The Science of Birds - Giant Birds: Go Big or Go Home

Episode Date: May 26, 2022

This is Episode 52. Today, we’re talking about bird species that are way, way bigger than your average chickadee or finch.Our focus will be on evolutionary lineages that spawned some very large bird species. Species whose ancestors had been much smaller, millions of years earlier.We’ll look at a bunch of interesting giant birds throughout history. Then we’ll talk about some scientific explanations for why these critters got so big in the first place.~~ Leave me a review using Podchaser ~~Links of InterestThe Time Terror Birds Invaded [Video]Takahe - Return to the Wild [Video]Island GigantismLink to this episode on the Science of Birds websiteSupport the show

Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners. This episode, which is number 52, is all about giant birds. The vast majority of birds living in the world today qualify as small animals. Most of them would fit in the palm of your hand, and they're so light that you'd hardly notice the weight.

But today, today we're talking about bird species that are way, way bigger than your average chickadee or finch. Notice that I said species there. We're talking about entire species made up of extra large birds. So this is not about a few individual birds that happen to have mythological proportions. Like the avian equivalents of Goliath in the Bible, the jolly green giant, Paul Bunyan, or the big friendly giant. Our focus will be on evolutionary lineages that spawned some very large,

bird species, species whose ancestors had been much smaller millions of years earlier. We'll look at a bunch of interesting giant birds throughout history. Then we'll talk about some scientific explanations for why these critters got so big in the first place. Okay, without further delay, let's get into it. Birds are dinosaurs, right? You know this, I know this, your dog knows this, but on the off chance that you didn't know that birds are dinosaurs and you're currently going into a convulsive fit of shock and disbelief,

might I suggest you go back and listen to the very first episode of this podcast? That might calm you down. Being dinosaurs, birds had some pretty massive ancestors. When we look back into the Jurassic epic, we find that some of the direct ancestors of living birds were theropod dinosaurs weighing over 500 pounds, which is about 227 kilograms. These animals then evolved to become smaller and smaller through natural selection, generation after generation. After 50 million years of this miniaturization process, the result was taincy-wincey, adorable creatures like

Archaeopteryx, which probably weighed only 1.8 pounds or 0.8 kilograms. But why did these animals get smaller over time? Clearly, there had to be some advantages to smaller body size. It's hard to say for sure what those advantages were over the long evolutionary history of birds. But at some point, the key factor was almost certainly flight. Because the less you weigh, the easier it is for you to resist gravity and take to the sky. As an adaptation, flight was a tremendous advantage for the first birds. This ability is likely a major reason that birds have continued to be so successful across the planet. But flight also has been a constraint in many ways. The physical demands of flight have forced most bird species to remain lightweight and small. How small are we

talking? What is the average body size, or better yet, the median body size of birds these days? The median is a better metric here because it's less sensitive to wacky outlier values. One scientific study looked at the body sizes of 6,000 bird species. After all the number crunching, the result was a median body mass of 1.34 ounces, which is 38 grams. That's pretty small. 38 grams is about what two AA batteries weigh, or what one hot dog weighs, minus the bun and all that. So you can think of a typical bird as having the mass of a hot dog. But of course, some bird lineages have produced species that are significantly larger, even larger than a jumbo hot dog. In other words, freaking huge!

Now let's travel into the past to look at the motley crew of oversized prehistoric birds, as well as some that went extinct more recently. Just to clarify, all the birds I'm going to talk about in this section are extinct. Sadly, they're no longer with us. Also, I could probably do a full episode on each of them. For brevity's sake, though, I'm just going to do an overview today. first up the terror birds these guys win for having the coolest name the terror birds the 20 or so species belonged to the family

forest racity they were all flightless carnivorous and large terror birds ranged from three to ten feet tall or one to three meters their beaks were massive axe-like and hooked This shape was perfect for delivering lethal blows to their prey, which included deer-sized mammals. Like the latest incarnation of Batman in the movies, terror birds were sort of a reboot. They were an evolutionary echo of the bloodthirsty theropod dinosaurs of the maceozoic.

This summer, just when you thought it was safe to walk around outside and stuff, Just when you were getting all nostalgic about T-Rex and Velociraptors, the creative team at Natural Selection Studios brings you a new reason to run and hide. Terrorbirds. They're just like Jurassic Park, but this time with more feathers. Seriously, though, similar to Tyrannosaurus Rex, terror birds were imposing predators that stalked around on two legs. Oh, and like T-Rex, they also had, short, silly-looking, little useless forelimbs.

For millions of years following the big extinction that wiped out the non-avian dinosaurs, terror birds were the fast-running apex predators of the open plains. Most of them lived in South America. But some species made it up to North America. Titanus Wallerai, for example, roamed the grasslands of Texas and Florida,

spreading terror among the local mammals wherever it went. It was over eight feet tall. This giant, Titanus Wallerai, went extinct, along with all the other terror birds, about 1.8 million years ago. The closest living relatives of the terror birds today are the two species of seriamas found in South America. Most of the extinct birds we're looking at today were flightless. But a few of the most magnificent species had fully functional wings and they soared the skies. Imagine, if you will, something like a turkey vulture or an Andean condor. A turkey vulture has a wingspan of about six feet or two meters.

Now take that bird and supersize it up to three and a half times larger. That is Argentavis Magnificens, the giant Teratorn. That's Teratorn, not Terror-Torn. It's spelled T-E-R-A-T-O-R-N. The giant Teratorn had an estimated wingspan of over 21 feet. It was probably the heaviest flying bird that ever lived. This condor-like monster lived in the mountains of South America between nine and six million years ago.

But wait, what's that enormous shadow blocking out the sun? No, it can't be. It is. It's an even bigger bird. Pelagornis Sanderci had a wingspan of 24 feet. That's twice the wingspan of the current champion, the wandering albatross. Pelagornis was a fish-eating beast that lived about 25 million years ago in what is now South Carolina.

The only fossil of this ridiculously large bird was found at Charleston International Airport. Yes, an airplane-sized bird was found at the airport. Is that just a bizarre coincidence? Is it a government conspiracy? Aliens? Yeah, I think aliens is the most logical explanation, as usual. Argentavis, the Great Territorn, may have been the heaviest flying bird of all time.

But the award for the heaviest bird, period? That title goes to the flightless behemoth known as Vorombe Titan. This was the largest member of the family Epiornithity, the elephant birds of Madagascar. Elephant birds looked sort of like big-boned ostriches, but they had no visible wings. Voronbe Titan had a most excellent scientific name, and also it was 9.8 feet tall and weighed 1,600 pounds. Yeah, that bird was large and in charge. In metric terms, Vorombe Titan was 3 meters tall and weighed 725 kilos. For comparison, that's as heavy as the largest of grizzly bears, or a Holstein dairy cow.

Elephant birds, of one species or another, were wandering around on the island of Madagascar from at least as far back as 30 million years ago until just about a thousand years ago. They were flightless, massive, and herbivorous. There's also some evidence that elephant birds were nocturnal, like their closest living relatives, the Kiwis. And speaking of Kiwis, New Zealand! Before Homo sapiens showed up, New Zealand was a bird nirvana, an avian paradise where there were none of those stinky, pesky land mammals messing things up. With no mammals around, birds in New Zealand could evolve to fill all kinds of ecological niches.

One group of birds became massive flightless herbivores. These were the moas. There were about nine species, and the biggest of them were 12 feet tall and weighed 500 pounds. They might have looked a little bit like their distant cousins, the elephant birds, but moas weren't as heavy-bodied. Moas were the largest land animals in New Zealand until they were all killed off by the first Polynesian settlers. But moas weren't the only big birds that evolved in New Zealand.

There were also the two Adsbill species, the New Zealand. goose and the Hercules parrot, Heracles Inexpectatus. All of these were apparently flightless. But no ecosystem would be complete without at least one predator, right? Enter Host's Eagle, Hieraitis Mori. It was the largest eagle that ever lived, weighing 33 pounds or 15 kilograms. For comparison, a wedge-tailed eagle living today in Australia might be 8 pounds, and a bald eagle can weigh at most 15 pounds. Unlike so many other large New Zealand birds, Haast's eagle could actually fly. It had a wingspan of about 10 feet. That's actually small relative to the size of the bird's body. It's thought that these relatively short wings made the eagle more maneuverable as it

flew through the trees in forested habitats. Host's eagle hunted moas, adsbills, and other large flightless birds. When humans arrived and killed off the eagle's prey, it too went extinct. The list of large extinct bird species goes on. For example, what about the famous Dodo, Raphis Cucilatus, from the island of Mauritius? At 3.25 feet or one meter tall, you might not think the dodo qualifies as a giant. But this flightless darling was in the family Columbadi, the family of pigeons and doves that we covered in episode 32 of this podcast.

At over three feet tall and up to 40 pounds, the dodo was a monster of a pigeon. A close relative of the dodo, the Rodriguez Island Solitaire, lived on a nearby island in the Indian Ocean. Males of this flightless species weighed up to a whopping 62 pounds, which is 28 kilograms. Other king-sized birds included the Great Ock of the North Atlantic, the giant swan of Sicily, and the giant ducks of Hawaii, known as Moa Nalo. There was also the giant megapode of New Caledonia, a cousin to modern brush turkeys and scrubfowl. Giant rail species evolved in various places around the world, including Mauritius, the Chatham Islands, Puerto Rico, and Cuba. The latter island was also home to the Cuban giant owl. It stood 3.6 feet

or 1.1 meters tall, making it the largest owl ever. In all likelihood, the Cuban giant owl was flightless. It may have killed its mammalian prey by leaping out of the bushes at night and attacking with its powerful talons. Sounds like the stuff of nightmares to me. Now, besides the fact that so many of these birds are named giant this and great that, have you noticed any other patterns here? Starting with the elephant birds of Madagascar, all the large extinct birds I've been talking about evolved on and lived on islands. That's an important pattern. I'll return to the topic of islands in a few minutes. But first, let's move on to consider some bird species that are both

large and, hooray, not dead. We're lucky enough to have some big birds that are still alive and kicking. The largest of the living birds today are members of an avian lineage we call the ratites. Rattite is spelled R-A-T-I-T-E. The two ostrich species of Africa's are both the tallest living birds and the heaviest. The largest of the two, by a narrow margin, is the common ostrich. It gets up to 320 pounds and is over nine feet tall. That's 145 kilos and 2.8 meters. Other hefty rat heights include the Reyes of South America, and the cassowaries of Australia and New Guinea. All of these big boys are flightless. The only ratites that can fly are the 46 species of tinamus, and they are the smallest of the

bunch. Less dramatic, perhaps, but still relatively ginormous, are a couple of bird species in New Zealand. The South Island Takahe, Porfirio Hachstetteri, is a man. member of the rail family. Like most species in the genus Porfirio, the Takahe is a beautiful blueish-purple bird. It also has some green accents and a thick orange bill. It looks a bit like an Australasian swamp hen, otherwise known as the Pukiko. But the Takahe is, well, to put it bluntly, thick. That's T-H-I-C-C-thick. It's flightless, it's endangered, and it's

the largest living member of the rail family. Then we have the beloved Cacopoe of New Zealand, Strygops Habraptala. This is a moss-colored, flightless parrot that's active mostly at night. The Cacopo is not only the world's only flightless parrot, it's the heaviest parrot species as well. It can weigh up to nine pounds, which is four kilograms. So the Taka Hay and Cacopo are giants in comparison.

and with their closest relatives. At this point, you might be wondering when or if I'm going to talk about Big Bird from Sesame Street. You are about to hear the loudest, angriest bird you have ever heard. I wasn't going to include Big Bird because I thought he was just a one-off anomaly. A unique and freakishly oversized individual. belonging to an otherwise normal-sized bird species. But I did a little research on the Google webs, and it turns out Big Bird claims he's a golden condor.

I've never heard of a golden condor, but apparently this species is eight feet tall, flightless, and has a childlike innocence that people seem to find endearing. So far, I've given you a long laundry list of overgrown birds. We've had some fun, haven't we? But what's the point? What's the deeper story here? One of the most interesting questions, I think, is why?

Why do some bird species go from being small to friggin' huge over evolutionary time? We know that the common ancestor of all birds, way back in the Jurassic epoch, was a small flying creature. And that creature itself was the end result of 50 million years of miniaturization. So why go through all that trouble to become tiny and volent, only to abandon the ability of flight and grow large? Well, evolution is funny that way. To survive and reproduce, all that matters is what traits you have today, right now. Who cares if your ancestors got smaller and smaller? If being large is an advantage today, that's what natural selection will favor. There are multiple reasons a bird lineage might produce giant species. Every giant bird has its own backstory, its own unique

circumstances that caused it to evolve. And you can see that this phenomenon of gigantism has happened independently again and again in a bunch of distantly related bird groups, rails, owls, pigeons, ducks, and so on. We can point to a few reasonable hypotheses for why birds go big. First is the idea that, other things being equal, large body size may be an advantage when dealing with predators or competitors. For example, a larger individual might out-competeen its rivals to win more mates. Larger birds like this would then leave behind more offspring, and therefore more of their own genes. At least some of those offspring would inherit genes for large body size. Another hypothesis is that some bird lineages trended toward large body size

mostly in the last nine million years, when the earth entered a long cooling phase. Larger body size allows a bird to conserve more heat in cold environments. There are other hypotheses like these, but I want to return now to the subject of islands, as promised. Other than a few exceptions, the large bird species we've been talking about today are or were found on islands. For decades, biologists have described a phenomenon called island gigantism. This is the situation where a bird, or whatever, colonizes a remote island. Then its ancestors grow larger and larger until the result is a giant species that exists only on that island. A species much larger than its relatives on the mainland.

What causes island gigantism? We don't know for sure, but biologists suggest that because isolated islands often lack large mammal, predators, small animals don't have to hide from anything. They can just saunter around on the island, foot loose and fancy-free, you know, like when the cats away the mice will play. But in this case, the saying should be, when the cats away, for millions of years, the birds will get all huge and flightless and stuff. Not as catchy, I know. As for flightlessness, many bird lineages have independently abandoned their superpower of flight after colonizing islands. So flightlessness must be advantageous in these places. Again, if predators are nowhere to be found on an island, why waste all

that energy flapping around? Ditch the wings, get large, dominate the scene, party like it's 1999. Besides having no predators, a young island may also lack competition from other species, including mammals. Elephant birds and moas didn't have to compete with large herbivorous mammals on their respective islands. So these birds became the large herbivores. They evolved to fill that niche. Because they can fly long distances over the ocean, birds are heavily, disproportionately represented on remote islands. They usually reach islands before any ground-dwelling mammals do. if the mammals ever do. But island gigantism isn't limited to just birds.

One of the best known examples is the giant tortoises of the Galapagos Islands. And there's the Komodo dragon and other such fantastic beasts. Also, island gigantism is just one component of something called the island rule. The flip side of the island rule is that sometimes species on islands evolve into smaller forms than their mainland cousins. That's the phenomenon of island dwarfism. So, as usual, things are more complex than we might think at first. To keep things moving, I won't go any deeper in talking about the island rule right now,

much less the related concepts of the island syndrome or island biogeography. Being enormous may be advantageous in many situations, but mingling with humans ain't one of them. Large body size has proven to be a major liability for birds, and many other animals once old Homo sapiens arrives on their shores. On islands like Madagascar, New Zealand, and Mauritius, large flightless birds with no fear of predators, were easy pickings for ravenous humans. These birds were conspicuous, ambulatory mounds of tasty meat, lacking defensive behaviors or weapons. They had no chance against humans. The last elephant birds, the heaviest birds that ever lived, were killed off a thousand years ago.

Their enormous eggs are still sometimes found in Madagascar. People reached the shores of New Zealand for the first time around AD-1300. Within 200 years, the Moas were all gone. So too were the ads bills and Host's Eagle. Dodoes were wiped out by 1662, and the last Great Ock was killed in 1844. Given this track record, I think we're lucky to have any large birds left in the world. We still have the wonderful ostriches, casawares, emus, and rea's. I'm not sure what's going on with the golden condor, but the Takehaye and Kakapo are still hanging on in New Zealand. Just barely, and only with lots of help from conservationists. If we can somehow protect the remaining avian giants, if we can provide them with their natural habitats and just leave them to live in peace,

Maybe their stories will carry on for millions of years more. Hey, thanks for being here with me today to learn about some big old birds. I hope you had some fun and added some new facts to your quiver. The Science of Birds podcast is powered in large part by my supporters on Patreon. They each kick in a little hard cash every month to keep. keep this one-man operation running smoothly. I want to welcome my newest patrons, Rebecca Michelson, David Booth, Susan Stone and Jeff Weaver,

Art Barnett, Dan Haman, Jacqueline Wells, and Alyssa and Thomas Mecha. Thanks very much to all of you for joining my Patreon community. And with these recent editions, I now have 100 patrons. Wow, 100. That is just so cool. I'm honored and just all fired up to keep pushing forward with the Science of Birds. Thank you, thank you. If you, dear listener, are not yet a patron, I invite you to check out my Patreon page at

patreon.com forward slash science of birds. You can join the party and see what. all the fuss is about. You can also zap me an email if you have something you'd like to share. Thoughts about the podcast, or maybe you want to tell me what you would like to do when the cats away for millions of years. In any case, my email address is Ivan at Science of Birds.com. You can check out the show notes for this episode, which is number 52, on the Science of Birds website, scienceofbirds.com. As always, I'm Ivan Philipson. I hope that in this moment, right now, you're feeling happy and loving life. Cheers.