A Tour of Flightless Birds

Contents

Endemic to the Galápagos Islands, the flightless cormorant is the only cormorant in the world that cannot fly. Instead, it is adapted to hunting in water — with larger, more powerful webbed feet, and insulating fur-like feathers. It still spends much time drying after a dive, spreading its tiny wings in the sun.

*Sources for information and photos are at the bottom of the page.

Why Fly?

Isolated islands lie scattered across the oceans. Study their fauna and you’ll begin to notice a few patterns, with one pertaining particularly to birds. These feathered fliers are perhaps the most adept dispersers of all animals, and as such, are some of the first to arrive on a new island or archipelago — say, one formed by recent volcanic activity. The first avian colonisers might be a handful of songbirds caught in a storm and blown out to sea or a flock of pelagic travellers discovering new land where they can perch and nest amidst the waves. Whatever the case, it is flight that enables their colonisation of new worlds.

Flight is a supremely useful ability. It allows birds to search for food and resources from high in the sky, travel quickly to more plentiful areas, and perhaps most importantly, escape terrestrial dangers with ease. At the same time, flight is extremely energetically expensive. The breast or pectoral muscles in birds — the primary muscles that power flight — are typically very large, and they take a lot of energy to develop and maintain. The activity of flight itself is also very costly. A pigeon-sized bird, for instance, consumes about ten times more energy in flight than at rest.

It’s not simply wings that give birds the ability to soar. If you, as you are now, suddenly sprouted wings proportional to your body size, you still wouldn’t get off the ground. Your weight would be too great, and your muscles too weak to generate enough lift (no offence). Birds have evolved countless adaptations that make flight more energetically efficient — or possible at all. They possess a unique bone known as the keel: a ridge on the sternum shaped like the hull of a ship, that acts as an anchor for large wing muscles. Their bones are pneumatic (or hollow) to lighten their weight — the skeleton of a frigate bird, a black pterodactyl-like, pelagic traveller with a 2-metre (6.6 ft) wingspan, weighs less than its feathers. Air sacs run throughout a bird’s body, connecting to the pneumatic bones (apart from those in its head), lightening the bird further and allowing air to flow continuously through its lungs, both on an inhale and exhale.¹

Some migratory birds, like godwits, can increase their number of red blood cells to extract more oxygen with every breath. Other migratory birds, who must sometimes fly non-stop for thousands of miles, can put on muscle and fat at an extraordinary rate — to the point where a human would be considered obese, likely have diabetes, and die from a heart attack — and they can burn fat for energy 10 times more effectively than we can. A bird’s anatomy has been parred down to the bare essentials, with only one functional ovary on the left side and much shrunken sex organs outside of breeding season. All to enable and optimise the energy-expensive activity of flight.

But because everything in evolution is a trade-off, the ability to fly can also be a limitation. Hollow bones are fragile and easily broken, and wings themselves, with their light frames and large surface areas, are easily injured. Flight limits the body type, size, and weight of a bird, and thus the niches it can fill. A bird can only become so heavy before flight becomes impractical (as dictated by the laws of aerodynamics), so it's no surprise that the largest and fiercest birds to ever exist were flightless. And perhaps most importantly, evolutionarily speaking, the enormous energy investment required for flight could instead be redirected toward producing more offspring, and thereby gaining a reproductive advantage.

So the pattern emerges. As birds arrive on their new and isolated island homes — finding rich bounties on the ground, since such islands may still lack trees — and encounter few or no land predators, they lose their ability to fly. On these relatively safe and resource-rich islands, where there is much less pressure or incentive to fly, the birds that wasted less of their energy and resources on unnecessary flight adaptations could invest them in other, more useful endeavours, such as laying more eggs. These individuals became more successful within their population, outbreeding their flight-adapted variants and passing on their fly-less traits to their offspring. Eventually, over many many generations, the breast muscles, keel bones, and wings of these island birds atrophied, and they became fully flightless.

¹ Given the pneumatic nature of a bird’s bones and the way in which they connect to its lungs via air sacs, if a bird were to have its airway obstructed, but had a broken bone poking out of its body, it would be able to breathe through that bone — until it bled out, at least.

A Series of Skeletons

A spectrum of wing atrophy: from a fully-flighted swan on the left, to the flightless parrot (kākāpō) of New Zealand, the giant, land-dwelling cassowary, and the kiwi, with tiny vestigial stumps for wings.

Flightless Birds of Today

This story has played out hundreds of times over millions of years, on islands across the globe. A testament are the few flightless species alive today. Let's begin our world tour of flightless birds in a country known for its utterly unique avifauna, and a land that was once paradise on Earth for the feathered and ground-bound.

New Zealand had no terrestrial mammalian predators — apart from two species of tiny bats — until humans arrived some 700 years ago. In their absence, many of the birds that colonised the North and South Islands long ago took up the niches typically occupied by mammals. The most famous include the world’s only flightless parrot, the kākāpō, and the iconic kiwis. While the kākāpō still has wings, which it uses for balance and to marginally slow its nosedives from trees, the kiwis wings are little more than tiny stumps hidden beneath its fur-like feathers. The kākāpō occupies the niche of a ground-foraging herbivore, finding buds, roots, and fruits not unlike a rabbit or small wallaby. Kiwis, meanwhile, fill the niche of insectivorous mammals like hedgehogs, eating worms, millipedes, spiders, and insects, as well as nocturnal burrowers like badgers, with one kiwi owning as many as 50 burrows dotted across its territory. A mother kiwi chooses one of these burrows as her nest.

Flightless birds have the opportunity to reinvest energy saved from flight adaptations into producing more offspring. Released from the constraints of flight, a kiwi doesn’t opt to lay as many eggs as possible, but the largest possible. While ostriches hold the record for the largest eggs of any living bird, kiwis have among the largest egg-to-body weight ratios of any bird. The egg of an ostrich is just 2% of its mother’s body weight. A human baby, soon to be born, makes up 5% of its mother’s body weight. A kiwi egg takes up about 20% of a kiwi mother’s body. The mother walks with her legs splayed, her belly distended and dragging against the ground, and — with the egg taking up so much space that there’s little left for food — the mother fasts for two or three days before she lays. A single kiwi may lay up to 100 eggs in her lifetime. On the up-side, the chick hatches fully-feathered and open-eyed, already venturing from its burrow after just five days.

New Zealand is also home to several lesser-known flightless birds. Among them are two endemic rails — a group we’ll become well acquainted with during our tour. One is the takahē, a large waterhen with a broad red bill, face shield, and a rotund purple-green body. The other is the weka, also known as the wood- or Māori hen, a somewhat plain, brown bird that's often very curious about humans. Two flightless ducks are also endemic to New Zealand. The Auckland Island teal is found on the Auckland Islands, 725 km (450 miles) south of mainland New Zealand, and the Campbell teal is endemic to the Campbell Islands even further south — and was believed to be extinct for nearly 100 years.

We travel northwest, past the Solomon Islands and New Guinea, to the island of Guam, where we meet the Guam rail, or rather, we once would have. Known locally as the ko'ko', a population of over 10,000 is thought to have existed on the island prior to the 1960s. By the late 1980s, it was considered extinct in the wild. Evolving on an island free of rats and snakes, the introduction of these voracious predators — the brown tree snake arriving sometime after WWII, likely as a stowaway on a military cargo ship — dealt a fatal blow to this flightless bird. Not even the flying, arboreal-nesting birds could escape the invader, as the brown tree snake eventually eliminated 10 of the 12 native land bird species on Guam. Now the forests of Guam are bereft of birdsong. Beginning in the 1990s, a captive breeding and release effort has reintroduced the Guam rail to nearby islands, and in 2019 it became the second bird (after the California condor) to ever be reclassified from ‘extinct in the wild’ to ‘critically endangered’ by the IUCN. Today, around 70 individuals live on Cocos Island (Islan Dåno') and about 150 live on Rota. A victory for conservation, but a sad proclamation too, that the Guam rail can no longer live wild on Guam.

From the tropical coasts of Okinawa, we embark on a long odyssey across the Pacific Ocean, passing over the Polynesian Islands and shooting for Ecuador. Some 600 kilometres from mainland South America, a young archipelago is in a constant process of recycling, its islands birthed and sunk by tectonic forces. The oldest of the islands is likely no more than five million years old, some only a few hundred thousand, while others are being formed to this day. These islands, known as the Galápagos, are famous for inspiring Charles Darwin’s theory of evolution by natural selection. We owe one of the most important breakthroughs in biological science to the archipelago’s singular fauna.²

On the islands of Isabela and Fernandina live flightless cormorants. Their silhouettes line the black coastline, standing up to a metre (3.3 ft) tall with wings proudly spread to the sun. But their wings are stubby, sparsely feathered little things — each only measuring some 25 cm (9.8 in) long, about one-third the size of other cormorant species. The only way they "fly" today is by gliding beneath the waves. But everything, remember, is a trade off. Of the 40 or so cormorant species — the rest all flighted — these Galápagos divers are probably the most skilled in the water. As they dive, they tuck their dwarfish wings against their sides and extend their necks forward, becoming sleek torpedoes propelled by the powerful kicking of their webbed feet, harrying aquatic prey to depths of 70 or 80 metres (230–260 ft). Reflecting the relative youth of their home archipelago, these cormorants only lost their flight in the last two million years. Imagine how they’ll dive given another few million.

³ The Falkland steamer duck has two flightless cousins. In fact, we might’ve seen one, the Fuegian steamer, as we sailed along the southern coastline of Chile and the shattered shores of the Tierra del Fuego. The other, the white-headed steamer duck, lives along the southern coast of Argentina.

Zooming out from double-helixes, we travel on to meet our last flightless island dweller. To reach it we must sail for the middle of the South Atlantic Ocean. And I do mean middle. The Inaccessible Island rail is perhaps the most isolated — and certainly the smallest — flightless bird in the world. This pocket-sized, dark-brown rail is endemic to the aptly named Inaccessible Island of the Tristan da Cunha archipelago. Situated in the South Atlantic, this is the most remote inhabited group of islands in the world; lying, as it does, some 2,800 kilometres (1,750 miles) from the nearest landfall to its east in South Africa and some 3,200 kilometres (2,000 miles) from South America to its west. As of a 2016 tally, the tiny rail’s population hovers around 5,600 individuals. And although Inaccessible Island itself is, and always has been, free from invasive predators, one careless fishing vessel from the nearby Tristan da Cunha Island — which harbours house mice, brown rats, and feral cats — could break the rail's fragile ecosystem, causing it to suffer the same fate as the Guam rail.

Across the plains of Australia, the “island continent,” bounds the world’s second-largest bird. The emu stretches to nearly two metres (6.5 ft) tall. It’s draped in a grey-brown coat of shaggy feathers, hiding vestigial wings, no more than 20 cm (8 in) long, underneath. The emu’s wing bones aren’t only shortened, as is typical in flightless birds, but fused in a most curious way. For a skeleton to form properly during development, an embryo/fetus needs to put mechanical stress on its developing bones. To do that, it needs to be able to move, and movement requires muscles. An emu embryo doesn’t form muscles in the far parts of its wings — or rather, it does, but the muscle cells undergo cell death — meaning it can’t put the necessary stress on its wing bones. The result is bones that don’t elongate or grow in a symmetrical fashion; the wing bones of emus differ in length and fusion patterns between individuals, and even between the wings of the same individual.

With its wing growth impeded during development, the emu is born a runner. The usefulness of its wings extends to cooling down and steering as it sprints at a top speed of nearly 50 km/h (31 mph) — fast and agile enough to outmaneuver machine gun fire and win the 1932 "Emu War". This so-called war was a military operation to rid Western Australia of crop-destroying emus, ultimately failing as the emus proved too hard to hit and surprisingly resistant to bullets (out of some 20,000 emus, only 986 birds were killed with a further 2,500 dying from their injuries).

A southern cassowary (top), northern cassowary (middle), and dwarf cassowary (bottom).

Ostriches can stand up to 2.7 metres (8.8 ft) tall and are the biggest birds alive. There are only two species: the larger common ostrich, with a bare pink neck and legs, and the slightly smaller Somali ostrich, whose skin is darkish-blue, almost bruise-like. Together, they make up an entire bird order, the Struthioniformes, with Struthio derived from the Ancient Greek strouthokắmēlos — “camel-sparrow”. Closer in size to a camel than sparrow, the ostrich is indeed a bird of deserts and savannahs, living out in the open alongside some of Africa's largest, most proficient predators (lions, cheetahs, leopards, hyenas, and jackals — quite a cast of killers).

Of the flightless, feathered giants, the ostrich flaunts the most impressive wings — reaching a span of 2 meters (6.6 ft), as expansive as some large, flying birds (such as the bald eagle). The ostrich isn’t taking off, of course, given that it weighs upwards of 135 kg (300 lb) — compared to a bald eagle’s max weight of 6.4 kg (14 lb) — but it can outrun any feathered creature in existence. Which is exactly what it does when it’s frightened (it does not, as the popular myth states, bury its head in the sand). An emu may outpace machine gun fire, but it would be left in the dust by an ostrich. As the African ave sprinted ahead at a top speed of 70 km/h (45 mph), its uniquely two-toed feet striking the ground hard, each stride of its heavily muscled legs covers more than 3 metres (10 ft).

An ostrich's entire anatomy is built around its legs, it’s true. But just because its wings don’t serve their previous function of flight, doesn’t mean they don’t serve a function at all. A vestigial structure or organ, can be one which was useful to an ancestor but changed to no longer serve any purpose — the tiny, nub-wings of a kiwi fit this definition, as do arrector pili muscles in humans, whose purpose in other mammals is to raise their fur and make them appear more intimidating, but just enable us to have useless "goosebumps". Another type of vestigial structure is one whose purpose has changed from that which it once served. In a way, this makes all structures vestigial — wings weren’t always wings, after all, but the arms of theropod dinosaurs, perhaps used for grabbing and climbing rather than flight. Even further back, before tetrapods took to land, their ancestors' limbs served the function of pushing through water as fins. But I digress.

An ostrich’s wings are vestigial in the sense that they no longer serve to enable flight, but they still serve a purpose. A bird that sprints at such high speed must be able to slow and steer, and so its wings have become air-rudders; instead of catching air to soar, they push against it, using drag to break a sprint or swiftly change directions. The other purpose of an ostrich’s wings is romance. To court a female, a male ostrich fans out his wings around his neck, revealing plumy white feathers, and shakes them while tip-tapping his feet in a little dance as if he was a feathery showgirl. Then he pops a move any human dancer would be hard-pressed to perform: he squats down backwards,⁴ flaps his wings out, draws his neck in, and gyrates his entire body to and fro, his white wing feathers sweeping the dusty ground with each rotation. In such a manner, the largest bird on Earth uses his vestigial wings to perform the goofiest dance in the animal kingdom.

A group of greater rhea, also known as ñandú guazu (“big spider”).

⁵ The lesser rhea is also known as Darwin's Rhea because he first brought this more elusive rhea to the attention of science — only after he brought the rhea into his stomach, realising afterwards that this was the shy bird he’d heard about from the gauchos (nomadic horsemen of the Argentine and Uruguayan plains) and not a juvenile of the greater rhea.

A lesser, or Darwin’s rhea.

Emus, while a potential danger to crops, aren’t particularly aggressive towards humans. In the rainforests of northeastern Australia lives a cousin of the emu and, by reputation,“the world's most dangerous bird”. The southern cassowary is testament to the dinosaurian lineage of the aves. Slightly smaller than an emu, its body is a barrel of glossy black, fur-like feathers, its naked neck dangles with two red wattles, and its face is coloured hues of bright blue. The cassowary’s head is crowned with an ornate casque; a dark, bone-like crest with a spongy, honeycomb interior. Its purpose? Debated. It’s been suggested that the cassowary uses the casque to sweep aside thick foliage as it barrels through the rainforest or to amplify its deep, booming calls. The casque may be a result of sexual selection; an indicator of health, an ornate crown meant to attract a mate. More recently, the casque has been described as a “thermal radiator, offloading heat at high temperatures and restricting heat loss at low temperatures”.

New Guinea, just north of Australia across the Torres Strait, is the true kingdom of cassowaries. The southern reaches are ruled by the southern cassowary — its presence in both Australia and New Guinea is testimony to the bygone land of Sahul, when the two landmasses were one up until around 8,000 years ago. In the rainforests to the north, live the northern cassowaries, slightly smaller versions of their southern sisters with a single red wattle instead of two. These lowland species rarely venture any higher than 500 metres (1,640 ft) above sea level. The last species, the 1.3-metre (4.4-ft) dwarf cassowary, stands in their shadow. But only metaphorically. In reality, it looks down upon them from its high castle, living at elevations of up to 3,000 meters (9,840 ft) on the mountainous spine that runs through the centre of New Guinea. The dwarf weighs around 18 kg (39 lb) — for comparison, the largest southern cassowaries (the females) can weigh up to 80 kg (175 lb) — it lacks any wattles, and its casque is reduced to a quaint, black crest.

Whatever the cassowary’s casque is, it is not a weapon — it’s not what makes a cassowary so dangerous. Like a velociraptor with its decurved, tapping claw, the southern cassowary bears 13-cm (5-in) long claws on the inner toes of both feet. A kick from its immensely powerful, black-scaled legs — its spear-like claws tearing through skin and muscle — could and has been fatal to a human. Its reputation as “the world's most dangerous bird”, however, is an exaggeration. Firstly, the southern cassowary is primarily a herbivore, and specifically a frugivore; eating the fruits of at least 75 different plants and spreading their seeds in piles of colourful dung. Secondly, only two cassowary-caused human deaths have been reported since 1900. The potential for great violence is certainly there. Luckily for denizens of Australia and New Guinea, the cassowary is a shy forest-dweller. In contrast, it’s estimated that, in South Africa alone, ostrich attacks result in two to three cases of serious injury or death every year.

A common ostrich (above) and a Somali ostrich (below).

⁴ When an ostrich squats down, it appears as if its knees bend backwards, but this is actually its ankle joint. Its actual knee is all the way up its leg, near the rest of its body.

Leaving New Zealand behind, we sail northwest across the Tasman Sea until we reach Lord Howe Island, off Australia’s eastern coast. Here lives the Lord Howe woodhen: a small, olive-brown, flightless rail with striking blood-red eyes, currently considered endangered. Its population dropped to less than 30 individuals in 1980, but a survey in March of 2022 found 778 individuals — the highest count ever. This is a rare recovery, as we’ll come to see.

Setting off eastward, about 1,500 km (900 miles) east of Australia, we reach the islands of New Caledonia in the South Pacific, home to a species of large, drab, flightless rail unimaginatively known as the New Caledonian rail, which is either critically endangered or possibly extinct. Alongside it (if it still exists), lives the kagu: not a rail, but an utterly unique flightless bird with blue-tinged greyish-white feathers, long orange legs upon which it struts, and a pompous-looking crest of head feathers that it can erect at will. This avian supermodel is the country's national animal. It’s also a perfect example of what’s referred to as ‘island tameness’ or ‘naivete’. The kagu seems to completely disregard humans as a potential danger. The most it’s willing to do is walk away and stop behind a nearby tree trunk until the person goes away. And if someone rustles a pile of leaves, the kagu will come strutting back — likely mistaking the sound for another kagu searching for insects.You can imagine how such a trusting nature served it when the first, no doubt hungry, humans arrived, and much later, the hungry French colonists. Today, fewer than 2,000 kagus remain in the wild.

We continue our route northwest until we hit the centre of the Ryukyu Islands: a Japanese archipelago that stretches like a string of pearls between Japan’s southern island of Kyushu and Taiwan. The largest of these islands is Okinawa, a land of white beaches, coral reefs, and, in the very north of the skinny island, rich subtropical forest. An unidentified, feathered cryptid lived in these wild woods. After seventeen years of sound recordings, sightings, photographs and loose feathers, the Okinawa rail was officially described as a species in 1981. But Okinawa is no paradise for flightless birds. Unlike New Zealand, with its lack of land predators, Okinawa has long had a native snake — a habu, a type of pit viper, which comes out to hunt along the ground at night. The Okinawa rail didn’t perish, like the birds of Guam did in the face of the brown tree snake. This flightless rail evolved alongside the viper, adapting to survive by taking to the trees; gripping bark with its orange toes and ivory claws, climbing up a step at a time. Safe in the branches, it would sit out the night before gracelessly fluttering down to the ground with a flurry of its undersized wings in the morning.

However, as with the rails on Guam, those on Okinawa couldn’t anticipate an invasion. This invasion was furry, bearing sharp claws and teeth. It was also intentional. The people of Okinawa liked the venomous vipers not one bit, and neither did they appreciate the proliferating rats which they accidentally introduced. Their solution was to introduce yet another mammal: biological exterminators in the form of small Indian mongooses. Did these exterminators take out their intended targets? Sometimes. Did they kill everything else too? Certainly. The small mongooses ate anything, from other mammals to native reptiles to bird eggs. Not even adult rails were safe in the trees. Oh, and I nearly forgot to mention that Okinawa also has invasive cats — those hunters which, in the United States, kill around 2.4 billion birds every year. The Okinawa rail began to shift its activity from primarily nocturnal to diurnal, only to run into the jaws of introduced feral dogs. Endangered Okinawa rails still dash across roads and scream their shrill songs in the dark, but there aren't many left. The last census estimated some 720 individuals.

The Galápagos finches are famously given the credit for sparking in Darwin his idea of evolution by natural selection, but it was actually the archipelago's mockingbirds that "first thoroughly aroused" Darwin's attention to the peculiar distribution of species on the Galápagos.

Tracing Darwin’s journey on the HMS Beagle in reverse, we sail down the western coast of South America, round Cape Horn, and head north towards the Falkland Islands. Darwin made landfall on this chilly, hilly archipelago in 1833, where he was lucky enough to encounter one of the vanishing Falkland Islands wolves — even “collecting” a specimen for London’s Natural History Museum. The unique, fox-like wolves of the Falklands went extinct in 1876 (due to hunting, go figure). Darwin also bore witness to another creature, perhaps less regal than the wolf, but one that can still be found along the archipelago's rugged shores. He devoted two whole paragraphs in his book The Voyage of the Beagle to this duck, shortened here for your convenience:

“Their wings are too small and weak to allow of flight, but by their aid, partly swimming and partly flapping the surface of the water, they move very quickly. The manner is something like that by which the common house-duck escapes when pursued by a dog; but I am nearly sure that the steamer moves its wings alternately, instead of both together, as in other birds. These clumsy, loggerheaded ducks make such a noise and splashing, that the effect is exceedingly curious.”

This flightless bird is known as the Falkland steamer duck, named so for the water treading behaviour that Darwin described, which apparently resembled the motion of an old paddle steamer. With technology scarcely imaginable in Darwin's day, we’re now uncovering how flight loss occurs, and the steamer duck is helping do it. A genetic study comparing the flightless Falkland steamer with a flighted sister species, found, quote, “a mixture of both flight- and flightlessness-related versions of the genetic sequences linked to wing length. Thus, the evolution of flight loss seems to be caught in the act in steamer ducks.” Across all cases of flight loss in birds, no matter the specific circumstances — terrestrial, arboreal, aquatic — we see the wings shrink relative to the rest of the body. The steamer study even identified a gene, DYRK1A, that might be partly responsible for the shortening of wings — mice carrying more copies of DYRK1A show differences in limb skeleton development. Perhaps this, or a similar, gene is responsible for wing reduction in other flightless birds.

Or perhaps not. It’s been proposed that the changes in steamer duck genes and wing-shape — which appear like adaptations to a flightless lifestyle — occurred at the same time as steamer ducks began ‘steaming’, where they use their wings somewhat like oar to propel themselves across the water. Birds like auks and puffins, who’ve adapted to moving through water, also display shorter wings. So perhaps the shortening of steamer duck wings to the point of flightlessness was caused by an evolutionary push towards more effective steaming. So far, we only have the first few clues. We need to gather many more before we can piece together a solution to the genetic mechanisms of flightlessness.³

But what about that giant, ice-covered “island” on our southern pole? No tour of flightless birds would be complete without those tuxedoed divers: the penguins.

There are 18 living species and all of them, with one notable exception, live in the Southern Hemisphere. The most famous are found on Antarctica and nearby islands. Iconic emperors, the world’s largest living penguins, stand up to a metre tall on the ice, accompanied by their smaller cousins the king penguins, and the even smaller royal penguins with their feathery golden crowns — together forming a regal retinue. Little Adélies hop along Antarctica’s icy coastline and chinstraps gather in mass colonies. Macaroni penguins, with thick beaks and dishevelled, golden crowns (or eyebrows, depending on how you look at them) crowd the Antarctic Peninsula and Subantarctic islands, their population estimated at 12 million breeding pairs. Emperor, Adélie, or macaroni, all penguins take to sea to hunt for food. They transform from dumpy bird shuffling across the ice — emperors waddling at a speed of 2.5 km/h (1.55 mph) — into sleek swimmers that glide through the water — the fastest penguins, the gentoos, reaching swim speeds of 36 km/h (22 mph), about 5 times faster than the fastest human swimmer. Penguins traded in their wings for flippers long ago. However, unlike other flightless birds, their wing and breast muscles never atrophied but were repurposed for pushing water instead of air. Flapping with their wings-turned-flippers, they “fly” through the sea.

In a game of word association, ‘penguin’ is likely to be followed by ‘Antarctica’, or vice versa — after all, when we were young, we learned that polar bears live in the Arctic and penguins in Antarctica. But not all penguins are partial to the frozen continent and its barren surrounding islands. African penguins live along the shores of southern Africa, southern rockhoppers and Magellanic penguins make landfall along the tip of South America and can be found mixing with steamer ducks on the Falkland Islands, and Humboldt penguins live along the western coast of South America, all the way up to Ecuador. It would be more accurate to say that polar bears live in the Northern Hemisphere and penguins live in the Southern Hemisphere, but not even that is strictly true. On the Galapagos Islands, alongside the flightless cormorants, live Galapagos penguins — the only penguin species found north of the equator.

On those fated isles, penguins and cormorants shoot through the water side by side. But while the Galapagos cormorant began its journey to flightlessness some 2 million years ago, the first penguins appeared in the fossil record around 60 million years ago, not long after the K-T extinction that wiped out the (non-avian) dinosaurs. And the oldest penguin fossils didn’t turn up in Antarctica, but in that incubator for flightless birds, New Zealand. You’ll find four endemic penguins there today, including the yellow-eyed penguin, an endangered species that may be the oldest surviving lineage of them all. In total, 13 of the 18 living penguin species have been recorded in and around New Zealand’s shores. There were once many more.

So penguins, like most other flightless aves, appear to have evolved on islands. But exactly when and how they lost their flight, we don’t know. As for why, it was likely a mix of factors: the absence of land predators reduced the pressure to escape by air, while strong selection favoured swimming over flying.

But is island life the only path to flightlessness?

So far, we’ve travelled across the Pacific and Atlantic, hopping from one island to another and hugging the coastlines, but we’ve yet to trek into the interior of any continent. There are, however, flightless birds on the mainland — one group of birds stand out in particular, which, like the penguins, has greatly diversified after losing the ability to fly. They are also about as distantly related to penguins as possible. We must journey inland to meet the biggest birds alive today.

Upon hearing the name ñandú guazu, translating to “big spider,” and learning that it refers to a creature nearly as big as a man, you might be frightened, understandably, of some monster skulking across the grassy pampas and sparse woodlands of Argentina and Brazil. Despite its nickname, this isn’t some colossal arachnid, but a bird that early European explorers referred to as the “South American ostrich”. Our last avian giant is the rhea — its name lifted from a titan of Greek myth, whose name, in turn, carries the meaning of 'ground' or 'earth', fitting for a flightless bird. There are two species. There’s the lesser, or Darwin’s rhea, described as being built like an outsized, long-necked turkey ⁵ — a bit insulting, and unfounded, given that it looks quite charming, with a body about the size of a sheep, pale fringes to its dusty feathers, and a stoutness that gives it a babyish cuteness. The other is the greater rhea, the largest bird in the Americas. It’s taller and more slender than its “lesser” counterpart, and, with only two limbs (its legs) visible while at rest, it resembles a big spider not at all. The comparison likely arises from the way a rhea employs its substantial wings. Much like an ostrich, it opens them to steer while running, and with dark feathers instead of white streaming behind it as it sprints, the bird may replicate the many appendages of an arachnid. It also uses its wings for courtship.

Like ostriches, rheas form harems. Both male and female rheas are polygamous, mating with many different partners, but in different ways. Males court and mate with anywhere between two and twelve females at one time. Females, just as promiscuous as males, mate with one dominant male, dump their eggs in his nest (on the ground, of course), then move on to another male, and so on and so forth, until the breeding season ends. The males are then left caring for anywhere between ten to sixty eggs, depending on how charming they’ve been that season. One upside of having so many eggs is that they become somewhat expendable; a male is known to use some of them as “decoys,” placing them outside the nest as a sacrifice to predators. The rest of the eggs he incubates for some six weeks and then cares for as chicks for up to 6 months — charging at anything that gets too close to his young, including humans and female rheas. So strong is the paternal instinct that male rheas have been known to adopt lost or orphaned chicks into their brood.

The wing bones of emus differ in length and fusion patterns between individuals, and even between the wings of the same individual.

All of these far-flung, flightless giants — the war-winning emu, raptorial cassowaries, enormous ostriches, and paternal rheas — are ratites (from the Latin ratis, meaning 'raft', a boat without a keel for a group of birds without keels). Somewhat unexpectedly, joining these titans are the tiny kiwis of New Zealand. The traditional view was that these birds all descended from a single flightless ancestor, which was split into separate populations when the supercontinent of Gondwana broke up and drifted apart. But more recent evidence, in the form of DNA recovered from Malagasy elephant bird bones (more on these mammoths later), suggests that this isn't the case. The elephant bird's closest relatives, it turns out, are not the geographically closest ostriches, as would be expected from the orthodox theory, but kiwis, from the other side of Gondwana. On top of this, kiwi fossils suggest a more recent evolution from flighted ancestors. And then there are the tinamous, an order of plump New World birds that spend pretty much all their time on the ground. These shy ground-dwellers were once considered a sister-group to the ratites, but more recent genetic evidence places them well within the group, most closely related to the extinct moas of New Zealand (more on them later too). But here’s the thing: the tinamous have keeled sternums and, although they don’t do it often or very well, they can fly. All of this — the geographic relations of ratites, kiwi fossil dates, and the flighted tinamous — advocates for a familiar story: the ratites flew from island to island (or continent to continent), each time settling down and becoming large (most of them) and flightless.

Flightless Birds of Yesterday

If you chronicled the tales of flightless island birds, their stories would be struggles for survival. A few — such as those of the Lord Howe woodhen and Guam rail — are hopeful. Unfortunately, the majority aren’t. They are, if I may be dramatic, tragedies. The variety of flightless island birds alive today pales in comparison to those that have gone extinct. ‘Gone’ may be too soft of a word, for most were hunted, beaten, and eaten by the first mammalian land predators to arrive on their islands: humans. Others suffered from the passengers we brought with us, whether intentionally or not: our rats and mice, cats, mongooses, and snakes. Most didn’t survive to bounce back.

We’ve met the modern ratites of the mainlands, but it was actually on Islands where feathered giants — the largest birds to ever live — once roamed. In 1839, the famous paleontologist (and famous Darwin critic) Richard Owen⁶ received a giant femur from New Zealand. As more fragments arrived, he pieced together a new type of bird that he determined to be flightless, a bird that towered over the man himself. He named it the moa. New Zealand was once home to some ten, perhaps more, species of moa. Part of the ratite group, they resembled their emu and ostrich relatives but ranged from around turkey-sized to the tallest bird known to ever live: the North Island giant moa, stretched up to 3.6 metres (11.8 ft) tall, although it was shorter when not stretching (think of the more horizontal posture of an ostrich). These beastly birds were so adapted to life on the ground, that they lacked any vestigial wing bones at all. They thrived until shortly after 1250 AD, around the time the first people, the Māori, arrived.

Today, across southern Australia, Tasmania, and the islands in between, lives the Cape Barren goose. It is a bulky, grey bird with a knobby beak that prefers grazing in grassy fields over dabbling in the water. It flies — slowly and somewhat clumsily — to find favourable breeding sites on offshore islands (like Cape Barren). If you took this goose and sized it up to a metre (3.3 ft) tall, as large as some of the smaller moas, and increased its weight from around 6 kg (13 lb) to 18 kg (40 lb), you’d have something like the South Island giant goose. Larger than its sister species on the North Island, this goose was a terrestrial browser with a squared-off bill for clipping grass, flaunted a short tail, and had wings too small to carry it aloft to any islands. Its eyesight was thought to be sharp in response to predation by Haast's eagle — an extinct raptor that weighed as much as the goose but soared on a wingspan of up to 3 metres. The giant flightless goose survived this real-life roc, but was likely hunted to extinction by early Polynesian settlers. (Haast's eagle, which also ate moas, followed its prey to extinction).

The sizes of different moa species; Richard Owen with a moa skeleton.

The kākāpō clings on to existence, if barely — considered ‘critically endangered’ with an estimated 242 individuals alive today. It is the heaviest living parrot with an average male weighing 2 kg (4.4 lb). It’s also the fattest parrot, putting on a healthy layer in preparation for breeding season, with some individuals reaching breeding weights of 4 kg (8.8 lb). It was the heftiest parrot species known to ever exist. Until 2008, that is, when a fossil was discovered in the South Island interior and dubbed Heracles inexpectatus, the Hercules parrot. Like its mythological namesake, this parrot was big; about twice the size of the kākāpō, weighing some 7 kg (15 lb) and reaching a height of about a metre (3.3 ft). It was so large that its bones were first attributed to an extinct species of eagle — although the Hercules parrot’s diet may not have been far off from that of a raptor. It’s thought to have used its giant beak to “crack wide open anything it fancied … perhaps even other parrots”. It probably never got its beak on a human, however, given that it lived some 19 million years ago.

Wrens notwithstanding, New Zealand is famous, in certain circles, for its giant extinct avifauna. But no bird of New Zealand, no bird anywhere for that matter, living or extinct, is or was as behemothic as the elephant bird of Madagascar — specifically, the species Vorombe titan. Another ratite, it was not as tall as the giant moa, reaching a height of “only” 3 metres (9.8 ft), but it was more than twice as heavy — weighing over 750 kg (1,650 lb) — making it the heaviest known bird to ever live. Its eggs reached sizes of a metre (3.3 ft) in circumference and held the contents of around 200 chicken eggs. The elephant bird may well have been the inspiration behind the roc; described by explorers like Marco Polo and Ibn Battuta, this giant bird was said to prey on elephants, lifting them into the air in its talons. Alas, no such elephant-snatching bird existed (physics wouldn't allow it) and the real-world elephant bird was likely herbivorous. It thundered across Madagascar until around 1000 AD, when it was driven to extinction, probably as a result of human activity.

The oldest known (real) penguin is Mannering's penguin. It lived nearly 62 million years ago, not long after the extinction that killed off most of the dinosaurs — raising the tantalising possibility that penguins may have waddled alongside the terrible lizards. And where else would its fossils be found but New Zealand? Fordyce’s penguin, the largest penguin ever discovered, likewise hails from Aotearoa. It stood over 2 metres (6.6 ft) tall and weighed 150 kilograms (330 lb) — the emperor penguin, the largest living species at 1.3 metres (4.3 ft) and 30 kg (66 lb), could have been its young. Despite living some 60 to 55 million years ago, Fordyce’s penguin would still be, unmistakably, a penguin: a behemoth penguin, yes, with an elongated, spear-like bill, and less flattened flipper bones, but a penguin still. It may not have been fully optimised for swimming just yet, but penguins were already entirely aquatic by 60 million years ago.

Number 8 indicates both left and right tarsometatarsus bones.

More than any other group of birds, rails have suffered and died at our hands.

We've already met several flightless rails — the takahe and weta of New Zealand, the rails of New Caledonia and Guam, Okinawa and Inaccessible Island. It's clear that this family of plump birds have an affinity for hopping islands, settling down, and becoming flightless. There is even evidence that the white-throated rails that settled the Aldabra Atoll did so twice. The first population arrived and became flightless but was wiped out by a flood. It was then followed by a second population who also independently lost the ability to fly — these are the Aldabra rail (Dryolimnas cuvieri aldabranus), a flightless subspecies of the white-throated rail, that live there to this day.

⁶ Richard Owen (1804–1892), a British anatomist and paleontologist, is perhaps best known for coining the term ‘dinosaur’ (Dinosauria). He used his knowledge of anatomy to classify many fossil vertebrates (like the moas), but he was also a divisive figure in Victorian science as a result of his unfriendly (an understatement) attitude to other scientists and his religiously-motivated attacks on Darwin’s theory of evolution by natural selection.

Another odd fossil, initially described by Owen as a small species of moa, turned out to be something else entirely. It was the first discovery of an adzebill, of which there were two species; one for each of New Zealand’s main islands. The bones of these great-bustard-sized birds⁷ — about 80 cm (31 in) long, in case you’re unfamiliar with a great bustard’s size — were found in the drier lowlands. They likely stomped through the scrub- and grasslands on their thick legs, hunting lizards, tuataras, and other birds with their strongly tapering, robust, down-curved beaks, and using their wings for nothing much at all given how insubstantial they appear to have been. With a reduced sternum, almost no keel, and a uniquely tiny carpometacarpus (the wing bone between the “wrist” and “knuckles”), adzebills certainly weren't flying anywhere. Both species went extinct sometime before European settlement in the early 19th century.

So far, we’ve met many flightless giants — birds that are giants compared to their relatives, and birds that are just flat out giants. Can little birds afford to lose their flight?

Out of some 4,000 species of songbirds, only five are known to have been flightless. Four of them were New Zealand wrens, and of those four, only one survived to European contact. Lyall's wren, also known as the Stephens Island wren, was first seen in 1892 by workers hired to build a lighthouse on a tiny island located at the northern tip of the South Island. The assistant lighthouse keeper, David Lyall, brought this bird to the attention of science, but it was his cat that provided the first “specimen” in 1894. The species was identified as a unique wren — with short, rounded wings and no keel on its breast bone for anchoring flight muscles, it was completely flightless. Early in the same year a pregnant cat arrived on the island.

Many specimens of this flightless wren, including those collected by the cat, were obtained from Lyall by a naturalist and taxidermist called Henry Travers, who then sold them on for a pretty penny (the two men would provide the wren with its scientific name: Traversia lyalli). Over the course of a single year, the island's bird population dropped significantly as its limited area was overrun by feral cats, prompting Travers to write that "in a short time there will be [no "wrens"] left". Whether he was writing out of genuine concern for the birds, or to boost the price of his specimens, he was right. The last of these flightless wrens was brought to Lyall in 1895 — held in the clutches of his cat. Lyall’s wren went extinct by the end of the century. No flightless songbirds exist today.⁸

An illustration of a Fordyce’s penguin (top) and a comparison of penguin skeletons: Fordyce’s penguin (left) and Petradyptes stonehousei (center) with a modern emperor penguin (right).

Ancestral penguins were likely similar to modern-day auks and murres — those black-and-white shorebirds with short wings that make them good swimmers, but ineffective fliers. Push an auk to further optimise for swimming and its wings would become shorter and flatter, its body larger, its bones heavier. You’d get something like a penguin. In fact, that’s exactly what happened with the great auk. This “penguin of the north” lived in the cold waters of the North Atlantic, where it dove beneath choppy waves to catch fish and waddled on to isolated, rocky isles to nest and breed. Standing around 70 cm (2.3 ft) tall with a white belly and black back, it looked very much like a penguin. In fact, it was the original penguin. The word “penguin” was used for this auk in the late 16th century and only later given to the birds we call penguins today. Contrary to appearance and original name, the great auk was unrelated to the flightless birds of the south. Instead, it was a member of the Alcidae family, which includes auks, murres, guillemots, and puffins. The 24 living species inhabit the rugged shores of the northern hemisphere and, although not particularly graceful, all of them can fly. The unique flightless outlier that was the great auk went extinct in the 19th century as a result of overhunting by humans — the last confirmed pair, seen on an island near Iceland, were killed by fishermen in 1844.

“There is evidence that rails settled the Adabra Atoll twice, becoming independently flightless both times.”

An elephant bird egg, an ostrich egg, and a hummingbird egg.

The razorbill and little auk — close living relatives.

In what is now the Chatham Archipelago — 800 kilometres east of New Zealand’s South Island — Stilwell’s penguins nested on the shores of ephemeral islands and dove through the seas in search of fish. Their wings were strong and flattened, clearly unfit for flying but well-adapted for propulsion through a denser medium. Their tarsometatarsi — a mouthful name for lower leg bones seen in birds — were short and wide, resembling those of modern penguins, rather than the narrower ones of flying seabirds like petrels. These archaic penguins were already using their feet as rudders for steering as they swam.

Between 37 to 40 million years ago, some 10 to 14 species lived together along the Antarctic coast, among them the 2-metre (6.6-ft) tall “mega penguin”. Not to be outdone when it comes to birds, New Zealand hosts the richest fossil record of penguins anywhere on Earth, with 30 described taxa spanning 60 million years. Many came and went long before our hominin lineage split from that of the other great apes. By the time the Chatham Archipelago formed some 3 million years ago, Stilwell’s penguins had long been dead. The islands, instead, were occupied by hefty birds with yellow “eyebrows” known as Chatham Island crested penguins. Their bones are found among archaeological middens — they were hunted and eaten, a valuable food resource for the first human settlers. They were the first, and so far only, penguins to go extinct because of us.

Once upon a time, it seems that nearly every island presented a unique species of flightless rail marooned thereupon. New Zealand, of course, used to have several more species than those alive today. Six of them lived on the Chatham Islands. The Chatham Island rail, or Mātirakahu, was first described in 1872, but by 1894 — not long after cats settled on the island — the rail was proclaimed extinct. That’s 22 years from discovery to extinction. The other five Chatham rails followed suit, all perishing in the 19th century.

Mirroring the Chatham Islands, six species of rails once inhabited the Mascarene Islands east of Madagascar. The island of Réunion had its own rail, which likely went extinct in the 17th century. To the east, the red rail shared its island home of Mauritius with the famous dodo, and around the year 1700 met with the same fate. Even further east and out to sea, a flightless rail on the small island of Rodrigues lasted into the 18th century before it too vanished. All likely met their end to the combined forces of rats, cats, and overhunting.

On an isolated volcanic island in the South Atlantic, lived the Ascension crake. Its story, if you can call it that, serves as a grim warning of what may befall the Inaccessible Island rail should its isolation ever be violated. Little was known about this endemic crake — some fossils, a sketch, and a short description — before it likely perished in the 18th century following the introduction of rats, and if not then, it surely didn’t survive long after 1815, when cats were introduced to the island.

Laysan, an atoll in northwestern Hawai’i, harboured a small endemic rail whose home was devastated by, among all things, domestic rabbits. The rabbits fed on the island’s vegetation, multiplied, and fed, and multiplied, and fed, and…eventually stripped Laysan of its foliage, turning it into a barren dust bowl. With insufficient nesting sites, the Laysan rail went extinct on its home island in 1923. A few individuals were evacuated to the Midway Atoll and seemed to thrive for a while before rats were introduced. The last Laysan rail died in June of 1944.

On a Pacific atoll named Wake, it was not rats or rabbits that devastated the endemic Wake rail (the only native land bird on the coral atoll). The species met its end between the years of 1942 and 1945, as a result of our Second World War. Occupied by the Japanese, a U.S. blockade trapped thousands of soldiers on the atoll. Starving, they relieved their hunger by way of these inquisitive, helpless birds.

Barely anything was known about the Ascension crake before it went extinct in the 18th century.

Six species of rail sequentially disappeared from the Mascarene Islands in the 17th and 18th centuries.

The Wake Island rail — the atoll’s only native land bird — was eaten to extinction during WWII by trapped and starving soldiers.

⁸ Aside from Lyall’s wren, the four known flightless passerines (songbirds) are the long-billed wren, North Island stout-legged wren, and South Island stout-legged wren — all New Zealand wrens — and the long-legged bunting from Tenerife of the Canary Islands. All are now extinct.

In the past 400 years, humans have caused the extinction of 26 rail species — these are just the documented cases.

The Rails of Yesterday

In the past 400 years, humans are known to have caused the extinction of 26 rail species. These are just the documented cases -— there were likely more.

⁷ The adzebills’ genus name, Aptornis, refers to their similarity in size to the great bustard (Otis tarda).

In the 19th century, six species of rail went extinct on the Chatham Islands of New Zealand.

The Chatham Island rail was only known for 22 years before it died out.

The Laysan rail went extinct on its home island in 1923 — while a few individuals were evacuated to the Midway Atoll, the last Laysan rail died there in June of 1944.

The Future of Flightless Birds

Even in our modern world, one where remote places are increasingly fewer and farther between, we still see this persistent lack of fear on islands. When the Bishop of Panama, on his way to Peru, accidentally discovered the Galápagos in 1535, he and his hungry crew were astounded by the birds who “did not fly from us but allowed themselves to be taken.” Nearly 440 years later, Peter and Rosemary Grant found little change in the attitudes of these birds. The Grant’s have been studying, in scrutinous detail, the finches of the Galápagos since 1973. One of the veteran finch-watchers on their team compared the island birds to their mainland counterparts: “In Kenya, finches flush as much as 30 meters away. In the Galápagos, the birds land on the rim of your coffee cup”.

The finches didn’t evolve in a pacific paradise. They had their predators — two species of endemic owl for instance, and the Galápagos hawk that Darwin pushed off a branch with his gun. “The finches are much more afraid of hawks and owls than they are of us,” observes Peter Grant. “When we walk up to them, the birds keep doing what they are doing; but when an owl comes near, they head for a cactus tree. A little while ago Rosemary was crossing a treeless spot. An owl flew over, and finches flew up from all around and landed on Rosemary!” The finches appear naive to us, showing little to no sense of the self-preservation we expect in wild animals, but they’re not naive to the dangers they evolved to survive. Marine iguanas fear predators at sea and finches fear those soaring above; we are neither, so they do not fear us. The same is true of the flightless cormorant which evolved on the Galápagos isles. Even if it could fly away from a stick (or gun) wielding human, it probably wouldn’t.

The concept of extinction once seemed a ludicrous notion; people believed that the slaughter could last forever, that a species was ever plentiful. That belief was shattered on Mauritius, one of the Mascarene Islands to the east of Madagascar. The dodo, Raphus cucullatus, is often depicted with greyish plumage, yellow feet, a naked face and a bulky bill. Usually, it’s given a very dumpy frame, flanked by small, useless wings. While many illustrations exaggerate its plumpness (depicting its body as a meaty sphere), the real dodo was likely no slim stork — it was a pigeon, actually. Its closest living relative is the stunning Nicobar pigeon, a species found on islands around Southeast Asia, boasting multi-coloured wings that shimmer with iridescence. But no pigeon today is as large as the dodo — which stood almost a metre (3.3 ft) tall and weighed around 20 kg (44 lb) — and none is flightless.¹⁰

The Nicobar pigeon, while no great flier, is nonetheless a nomad: travelling from rich islands where it forages, to small islands where it breeds, to predator-free islands where it sleeps. The dodo had no path of retreat, even if it wanted to flee. It first met with Portuguese sailors around 1507, who described it as "tame and easily approached", easily captured and killed. Then came the dogs, cats, rats and pigs, altering habitats and eating dodo eggs served atop easy-to-reach ground-nests. The last dodo was seen in 1662. By the 1700s, the entire species, with all of its millions of years of evolutionary history was gone. The dodo was not the first species we’d wiped from existence, but it was “the first species whose extinction was conceded — in writing — to have been caused by humans”. This was a grim realisation of the power we, humanity, hold over the rest of life on Earth. And, although most people didn’t see it for some time yet, it was a charge to wield that power with forethought and responsibility.

¹⁰ For a species we wiped from existence, we have little direct evidence to inform us of what the dodo was like: a foot here, a head there, and a few skeletons in various states of completion. It was certainly quite unique among the pigeons — placed alone in the genus Raphus — with its large head and beak, and its large size overall.

The largest living pigeon, the Victoria crowned pigeon, measures up to 85 cm (2.8 ft) long, similar in dimensions to a dodo, but only weighs around 3 kg (6.6 lb). A single dodo likely weighed more than six Victoria crowned pigeons. This is, of course, because the crowned pigeon still flies (although only when it's forced to), while the dodo certainly did not, and so could afford the extra heft.

On the island of Rodrigues, 600 km (370 mi) east of Mauritius, lived the endemic Rodrigues solitaire. Also flightless, the Rodrigues solitaire, was perhaps the largest pigeon to ever live, slightly taller and heavier than the dodo. It was known for its aggressive territorial behaviour and large bony knobs on its wings, with which it would do combat. It outlived the dodo, but not by long, driven to extinction in the 1760s.

It’s no great mystery why flightless birds have suffered the brunt — the blunt club — of human violence. It’s much easier to catch and bash a portly runner than a swift flier. But, even if they could take to the skies to escape such a fate, most wouldn’t have even tried. These island residents had no fear of humans when we arrived on our boats and came marching to slaughter them for the pot or simply for the fun. Isolated for millions of years with no predators on the ground, they lost their fear of anything moving over land. Countless travellers and naturalists have been astonished by the laxness of these animals, usually so quick to flee. A great number of the accounts written by these great historical figures involve poking (or killing) the native avifauna with sticks, like boys playing in the schoolyard.

According to the 17th century traveller Sieur Dubois “all the birds at Bourbon [Réunion] in 1571–72, with the exception of the flamingoes and geese, were so extremely tame, that they could be caught by the hand, or killed in any number with a stick”.

Describing the thrushes and buntings of the Tristan da Cunha Archipelago (of which Inaccessible Island is a part), Dugald Carmichael, the “Father of Marine Botany”, said they were "so tame as to suffer themselves to be caught with a hand-net."

Of the Polynesian ground-dove, Captain James Cook wrote, “They are so tame or foolish, as to stand and stare at us till we knocked them down with a stick.”

Island Tameness

The refusal to flee, or general unconcernedness about potential threats that we see in island species, is referred to as ‘island tameness’. Darwin made much of this “tameness” when meeting the creatures of the various islands he visited. During his five weeks among the Galápagos Islands, he observed that “Extreme tameness…is common to all the terrestrial species…A gun is here superfluous; for with the muzzle I pushed a hawk off the branch of a tree.” He wrote too about his encounter with the islands’ endemic marine iguanas, dumbstruck by the character of these “disgusting clumsy lizards”. They were so lax that he could walk right up to an iguana and it would not flee to sea, even though it had “perfect powers of diving and swimming.” So he picked one up and threw it in the water. Almost immediately, it returned to land, back at his feet. He tossed it in again and again, and every time it crawled back out. Eventually he realised that the iguana had an instinctual response to danger: get to dry land. This instinct had likely served it well, given that the only threats the Galápagos marine iguana evolved alongside were those in the sea (e.g. sharks and sea lions) and none on land. So naturally, when it felt threatened, that’s where it scrambled seeking safety.

The finches of the Galápagos; 17 to 18 species descended from one ancestor species.

Darwin's two visits to the Falkland Islands, understandably, receive much less attention than his adventures in the Galápagos. While the Falkland steamer duck presents a curious case of flightlessness, the archipelago’s most striking residents were its wolves. Of them, Darwin writes, “These wolves are well known…[on] account of their tameness and curiosity; which the sailors, who ran into the water to avoid them, mistook for fierceness. To this day their manners remain the same. They have been observed to enter a tent, and actually pull some meat from beneath the head of a sleeping seaman. The Gauchos, also, have frequently killed them in the evening, by holding out a piece of meat in one hand, and in the other a knife ready to stick them…” Friendliness, or at least a lack of fear, is apt to be taken advantage of by humans. By the time Darwin took sail on the Beagle (1831–1836), he was aware of entire species destroyed at the hands of humans. Darwin speculated — accurately — about the fate of the Falkland wolf: “Within a very few years…in all probability this fox will be classed with the dodo, as an animal which has perished from the face of the earth.”

The Discovery of Extinction

“The last dodo bird was seen on it’s Mauritius Island home in 1662.”

On The Path of the Dodo

In his most engrossing book, The Song of the Dodo, David Quammen writes: “Almost all of the historical examples of inherent tameness concern island endemics reacting to humans with astonishing passivity, in situations that would, in normal circumstances, be perceived as being fraught with imminent danger.”

The situations that island endemics find themselves in today are fraught with imminent danger. Theirs is now a much changed world from the one they evolved in. The birds of New Zealand have been isolated from the mainland and all of its predators for some 80 million years — plenty of time for forgetting fears, their genetic memories overhauled long ago. Humans, along with all of our pets and pests, have been present in New Zealand for about 750 years; not enough time to relearn those fears and change instincts evolved over millions of years of our absence.

The phenomenon of island tameness isn’t limited to flightless birds, but given that flightless birds so often evolve on islands free of land predators, they are especially vulnerable, as a consequence of this tameness, when land predators do arrive. Their combination of flightlessness (lack of escape options) and tameness (unwillingness to escape) make these island birds the prime targets for feral dogs and cats, for mongooses and rats.

The naturalist E.O. Wilson described New Caledonia's kagu as “distressingly tame. When approached by a human, it just walks away, occasionally stopping out of sight behind a tree trunk and waiting for the intruder to leave.” The French colonists of New Caledonia trapped the kagu for food and kept it as a pet. Today, the kagu is a fully protected species — it’s also an endangered one. It lays its egg, a single egg per clutch, in a simple, unconcealed nest on the ground. To the invasive pigs and rats, it might as well be breakfast on a platter. This pale bird, the so-called “ghost of the forest”, may soon be nothing more than a memory, a phantom.

The rail of Okinawa, endemic to the sparsely populated northern forest on its namesake island, is wary of humans. It knows to avoid dangers on the ground — having evolved alongside venomous vipers — so, it’s not so much naive or tame, as it is helpless against the invading cats, dogs, and mongooses. Even the cautious birds are endangered.

One species we haven’t met before, the Titicaca grebe, is endangered by the use of gill-nets. This little diving bird is a picky eater, feeding almost exclusively (95% of its diet) on one type of fish. The high altitude Lake Titicaca, on the border between Bolivia and Peru, hosts most of the ~1,600 remaining individuals. Endangered too are the yellow-eyed penguin and the remaining South Island takahē of New Zealand — which is often simply called the takahē today, as its North Island counterpart is already extinct.

The kagu’s flightless neighbour, the New Caledonia rail, has not been recorded since 1890. It may already have passed on to the other side. Its status as critically endangered is a thin line of hope that a few, likely less than 50, exist somewhere in the inaccessible montane forests of the Island.

The Inaccessible island rail lives on an island vulnerable to invasion by mammalian predators, the weka of New Zealand is vulnerable to predation by ferrets, cats, stoats and dogs, as are all five kiwis save one (which is only near threatened). The Galápagos flightless cormorant, meanwhile, is vulnerable to intensifying El Niño events driven by global warming.

On the very edge, endangered to a critical degree, are the kākāpō, persecuted by invasive predators, and the Guam rail, dispossessed of its home. The woodhen of Samoa known as the puna'e ("one that jumps up") may have leaped into the abyss already.

All of these species are walking the path of the dodo. Some are closer to the precipitous drop at the end than others. Many of them share a similar story: slaughter by the first humans to arrive on their island, followed by a “clean-up” by the invasive species we’d brought. Today, with our knowledge of ecology and extinction, we’re conscious of the damage we’re doing. When we self-reflect in this new light — by retelling the stories of flightless island birds, for instance — we begin to see ourselves as a destructive force towards nature. With that realisation, with ignorance no longer an excuse, a duty was bestowed upon us as a species.

The phrase, “With great power comes great responsibility”, trite as it is, is also true. Taking the world as our own, we’ve taken too the responsibility of its stewardship. Now we are tasked with being destroyers no longer, but becoming storytellers, scientists, conservationists, and caretakers. Not invaders and butchers, but protectors and preservers.

Imagine if we’d done things differently. Imagine going on safari in Madagascar to drive alongside enormous elephant birds, hearing their thunderous footfalls over the sound of the car’s engine. Imagine watching the wrens on Stephens Island scuttle and hop about like feathered rodents, or the original “penguins” gathering on the shorelines of the north Atlantic. Imagine sailing to Mauritius, to see that strange pigeon called the dodo, so friendly that it’ll waddle right up to you and say hello. Or imagine a future where seeing a kiwi, a kagu, or a kākāpō is a fanciful notion: a reminiscence on a lost past.

Richard Owen, discoverer of the moas, once said: “There is no greater anomaly in nature than a bird that cannot fly”. There is nothing more intriguing, more curious and awe-inspiring, than an anomaly — an oddity that makes you question the working of a world you thought you knew. Birds are defined by their flight and yet, the ones that were grounded have the richest, strangest stories to tell. On remote islands and ancient continents, they traded the sky for the soil, the clouds for forest shade. They now face a fast changing world, and they stand their ground. They have little choice.

The dodo’s name is not remembered for what it was in life. The dodo is remembered for the way that it died, and the tragic fact that it didn’t have to. The name of this dumpy, flightless, island bird is synonymous with extinction. It’s a symbol for all the flightless birds that perished before it and the many that died after. On its island of Mauritius, the dodo ambled off past the horizon, crossing to a place from which it cannot return. It left behind a trail of its ample footprints. Today, the New Caledonian kagu and the rail of Okinawa, the yellow-eyed penguin, the takahē, and the kākāpō are all following in its tracks. We must make for them a different path — a gentler one, leading not to extinction but safety — so they may keep waddling, their flightless wings tucked at their sides, far into the future.