easily while in flight. This begs the question. Is that how these birds got their English name? Do we call them swallows because they swallow lots of bugs? I looked up the origin of this name, it's etymology, and it seems language

experts don't actually know why we call swallows, swallows. It's a mystery. The highly conserved body, wing, and bill shapes I've been describing for swallows is rather unusual for a songbird. The reason is that, unlike other songbirds, swallows and martens are highly specialized aerial insectivores. Their bodies are adapted to an exciting, high-speed life on the wing. Many of these birds spend about 60% of every day in flight. They catch and eat their food in the air. They also drink water while in flight by scooping it up in their bills from the surface of a lake or river. Swallows even bathe in flight by taking a quick plunge and then air drying as they fly off. This is all pretty impressive.

for sure. But one thing that swallows haven't quite figured out how to do while flying is to use their smartphones. This means they aren't able to obsessively check their smartphones every 30 seconds. Somehow, these birds get through the day having no idea what's happening on Instagram or TikTok. They can't watch YouTube, play video games, or check how their stocks are doing. They're really missing out, poor little guys. Moving on to plumage. Most swallow, and Martin species have a two-toned plumage pattern, dark on top, lighter underneath. Common colors on the upper side are brown, gray, or an iridescent blue or violet. The underside is white in many species, but others are grayish or streaked.

A few dozen species sports some large patches of orange or rust color. Some of the most colorful species are members of the genus Tachycinita. These birds have glossy, iridescent feathers on their heads, backs, and wings. Most are bluish on top, but the aptly named violet green swallow, Takicinita Thalasina, stands apart. This species from Western North America has a vibrant green head and back with purple upper tail coverts. All of that rich color contrasts beautifully with the swallow's bright white underside.

To really appreciate the iridescent colors of a violet green swallow, you need to see it in the right light and at the right angle, preferably while perched, the bird that is, not you. Otherwise, it can look deceptively dull and might not reveal the full spectrum of its beauty. Male and female swallows look mostly the same in terms of plumage coloration. Sexual dimorphism is rare.

That said, there are species like the Purple Martin, where the male is more richly colored than the female. Another interesting feature found in this bird family is the tiny hook-like structures on the outer edges of the primary feathers. Now, it's only a handful of species that have this. The barbs on these wing feathers stick out beyond the edge of the feather, giving it a rough, file-like margin. Two different groups of birds within the family Hyrendinity

have these modified barbs. One group contains the two rough-winged swallow species, and the other group contains the five saw-wing species. Saw wings are all African birds that belong to the genus Salidoprochny. The feather barbed tips are more hook-shaped in the saw wings and in male rough-winged swallows. But interestingly, female rough-winged swallows have barbed tips that are mostly pointy and not recurved into hooks. But why? What's the function of these rough edges on the primary feathers?

Well, ornithologists haven't figured that out yet. No one knows the function. What we do know is that the saw wings and rough wings swallows must have independently evolved to have feathers like this. Because these birds aren't closely related at all. So here we have another unsolved ornithological mystery. But wait, there's more! Birds in the family Hyrendinidae also have special adaptations that give them enhanced eyesight. First off, their eyes are elongated compared to the eyes of your average songbird. They're deeper, from the pupil to the retina, in that dimension. So I'd say swallow eyes are a little more like eye cylinders than eye balls.

Their elongated shape improves the spatial resolution of the bird. eyesight. The second special feature is that each eye has two foveas. Well, the plural is actually fovee-e. Remember that in the center of the retina, at the back of the eye, there's a small area where the photoreceptor cells are at their densest. This area is called the fovea, and it provides the highest resolution images. Humans and most birds have a single fovea per eye, but swallows have two per eye. This gives them the superpower of having sharp vision when looking both forward and out to the side. Eyes like these are unusual in birds, but they're not unique to swallows. What other birds have long eyes with two foveas, fovee? The answer is raptors. Birds like hawks and eagles have

independently evolved similar eyes that give them superb vision. For swallows and martins, their special eyes make them better equipped for catching fast-flying insects in the air. This is yet another adaptation for living life as a specialized aerial insectivore. One of the most outstanding features of swallows is their interesting diversity of nest types. Some nest in burrows, some nest in pre-existing cavities like holes and trees, and others make nests out of mud. Where and how a swallow species nests influences many of its behaviors. How social or antisocial it is, for instance. The most highly social species build nests using mud, and they live in dense colonies. For example, one of the most social songbirds in North America is the cliff swallow, Petro-Colidon, Pyrinoda. Cliff

swallows breed in large colonies. We'll talk more about nests and colonies when we get to the section on breeding. For now, let's move on to give some thought to the sounds that swallows and martins make. As I've mentioned, these are songbirds, but their vocal sounds aren't all that musical, at least not to the human ear. The vocalizations of swallows tend to be simple, single-note sounds. They're buzzy or coarse. To describe these sounds, ornithologists use words like chur, tick, chirp, chirp, cheap, rasp, and gurgle. Here's a male Purple Martin in Arizona, calling while perched on a saguaro cactus near his nest. And here's a female Purple Martin at the same location in Arizona. Notice that her vocalizations

differ greatly from what the male is doing. The next species here is the cliff swallow. These are cliff swallows near their nesting colony in Washington State. And last, here's a tree swallow recorded in New Hampshire. You can probably hear the similarities in the vocal sounds of these few species. I'd say these are pretty typical for birds in the family high rindinity. We'll move on now to learn about the diversity, distribution, and habitats of swallows and martins. The family Hyrondinidae gets its name from the Latin word for swallow, which is Hyrundo.

Hyrundo is also the genus of the barn swallow and its close relatives. There are 86 species in this family, and these are divided into 20 genera. I'd say that's a respectable amount of species diversity. So far, I've mostly been using the word. swallow to describe these birds. But there are also Martins and those five sawwing species, right? Most of the 86 species are called swallows, but 26 are called Martins. What's the difference? Well, there isn't really any biological distinction between what's a Martin and what's a swallow. It's arbitrary, another one of those quirks of using common names. My understanding is

that in the old world, people call the fork-tailed species swallows, and the ones with squared off-tails are called martins. But we don't use this system in the new world. For example, there's a bird in this family with the scientific name, riparia riparia. Over here in the Americas, our name for this bird is bank swallow. However, across the pond in Europe and elsewhere, the same bird is known as the sand martin. It's a situation of use of use, say tomato, I say swallow. We know Hyrendinity is a family in the order Paceriformis, the enormous group of so-called perching birds or songbirds. But who are the closest relatives of our swallows? As far as I can

tell, ornithologists don't yet have a clear answer. Hyrendinity is one of about 25 families that belong to a distinct branch of the avian evolutionary tree. This lineage, or superfamily, is called sylvoidia. Most of the birds in this group, sylvoidia, are found in the old world. The genetic evolutionary relationships of the 25 families are still being unraveled by scientists. But research using genetic data suggests that the closest relatives of swallows might, might be birds in the family pictonotidy. These are the bull-bulls that's spelled B-U-L-L-B-U-L-B-B-B-B-B-B-B-B-B-B-B-B-B. It's hard not to laugh when I say that one. Fantastic name.

Bull bull bulls don't look much like swallows. They have a more typical songbird appearance. So just looking at them, you'd probably never guess that bull bulls are close relatives of swallows. I'm trying not to laugh. It's like mot mot mot. Bull bull, mot mot, awesome. But there are some other look-alike birds out there that many of us could easily mistake for swallows. Who am I talking about? The Swifts, of course. Swifts are in the family apodity. Based on outward appearances, we might assume that swifts and swallows are closely related. Both groups of birds have streamlined bodies with long pointed wings. Swallows and swifts are all specialized aerial insectivores. And most importantly, their names both begin with the letters SW. What more evidence do you need to be convinced

that these birds are relatives. Well, you'd need a lot more evidence, actually, more than you could possibly get, because Swifts are in no way close relatives of swallows. Swifts are not just in another family, they're in a totally different order. So they aren't even songbirds. Genetically speaking, swallows and swifts

are about as closely related as humans are to rabbits. The superficial similarities between these birds is yet another good example of conversely. evolution. Swallows and Swifts look similar, not because they share some recent common ancestor, but because they share a similar lifestyle, the lifestyle of swooping around nonstop to catch bugs in the sky. Swallows and Swifts have, through natural selection, converged to have similar body and wing shapes. So that's a little about the diversity of swallows. How about their geographic distribution.

The family Hyrendinity, with its 86 species, is spread around the world. It's a cosmopolitan family, with representatives on every continent. Every continent, that is, except Antarctica. Wait, what? Really? Actually, I've just been informed that barn swallows and Chilean swallows are, on rare occasions, seen flitting around in Antarctica. Well, paint me pink and call me a flamingo.

That is a surprise. Swallows in Antarctica. What's next? Penguins in Las Vegas? But swallows don't breed in Antarctica. A few confused swallows might get lost and end up on that frigid continent, but that's it. And apparently, it's likely that some of these birds get to Antarctica as stowaways on cruise ships. Ornithologists would call them ship-assisted vexed.

vagrants. That's pretty wild, right? Now, looking at the worldwide distribution of swallows and Martins, we see that this is another special feature of the family Hyrendinity. Few other songbird families are so widespread. Among songbirds, only the crow, thrush, and pipet families are similarly cosmopolitan. And dig this, the barn swallow, good old Hyrundo Rustica, is not only the most widespread species in this family, it actually has the most widespread natural distribution of any songbird in the world. But it doesn't stop there. Riparia riparia, what you might call the sand martin, but I call the bank swallow, that scrappy little bird also has a crazy huge distribution. It ranks up there with the barn swallow as one of the world's most widespread

songbirds. The ranges of some species are actually expanding. The cliff swallow, for example, has spread across North America in the last 150 years or so, as humans have built bridges and buildings everywhere. These structures provide nesting sites. In other parts of the world, the red-rumped swallow, Sacropis Darica, is expanding northward in Europe. And the welcome swallow, Hirundo Neoxina, formerly found only in Australia, has colonized New Zealand over the last 120 years. Species diversity in the family Hyrindinity is not distributed evenly across the world.

Africa has the greatest concentration of species, with 42. Asia has 19 species, North America has about 16, Australasia has 7, and Europe has only 5. A couple species, like the Pacific Swallow, Hyrundo Tahitika, breed on remote islands. swallows and martins that breed in tropical regions tend to be relatively sedentary. In other words, they don't really migrate. And why should they? Their insect prey are abundant all year long. This is the case for most of those 42 African species.

And of course we all know that from watching Monty Python and the Holy Grail. But then of course African swallows are non-migratory. Oh, yeah. But the same can't be said for swallow species that breed in more. northern or southern latitudes. In those regions, flying insects can be almost non-existent in winter. So these birds are migratory. Or, as the Monty Python guys would say, Magratery. For example, all the swallows and martens in the U.S. and Canada are long-distance migrants. They disappear from most of the continent in the winter. They fly south to warmer climates,

where the sultry skies are a buzz with flying insects. During migration or in their non-breeding habitats, these swallows usually gather by the thousands to roost together at night. Back in the day, hundreds of years ago, people in Europe had a silly explanation for why swallows disappeared in winter. They believed the birds hibernate while buried in mud at the bottom of ponds or in riverbanks. I say this is a silly idea, but to be fair, this was before scientists understood the phenomenon of bird migration. And other animals like

frogs and bears hibernate in winter, so why not birds? Given the vast geographic distribution of swallows and martens, you probably won't be surprised to hear that these birds are found in a wide variety of habitats. Pretty much wherever there are abundant aerial insects, you'll find some swallows. Clouds of insects are often found near water. So, swallows forage over ponds, lakes, rivers, and estuaries. But they also swoop around in open terrestrial habitats, like grasslands, scrublands, and savannas. Some species seem to thrive in agricultural or suburban areas. In the vertical dimension, you can find swallows way up in the mountains and all the way down to sea level.

The sky itself is a habitat for these aerial hunters. They spend so much time on the wing that things like air temperature, humidity, and wind might matter more to them than any particular vegetation on the ground. Let's briefly turn our attention to the evolution of the family high rendinity. I've touched on this a couple of times already. We talked about the evolution of the forked tail. and about convergent evolution with swifts. Now, remember that Africa is where we find the greatest number of swallow species.

Why do you suppose that is? Is it A, because Africa has the tastiest insects? B, because there are 54 countries in Africa? Perhaps more countries means more swallows, much like the well-known correlation of mo money, mo problems. Or is it C, because Africa is where swallows first, evolved. The best hypothesis ornithologists have come up with to explain the rich diversity of swallows in Africa is that

this is where the group originated. It's uncertain exactly when this happened, but research using genetic data suggests that between roughly 15 and 5 million years ago, swallows spread out from Africa in several waves of colonization. They eventually colonized most of the world. Some of the most recent research on this topic was conducted by Dr. Claire Brown, while she was a graduate student at Louisiana State University. Dr. Brown studied several aspects of the evolution of swallows using genetic data. Her research gives us that time frame and location for the origin of swallows. It also suggests that the ancestral bird in this family, the first swallow, you could say,

made its nest by excavating a burrow, possibly in San Francisco. Andy Riverbanks. Dr. Brown studied how nest type varies across different lineages within the swallow family. It turns out that each lineage is strongly associated with a particular nest type. By looking at the phylogeny of all swallow species, at their evolutionary tree, Dr. Brown could run statistical tests to determine the most likely sequence of nest type evolution. Each time a new type of nest was, quote-unquote, invented, this led to a rapid diversification in species. Maybe this was sort of like ancient humans spreading rapidly after they invented houses.

Who knows? In any case, the most likely scenario for swallows is that burrow nesting came first. Then some species started building nests out of mud. And finally, some mud nesters transitioned to using only pre-existing nests. cavities as their nest sites. Cavities like crevices in dead trees or old woodpecker nests. You have to wonder how cavity nesting first started. Maybe a pair of swallows lands at the entrance to a woodpecker nest.

Hey, have a look at this. What do you think, honey? What if we didn't have to make our own nest? No more filthy mud. We could just move in here. Knock knock, hello. Anybody home? Anyone? No?

Well, my dear, looks like the place is empty. Finders' keepers, right? But seriously, we should read up on squatters' rights first. We'll talk a little more about nests when we get to the topic of breeding in swallows. Of course, all of this evolution happened over millions of years. The innovation of mud nesting appears to be associated with the spread of swallows across the old world. Likewise, the innovation of using natural cavities might be linked to colonization of the new world, which was a more recent event in the evolution of swallows.

How about the conservation status of swallows and martins? How are these little guys doing around the world? Some species, as I mentioned, appear to have to have. expanded their natural ranges alongside humans. Barn swallows, cliff swallows, common house martens, and some other species build their nests on top of or inside human structures. These birds have been able to move into new landscapes as more nesting sites became available. Barn swallows have been nesting near human settlements for thousands of years. Before we came along, they nested mostly in caves.

These days, however, it's rare to ever find a barn swallow nest that is not inside of a barn or some other man-made structure. Are barn swallows better off for being so tightly connected with humans? It's hard to say. That's kind of a philosophical question, I suppose. I can tell you who isn't doing so great thanks to humans, the white-eyed River Martin, pseudocallidon Syrinteri. This critically endangered species is known from only one location in central Thailand. The last reliable record of the species is from 1978. Since then, trapping for food and habitat destruction may have driven the white-eyed River Martin to extinction.

Losing this bird would be a terrible loss. One reason is that it's one of only two species that represent a unique subfamily within Hyrendinity. The other species is the African River Martin. This subfamily, this lineage, is ancient. The two river martins appear to have characteristics, such as relatively thick bills and large feet, that are intermediate between those of typical swallows and other songbirds. Besides the critically endangered slash possibly extinct white-eyed river martin,

there are some other species that are in trouble. According to the IUCN Red List, two species are endangered, the Galapagos Martin and the Bahama Swallow. Four others are in the vulnerable category, and one is considered near-threatened. Swallows and Martins in general face several major threats. First off is habitat destruction. In particular, the loss of nesting sites can be devastating. species that nest in tree cavities lose habitat when forests are logged and large dead trees are cut down. Development and channelization of rivers and streams reduces the sandy banks that burrowing nesters need.

Another problem is invasive non-native house sparrows. That's sparrows not swallows. The house sparrow is also a cavity nester. These birds are super aggressive and they frequently attack. hack and take over the nests of cliff swallows, tree swallows, barn swallows, and others. Swallows and other aerial insectivores in general are declining in North America and Europe. We don't know exactly why this is happening. One leading hypothesis is that the enthusiastic use of pesticides in agriculture has decimated

populations of flying insects. No flying insects, no aerial insectivores. Climate change too may be playing a role in the decline of these birds. Among other things, a warming climate affects the growth and reproduction of plants. When and where insect populations reproduce is often closely linked to what plants are doing. So there can be a cascading effect, from the climate to plants to insects to birds. Last, there's the trapping of migratory swallows and martens that happens in parts of Europe and the Middle East. Every year, millions of these and other songbirds are trapped by people

and killed, mostly illegally, but in some countries legally. The little birds are then sold for food as a quote-unquote delicacy. Pretty awful, right? People suck sometimes, don't they? All right, let's put this gloomy subject behind us and get into what and how swallows eat. These aerial insectivores eat a wide assortment of flying bugs, pretty much exclusively. On the menu are mosquitoes, flies, beetles, moths, aphids, winged ants, mayflies, caddisflies, and the list goes on. Swallows are opportunistic foragers. They snatch up whatever insects happen to be in the vicinity on that particular day, the insect de jour. In many regions, the available insect species varies a lot, depending on the weather and the season. But hyrindinids are not always indiscriminate in their

dietary choices. Some will seek out large, easy-to-catch insects, and many swallows will choose to avoid venomous critters like wasps and bees. They leave those for the bee-eaters, birds who specialize in eating those stinging insects. Some habitats are home to several swallow species. The birds may all be zipping around foraging over a lake or a meadow at the same time. Some ornithologists hypothesize that when species overlap like this, they tend to sort themselves out by flying at different heights over the ground or water. This would reduce competition among the species. A recent study of three species in New York State used tiny harmless data loggers attached to the backs of Purple Martins, barn swallows, and tree swallows. The devices

continuously measured flight altitude for each bird. Sample sizes in the study were small, like five birds per species, but there was a pretty obvious pattern. Barn swallows flew closest to the ground, above them were the tree swallows, and up high were the purple, Martins. These results agree with some previous studies on the subject. I imagine that as data loggers continue to become smaller and cheaper, we'll learn more about how birds divide up the sky by altitude. It's pretty cool stuff. Some swallows forage alone, others forage in small groups or large flocks. Few species make the effort to defend a feeding territory. Insect prey are usually too unpredictable to make that worthwhile. So wherever swarms of insects show up, swallows swoop in for

an opportunistic aerial feeding frenzy. It's every bird for itself. I was recently in Wahaka, Mexico, leading a birding tour. One warm evening, I took my group out to some scrubby habitat mixed with farmland. At sunset, the sky was full of northern rough-winged swallows and a few violet green swallows. It was a beautiful sight. I looked away from the cloud of birds briefly to chat with someone, and when I looked up again, all of the swallows had vanished. Poof. We were laughing about it when just as quickly they were back. The birds were moving together over the fields as an enormous mass, tracking the swarm of their tiny insect prey. Besides eating, avoiding predators and mindlessly checking social media on their phones,

swallows spend a lot of energy in the business of making more swallows. Birds in the family high rendinity are monogamous with biparental care. In other words, both mom and dad take care of the bebezz. Some species may appear to be faithfully monogamous to the casual observer, but there can be more going on behind the scenes. Take the tree swallow, tachycinita bicolor, for example. Studies have found that as much as 89% of the nests in a tree swallow population can contain at least one baby that doesn't belong to the male at that nest.

This means females are mating with other males besides their partner. Females will mate with neighboring males, males from other populations, and floater males. Floaters are birds that are just loitering in the area, drifters who don't pair up or make a nest. So, 89%, that rate of what we call extra pair paternity is about as high as it gets in birds. But no matter who the daddy is, male swallows in general are incredibly helpful parents. They share in most of the duties, from building and defending the nest to feeding the chicks. Males of some species even help in incubating the eggs. Among the males of all songbirds, male swallows and martins show the highest level of parental care.

That's pretty cool. As I mentioned earlier, hyrindinid birds make nests of several models. Some dig burrows in sand, others construct a nest from mud, and some just find a cozy tree cavity to stuff with soft material. Most bird families don't show this level of diversity in nest types. This is another special feature of high rindinity. And there's actually more nest diversity, because not all mud nests are the same.

There are open cup mud nests like those made by barn swallows. There are also high-walled mud nests with an enclosed cup shape. An example here would be what common house martins build. Last, some species like cliff swallows build a fully enclosed mud nest with a little entrance tunnel. This shape looks sort of like a gourd. Each genus or other lineage within the family Hyrendinity is hardwired to make nests using only one of these distinct architectures. Mud nesters build their nests by scooping up wet mud in their beaks. The male and female work together on this.

Each bird deposits a pellet of mud onto the growing structure with a shaking movement of its bill. As they dry, the pellets bond with each other. A complete nest might require 1,000 mud pellets or more. Once a nest is constructed, or is excavated in sand, or once a suitable cavity is located, grass and other soft material like feathers are used to line the nest. Depending on the species, nesting swallows may be solitary or they may join large colonies. Males and females of every species fiercely defend their nest. But social species are less aggressive than solitary species.

So, a swallow colony, a swallony, you heard it here first, guys, I just invented the word swallony, some of these colonies can be massive. For example, cliff swallows. plaster up to 6,000 of their little mud nests side by side on cliffs or on buildings. This is the most highly social of all the swallows. There are pros and cons for birds that breed in large colonies like this. On the pro side, living so close to other members of your population might help you get information,

information about where to find food, or the best source of squishy mud for nest building. And then there's all the juicy gossip about your neighbors, right? Oh my God, did you see what Sally did the other day? She totally went into Becky's nest and she stole like a whole beak full of grass. She did. I saw the whole thing. But Becky has no idea.

She's so stupid. Becky was all like, where'd my grass go? Duh. I'm Becky. Where's my grass? There are, of course, some cons, some downsides to living in a dense swallony. These include getting mocked behind your back by your neighbors, but also being more conspicuous to predators and dealing with parasite infestations.

On top of that, there's egg dumping. This is when one or more females lay eggs in another female's nest. Egg dumping is a form of brood parasitism. See episode 12. of the podcast to learn all about brood parasitism. In this case, we're talking about intraspecific brood parasitism, which occurs between members of the same species. The more nests you have packed into a colony,

the more opportunities there are for some sneaky egg dumping. Whether breeding in a colony or just a solitary nest, the parent swallows work hard to raise their offspring. They incubate the eggs for two to three weeks. The young birds eventually leave the nest after about a month, but mom and dad keeps stuffing their gaping mouths with wads of mashed up bugs for perhaps another week or so. The adults will sometimes hover acrobatically as they feed their young without needing to perch. We don't have lifespan estimates for most of the 86 swallow species, but it seems that these birds generally live for five to ten years. When I was a kid growing up in California, I used to hear about the near-mythical

swallows of San Juan Capistrano. If you haven't heard of the place, it's one of the so-called missions established by Catholic priests from Spain. They built San Juan Capistrano in 1775. These days, it's surrounded by the sprawling urban madness of Orange County, California. For hundreds of years, migratory cliff swallows returned to the mission every spring. They would reoccupy or rebuild their mud nests tucked under the arches and eaves of some of the stone buildings. The birds were so faithful that the return of the swallows came to be a major event, celebrated every year on March 19th. It's actually a week-long fiesta, complete with the present. parade. As a kid, I was more excited about the return of the Jedi than the return of the

swallows, but I have to credit this San Juan Capistrano business as my first introduction to swallows and to the marvel of long-distance migration. Sadly, flocks of cliff swallows no longer return to the mission. Habitat loss in the area and a misguided restoration project in the 1990s made the place less attractive to the birds. But apparently there's an effort to bring them back, somehow. Fingers crossed. As an adult, I have grown to love Swallows and Martens. I'm a fan of Hyrandinids. As I hope you'll agree, these birds have a lot going for them. They're masters of flight, they're cute and perky, they make an assortment of interesting nests, they're found all over the world, and some of them might even sneak on to cruise ships to go visit Antarctica. Cheeky little

buggers. Thank you very much for hanging out with me today to talk about Swallows and Martins. I really hope you enjoyed listening to the episode as much as I enjoyed researching and writing it. As I mentioned, my patrons voted to select today's topic. It's great to have this input from my supporters. So, cheers to you guys for participating in the poll. My newest patrons are Kayla Alley and Brenda Graham. Welcome to the community, Kayla and Brenda, and thank you so much for your generous support. If you, dear listener, are thinking about supporting the Science of Birds by becoming a patron, you can check out my Patreon page over at patreon.com forward slash science

of birds. I also want to thank Dr. Claire Brown for sharing a copy of her PhD dissertation with me. Dr. Brown did some great research on swallow evolution, and I'm sure we'll see that work published in scientific journals soon. If you have something you'd like to share with me, feel free to send me an email. Maybe you have a comment about the podcast, or you want to spread some juicy gossip about your neighborhood swallows. Whatever the reason, you can reach me at Ivan at scienceofbirds.com. I am your host, Ivan Philipson. Thanks for listening and I'll catch you next time. Cheers.