The Science of Birds - Earthbound: How Birds Become Flightless

Episode Date: August 3, 2023

This is Episode 80. It's all about flightless birds, and about the evolutionary processes that lead to flightlessness.Flightlessness in birds is, in my opinion, a fascinating scientific topic. And so here we are with this episode.Alive on the planet today, there are about 60 bird species that can’t fly. That’s only about 0.54 percent of the world’s approximately 11,000 species.It turns out there were way more flightless bird species out there before humans started exploring and colonizing every corner of the Earth. It wasn’t just the Dodo that was killed off by people.In today’s episode, we’ll look at the wonderful diversity of flightless bird species—in both the present and the past. We’ll also talk about conservation and—perhaps the most interesting thing—the evolutionary process that leads to flightlessness. How does this weird thing happen in nature? What causes a bird species to give up its greatest superpower?  ~~ Leave me a review using Podchaser ~~Link to this episode on the Science of Birds website Support the show

On April 28, 1789, a group of crew members on the Royal Navy ship HMS Bounty forcefully took control of the vessel in perhaps the world's most famous example of a mutiny. The mutineers put Captain Bly and those loyal to him in a small boat and set them adrift in the South Pacific Ocean. The bounty and her reduced crew then sailed around for while, and after some misadventures, they eventually arrived at Pitcairn Island, about 1,200 miles or 2,000 kilometers east of Tahiti. Pitcairn Island was the kind of isolated refuge the mutineers had been looking for. It had enough resources like food and water, and its climate was mild. Those aboard the bounty decided to make the island their permanent home, to destroy the most glaring

evidence of their crimes, they stripped the ship and burned it. In doing so, the mutineers gave up their only means of ever getting off the island. To burn your boats is another way of saying to burn your bridges. If you burn your boats, you cut off all chances of escape. You're staking everything on being successful where you are. And this brings us to birds. Some birds that long ago made their way to an island or a similarly isolated place ended up, in a manner of speaking, burning their boats. Because those birds had to fly to reach their new homes, but then their ancestors eventually lost the ability to fly. Through the process of evolution, they became flightless birds. Evolution has cut off all chances of escape for them. Now, think of your own

greatest talent, your biggest advantage in the game of life. For you, it might be artistic talent or computer coding skills or perhaps bravery in tough situations. My greatest talent in life, in case you were wondering, is being able to guess the time within plus or minus 15 minutes, even when I haven't looked at my phone or my watch for like a couple hours. But now that I think about it, I usually can't go more than three minutes without looking at my phone. So imagine having to give up your greatest strength, your superpower. Well, that's what flightless birds have done. The ability to fly is, some would say, the biggest advantage that birds have.

It's one of the main things that defines them. But flightless birds have forsaken the skies. They've turned their backs on their airborne heritage. Amazingly, the evolution of flightlessness in birds wasn't just a one-off fluke that happened in a single lineage. No, birds have burned their boats again and again, independently and across many branches of the avian tree of life. Hello and welcome. This is the science of birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted exploration of bird biology for lifelong learners.

This episode, which is number 80, 80, is all about flightless birds and about the evolutionary processes that lead to flightlessness. A flightless bird is a strange, sort of ironic thing, isn't it? It's like a living, breathing oxymoron. Flightlessness in birds is, in my opinion, a fascinating scientific topic. And so here we are with this episode. Alive on the planet today, there are about 60 bird species that can't fly. That's only about 0.54% of the world's approximately 11,000 species. But some flightless birds get an inordinate amount of attention from us humans.

I mean, what pops into your mind when I say flightless bird? A penguin, perhaps, an ostrich? How about a kiwi? Birds like these are some of the superstars of the avian world. Or maybe you thought of the dodo. That ill-fated bird represents one of the many flightless species that went extinct only recently. and by recently, I mean sometime in the last 500 years, as opposed to 50,000 years or something like that. It turns out there were way more flightless bird species out there before humans

started exploring and colonizing every corner of the earth. It wasn't just the dodo that was killed off by people. In today's episode, we'll look at the wonderful diversity of flightless bird species in both the present and the past. We'll also talk about conservation and perhaps the most interesting thing, the evolutionary process that leads to flightlessness. How does this weird thing happen in nature? What causes a bird species to give up its greatest superpower? First, let's get to know the flightless birds that we're lucky enough to still have around. These are the extant species. I'm not sure I've explained that word here before, extant, E-X-T-A-N-T.

It's basically the opposite of extinct. Extent means still in existence, not lost, not extinct. Being extinct really sucks. You don't want to be extinct. But being extant is terrific. Take it for me. I'm extant, and I have to say that the experience is, on average, pretty groovy so far. As I mentioned, there are about 60 extant flightless bird species. By my reckoning, these belong to 12 avian families, and those families belong to nine avian orders. First up, we have the penguins. These charming birds. belong to the family Sphanicity, which I covered in episode 36 of this podcast.

The 18 penguin species alive today are all descendants of a single common ancestor, and that ancestor, that proto-penguine, was flightless. These birds have been flightless for a long, long time. We're talking over 60 million years. The next major group of flightless birds is the ancient lineage known as paleognathy. I've mentioned it at least a couple times before on the podcast. I did an entire episode on ostriches, and ostriches are in this group. They're paleognaths. Other extant birds belonging to this branch of the avian tree include cassowaries, emus, reas, kiwies, and

tinamus. Have you ever heard of tinamus? Tinamu is spelled T-I-N-A-M-O-U. These are sort of of grouse-like birds found in Mexico, Central America, and South America. There are 46 tinamu species, and they're the only living paleognaths that can fly. So a moment ago, I should have said that paleognathy is a group of mostly flightless birds. The evolution of paleognaths is a complicated and fascinating story. We don't have time to do it justice today. For now, I'll just tell you that flightlessness evolved independently more than once in this group, possibly more than five times. All right, so far we've got penguins and paleognaths.

Then we have the rails. The family Raleady includes all the rails, galanules, coots, more hens, swamp hens, crakes, and those sorts of birds. Of the approximately 135 species in his family, about 30,000, are flightless. Now, if you do a quick mental calculation, you'll realize that means about half of all the flightless bird species alive today are rails. And get this, all these flightless rails are not the descendants of a single ancestor that was itself flightless. Pretty much every flightless rail species today is the outcome of a unique, independent evolutionary event,

an independent loss of flight. Rails are apparently predisposed to this sort of thing. Time and time again, these little buggers have ended up on some remote island, and before you know it, a new flightless rail species evolves on that island. It's crazy. We'll talk about why rails are really good at becoming flightless in a few minutes. Some notable flightless rail species are the South Island Takahe and the Weka, both in New Zealand,

the Tasmanian native hen, the Lord Howe Rail, the Guam Rail, and the Inaccessible Island Rail. The latter species is actually the smallest flightless bird in the world. The inaccessible island rail is only about six inches long from beak to tail, which is 15.25 centimeters. Another group of birds with some tendency towards flightlessness is the family anatidae. Remember which birds are in that family? We talked all about them in episode 18 of this podcast. That's right, the ducks, geese, and swans. Two species of flightless duck live in the far south of New Zealand, in the sub-Antarctic islands.

Each species is named for the cluster of islands it's found on. We have the Auckland Islands Teal and the Campbell Islands Teal. On the other side of the world, but also in the far south, we have the steamer ducks of South America. There are four closely related steamer duck species, all belonging to the genus Tachieres. Three of the four species are flightless. Grebes! Grebes are waterbirds in the family Podisipedity. There are two living species.

of flightless grebe. Both of them swim around in high-elevation lakes in the Andes in South America, but they live in separate lakes. There's the Hunine grebe and the Titicaca grebe. I was lucky to get to hang out with some wild Tidicaca grebes a few years ago in Peru. I remember it was October 31st, so yeah, Halloween. I was lazily paddling a kayak around in the shallows of Lake Tidikaka. There were these lovely little grebes paddling around with me, moving in and out of the bulrushes. The grebes had gray backs, white throats, and chestnut brown caps. Their eyes had bright yellow rings around them, and their bills were similarly yellow.

They were super cute and really interesting to watch. But I guess the grebes didn't know it was Halloween because they weren't wearing costumes. How fantastic would it have been if they were dressed as tiny ghosts? Like if they had little white sheets draped over them with holes cut out for their eyes. Oh man, I would have given them all the Halloween candy. I'd pay good money to see that. Anyway, I'm embarrassed to say that at the time I didn't know much about these birds. I knew they were Tidicaca grebes, yes, but I didn't know that this is an endangered species,

and I didn't know that they can't fly. Next on our list, we have a flightless cormorant. It's the flightless cormorant, actually, with a capital F and a capital C, because that's the official name of the species, flightless cormorant. This bird lives on two of the Galapagos Islands in Ecuador. The flightless Cormorant is the only living member of its family that can't fly. In fact, it's the only flightless bird out of about 60 species in the avian order, Sulaformis.

Another bird, with the distinction of being the only species in its order to forsake the skies is the Cacopoe. I'm sure you've heard of the Cacopo. It's a weird and wonderful flightless parrot found in New Zealand. a flightless parrot. The cockapoe is a mossy green color, it's nocturnal, and it eats all kinds of plant material. It's a fascinating little beast, and it's critically endangered. I'll definitely do an entire podcast episode on the cockapo at some point. Now we come to the order Pacerraformis, the order of the perching birds. Recall that this group includes more than half of all

the world's bird species, including all the songbirds. That means there are well over 5,000 passerine bird species. Given that large number, it seems like there has to be a bunch of flightless passerine bird species hopping and skittering around out there. Right? Wrong. The number of extant flightless birds in this group is a big fat zero. There are some extinct flightless passerine birds, however, and we'll get to them in a moment. I should point out, though, that there are some extant passerine bird species that might be flightless. I say might because ornithologists have yet to see these birds either get off the ground at all or to flit through the air for more than a few meters. These possibly flightless birds include the three mesite species of Madagascar and some

Tapaculos. Tapaculos are birds in the family rhino-cryptody, found in South and Central America. The ones that might be flightless are members of the genus Cytalipus. These tapaculos are small forest birds that scurry around acting like mice. They have short, rounded wings. And, interestingly, their clavicle bones are not fused. That's important because one of the key anatomies anatomical adaptations that makes flight possible in birds is the furcula bone, which is formed from the two fused clavicles. And this brings us to a philosophical question about topaculo's. You've probably heard the question, if a tree falls in a forest and no one is around to hear it, does it make a sound? Well, if a tapakulo flies in the forest and no one is

around to see it? Does it actually fly? I mean, who can say, right? These are the kinds of questions I ponder while taking long walks on the beach by myself or while looking up at the stars on a moonless night. Some would say mesites and tapakullos are semi-flightless. A fun, sciencey way of saying semi-flightless is semi-volent. Volent means being able to fly. Other semi-flightless birds include the Lysan duck, Zapata Rail, Okinawa Rail, the Kagu of New Caledonia, the New Zealand Wrens, and the Australian scrubbirds. Scrub birds look and act a lot like topakullos, and they too are missing a true furcula bone. We can't say for sure, but maybe each of these semi-flightless, semi-voluntless, semi-volent.

birds is on its own evolutionary path towards full-blown flightlessness. In any case, they rarely fly, and if they do, they do so only very weakly. None of them is ever going to soar through the clouds on an epic intercontinental flight. Heck, most of them can barely stay airborne for more than a few wing beats. So it seems some bird lineages are in the process of becoming flightless as we speak. That's pretty cool. But flightlessness as a thing that birds sometimes do has a long history. So let's go back in time now to look at some.

examples of flightless birds that have gone extinct. Way, way back when birds had barely distinguished themselves from other dinosaurs by gaining the ability to fly, some of them were already like, eh, I'm done. Flying is overrated. It's too hard, with all the flapping and whatnot. I'm just going to take it easy and let gravity do its thing. I'll hang out here on the ground, or, ooh, maybe I'll float around in the water. or something. Whatever. The first birds evolved about 165 million years ago. That was during the Jurassic period. Archaeopteryx was flapping around about 150 million years ago. In the late Cretaceous period, between 166 million years ago, there was a group of flightless birds in a lineage

called Hesperornathies. These critters were aquatic fish eaters. They probably looked something like a cross between a loon, a cormorant, and a grebe. But, you know, with dozens of pointy teeth in their mouths. They were fully committed to being flightless. Their wings, their forelimbs, were almost completely gone. They kicked their powerful legs to zoom around underwater. You can see these birds beautifully brought to life in the animated documentary series Dinosaur Planet, produced by the BBC and narrowly.

narrated by David Attenborough. Check out episode four of season two. They just call the bird Hesperornus in the show, since that's the genus of the most well-known member of the Hesperonathies. Unfortunately, Hesperornus and all of its flightless Hesperornithian buddies went extinct when the asteroid slammed into Earth 66 million years ago. After the massive extinction event that followed, birds were the only dinosaurs left on the planet. Some birds evolved to fill niches left empty by much larger predatory dinosaurs. The most famous of these were the terror birds. They were huge flightless birds with massive hooked beaks. They lived in South America, mostly, where they ran around terrorizing and eating smaller critters like mammals. The name Terrorbird

is, in my opinion, a most excellent name. I applaud whoever came up with that one. There was another independent lineage of enormous flightless birds with an equally awesome name, the demon ducks. At least one species in this family grew to about 10 feet tall and might have weighed nearly 1,300 pounds, which is about 580 kilograms. Various demon duck species lived in Australia from about 25 million years ago to less than a million years ago. And yes, their closest living relatives include ducks and geese. Unlike the carnivorous terror birds, the demon ducks probably ate only plants. By the early Holocene epic, which started about 12,000 years ago,

there were about 40 bird families in 23 orders that included at least one flightless bird species. This was just after the last glacial period of the ice ages. As things warmed up, Homo sapiens got back to the business of spreading around the world and stirring up all sorts of trouble for birds and other animals. Paleognaths of the early Holocene included the now extinct moas and elephant birds of New Zealand and Madagascar, respectively. These had become the world's largest birds. The other major branch of the avian tree of life is neognathy.

You've got paleognathy on one side and neognathy on the other. Among the neignaths of the early Holocene, there were many more species of flightless rails, ducks, and geese than there are in the present. For example, there were the four Moa Nalo species in Hawaii. Moa Nalo were very large ducks that filled the role of domino. prominent herbivore on several of the islands. But in the Holocene, there were also a bunch of wacky flightless birds in a diverse array of other families, families that don't have any flightless members today. There were several flightless owls, a handful of flightless

pigeons, a couple flightless ibises, a flightless hoopoe, a flightless kara, a crane that might have been flightless, and several flightless songbirds. in the order Peseraformis. The latter included a flightless bunting on the canary islands and four species in the New Zealand Wren family, Acanthicidity. The Dodo was one of the flightless members of the Pigeon family, Columbadi. It lived on the island of Mauritius in the Indian ocean. The Dodo's closest relative was the Rodriguez Solitaire, which lived on another island in the same region. Alcadi, the family that today includes puffins, murs, and gillamots, once included a single flightless species, the great ock. This bird was penguin-like, but was in no way

closely related to penguins. It was the giant of its family, and it lived in the chilly waters of the North Atlantic. As the Holocene epic marched on, there were more humans in more places, wielding increasingly more advanced technology. Sadly, this led to the downfall of many of those fantastic flightless birds. Now, you have no doubt noticed that the common theme for almost all these flightless species is that they live on, or lived on, islands. The rate of extinction among these birds sped up in the last few thousand years, as humans landed their boats on pretty much every island in the world, no matter how remote. It's sure been a rip-roaring good time going through this survey of extant and extinct flightless

birds with you. But now it's time to pull up our sleeves and get down to business. It's time to talk about how flightlessness evolves. As I said earlier, flightlessness didn't just happen once in the history of birds as some kind of freak occurrence. Amazingly, this has happened hundreds or maybe even thousands of times over the eons. Biologists have been studying the evolution of flightlessness for decades. They still have lots of unanswered questions, sure, but they've also made some fascinating discoveries. One of the most important discoveries, I think, is that the evolution of flightlessness in birds is, to some extent, predictable. Under certain conditions and with certain types of birds, flightlessness just

happens. Not inevitably, no, and nature is messy, of course, so there are lots of exceptions. But still, this evolutionary path appears to be more predictable than most. Let's talk about the ingredients needed to make a flightless bird. First, we have several conditions. Condition number one, isolation. Birds are more likely to become flightless when they end up in a place where they're isolated from their relatives. An isolated bird population is free to evolve independently. It has its own destiny.

Evolutionary forces like natural selection and mutation are more likely to cause dramatic, lasting changes in an isolated population. And what was the common theme here today? That's right. Islands, like Pitcairn Island, isolated as it is way down there in the South Pacific. The words isolated and island are actually related. There was a Latin word insulated, which meant made into an island. Insulatus morphed into isolato in Italian and isolet in French. Eventually, the French word got absorbed into English as isolated. Something or someone that's isolated has been made into an island. The condition of

isolation might not be absolutely required for the evolution of flightlessness. but it sure seems to help. And birds don't have to live on a remote island in the ocean to be isolated. Certain habitats on continents can be similarly isolated. For example, remember those spooky little Halloween ghosts, the Tidicaca grebes? The high elevation lakes that those grebes call home are isolated. In some ways, such lakes can function like islands. Condition number two.

A Lack of Predators This condition is related to the condition of isolation. Isolation and a lack of predators are often linked. Because isolated places like oceanic islands and high elevation lakes are often free of predators. Imagine a volcanic island, like in Hawaii or the Galapagos. A new island like this forms from lava erupting on the seafloor. The lava solidifies and eventually piles high enough to rise above sea level. It's just bare rock, no predators so far.

Flying birds are really good at colonizing even the most remote islands, even if it's often by accident. So some birds get lost and end up on our newly formed island. If there's enough food for them, the birds might survive and establish a population. land-dwelling mammals, on the other hand, including the predatory kind with their pointy teeth, aren't likely to make it to the island any time soon, or ever, really. With no predators around, the birds are free to relax and let their guard down. They can go about their business without needing to look over their shoulders constantly

in fear of being jumped by a feline, a canine, or some other bloodthirsty meat eater. Flight has many advantages for a bird. One of the big ones is the ability to escape into the sky when a predator attacks. But if there are no predators, maybe flight isn't such an advantage anymore. So isolation is often a prerequisite for a lack of predators. And my understanding is that a lack of predators is the single most important condition that leads to flightlessness. But how about we toss in one more condition, just for fun. Condition number three, a mild, relatively stable climate.

Another useful thing about the ability to fly long distances is that when the weather gets lousy, during the winter, let's say, you can just fly to somewhere that's warmer and generally more pleasant. Islands in the tropical latitudes are just that, warm and generally pleasant. A migratory bird that gets blown off course and finds itself marooned on a tropical island, well, maybe it can just stay there without needing to make those arduous migratory journeys anymore. Maybe that's why flightless birds appear to have evolved more often on tropical and subtropical islands. Now, I mentioned that certain types of birds are more likely to become flightless.

Let's look at a couple features that make a bird species a strong candidate for becoming permanently grounded. Feature number one. The ability to find food without flying. Some kinds of birds forage primarily by walking around on the ground. And some other birds specialize in finding food while swimming and diving. Sure, these birds can and do fly for several reasons. But, but when it comes to filling their little bellies with food, running and swimming birds can do just fine without having to take to the air. But there's a caveat. These candidates, these flying birds that might someday evolve into flightless birds, they have to fly strongly enough and far enough to actually end up on an isolated island. They have to end up somewhere that is

delightfully free of predators. Okay, so feature number one is the ability to find food without the need to fly. Feature number two, synchronous molting of the flight feathers. Molding is the process of shedding old feathers and growing new ones. Birds molt one or more times per year, depending on the species. Many types of birds replace their feathers gradually so that they never lose the ability to fly. But some other types of birds shed all of their remigies at once. The remedies, spelled R-E-M-I-G-E-S, are the flight feathers on the wings, the primaries, secondaries, and all that jazz. Birds with a rapid, synchronous molt of their flight feathers include loons, grebes, ducks, geese, and most rails. So birds like these go through a period of

flightlessness every year. Why would this feature of temporary annual flightlessness predispose a bird to evolve into a forever flightless species? Well, the idea is that if you're a duck or rail or whatever that can survive weeks or months at a time without being able to fly, you're ahead of the game. If you happen to find yourself stranded on a remote island, you already know how to get along just fine without functional wings. Let's talk about rails. I said we'd come back to look at why species in the family Raleady are predisposed to becoming flightless.

First off, rails have both of the features we just talked about. They forage while walking or running around, and when they molt, they drop all of their remedies at once. They don't need to fly to go about their daily business. The wings of rails are relatively short and rounded. These birds aren't super strong flyers. But that said, many of them migrate long distances, and they can flap those little wings for days. Rails have a tendency to get blown off course because of this combination of migratory behavior and weak flight. They often end up as vagrants on far-flung islands. So, amazingly, rails have managed to

colonized just about every island on the planet. Time and time again, a rail species that colonized an isolated predator-free island has evolved into a new flightless species. By some estimates, there were over 1,000 flightless rail species strewn across the islands of the Pacific Ocean alone. This phenomenon in rails is a beautiful example of what biologists call parallel evolution. This is where two or more closely related species end up evolving similar traits independently. That's the key word independently. Rails all belong to the same family, so we can think of them as being fairly closely related. Any two rail species are way more closely related to each other than a rail is to an eagle, for example. When rails of

different species or different populations end up independently losing the ability to fly under similar conditions, that's parallel evolution. Convergent evolution, which I've talked about many times here on the podcast, is similar to parallel evolution. But with convergent evolution, the birds or other critters that end up with similar traits are not closely related. Okay, let's take a step back now. Let's ask an important question, one that you might already be wondering about. Why don't birds living in these isolated predator-free places just keep their ability to fly? Wouldn't it be better to at least have the option of flying? Just in case, even if it's not super useful on a daily basis? It's like me keeping those dumbbells collecting dust in the corner. I'm probably not going to ever work out again.

But it can't hurt to keep those weights, right? I might use them. There's at least a small chance I'll get motivated someday to do a few curls or whatever. Well, here's the thing about evolution. It's often a game of energy conservation. Birds and other organisms have only so much energy to use on a given day. Calories are a limited resource. A bird has to allocate the energy it gives.

from food to its survival, growth, and reproduction. It's all about trade-offs. Calories a bird burns up while escaping from a predator, for example, are no longer available for making eggs, and vice versa. Flying takes an enormous amount of energy, compared to pretty much every other way of getting around. You better have a really good reason to fly and to burn up all those calories. escaping from predators qualifies as a really good reason.

But what if there aren't any predators around? Just maintaining the machinery needed for flight burns up a ton of calories. In volent species, the flight muscles, keel, and wing bones can add up to 35% or more of a bird's total mass. It takes a lot of energy just to supply those body parts with nutrients, to remove wastes, etc. One of the rules in evolution is

use it or lose it. If an anatomical or behavioral trait isn't all that useful anymore, it's more economical to get rid of it in terms of energy use. A bird can spend the energy it saves by becoming flightless on more useful things. Things like making baby birds.

I mean, which of the following birds do you think natural selection would favor? Bird A, who has tiny vestigial wings, but has energy to spare as a result, and can produce a boatload of adorable offspring, or Bird B, who can produce only a couple offspring because it needs to maintain large, functional wings that offer no real survival advantage.

That's right, Bird A wins the game of natural selection. I hope we've answered the question of why don't birds just keep their ability to fly? A bird living in a predator-free paradise that keeps its ability to fly is less like me keeping some dumbbells in my house and more like me paying every month for a gym membership that I don't use. It's a total waste of resources. If I cancel my gym membership, I could spend that money on something truly useful. like lottery tickets or stacks and stacks of books about birds.

Some types of flightless birds have saved energy in other ways. They grew to be much larger than their ancestors. Elephant birds, demon ducks, moas, the dodo. Big birds like these tend to have lower metabolic rates than small birds, and therefore they need proportionately less food to survive. Another thing about the Moas of New Zealand, they went to the extreme with reducing their wing muscles and bones. The entire pectoral girdle in moas shrank down to a pair of tiny vestigial bones called scapulocoroids. Each of these bones was about the size of a human finger.

That's it. That was all that was left of their wings. Scientists studying the genomes of birds like the flight. Cormorant and the steamer ducks of South America have been able to identify genes that may be involved in the reduction of wing muscles and bones. That's really cool. Having this kind of genetic information will hopefully go a long way towards unraveling the evolution of flightlessness. All right, so we've got what appears to be a recipe for flightlessness. For the ingredients, you'll need one rail or another type of bird that's predisposed to flightlessness and an isolated place

like an island. Make sure there are no predators on your island and that its climate is generally stable. Mix the ingredients together, then set a timer for about 20,000 years, maybe a bit more or less. The time needed is quite variable, so you'll need to experiment a bit. In any case, the end result should be a nice flightless bird species, just like grandma used to make. Yes, I'm exaggerating here, but the evolution of flightlessness can be so by the numbers sometimes, so predictable, that the same flightless bird has evolved more than once in the same location. Well, sort of. You see, a few years ago, there was this scientific study of the white-throated rail that made the headlines.

headlines like How Evolution brought a flightless bird back from extinction And bird that went extinct comes back from the dead The study published in the zoological journal of the Linnaean Society in 2019 was specifically about a subspecies of the white-throated rail that lives only on the small island of Aldabra in the Indian Ocean

Looking at fossils and geological data, the researchers discovered that about 136,000 years ago, rising sea levels completely inundated the island, wiping out all land animals living there. One bird that went extinct because of the flooding was a flightless rail. It was a flightless subspecies of the white-throated rail. I should point out that the main subspecies of the white-throated rail lives on the nearby island of Madagascar. and it can fly. About 20,000 years after the drowning of Aldabra, sea levels dropped and the island re-emerged from the waves. Guess what happened next? Some cheeky little white-throated rails flew over from Madagascar and set up shop on Aldabra. They established a new population. There were no

predators around, so yep, the white-throated rails on Aldabra burned their boats, so to speak, and evolved into a new flightless subspecies. The subspecies that had gone extinct sort of got rebooted. Those headlines about a flightless bird coming back from the dead were a bit exaggerated. But the extinct subspecies of the white-throated rail and the subspecies that eventually replaced it are anatomically, morphologically remarkably similar. So it's not entirely wrong to say that evolution, more or less repeated itself.

We can't talk about flightless birds without getting into the topics of human-caused extinctions and conservation. But Ivan, you say, we don't have to worry about flightless birds going extinct. You just told us that if they go extinct, they'll just re-evolve. like those rails on that island that I already forgot the name of. We don't really have to talk about extinctions and all that depressing stuff, do we? Oh, how I wish all that were true, my friend. But the take-home message from that white-throated rail study is not that flightless birds will just re-evolve whenever they go extinct.

Don't count on it. And even if they did, this sort of evolutionary process takes at least tens of thousands of years, if not millions. Flightless birds could never re-evolve fast enough to keep up with the rate of human-caused extinction. Because in just the last few thousand years, Homo sapiens has killed off at least 160 flightless bird species. And that number is probably a gross underestimate.

Flightless birds living on islands have been especially vulnerable to the ravages of humankind. Almost all of those 160 known extinctions happened to island-dwelling birds. Because birds like moas, dodoes, cockapos, and all those flightless rails evolved in the absence of terrestrial predators, they weren't all that wary when humans first landed on the shores of their island homes. They weren't afraid of people. Large naive birds like the dodo were easy-picking for hungry sailors. So hunting by humans has caused many flightless bird declines. But one of the most destructive forces unleashed by humans has been alien predators. No, not like predator with a capital P, the one that Arnold Schwarzenegger fought in the jungle in that movie. I mean alien as in

non-native, non-native predators like rats, mongooses, dogs, and cats. Pretty much every time humans have pulled their boats up to an island, we've left behind some of these mammalian carnivores to wreak havoc on the native birds. Cats are particularly devastating. I talked about them ad nauseum in episode 23 of the podcast titled Cats vs. Birds. In that episode, I told the story of how in the late 1800s, the cats of a lighthouse keeper drove the Stevens Island Wren to extinction. Stevens Island is in New Zealand. That little wren was the very last

flightless songbird species on earth. About half of the remaining flightless bird species are endangered. We could lose many more of them to extinction if we don't act to save them. Conservation groups are working to protect many of these species, thankfully, but they face many challenges. In places where non-native predators are still running around, it's extremely difficult to protect

wild populations of flightless birds. And habitat destruction is a major problem for most of these endangered species as well. One species, the Guam Rail, was driven to the brink of extinction by invasive snakes, cats, and habitat loss. Guam is a U.S. island territory in the western Pacific Ocean. In the mid-1980s, conservationists captured the last 22 wild Guam rails on their namesake island. The birds were brought into a captive breeding program. Over the last 20 years or so, many captive-bred Guam rails have been released into the wild on small islands near Guam. The wild populations were healthy enough by 2019 that the International Union for the Conservation of Namesian, nature, the IUCN, changed the status of the Guam Rail from extinct in the wild to critically

endangered. So that's a wee bit of good news, a sort of conservation success story. The little Guam rail certainly isn't out of the woods yet, but thanks to the hard work of many compassionate people, there's now some hope for this species. There's also hope for the wonderful flightless parrot of New Zealand, the Kakapo. This critically endangered species was down to just 51 individuals in the mid-90s. Forest clearing and alien predators like ferrets, stotes, rats, and cats had devastated its populations. Intense and successful conservation management of the Kakapo has increased the population to about 250 birds today. All of them live on small, present, Predator-free islands offshore.

But just this year, conservationists moved a group of these parrots to a site on the mainland of New Zealand. This is the first time in almost four decades that wild Cacopo will live on the mainland. That's some really good news. The only way this recent reintroduction of Cacopo on the mainland could work is because the site where they were placed is surrounded by nearly 30 miles, or 47 kilometers, of predator-proof fencing. All of the mammals inside the fenced perimeter were removed. Removing non-native predators from islands is often the most effective,

but also the most challenging method of saving flightless bird species. It's also what needs to happen if we hope to maintain the processes of evolution on islands. Flightlessness can be a predictable evolutionary outcome given the connection, given the conditions that we talked about today. But when humans come along and change one or more of those conditions, we disrupt the natural progression towards flightlessness. We throw a wrench in the gears of the evolutionary machinery. I don't know about you, but I sure would like for evolution to keep cranking out new flightless bird species. Our world is a better place for having wonderful creatures like cacopos, kiwis, flightless rails, steamer ducks, and my little kayaking

buddy, the Tidicaca grebe. I thought this episode would be on the shorter side, but once I got into writing it, there was just so much more to talk about. I even had to restrain myself from writing an entire section on steamer ducks. We'll have to save that for another day, I guess. Anyway, I hope you find this topic as fascinating as I do, and I don't know, I just have a special place in my heart for flightless birds. I also have a special place in my heart for the lovely people who support my work on Patreon. The generous contributions of my patrons go a long way to making the science of birds a sustainable job for me. So thank you. My newest lovely patrons are Wen Yi Zhao, Tori Solis, Catherine Hunter, Ginny, Sarah Detman, and Douglas Sellers.

Welcome and thanks a million for stepping in to help. If you would like to know how to support this podcast, you can check out my Patreon page over at patreon.com slash science of birds. You can also shoot me an email if you have something you'd like to share with me, perhaps a comment about birds or about the podcast? Or about your own greatest talent? Did you win a silver medal at a hot dog eating contest? Are you really good at making forts out of sofa cushions in your living room?

Do you have x-ray vision? Let me know. My email address is Ivan at Scienceofbirds.com. You can check out the show notes for this episode on the Science of Birds website, scienceofbirds.com. This is episode number 80. 80. Woo, 80 episodes. And this is Ivan Philipson, wishing you the best day possible. Peace.