The Science of Birds - Nests: Types, Construction, and Challenges

Episode Date: April 6, 2022

This episode—which is Number 49—is all about bird nests. There are tons of fun facts fun facts here, since nests are one of the more impressive aspects of bird behavior and breeding biology.We’ll go over the functions of nests, the challenges that nesting birds face, nest site selection, the many types of nests, and nest construction.That’s a lot to cover, but I’ll try to keep this at more of an overview level. This is sort of Bird Nests 101.~~ Leave me a review using Podchaser ~~Links of InterestWhy a Hawk Is a Hummingbird’s Best FriendTime Lapse Video of Blue Tit Building a NestBBC Video of Baya Weaver Nest ConstructionLink to this episode on the Science of Birds websiteSupport the show

When I was in my early 20s, I had an influential experience with bird nests. I was an undergraduate studying zoology at Cal Polypamona in Southern California. At the edge of campus, there was a little remnant patch of scrub habitat, the sort of habitat that, for thousands of years, blanketed the coastal lowlands of Southern California, before the landscape was transformed into the nightmare of urban sprawl that it is today. This patch had some western sycamore and native walnut trees overshadowing shrubs like Toyon, Blue Elder, and Black Sage, and some coastal prickly pear cactus in there, too. I was becoming more and more intrigued by birds back then, so I volunteered for a research project that my ornithology professor was running.

The bird of interest was the cactus wren, Campilorincus Brunea Capillus. It's a large, noisy wren with a spotted breast, a streaky back, and lots of personality. The goal of my professor's project was to gather data on cactus wren nests, to find any general patterns in nest site selection, nest orientation, stuff like that. Honestly, this was a long time ago, and I don't remember all the details. But I do remember loving the experience of going, out into that scrub habitat in the early morning, breathing the cool air, redolent with the spicy sweet scent of sage, and hearing the cactus wrens and other birds singing. I had my data sheet

on a clipboard, and I'd go check on the cactus wrens and their nests to record data. These wrens use dried grasses and sticks to build an enclosed spherical nest with a side entrance hole. And just where do they like to place these nests? You guessed it, in cactus. Cactus wrens prefer to tuck their nests in among the wicked spines of dense cactus. At the habitat at my college, the only cactus option was coastal prickly pear. You can imagine that this is a pretty safe place to raise your chicks, because not too many predators can get past that spiny defensive perimeter.

So that Cactus Wren project, all those years ago, got me to pay more attention, not only to birds, but to their nests. Since then, I've seen all sorts of nest types made by a wide variety of species. I'm sure you've seen some interesting nests, too. If you're like me, you find it exciting to come across a nest, whether on purpose or by accident. There's some of the most amazing structures in all of the now. natural world. Hello and welcome. This is the Science of Birds.

I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners. This episode, which is number 49, is all about bird nests. At the time I'm recording this, it's early spring in the Northern Hemisphere, so it's a great time to be learning about nests. There are tons of fun facts here,

since nests are one of the more impressive aspects of bird behavior and of their breeding biology. We'll go over the functions of nests, the challenges that nesting birds face, nest site selection, the many types of nests, and nest construction. that's a lot to cover. I do it to myself, you guys. I can't seem to help it. But I'll try to keep this

at more of an overview level. This is sort of Bird Nests 101. I'm sure I'll cover other aspects of nests in future episodes in more detail. All right, get comfortable, pour yourself a cup of coffee or tea, maybe a glass of wine, or if you're too young for such beverages, maybe have some Kool-Aid or pop a straw into a pouch of Capri Sun or something. I don't know. What do kids drink these days? Mountain Dew? It matters not. Because now we're going to take a look into the wonderful world of nests. We should probably start by defining what a nest actually is. Simply put, A nest is any structure or place where a bird drops its hot little eggs and where the young are raised. The nest, then, is primarily for breeding, for reproduction.

More rarely, some bird species will build nests as shelters for roosting overnight or during rough weather, even in the non-breeding season. But again, that's relatively rare. So the nests' function is to provide a safe space, for eggs and baby birds. Ideally, it also protects the parent birds while they incubate the eggs and when they're coming and going to bring food and whatnot. Many nests also create a sort of microclimate.

Compared to the outside world, temperature and humidity within the nest are often much closer to ideal for the developing eggs and chicks. Nests of many types of birds are used to shelter relatively helpless chicks. You know, the wiggly, sort of ugly ones that are blind and featherless when they hatch? The term for these little buggers is altricial. Chicks like this need to stay in the nest until they fledge, that is, until their feathers have grown enough that they can actually fly. All songbirds, for example, have altricial young, and so they use their nests until the young

fledge. Then there are other types of birds that have precocial chicks. Remember that precocial chicks are born with their eyes wide open and they're covered in fuzzy down feathers. And nine out of ten doctors agree. Precocial chicks are just way cuter than altricial chicks. Precocial chicks are ready to rip within hours after hatching. Sure, the parent bird or birds are there to protect them, but precocial chicks can often start feeding themselves early on. Just picture newborn chickens or ducklings, and there you go. Unlike those helpless altricial chicks, precocial chicks often leave the nest soon after hatching. They don't need to stay in that one place. They just start running around and getting themselves into trouble. There are many challenges and dangers

faced by nesting adults, their eggs, and their nestlings. Through millions of years of natural selection, birds have refined the designs of their nests to deal with these challenges. First off, there's the challenge of the elements. Elements like the baking sun, the bitter wind, the rain, and, if we're to believe the conspiracy theorists, the mind control waves radiating out of 5G cell phone towers.

J.K., please don't believe the conspiracy theorists, please. Nests are constructed to keep eggs and young birds suitably cool in hot climates and warm in cold climates. Where pounding rain is frequent, like in the tropics, birds make nests under the shelter of overhanging plants or rocks, or they build their nests with little watertight roofs. Small birds lose body heat faster than large birds. So that might be the reason that many small songbirds tend to make enclosed rather than open-topped nests.

A nest with four walls, so to speak, is better for keeping the heat in when it's chilly outside. Another challenge comes in the form of parasites and disease. There can be a taming community of insects and other invertebrates living in a bird nest. Some of them are harmless and even beneficial to the birds. but many are parasites that can hurt the nestlings or parent birds. For example, there's an entire genus of flies, protocallifora, that are obligate parasites of bird nestlings. These insects are called bird blowflies, and their larvae suck the blood of baby birds. There are also bloodthirsty mites that infest nests, and a motley crew of fleas, ticks, bugs, and lice that can all cause trouble.

On top of all that, an occupied nest gets dirty after a while and becomes an inviting home for nasties like bacteria and fungi. There are several ways that nest owners can combat the threat of parasites and disease-causing microorganisms. For starters, they can keep the place tidy. Those altricial nestlings are eating and eating, which means they're also pooping and pooping, and pooping some more. But for many songbird species, you won't find much, if any, feces in their nests. Why is that?

Because the nestlings make what are called fecal sacks. When one of the little guys needs to empty its bowels, it makes a small satchel of poop sheathed in a thin membrane. It works sort of like a baby diaper, or like a tiny water balloon that you would not want to get hit with. A parent bird will grab the fecal sack and carry it away from the nest. Or, and yes, this is super gross, some adult birds will eat the faecal sacks. Down the hatch, no must, no fuss. Ew! This keeps the nest sanitary so that it doesn't stink and get all yicky. It minimizes the

growth of bacteria and harmful fungi. And a nest that doesn't stink is a nest that doesn't attract predators, right? Some bird species bring nice-smelling aromatic plant material to line their nest, green herbs like yarrow and lavender, or things like cedar bark. These exude what we might call essential oils that repel parasites, pathogens, and quite possibly evil spirits. And some research has actually shown that nests decorated with these aromatic plants do have fewer periscites. parasites. There are even house finches in Mexico City that gather cigarette butts off the street to line their nests, for real, and I've talked about this before. The cigarette filters are soft and fluffy, which makes a good lining. But the filters also reek of nicotine, which happens to

work as an insecticide. Researchers found that the more cigarette butts there are in a finch nest, the fewer parasites that nest has. Now I know what you're thinking. You're thinking, great, now I don't have to feel bad about tossing my cigarette butts on the street. The finches will snatch them up and put them to good use. There are two problems with that line of thinking. One, smoking is bad for you. Stop it. And two, we shouldn't count on animals cleaning up our messes.

That's not fair to them, and let's face it, they're probably not going to do a very good job. One more way that birds can reduce the problems of creepy-crawly infestations in their nests is to make sure they build a new nest every breeding season. Because no matter how many fecal sacks you eat, no matter how many cigarettes or sprigs of nice-smelling herbs you pile in your nest, the place is going to get dirty over time. By the time the nestlings are about to fledge, the nest might be almost as disgusting as the college dorm room of an average human male. So just build a new nest from scratch next time. Sure, it's a lot of extra work, but it will be all fresh and clean, and it'll have that new nest

smell. Besides invertebrate parasites, many birds have to worry about being infiltrated by brood parasites. Remember that brood parasites are bird species that don't make their own nests. They sneakily drop their eggs into other bird's nests and let them do the hard work of raising the chicks. I won't say more about that right now since I did an entire podcast episode about brood parasitism, episode 12. So check that out if you haven't already. So we have the challenges of the elements and of parasites. But the Numero uno challenge for most nesting birds is the threat of predators. Animals like snakes, monkeys, apossums, raccoons, and squirrels are all looking for some delicious and nutritious eggs or baby birds

to eat. But avian predators are often the worst offenders. Crows, jays, and other crafty corvids are particularly notorious for raiding the nests of other birds. Given that predators are the worst threat, birds have evolved many anti-preditor strategies for keeping their nests safe. Perhaps the most common strategy is to keep the nest hidden, build it in a secluded place, and use camouflage to make the nest blend in. Many birds decorate the outside of their nest with moss, lichen, and leaves, probably as camo. Another strategy is to build multiple nests. For example, some male wrens of the family troglodytidae build dozens of nests within their territory. There are competing hypotheses about why they might do this, but one idea is that it's to trick predators.

Most of the nests are just decoys. Maybe it's like a house of mirrors at the carnival. The wren is like, you think you're so smart, Mr. Snake? Then tell me, which nest is the real nest and which of them are merely illusions. The snake doesn't know which nest actually contains a tasty treat inside, so it gets all flustered and slithers off in shame and disgust. At least that's how I think it works. Birds foil the plans of predators in other clever ways, by building enclosed nests with secret entrances, for example, or entryways that a predator can't squeeze through. Many bird species simply build their nests in inaccessible places, on vertical cliffs

or hanging over water, or surrounded by water like a tiny island, or maybe dangling way out at the tips of flimsy branches. And there's the highly effective trick of tucking your nest in among the wicked spines of a cactus, like our buddy, Kampilorincus Brunea Kapilis, the cactus wren. One of the coolest things that birds have figured out is to intentionally build their nest right next to either the nest of a more aggressive bird species or a colony of stinging insects. For example, black-chinned hummingbirds in Arizona

build their nests near those of Cooper's hawks and northern gosshawks. Even though these raptors are voracious eaters of small birds, they don't eat the tiny hummingbirds. Not worth the effort, I guess. So the hawks aren't a threat to the hummers, but they are a threat to Mexican Jays, and it's marauding bands of Mexican Jays that eat the eggs and nestlings of black-chinned hummingbirds.

But the Jays steer clear of the hawks. It seems every hawk nest provides a cone of safety around it, a J-free zone where hummingbirds can nest in relative peace. So these hummingbirds are following the wisdom of the old proverb, The enemy of my enemy is my friend. Other bird species, mainly in the tropics, will build their nests in a tree right next to an active ant, wasp, or bee colony.

The birds get protection from the stinging insects, which keep away not only many predators, but also some invertebrate parasites like flies. That's pretty cool, isn't it? So when a hungry monkey comes lurking around, looking for eggs, it's going to wish it was never born when it gets a face full of bees. With all those predators to worry about, not to mention harsh weather and parasites,

a bird's choice of where to make its nest is crucial. Once the nest site is chosen, it can be a long-term commitment. For some species, that might mean only a few weeks. But for others, it might be for most of a life. lifetime, years or perhaps decades. Birds make their nests in pretty much every terrestrial habitat on the planet. Forests and grasslands are crammed with nests. There are gazillions of them on sea cliffs. They're littered across mountain tops, swamps, and deserts. You may not always see the nests around you, and that's usually by design on the birds' part, but they're all

over the place. There are many factors a bird has to consider as it chooses a nest site. How exposed is the site? Exposed to predators, to the sun, the wind, and the rain. How about temperature and humidity? Are other birds nesting nearby? If so, are they friends or foes? Is there plenty of food around for both the chicks and the parents? And how about nesting material? That's a lot to consider, isn't it? Some birds solve this problem by simply reusing their old nest from last year, especially if it worked out okay last time. Or they might take up residence in an abandoned nest built by another bird,

of the same species or another species. But most birds need to find a new nest location every breeding season. In general, birds seem to be born with a lot of instinctual knowledge of where they should build their nests. In fact, biologists used to think that nest site selection and nest construction were entirely instinctual behaviors, that birds performed these tasks on autopilot, programmed by their genes. But more recent research has shown that previous experience, learning, and improvisation also play big roles here. As an example of nest site selection, let's look at the horned lark.

Aramophila alpestris. This is a widespread songbird that lives in barren habitats across the northern hemisphere. The female horned lark chooses the nest site, which is always on the ground. She inspects small clumps of grass until she finds just the right one. The female lark places her nest snugly against the clump of vegetation in such a way that the eggs and chicks will be in the shade during the hottest part of the day. The grass may all also block chilly evening winds. So the horned lark tends to choose a nest site with a specific orientation relative to the sun and wind. Sometimes it's not a clump of grass that provides shelter.

Sometimes it's a dried pile of cow poop. Whatever works, right? And get this. Horned larks often place their nests in little depressions so that the eggs rest slightly below ground level. Sometimes that depression is actually a cow or horse's hoof print, formed in dry mud. When the lark eggs and chicks are tucked in a shallow hole like this, not only are they even more protected from the elements, they're less likely to be crushed by other large mammals tramping around.

The horned lark is a bit picky about where to place its nest. Plenty of other species are similarly picky. For example, the superb parrot of Australia, Polytilis Swainsoniye, makes its nest in natural pre-existing tree cavities. One study found that these parrots choose cavities with particular dimensions. The cavity depth, the entrance size, and the floor space inside all have to be just right. But other bird species aren't so picky. Take, for example, the morning dove in North America.

These birds will make their flimsy platform nests seemingly anywhere. On the ground, way up in a tree, any kind of tree, in a shrub, or on man-made structures and objects. Objects like light fixtures, a shelf in your shed, or that beat-up car in your yard that you keep thinking you're going to fix up someday and drive off into the sunset, to escape all of your troubles and maybe get rich playing the slots in Vegas. I hate to say this, but you got to let that dream die. You're never going to fix that rusty piece of junk. Besides, it belongs to the morning doves now. Like so many other species, horned larks, superb parrots, and morning doves are solitary nesters. But other species prefer to build their nests in a colony. Colonial species cram their nests together side by side where the nesting habitat is good. Examples can be found across a wide variety of birds. Herons, storks, parrots, doves, swallows, weavers, bee-eaters, many sea birds, and so on. For both solitary and colonial nesting birds, there can be some serious competition for good real estate.

The pickier a species is, the fewer the sites out there that will fit the bill, right? so it's more likely to face competition from other members of its species. It's sort of like when I insist on finding the absolute best parking spot when I go out for a nice dinner at Taco Bell. I'm going to have to deal with competition from those other cars circling the parking lot like sharks. Cavity nesting birds can be especially competitive. I'm talking about those birds that use existing cavities

because they can't carve out their own. So not woodpeckers so much, but birds like chickadees, tits, nut hatches, house wrens, starlings, and so on. In some environments, pre-existing cavities can be a very limited resource. Birds sometimes have to fight each other with beaks and claws to get and then keep these nest sites. Now we come to what some might say is the fun. part. We're going to look at all the wild and wonderful types of bird nests. I think this is one of the most amazing things about nests, the diversity of their architecture and of the materials used to build them. There's no one nest shape that works for all species or in all environments.

Of course, I'm using words to describe shapes to you, so I'll do my best. I'll also put some photos of nests in the show notes for this episode on the Science of Birds website. Ornithologists have categorized nests in different ways, but today I'm going to describe the following nest types. Scrape, mound, burrow, cavity, platform, cup, globe, trapezoidal prism, and four-dimensional hypercube, otherwise known as a tesseract. If you were paying close attention to, of that list, you might think a couple of those were bogus. But I can assure you that mounds and scrapes are indeed real nest types. Seriously. Not only is there this diversity in nest shapes or types, there's also an enormous range in their sizes. The world's smallest nest, according to the

Guinness Book of World Records, is made by the Vervein Hummingbird, Melasuga Minima, which lives on the islands of Jamaica and Hispaniola. It's the second smallest bird species in the world, and its nest is only a couple centimeters across. The largest bird nest is generally attributed to the good old bald eagle. This species' nest is often several meters in diameter. So that's a couple orders of magnitude larger than a hummingbird nest. Pretty wild.

All right, let's actually get into each of these nests. nest types. First off, there's the nest of no nest. It's like the old Zen koan. What is the sound of one hand clapping? What is the nest of no nest? Some birds just don't have a use for a nest. In king and emperor penguins, for example, the male incubates the single egg that rests on his feet and it's covered by warm folds of the male's skin. Some ox, birds in the family Al-Sadi, like Razor bills and meurs don't make a nest. They just place their eggs on a little rocky ledge and call it good. Other bird species will find some sort of shelter to place their eggs in, like a crevice, but within that space they don't add any nesting material or make any modifications.

And of course, brood parasites, like many cuckoos, don't make their own nests. Again, check out episode 12 of the podcast to hear more about those guys. The first type of actual nest, though, is the scrape. A scrape is super simple. It's just a shallow depression on the ground that provides the bare minimum of structure for keeping the eggs in one place. Many birds make scrape nests, from some ducks and shorebirds to turns, falcons, quail, night jars, new world vultures, and busters.

A scrape nest on the ground rarely conceals the eggs or the young very well. The brooding parents have to defend their nests from predators. So the parents often have camouflaged plumage, so that they're hard to spot when sitting still on the nest. Next up we have the mound nest. This is a pile of soil, mud, rocks, vegetation, or some combination of these. The most famous mound builders are birds in the family Megapodeodeodee, the Megapodes. These guys live in Australia and parts of the Indonesian archipelago.

They deserve their own podcast episode, and I'll do that someday, because the breeding biology of Megapodes is fascinating. Briefly, though, a male megapode, like an Australian brush turkey or an orange-footed scrub fowl, makes an immense pile of soil and decaying plant matter. Multiple females deposit their eggs in this moldy mound and then split, never to be seen again. The male sticks around, however, and carefully attends his mound, moving the litter around with his big feet. He works to maintain a constant incubating temperature for the eggs in the mound, because those decaying plants are actually giving off heat. Crazy stuff, and yeah, I'll go into more detail in a future

episode. There are other forms of mound nests. Flamingos make a tall pile of mud with a shallow depression on top to hold the eggs. And in high altitude lakes of the Andes, the horned coot Fulika Cornuda builds an amazing mound out of rocks. The nest is built in the lake, about a hundred 30 feet or 40 meters from the shore. The coots use surprisingly large rocks to create their own little island. Other mound builders include the sociable weaver, some grebe species, and the unique hammer cop of sub-Saharan Africa. The next nest type is the burrow.

This is generally a hole that the adult birds dig themselves in soft soil, mud, or sand. Burrow nesters include puffins, many kingfishers, sheer waters, some swallows, bee eaters, mott-mots, leaf tossers, puffbirds, and so on. Some species dig relatively short tunnels for their subterranean nests. Others excavate long passageways illuminated by tiny torches along the walls. For example, the burrowing parakeet, Cyanolicea Patagonus of Argentina, digs burrows up to several meters deep in sandstone or limestone cliffs. Their tunnels can also be complex, forming a little labyrinth of multiple passageways that lead

ultimately to the nest chamber. Then we have cavities. These are holes in trees, large cactuses, or even inside termite or ant nests. Some cavity nesters like woodpeckers and, to some extent trogons have adaptations that allow them to excavate their own cavities. Many other types of birds, however, are what we call cavity adopters, or secondary cavity nesters. They can't make their own cavities. Examples of the latter include some species of tits, nut hatches, wrens, bluebirds, hornbills, owls, flycatchers, and ducks. To protect their eggs and nestlings, some cavity nesters use defenses like smearing tree sap

around the entrance hole to thwart snakes. Hornbills go a step further. A female hornbill seals herself inside the nest cavity by reducing the entrance hole's width. She does this by applying a sort of plaster made of mud, food scraps, and feces. The remaining hole is just big enough for the male, who remains free on the outside, to pass food through to the female and her chicks. In some large hornbill species, the mother and her babies will be sealed up like this and utterly dependent on dad for several months. Okay, so far we've covered scrapes, mounds, burrows, and cavities. Next up, we have platforms. A platform nest is a pile of stuff, usually sticks that has a depression on top to hold the eggs, chicks, and brooding parents.

Some are relatively delicate and small, like the nest of the morning dove and other members of the family, Columbia. But some other birds build platform nests that are enormous. The bald eagle is the best example. Biggest nest in the world, yada, yada. Eagles, hawks, osprey, and other raptors make platform nests. So do, cormorants, herons, and storks. Some ornithologists might classify these nests as mounds. It seems the difference between what's a mound and what's a platform is a bit of a gray area. I imagine there are scientific conferences where heated, borderline violent debates

rage between ornithologists in these two camps. The most contentious question continues to be whether the horned coot with its pile of rocks in the lake builds a mound nest or a platform nest. Now we come to the cup nest. This is the iconic nest shape that we've all had burned into our brains since we were three years old. It looks like a little cup or bowl.

It's made of interlocking twigs or maybe woven grass, and it's lined with soft things like feathers and moss. This is the nest of familiar birds like the American robin and the European robin, as well as thousands upon thousands of other songbird species. Hummingbirds and swifts too make cup nests. To qualify as a cup nest, the structure should be at least half as deep as it is wide. But just when you and I thought we had cup nests all figured out, ornithologists went ahead and categorized them further into several

sub-types. You've got your statent cup nests, suspended cup nests, and adherent cup nests. Statened cup nests are the ones supported from the bottom by something sturdy like a tree branch or the ground. Suspended nests, on the other hand, hang from their rims or sides. Some suspended nests have relatively stiff walls, while others are more flexible and tube-shaped. The latter are are called pendulous nests. A pendulous nest is sort of like an old gym sock dangling from a telephone wire. Some birds in the Oriole and Blackbird family, Icturadi, are famous for having pendulous nests. The Montezuma or a pendula, for example, makes a nest that's over 40 inches long. Adherent cup nests are attached to a cliff face or some other hard vertical surface

with a glue-like substance. That substance might be mud, in the case of swallows, or it might be sticky saliva. Yes, saliva. What some refer to as spit, drool, or slobber. Amazingly, Swifts, birds in the family apodidae, have saliva that acts like glue. One species even makes its entire nest out of nothing

but its own hardened saliva. It's totally ridiculous. We'll talk more about that at some point in another podcast episode. All right, so for cup nests, the subtypes are statent, suspended, and adherent. Got it? Good. Moving on. Another major type of nest is spherical, otherwise known as globular. Just as it sounds, these nests are ball-shaped. They're completely enclosed with a little entrance hole.

Those cactus wren nests I was looking at back in the day were globular. Many other wren species make this type of nest. So does the Verdon, a small songbird of the American Southwest. Pittas in the family Pitidae make globular nests, as do some ground nesting New World Warblers, and a bunch of birds in the very large family, Fernaridi. The list goes on. So those are all the major nest types.

scrapes, mounds, burrows, cavities, platforms, cups, and globes. But what about the trapezoidal prism and the four-dimensional hypercube? Well, sadly, no bird that I know of has yet evolved the ability to construct nests that conform to such wacky and improbable shapes. Maybe someday! Let's move on to talk a little about how nests are built. Since nest structures among species vary from absurdly simple to highly complex, there's a wide range of construction methods.

As I mentioned earlier, birds are born with the know-how for nest making, at least the basics. But through their lives, they refine their knowledge and improve their skills with experience. Also, as I mentioned earlier, some bird species tend to build a new nest every year, or maybe a new nest for every brood. Other species prefer to return to the same nest site again and again. They just repair and refurbish the old nest. In extreme cases, generations of birds have returned to the same nest sites for hundreds or thousands of years. Geer falcons, for example, nest on the same cliff ledges over and over. Researchers took samples of guano from active geir falcon nests in Greenland.

Radiocarbon dating of the samples showed that some of the oldest layers of guano were laid down about 2,500 years ago. That means hundreds of generations of jeer falcons have used the same nest site. That is just amazing. But we're talking about nest construction. In most bird species, the female is the one who chooses the nest site and does the heavy lifting of building the structure. This is especially true in sexually dimorphic species where the male has colorful plumage, but the female is more drab, more camouflaged. If a brightly colored male helps to build his nest, he might unintentionally catch the attention of predators. No Bueno.

But in plenty of other species, like Corvids and gulls, the male shares in the work. More rarely, it's the male alone who makes the nest. It all depends on the type of bird and the species. For example, let me just push the random bird species button. We got the bar-winged weaver, Ploseus Angolanus. which lives in the woodlands of South Central Africa. In the bar-winged weaver, the female and male both help to build their nest. The basic blueprint for most cup and globular nests is that there's an outer layer and an inner layer.

These differ in hardness or rigidity. The outer layer is the most rigid. It's made of sticks, bark, thick grass, or hardened mud. Birds will sometimes upcycle human garbage, too, like candy wrappers, ribbon, rubber, metal, and in at least one case, a Barbie doll. Seriously, I'm not joking. A weaver in South Africa carried a Barbie doll to its nest and wove the doll's hair into the outer layer of grass. The naked plastic body of the doll was just hanging there.

It's hilarious. Birds of many families use spider silk as a construction material. Spider silk is incredibly strong while also being lightweight. Hummingbirds, kinglets, and some New World Warblers are examples of birds that weave spider silk into their nests. This makes the nest both strong and flexible. Using spider silk is just brilliant. It's sort of like natural duct tape. So these nests are crunchy on the outside and soft in the inside, right?

So how about the inner layer? Like a baby blanket in a crib, the inner layer of the nest needs to insulate and protect the young. It's made of flexible, soft stuff. A wide variety of materials are used. Things like mammal hair, seed fluff, moss, lichen, bark strips, soft grass, and feathers. Feathers seem like an obvious choice. Some brooding females, especially ducks and geese, will pluck their own down feathers to line the nest. Other birds collect feathers they find lying around and bring them to the nest.

For example, the long-tailed tit of Eurasia, Egythelos Codatus, can pack thousands of small feathers into its nest. birds shape the insides of their nest using their beaks, legs, and body. They rotate around inside, pressing their legs and breast into the material to tamp it down. The bird may also do little belly quivers, acting like a tiny compactor tool. These days, many people use nest cams in their backyard bird boxes. If you're listening to this during the breeding season, see if you can find some live-streaming nest cam videos on YouTube or wherever. I'll put a link to a time-lapse video of a blue tit in the show notes.

It's a real joy to watch birds like this as they build their nests and raise their young. As an ape with hands and opposable thumbs, I find it amazing that birds can make complex structures using only their beaks and feet. Among the most amazing of all nest builders are the weavers. I've mentioned them a few times today already. Weavers are all the birds in the family Ploseidae. There are about 117 species sprinkled across Africa and Southern Asia. Many weaver species use a variety of complex knots to weave green grass and other plant fibers together

to make a pendulous or globular nest. When the green plants dry out, the outer layer of the nest becomes relatively rigid and strong. The Baya weaver, Ploceus, Philippinus, is a great example. This is a colonial species found from the Indian subcontinent to Southeast Asia. Male Baya weavers are the ones that make the nests. A male starts his nest on a narrow branch or palm frond. He gathers thin strips of the wooders.

of grass, palm leaves, or rice leaves, and ties these to the branch using half-hitch knots. Then he works his way downward. Some of his building material might be plunder that he stole from the nests of other males. The structure he's working toward is a suspended pendulous cup nest. After making a central suspension cable, the male weaver makes a ring of fibers at the lower end. At this point, the whole thing looks sort of like a helmet. some mud or cow dung might be added as mortar for extra rigidity. Before the male bio-weaver finishes his nest, he needs to know if a female is even going to be

interested in using it. Otherwise, what's the point? This isn't a bachelor pad after all. The male clings to the side of his half-completed masterpiece and puts on a show to any female passing by. He makes chattering calls and flutters his wings. sort of like a begging chick. He's like, Hey, over here, hi, hi, how are you today? Can I interest you in this exemplary display of nest craftsmanship? Or crafts bird ship, I guess?

Anyway, I made this all by myself. I am very good at weaving. But you don't have to take my word for it. Have a peek inside. Give it a test drive. Wait, wait, where are you going? No, come back. Was it something I said?

If our lonely, desperate male doesn't pair up with a female soon, his green nest will dry out and turn brown. At that point, he might as well give up and start all over again. On the other hand, if a female approves of his nest and his weaving skills, well then, lucky day! The two will become a mated pair. Let the nest construction resume! Ultimately, the male builds a bulbous nest chamber and adds a long tube that hangs down from the side entrance. This is called a retort. A retort-shaped entrance hole like this is thought to deter predators.

All in all, it might take a male Baya weaver three weeks and 500 trips to collect plant material to complete his nest. It's not unusual among birds, in general, to take several weeks like this to build a nest. Smaller birds living in temperate climates tend to build more hastily, sometimes finishing up in a week. You know, because winter is coming. Birds in tropical regions aren't usually in such a hurry. They take a little longer to build their nests on average. Birds aren't the only animals that make nests. Nests of one kind or another are made by mammals, reptiles, amphibians, fish, and insects.

But bird nests are among the most complex of all. Could it be that some of the success of birds, of the class avies, can be attributed to their nest-building awesomeness? Birds in the order Paseroformis, the songbirds, show the greatest variety of nest architectures. And we find the most elaborate nests in this group. Maybe that's not surprising when you realize Paseraformis is the most recently evolved group of birds.

Nest diversity and complexity in this group are evolutionary innovations. Maybe nests have helped songbirds to become so wildly diverse and successful across the planet. Who knows? The connection between nest diversity and species diversity also shows up at the family level, especially in the mega-diverse family, Fernariadi. These are the oven birds and wood creepers of the New World tropics.

This enormous family has over 300 species. These guys are insanely diverse in their body and bill shapes and in their lifestyles. If you've ever gone birding in Latin America, you have ever gone birding in Latin America, you have definitely seen a bunch of species in this family. Birds like wood haunters, ground creepers, foliage gleaners, orneros, and scythe builds. One of the few common features I see among all these birds is that most of them are some shade of reddish brown. Fernarids also have the most diversity of any bird family when it comes to nests. Some are famous for making sophisticated globular structures out of mud.

Others make cup nests, platforms, or spherical nests out of sticks or other plant material. And many place their nests in burrows or cavities. I think it's really interesting how species diversity seems to go hand in hand with nest-type diversity. This is cool stuff.

And the family fernariadi itself is super cool. I'll definitely do a podcast episode on it at some point. I'll leave you with one more thing to think about. For as much as we know about bird nests, there's still a lot that we don't know. Of the approximately 11,000 bird species in the world, the nests of over 2,000 of them have either never been discovered, or at best we know only a little about them. And it's not like ornithologists haven't been out there for hundreds of years,

figuratively and literally beating the bushes looking for all those nests. Those nests mostly belong to solitary species that live in remote or difficult to access habitats. Difficult for us, anyway. The fact that we have yet to find these nests is a testament to the skill with which the parent birds choose their nest sites, and the skill with which they hide their nests from view. Maybe we'll find them eventually. But, Maybe not. And, you know, I'm okay with that. I find pleasure in the idea that there will always be mysteries out there in the natural world. There will always be new things to discover and no end to our explorations. I hope you enjoyed this brief overview of bird nests. One could spend an

entire lifetime studying nests. This is such a broad topic. Hopefully you picked up some new knowledge today that you can share with your buddies. And maybe you're fired up to go on an expedition to find some of those undiscovered mystery nests. Who knows? Maybe some of my young listeners will grow up to be ornithologists and make those discoveries. That's a fun thought. In any case, thanks for hanging out with me today to learn about birds. I want to welcome the newest patrons of the Science of Birds podcast. Michael Nolan, Kelly Joy, Gennedy, and Artie Stiddlefish. Thank you so much for becoming patrons to support the show.

Now, if you're listening right now and you're thinking, what's this guy talking about? What the heck are patrons? Well, friend, let me direct you to the World Wide Web, where you can get answers to such questions. You can have a gander at my Patreon, page by typing Patreon.com

forward slash science of birds into your favorite web browser. That's patreon.com forward slash science of birds. I do my best to be accessible to you by email, so you can shoot me a message if you have something to share. A comment about the show, a bird-related

zen co-on, whatever it is, send it to Ivan at scienceofbirds.com. You can check out the show notes for this episode, which is number 49, on the Science of Birds website, scienceofbirds.com. I'm Ivan Philipson, your humble and grateful host. See you next time. Peace.