The Science of Birds - Hornbills

Episode Date: January 16, 2023

Today’s episode is number 68. It’s all about the family of birds called Bucerotidae. These are the hornbills.Maybe you’ve heard about hornbills and know a few facts about them. Or maybe you’ve never even heard about these birds. Either way, I think you’ll enjoy today’s podcast episode. Hornbills are just so cool!The family Bucerotidae includes several dozen hornbill species. But there’s a second, much smaller avian family that contains birds we also call hornbills. The name of that family is Bucorvidae, the ‘ground-hornbills.’ There are only 2 species of ground-hornbills. I’ll be including them in our conversation today too. Besides, until recently, scientists grouped ground-hornbills into the larger Bucerotidae family. Hornbill are key players in the tropical ecosystems of both Africa and Asia. There are many fascinating things for us to learn about them. Links of InterestHunting the Helmeted Hornbill [VIDEO]Hornbills Pluck Bats Mid-flight [VIDEO]~~ Leave me a review using Podchaser ~~Link to this episode on the Science of Birds website Support the show

You're standing in a tropical rainforest in West Africa. Towering trees and deep green vegetation surround you. It's warm and humid as a light rain falls. Things seem pretty groovy and you're vibing on the humming sounds of the jungle. But suddenly, you're startled by a wailing cry up in the understory. What could be making that strange sound? A monkey? More likely, it's some kind of unholy spirit,

like a banshee coming to warn you of imminent death. Or maybe it's the ghost of Christmas past or something. I don't know. But then you see the creature, a black shape flapping noisily through the canopy. It comes to rest on a high branch. Using your binoculars, you get a good look at it. To your relief, you see that it's just a large bird.

A bird with a disproportionately, comically massive head. The head is pretty much all beak, including a weird tubular crest thing jutting from the top. Leathery blue skin surrounds the bird's large eyes. Blue waddles dangle from its chin. The bird looks at you while you look at it. Those eyes seem to reflect intelligence, or at least a kind of confidence. Consider yourself very lucky. You're in the presence of a hornbill. This one is a male Saratigimna Atreta, aka the black

casked hornbill. Birds like this one, members of the hornbill family, are key players in the tropical ecosystems of both Africa and Asia. There are many fascinating things for us. us to learn about them. Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a light-hearted exploration of bird biology for lifelong learners. Today's episode is number 68. It's

all about the family of birds called Bucerotidae. These are the hornbills, of course. Maybe you've heard about hornbills and know a few facts about them. Or maybe you've never even heard about these birds. Either way, I think you'll enjoy today's podcast episode. These birds are just so cool. The family Bucerotidae includes several dozen hornbill species. But there's a second, much smaller avian family that contains birds we also call hornbills. The name of that family is Bucorvidi, the ground hornbills. There are only two species of ground hornbills. I'll be including them in our conversation today too.

Besides, until recently, scientists grouped ground hornbills into the larger Bucerotidi family. So you got that? We're talking about two bird families here. One, Bucerotidae, the typical hornbill family, which contains dozens of species. And two, Bucorvody, which contains just two species, the ground hornbills. And with that, we're ready to travel to the old world tropics. Let me just sound the official hornbill horn, and off we go. We begin with the key traits of hornbills, what they look and sound like.

How does one describe the general shape of a hornbill? They're kind of wacky-looking, almost alien-like. Body shapes vary a bit among species, but the most obvious feature they share is a bill with massive proportions. The bill has a strong downward curve in almost all species. The large head is supported by a muscular s-curved neck. Hornbills have broad oval-shaped wings, and their tail tends to be long. The longest tail of all belongs to the helmeted hornbill. The central tail feathers extend well past the rest of the tail, giving the helmeted hornbill

a total length of about 45 inches, which is 115 centimeters. If you're familiar with toucans, then you might think a hornbill looks like a toucan. These two types of birds are not closely related, but there is a reason they look similar. We'll get to that later. The smallest species in the family Bucerotidae is the black dwarf hornbill, Horyserisaris Hartlubai. It weighs 3.5 ounces, which is 99 grams, and it's only about one foot long, or 30. centimeters. At the other extreme for size is the Great Hornbill, Buceros by Cornus. This hefty bird is up to 40 inches long, or 100 centimeters. It has a five-foot wingspan and weighs almost

nine pounds, which is four kilograms. The southern ground hornbill, Buchervis Ledbetterai, is about the same size as the Great Hornbill, except that it has a six-foot wingspan and weighs up to 13.6 pounds, or 6.18 kilograms. This is roughly the size of a wild turkey. In other words, pretty dang big. In some species, male hornbills are larger than females, so there can be body-sized dimorphism between the sexes. What about that beak, though?

Let's talk some more about the namesake of this bird family. Besides being long, large, and decurved, the bill of many hornbills has a bonus feature, A cask. That's C-A-S-Q-U-E, cask. This word comes originally from French and means a piece of armor for the head. In other words, a helmet. A hornbill's cask is an outgrowth of its bill, a protuberance. Each species has a unique cask in terms of its shape, color, and relative size. In some species, the cask is nothing more than a simple, ridge running along the top of the beak. For example, that's the case for the 10 African species in the genus Tokus. The cask is much more elaborate in the rest of the hornbills. The shape is indeed like a blunt horn in many species. In others, it's more like a rigid dorsal fin, or the crest of an ancient Greek helmet or something. Structurally, the cask is an extension of the bird's

upper mandible. Like the rest of the beak, the cask has a core of bone wrapped in a sheath of keratin protein. But most of the cask is hollow, so it's not as heavy as it looks, and that bony core is mostly lightweight, spongy bone, or more technically, cancellous bone. Maybe you remember I talked a little about the cancellous bone in woodpecker skulls in the last episode. Besides saving weight, the hollow structure of the cask makes it a great resonator for sound. It amplifies sounds of certain frequencies. So the cask works sort of like an organ pipe, or the wooden body of a clarinet, or, I don't know, maybe like a kazoo? Everybody loves the kazoo, right?

Okay, maybe not a kazoo. In any case, the cask helps to change and amplify the calls. of the hornbill. It's an acoustic resonator. The cask may also work as a sexual ornament in the game of mate attraction. Males and females in some, but not all hornbill species, have differently shaped or colored casks. This dimorphism suggests there's been some sexual selection involved in the cask's evolution. And males of at least a couple hornbill species use the cask in an exciting way. They do battle by smashing their heads together, like big horn rams or muscocks. The crazy thing about hornbills is that their jousting competitions happen in the sky.

Two males fly at each other and bam! Their casks slam together with a loud crack. One male is sometimes thrown backwards by the impact, tumbling through the air until he can recover and fly straight again. This behavior, called aerial cask budding, might be a way for males to defend territories or to impress any lady hornbills who happen to be watching from the bleachers. But it seems ornithologists still don't know exactly why aerial cask budding is a thing in hornbills, or even why casks exist in the first place. As I mentioned, there are several hypotheses out there. Another unique feature of hornbills, related to their ginormous bills and casks, has to do with their neck bones. In other words, the cervical vertebrae. The two cervical vertebrae closest to the bird's

skull are fused together into a single structure. It's called a sin cervical, and hornbills are the only birds in the world that have this anatomical feature. The sin cervical probably gives the neck some extra strength for supporting that big old head. Hornbill eyes are large and expressive. They stick out a little from the sides of the head so that the bird can look forward. Hornbills, like you and me, have binocular vision. But these birds can also rotate each eye independently about 15 degrees. That supersized bill takes up some of the space in the hornbill's visual field.

But that's actually a good thing because a hornbill can see the tip of its own bill. These birds use the bill tip as a precision instrument when handling prey or fruit. Their bills are like forceps or tongs. Unlike most other types of birds, hornbills have eyelashes. We're talking large, sumptuous lashes that would make Lady Gaga proud. But we know birds don't have hair, right? Bird eyelashes evolved independently from mammal lashes. Hornbills have hair-like bristle feathers that shade and protect the eyes.

And speaking of feathers, how about the plumage and skin coloration of hornbills? As a group, these birds have plumages with some combination of black, white, gray, brown, or rusty red. The featherless skin on their faces, necks, and waddles is sometimes a bit more colorful. Like that bird you met in the West African jungle, which, had blue skin on its face. The bill and cask are often the most brightly colored part of a hornbill's get-up. These parts are yellow, orange, or red in many species. A hornbill can even use red or yellow secretions from its preen gland to enhance the color of its bill. This makes me think of how flamingos use a pink, oily secretion from their pream glands to jazz up their feathers. Flamingos and

hornbills basically manufacture their own makeup, their own cosmetics. Males and females in some hornbill species have almost identical plumage colors. In other species, however, there's sexual dichromatism, where males and females are differently colored. For example, in the Rufus-necked hornbill, a seris nipelensis, the male is the one with orange-y rust-colored feathers on the head, neck, and belly. The female, on the other hand, is pretty much black. Dichromatic or not, male and female hornbills of most species often forage together as a pair.

Hornbills will also fly around in small flocks. In the non-breeding season, large flocks in the hundreds or even thousands will sometimes gather. Hornbills appear to live mostly in the same area all year. In other words, they're not strongly migratory. but they might fly a fair distance to reach different habitats or different elevations during the breeding season. And they can range far and wide in their searches for fruiting trees. But there's still a lot we don't know. Ornithologists are still learning about the seasonal movements of these birds. Okay, now let's turn our attention to the sounds that hornbills make.

These aren't songbirds, so their vocal sounds are relatively simple and not very musical. Dr. Juan Carlos Gonzalez, who studied hornbill evolution for his Ph.D. at Oxford University, came up with categories for many hornbill calls. His names for hornbill sounds include trumpet bleat, staccato bark, clucking call, and shrill cackle. In his research, Dr. Gonzalez found that the various evolutionary lineages within the hornbill family tend to have distinct call types. For example, Hornbills in the genus Buceros give a resonant honk call. And those in the genus Bichanestes give a nasal wail. What did these actually sound like?

Given that the birds are called hornbills, maybe you would expect their vocalizations to sound like horns. Like, here's the sound I imagine one hornbill makes when it sees another hornbill fail at something, like it crash-landed in a tree or got an F on its math test. And what about when a hornbill sees another very attractive hornbill across the room? Maybe its eyes grow enormous and bulge out, its jaw drops to the floor, and it makes this sound. Hilarious stuff.

But hey, kids, if you don't recognize those silly sounds, I suggest you go back and watch a bunch of cartoons from like a hundred years ago. Then you'll get it. But let's get serious. Here's the actual low-pitched booming calls of some southern ground hornbills in South Africa. Next are some clucking calls made by a pair of yellow-billed hornbills, Tokus Lukomilis. They seem to be chatting with each other while resting in the shade. This is also in South Africa. This following sound should be familiar to most of us.

It's the distinctive call of the Red-Billed Bozo Hornbill. All right, I'm sorry. I'll stop. I just had to sneak that one in there. There's no such thing as the Red-Billed Bozo Hornbill. even though I kind of wish there was. This next and very real bird is Hemprix Hornbill, Lofaceros Hemprichii. Its range is in northeastern Africa, mostly in Ethiopia. That call from Hemprick's Hornbill is described as a piping whistle.

This next one, though, is categorized as a nasal whale. These are some trumpeter hornbills by Canistee's buxenator, flying over a forest in South Africa. The largest hornbill in the family Bucerotidae, you might remember, is the great hornbill. Here's one in Thailand, calling in the forest. Here's another recording of the Great Hornbill. There are at least two of them here, and this time we're in southern India. The islands of the Philippines are home to 10 hornbill species, including the Samar Hornbill, Penelipides Samarensis, which has this call.

Our last sound is from the knobbed hornbill, Riddaceros Cassidix. This species is found on the island of Sulawesi in Indonesia. In the following recording, you'll hear the bird calling as it flies. Listen carefully for the sound of its wing beats. Many large hornbills flap loudly like this. Sometimes it's even possible to identify the species

just by hearing the sound of its wings. Okay, here's the knobbed hornbills. hornbill coming in hot for a flyby. Moving right along, let's get into the diversity, distribution, and habitats of hornbills. The two avian families we're looking at today are Bucerotiddi and Bucorvody, right? The root word for both families is Buceros, spelled B-U-C-E-R-O-S. This comes from the ancient Greek for cow horn or oxhorn. It's a reference to the cask of the hornbill, which in some species does look a bit like a cow's horn.

When you look at the scientific names of hornbills, you'll see that many of them include a piece like Cerro, C-E-R-O, or Sarah C-E-R-A. That refers to a horn. For example, the genus of the black cast hornbill from the intro to this episode is Cerato Gymna. Or, you know, there's the familiar words rhinoceros and triceratops, or Sarah Jessica Parker or Sarah Palin. But enough about the etymology of these words, let's consider the diversity of hornbills. The family Bucorvody has just the two ground hornbill species, both of which are African. The family Bucerotiddi, however, has 59 species, and these are divided into 14 genera. The genus with the most diversity is Tokus, which contains 10 species in Africa.

Hornbill species are split pretty evenly between Africa and Asia, and there's no overlap between these two continents. There's no mingling between African and Asian hornbills. Looking at citizen science data on the website I Naturalist, it looks like the species most commonly observed in Africa is the southern yellow-billed hornbill. In Asia, the most commonly reported species is the Oriental Pied Hornbill, anthracoceros alberostris

Anthraicoseros See, there's that serro root word again Asian hornbills are distributed in southern and southeast Asia East to the Philippines and the Solomon Islands The further east you go, the fewer hornbill species there are Especially after crossing Wallace's line from west to east Remember Wallace's line? From the Science of Birds podcast episode 46

Well, east of that biogeographical boundary line in the Indonesian archipelago, there's just one hornbill species, Blythe's hornbill, also known as the Papuan hornbill. And how many hornbill species do you suppose have colonized Australia? The answer is, zilch, not one. I've mentioned the genus Tokus. The ten species in this genus have similar body shapes and sizes. They might be the most familiar sort of hornbill to anyone who grew up in the 80s, 90s, and early 2000s. Why? Because pop culture, of course.

In the Disney cartoon, The Lion King, there's a character named Zazu and he's a hornbill. Zazoo in the original 1994 cartoon is illustrated in such an exaggerated, stylized way. I have no idea what species they were trying to make him. It's kind of like how the roadrunner in the cartoons looks pretty much nothing like the actual bird. But the new version of Zazu, the one from the 2019 photorealistic Lion King remake, that version, according to some sources online, is supposed to be a quote-unquote African red-billed hornbill. Okay, cool, but which one? Because there are five different red-billed hornbill species in Africa.

To me, the new photorealistic zazu actually looks a lot more like an eastern yellow-billed hornbill. In any case, I'd say he's definitely supposed to be one of the species in the genus Tokus. I guess we'll leave it at that. Okay, so pulling back our focus to the family level. The family's bucerotidae and bucorvody are each other's closest relatives. But what other birds are closely related to the hornbill? The two bird families most closely related to our hornbills are those of the hoopoos and wood hoopoos. Have you heard of these guys?

There are two or three living hoopoe species, depending on which authority you ask. The Eurasian hoopoo is a fairly familiar species across Europe, Asia, and Africa. On its head, there's this awesome, buffy orange crest that looks like a mohawk. It has a long, thin bill and a bold plumage pattern. of black and white in the wings. The Eurasian hoopoe is a cool bird, and I hope to do an entire podcast episode on it at some point. The wood hoopoos are woodpecker-like birds that belong to their own family. You'll find them only in sub-Saharan Africa. Based on the evolutionary relationships among these birds, scientists have put them in the taxonomic order, Bucerotaformis.

This order contains all the hornbills, ground hornbills, hoopoos, and wood hoopoos. Those are the birds in the order Bucerotaformis. Right. So, we've talked a bit about the geographic distribution of hornbills, but it's time to take a moment to look at their habitats. As a group, these birds live in a wide range of habitats. Some species live in open country, like in savannas or open woodland. That's the case for many African species. The two ground hornbill species are great examples.

Other hornbill species prefer dense woodlands or forests. Almost all the Asian hornbills are creatures of the deep rainforest. They depend on forest habitats because of what they eat and how they make their nests. We will, of course, get to all that in a few moments. But first, let me tell you a little about the evolution of hornbills. A lot of what we know about hornbill evolution comes from comparative anatomy, fossil evidence, and evidence from DNA. Scientists have analyzed the genetic information in hornbill DNA to figure out how the species

are related to each other, as well as how hornbills are related to other birds, like what I was talking about earlier with the hoopoos and wood hoopoos. Hornbills first evolved in Africa, most likely in the oligocene epoch, around 30 to 35 million years ago. Scientists think these ancestral hornbills were all carnivores that ate insects and small vertebrates like lizards. None of them had yet adapted to eating fruit. The ground hornbill lineage, the family Bucorvidi, split off and became distinct about 20 to 25 million years ago. Around that same time, other hornbill lineages evolved to become fruit eaters. They became specialized frugivores.

Hornbills, especially the frugivores, diversified into a bunch of species starting around 25 million years ago. Probably not coincidentally, rainforests spread across East Africa and the Middle East during that period. Africa and Asia became connected by a narrow corridor of tropical forest habitats. Fruit-eating, forest-loving hornbills moved east through those forests, colonizing Asia from Africa. The dispersal of hornbills out of Africa was probably made even easier when the African continent slowly smashed into Eurasia starting around 20 million years ago. Before then, the two continents were separated by a marine barrier called the Tethys Sea. There's evidence that some hornbill species even lived in Europe and northern Africa.

Their fossils have been found in Morocco and Bulgaria. And speaking of fossils, it was only recently that the oldest known hornbill fossil was discovered. A scientific paper from 2021 describes a fossilized upper jaw from a hornbill found in Uganda. The researchers dated it to about 19 million years ago. The bone probably belonged to a hornbill in the genus Tokus. Eventually, the wet tropical forests that provided a link between Africa and Asia disappeared. That process started roughly 9 million years ago. The Arabian Peninsula and the rest of the Middle East dried up and vast deserts expanded across the region.

This left hornbills in Africa completely isolated from their cousins over in Asia. and it's been that way for millions of years. Let's say that tomorrow, you set off on a journey on foot from India to Africa. I'd say you're crazy, but hey, it's your life. Heading west, the last hornbill species you'd see in Asia is the Indian gray hornbill. You'd keep walking across the desert for about 1,800 miles or 3,000 kilometers, across the entire Middle East. good luck surviving the elements in those arid landscapes.

If the scarcity of water doesn't kill you, the complete lack of hornbills might. Approaching Africa, the first of these birds you could possibly stumble across would be the African gray hornbill, somewhere at the western edge of the Arabian Peninsula. You might think the bird is a mirage at first, or that you're hallucinating. But then, when you realize it's a real, live African gray hornbill, you know that you've survived the perilous desert and found salvation at long last. Nearly half of the world's hornbill species are in some kind of trouble in terms of their population status. The biggest threats they face are hunting and habitat loss from deforestation.

These birds, especially those in Asia, need ancient forests with massive trees, because they make their nests in those trees. Three species are in the critically endangered category on the IUCN's Red List, the Rithe-billed Hornbill, Sulu Hornbill, and Helmitted Hornbill. Until recently, the Sulu Hornbill and Thracoseros Montenai lived on a few small islands to the northeast of Borneo. Now the species is likely found in just one patch of forest on just one of those islands. There are estimated to be fewer than 50 Sulu hornbills left.

People have decimated the forest ecosystems that are home to these birds, and people like to shoot Sulu hornbills for food and target practice. This critically endangered species is at risk of going extinct very soon. The helmeted hornbill, Buceros Vigil, could easily be worthy of an entire podcast episode. For now, I'll just tell you a little about this species, which is also critically endangered. The helmeted hornbill lives on the islands of Borneo and Sumatra,

and from southern Thailand down to the tip of the Melee Peninsula. Here are the calls of some helmeted hornbills on the island of Borneo. And you know what the birds in the family Bucerotiddy, the helmeted hornbill, I'd say, comes closest to being the odd bird. ball. We haven't had a weirdo alert for a while, so here we go. Why not? Weirdo alert. Weirdo alert. The helmeted hornbill is, in my opinion, the weirdest bird in a family full of weird birds. This species is so peculiar that some ornithologists still classify it as being all by itself in its

own genus, rhinoplacks. One reason the helmeted hornbill is weird is that it's really the only hornbill species whose beak doesn't curve downward. Not much, anyway. I already mentioned that this species has the longest tail of any hornbill. On the bird's neck, the thick, featherless ghouler pouch looks like a well-worn and well-oiled red leather satchel. And more importantly, its flat-fronted red-orange cask is not hollow. Every other hornbill species has a cask that's at least partially hollow. The back end of the helmeted hornbill's cask is made of spongy bone, but the front section is dense keratin.

The whole thing is solid. And that means the cask is heavy. It amounts to about 10% of the bird's total weight. This unique anatomy may have something to do with all that aerial, head bonging we talked about earlier. The solid, uniquely shaped cask of the helmeted hornbill is its biggest claim to fame. And sadly, it's also one of the main reasons this species is critically endangered. You see, for thousands of years, people have used the solid keratin cask of this bird for making

elaborate carvings. Hornbill ivory, as it's called, is like elephant ivory, but softer. Some people call it golden jade or red jade because of its texture and its yellow-orange color. The demand for hornbill ivory from our friend Buceros Vigil began to skyrocket a couple decades ago. It's an illegal product, several times more valuable than elephant ivory on the black market in China. In recent years, poachers have slaughtered many thousands of these birds for their casks. On top of that, there's the problem of habitat loss. These birds need big, old trees to make their nests in.

That means they require healthy old-growth rainforests. But deforestation has made such ecosystems rare across the helmeted hornbill's range. Without urgent and aggressive conservation efforts, the helmeted hornbill, this weird and wonderful bird, is going to suffer from catastrophic population losses in the next few decades. It's time to look at what and how hornbills eat. In general, these are omnivorous birds. They eat both animals and plants. Some lean more heavily towards a carnivorous diet.

That's true for species that live in open habitats, like the African savannas. Large, fleshy fruits are rare in those environments. Ground hornbills, for example, eat all sorts of small critters. beetles, grasshoppers, rodents, lizards, and snakes. They'll even subdue venomous snakes. Hornbills that haunt dense forests, however, have a diet that's much more focused on fruit and seeds. The diets of large Asian hornbills, for example, include only about 5 to 10% small animals. The rest is fruit. Hornbills eat the fruits of many types of plants, but figs are among their favorite.

In general, these birds prefer large fruits that are easily accessible in the forest canopy. So many hornbill species are frugivores. Like wax wings, another group of frugivorous birds I covered in a recent episode, these hornbills have evolved the ability to get almost all the nutrition they need from fruit alone. But they need to eat a lot of it. By some estimates, a fruit-eating hornbill needs to hork down between 20 and 33% of their body weight in fruit every day. That is a lot. I mean, if I had to eat that much of my favorite food, I'd be gorging on about 50 pounds of bean burritos from Taco Bell every day.

I mean, give me two or three days I could do it, but one day? Fruitivorous hornbills rarely ever drink water. Not surprising, perhaps, given that there's plenty of water in all that fruit. The long curving beak of a hornbill with its foreseps-like tip is great for plucking fruit and for snatching up small animals. For example, the oriental pied hornbill supplements its fruit-centric diet with creepy crawlies like insects, centipedes, scorpions, spiders, and worms. It'll gobble up small vertebrates too, like lizards, small birds, rats, and even the occasional fish, crab, or garden gnome. There's this video clip from the BBC showing Oriental Pied Hornbills snatching bats right out of the air while sitting on a tree branch. That's right, bats. Hornbill is just chilling, then suddenly it lunges out with that enormous beak and bam!

Bat snatch! It's crazy. I'll put a link to the video in the show notes. Whether a hornbill is eating a bat, a fig, or a burrito from Taco Bell, it can't actually swallow something its whole. holding in the pincher-like tip of its bill. The bird's tongue is too short to reach all the way to the bill tip. So the hornbill has to toss the food item into its gullet with a little jerk of its head. It basically throws food into the back of its own throat. A lot of these details about what and how hornbills eat is very similar to what toucans do. Two cans are found only in the New World tropics, on the other side of the planet from where hornbills live.

These two groups of birds are not closely related. Tucans are much more closely related to woodpeckers than they are to hornbills. The similarities in appearance and behaviors between hornbills and toucans result from them having similar adaptations to the lifestyle of a fruit-eating, but also omnivorous rainforest bird. The oversized colorful beaks of toucans, like those of hornbills, have large hollow spaces inside. These birds fill similar ecological niches in their respective habitats,

the niche of a large fruit-eating forest bird. So their superficial similarities are most likely the result of convergent evolution. Perhaps the most important job of these birds, their role in the ecosystem, is to disperse the seeds of tropical trees far and wide. Hornbills swallow fruits, digest the flesh in their guts, and then spit out the unharmed, still-viable seeds. Well, that's true for large seeds anyway. Large seeds are regurgitated.

Smaller seeds, like those of fig trees, end up in the hornbills' poop. The birds often pluck fruits from the canopy of one tree, then fly miles away before dropping the processed seed to the forest floor. If conditions are right, that seed will germinate and grow into a large forest tree. That tree makes fruit for the birds, and the circle of life goes on. So these rainforest trees get a tremendous advantage in their seed dispersal from hornbills, long-distance seed dispersal. That's why those fruits exist.

They evolved to attract animals like monkeys and birds. And in turn, the animals unwittingly provide the service of spreading the seeds across the landscape. So you can understand why hornbills are sometimes. sometimes called the farmers of the forest. There's evidence that when some hornbill lineages first became frugivores about 25 million years ago, the food plants that attracted these birds went through their own geographic expansion and a diversification of species. It's possible that hornbills helped these plants spread into new regions, helped them to overcome barriers like the saltwater channels between islands. The birds could carry the seeds from one island to another.

These days, some of the most important tropical trees that depend on hornbills are those in the mahogany and nutmeg families. What strikes fear into the heart of a hornbill? What predators do they need to worry about? For the larger hornbill species, they probably have to keep an eye out for big raptors like eagles and owls. and pesky humans, of course. Always humans. Other predators, particularly those that threaten hornbill nests, include snakes, cats, members of the weasel family, monkeys, and mongooses. But not all mongese, not all mongooses, are bad news for hornbills. In parts of Africa, there is a special relationship between the dwarf mongoose and hornbills. Two species,

Vonder Deccans Hornbill and the Eastern Yellow-Billed Hornbill, cooperate with dwarf mongooses for safety and for food. Dwarf monguuses are cute little carnivores. They're highly social and they hunt small animals together in dry grasslands and open forests. Hornbills follow the mongoose pack and snatch up any insects, lizards, or whatever that escape the mongooses. The hornbills warn the mongooses if raptors or other dangers are approaching. Likewise, the mongooses will warn the hornbills if they sense trouble first. These critters are so dependent on each other that they wait for each other before going out to hunt.

Dwarf mongooses sleep at night in abandoned termite mounds. If there aren't any hornbills around in the morning, the mongooses will wait until the birds arrive before starting their day. But if the hornbills show up in the morning and the mongooses are still passed out, sleeping in their little holes, the birds will make a racket to wake up their mammalian hunting partners. So much for sleeping in. It's like having young kids or a dog, isn't it? They come bouncing onto your bed early in the morning, whether you like it or not. The relationship between dwarf mongooses and hornbills is an adorable example of what

ecologists call mutualism. You've heard of parasitism, right? A parasite benefits while it causes harm to another species. Well, in mutualism, in a mutualistic relationship between two species, both species benefit. Dwarf mongooses get a free wake-up call in the morning, and they have the birds there as sentinels to warn them of danger. The hornbills also benefit from the vigilance of the mongooses, and, more importantly, from the prey the mongooses stir up as they hunt. It's a win-win situation. Hornbills are monogamous birds that form strong pair bonds.

One male pairs up with one female. In some species, a few of last years young will stick around to help their parents raise the next generation. The two ground hornbill species are full-on cooperative breeders, with a dominant pair being assisted by several helpers. All hornbills nest in natural cavities, but they don't carve out their own cavities. These are holes and trees that either form naturally or were hollowed out by woodpeckers or barbets. A cavity often forms where a large branch broke off of a tree. Then along comes some wood-eating fungi and other microbes to infect the wound.

The wood rots away and the hole gets deeper. Birds like woodpeckers may then come along and excavate the cavity even further. Cavities that work well for hornbill nests are a rare, limited resource. They're much more common in old growth forests with large trees. And here's where we get to one of the coolest, craziest things about hornbills. And I'm guessing you've heard of this before. When it's time to lay her eggs, the female hornbill seals herself into her nest cavity and she won't leave for weeks or months. The female hornbill enters the nest, then begins to seal the entry hole using mud. The male flies off and collects more mud.

He swallows it, forms it into pellets, and then regurgitates it back at his nest. The opening to the nest gets smaller and smaller. Eventually, the female uses sticky bits of uneaten fruit to plaster around the entrance. She might even use some of her own feces. In the end, there's just a small opening into the nest, a slit. It's just big enough for the male to pass food to his mate. This self-incarceration most likely evolved as an effective one. way to keep safe, a behavioral adaptation. Sealed up in the nest, the female and her chicks are

relatively safe from hungry predators like monkeys and arboreal cats. This is pretty much the same strategy I use for keeping myself safe at home. I stay holed up in my office for weeks at a time, writing scripts for podcast episodes. My wife occasionally cracks open the door and slides in a plate of waffles or french fries. Sounds extreme, I know, but so far it's worked. I haven't had any trouble with monkeys or arboreal cats. Anyway, the female hornbill is totally dependent on her mate while she's in the nest. She'll stay in there until her chicks are old enough to brave the world outside. Meanwhile, dad is going back and forth to the nest ten times a day or more. It's like he just gets home from a run to the grocery store and

his mate is like, thanks, honey, but you know, now I'm really craving some potato chips. Would you mind going back and getting me a bag? She bats her eyes with those big hornbill lashes and says pitty-pwees. The male sighs and says, okay, sure, anything else besides the chips? Nothing? Are you sure? He grumbles to himself as he flies off to the store for the eighth time that day. Over the course of a single breeding season, a male hornbill will bring thousands of fruits and other food items to the nest. Hornbills lay between one and eight eggs per season. The larger the species, the fewer eggs per clutch, in general. Once her first eggs are laid, the female drops all of her flight feathers.

She goes through a rapid molt. And that's pretty unusual for birds. The helpless chicks stay in the nest between one and four months. It's the larger hornbill species that stay in the nest longer. While mom and her babies are sealed up in the nest, food is coming in thanks to dad. But after the fruit or whatever is eaten and digested, then what? Does the nest slowly fill up with disgusting bird poop? In general, no. It's not as bad as you might expect, because the female and her chicks push their little bird butts up to the narrow

opening and eject their droppings out the window, so to speak. How the hornbills leave the nest varies from species to species. For example, mom and her fledglings bust out of their jail cell all at once in some species. In other species, the female breaks out well before her chicks. The young then seal themselves back in, and both parents share the duty of flying back and forth to the grocery store. Eventually, the young birds will all emerge to face the uncertainties of the outside world. They probably have many adventures in their futures, because hornbills, are long-lived birds. The larger species tend to live the longest.

For example, southern ground hornbills in captivity can live for at least 70 years. The similarly large, great hornbill, can live about 50 years in captivity. Smaller species like the southern yellow-billed hornbill live more like 20 years in the care of humans. And of course, the lifespans of all these birds are probably a lot shorter out in the wild. In any case, the impressive cask of a hornbill takes years to grow to its full size, up to five years for the great hornbill, for example. We still have a lot more to learn about hornbills. I doubt this is the last time you and I will talk about these big-headed, seed-dispersing,

bat-snatching, self-incarcerating birds. But for now, I'll wrap things up by blowing the hornbill horn one more time. I don't get many opportunities to use this thing, and believe me, it was not cheap. Thank you for spending time with me today to learn about hornbills. I really hope you enjoyed the episode. Maybe you can remember a few of the fun facts to share with your friends. You can spread the love of birds and make yourself look sweet. smart at the same time. And speaking of super smart, I want to thank the highly intelligent

humans who support my work via Patreon. My patrons pitch in every month to keep the Science of Birds free for the masses. This podcast reaches people of all ages around the world. My supporters help to make that possible. My newest patrons are Rita Minkie, Sedge Hen, Wanda Rice, and Emily Rice. Welcome, you guys, and thank you so, so much for the support. support. If you'd like to become a patron, just check out my Patreon page over at patreon.com slash science of birds. And if you have something you'd like to share with me, please go ahead and shoot me an email. Maybe you have a comment about the podcast or a question. Or you could tell me which animal species you'd like to have a mutualistic relationship with. Anyway, my email

address is Ivan at scienceofbirds.com. You can check out the show notes for this episode, which is number 68 on the Science of Birds website, Science of Birds.com. As always, I'm your humble host, Ivan Philipson. Have an excellent rest of your day. Cheers.