Drew Rooke
As part of the Ultramarine project we are republishing some paid content for free. This long read was originally published in issue 99 of Cosmos print magazine, in July 2023. You can read more amazing long reads if you subscribe now.
Compact and easily overlooked, bar-tailed godwits make the longest known nonstop flight of any animal on Earth. Drew Rooke reports on the research that led to the amazing feat’s discovery – and that is changing much of our understanding of the science of these epic crossings.
22 December 2022
The large tinnie cruises the calm waters, charting a course from the boarding jetty, past moored yachts and waterfront mansions that crowd the shoreline of Georges River at Taren Point, on Dharawal country in suburban southern Sydney. A veil of cloud softens the sunlight and a gentle sea breeze keeps this late-December morning’s heat in check.
I’m seated at the bow of the boat, which gathers speed after it passes beneath Captain Cook Bridge, where the river widens into Kamay/Botany Bay. In the distance I can see Sydney’s CBD skyline and the towering red-and-yellow cranes of Port Botany that look like giant steel giraffes.
From the stern, captain and coxswain Robert Dixon looks across the water through warm brown eyes shielded by sunglasses. The wind ruffles his long-sleeved polo shirt and threatens to rip off the Akubra pulled down over his short black hair.
Dixon knows this area well. An Environmental Officer from Georges Riverkeeper, a catchment management group that coordinates environmental projects on behalf of eight local councils, he’s been in charge of the group’s long-running monthly shorebird and waterbird survey for the past three years. This is why he’s out today with three volunteers. It’s currently high tide, ideal for our purposes. As Dixon explains in his deep, gentle voice: “That’s when the birds congregate.”
Travelling around the bay over the next hour or so, a pencil dangling from his mouth, Dixon carefully manoeuvres the boat around submerged hazards and reaches over the side to collect rubbish that we pass in the water. At each survey site, he kills the outboard motor and keeps enough distance from the shoreline to avoid disturbance. He records the 18 species of birds we see – pied cormorants, little terns, red knots – on a count sheet secured in a clipboard on his lap. At one site on the bay’s southern shore, he’s surprised to find only a handful of pied oystercatchers perched on a row of wooden posts protruding from the water. “There were a lot more shorebirds using this area this time last year.”
The site with the most birds is a roughly 350-metre-long squiggle of sand called Towra Spit Island. Of Botany Bay’s scant shorebird habitat that’s endured since Captain James Cook moored Endeavour here more than 250 years ago, this is the most important: unlike much of the other surviving habitat, it’s predator-free and largely undisturbed by human activity. But it is slowly disappearing, prey to changes in wave energy and sediment deposition caused by major development projects throughout the bay.
Hundreds of birds roost on the island; most are annual migrants only recently arrived from very far away – further, in fact, than most of the planes coming in to land at the international airport just north, across the bay.
The birds that have made the most extreme journey to get here are the 200 bar-tailed godwits (Limosa lapponica) – more specifically, baueri, one of six subspecies – that are packed together on the island’s northern edge. These champions of long-distance migration have been here for about two months. Today, they’re waiting for the tide to drop so they can feed on the crabs, yabbies and worms that live in the few sand and mud flats that remain in the bay. Individuals with streaked greyish-brown non-breeding plumage are camouflaged well against the sand; a long, graceful, upturned bill – pinkish at the base, with a black tip – protrudes from a small, white head.
The flock is quiet and calm. Apart from a few birds squabbling for space, most are standing still on the water’s edge – many on only one of their spindly, dark grey legs – unbothered by the small waves washing over the sand. Some have their heads twisted backwards, bills buried in between folded wings. Others scratch under their neck with clawed toes and ruffle their feathers as if waking from a nap. They are scrawny, their 40-centimetre-long bodies carrying very little fat.
But although these birds might not look like ultra-marathoners – at least not at this time of year – one of their kin has just broken the record for the longest nonstop flight of any animal on Earth, clocking more than 13,000km on a globe-spanning journey from the far north to the far south.
The decades-long research that led to this discovery calls into question much of our historical understanding of migratory birds – and animal biology more broadly. It demonstrates that these small but sturdy creatures aren’t just like programmed machines that possess innate powers of endurance and navigation. The truth of their annual epic is far more complicated, and far more fascinating.
Avian migrators are birds of no nation – even the most strictly controlled ones. They live a life of joined dots, constant movement and journeys spanning entire oceans and continents. Their urge to move is so irresistible that in the lead-up to their scheduled departure (and when they are held in captivity) they experience Zugunruhe – German for migration anxiety. They become restless; they start to flutter their wings, hop in place and call loudly. Many suffer sleeplessness.
For a long time, the coming and going of particular birds baffled humans and hatched some farcical theories about their seasonal movements and extended absences. Aristotle, for example, believed that migratory birds didn’t actually leave a place but transformed into different species, while Swedish archbishop Olaus Magnus theorised in 1555 that swallows hibernate in the mud at the bottom of lakes and streams. A century later, English minister Charles Morton suggested some birds migrate to the Moon for the winter.
Instead of hypothesising about destinations, early Polynesians decided to follow the huge flocks of bar-tailed godwits they saw flying southward over the Pacific Ocean each year. A source of wonder, the sight of these birds was believed to point to land beyond the horizon, for it was clear from their shape and size that they weren’t of the sea. In fact the Māori, who know the bar-tailed godwit as kuaka, credit it for inspiring and guiding their ancestors on their seafaring voyage from northern Polynesia to their new home of Aotearoa, later New Zealand, roughly a thousand years ago.
Revered in Māori culture, the kuaka is also now loved by many others in Aotearoa New Zealand, the birds’ principal stopover site in the Southern Hemisphere. When the first of several thousand bar-tailed godwits arrive there every September, they’re welcomed by the ringing of cathedral bells in the South Island town of Whakatū/Nelson. When the birds are due to leave from late February, hundreds of people attend a ceremony at the Avon-Heathcote estuary in Ōtautahi/Christchurch to say goodbye to the 1,500 to 2,000 godwits that visit that particular site every year.
“We have a little barbecue and then take people in groups to the edge of the estuary where we have telescopes set up, so everyone can get a really good look at the birds,” says Tanya Jenkins, manager of the Avon-Heathcote Estuary Ihutai Trust, who helped establish the ceremony in 1999. “This year, the youngest person who came was in a pram and the oldest was 93 years old.”
Their urge to move is so irresistible that in the lead-up to their scheduled departure they experience Zugunruhe – migration anxiety. They become restless; they start to flutter their wings, hop in place and call loudly.
The ceremony gets bigger every year, and it can occasionally get quite emotional. “I’ve actually seen people in tears because they are so amazed by the movement of these birds,” says Jenkins.
It’s largely because of the work of people like Robert Gill that others have recently learnt to love this little bird. For the past 40 years Gill has worked as a wildlife biologist at the US Geological Survey’s (USGS) Alaska Science Centre. Over a video call from his home – which is decorated with framed photographs and wood carvings of shorebirds – he tells me that he first encountered bar-tailed godwits in the Arctic summer of 1976, when he took a job on the Alaska Peninsula assessing shorebirds to better understand the impact of the expanding gas and oil developments along the US Pacific coast.
“I’d never seen a bar-tailed godwit in my life,” he says. “And suddenly, I’m in a setting where there are thousands of them.”
As Gill, fascinated, observed the birds over the course of their breeding season, he noticed strange changes in their appearance and behaviour. They gained huge amounts of fat, for example, and their bright, cinnamon plumage faded to a dull light grey. They also started to become much more active, flying together in large flocks.
Then, one clear morning after several days of heavy storms, Gill woke up to find that the birds had all disappeared. “I scratched my head thinking, ‘Where did they go?’”
Gill went hunting data. He trawled through references in serial publications; field notes from earlier scientific expeditions and surveys; ornithological collections from museums in places like Australia and Hawaii; and unpublished databases maintained by ornithologists. He discovered the bar-tailed godwits he had seen breeding in Alaska flew annually to Aotearoa New Zealand and eastern Australia. From there they travelled to the intertidal mudflats of the Yellow Sea region of East Asia, and then back to Alaska.
But this raised another, even more intriguing question: what path did these birds fly to reach these distant places?
Gill’s initial hypothesis was that they island-hopped from Alaska across the Pacific or perhaps followed Asia’s coast to travel the more than 11,000km to their antipodean destination – paths with plenty of refuelling sites and navigational landmarks. But research that he and many others around the world conducted over the following decades proved that the birds took a different route, one that was seemingly incomprehensible.
“Everyone needs a passion in their life,” says Adrian Riegen, who formed the New Zealand Wader Study Group in 1994 and continues to survey shorebirds after a hard day’s work building houses. “And shorebirds are my passion.”
Riegen first became interested in birds in the late 1960s as a twitcher, “racing after the rarities”, but quickly realised “there’s more to birdwatching than just ticking off new species”. Now, he’s one of what he calls the “unpaid professionals”: citizen scientists who have worked over decades and countries to survey and band bar-tailed godwits along their entire migratory pathway.
“If you spend 50 years studying these birds, you build up a huge amount of knowledge about them, even though it might not be published.”
The knowledge that people like Riegen gathered in the late 20th century proved invaluable, particularly in building a better understanding of the precise timing of the bar-tailed godwit migration. Largely based on this knowledge, paid professionals like Gill started to investigate an idea first proposed by ornithologist Dick Sibson in the mid-1980s: that bar-tailed godwits fly nonstop from Alaska to their destinations, directly across the Pacific Ocean.
This idea gained substantial weight following a fortunate and incredible discovery about the biology of these birds.
“Based on knowledge gathered by citizen scientists, paid professionals started to investigate the idea that bar-tailed godwits flew nonstop from Alaska to their destinations.”
Shortly before midnight on 19 October 1987, a large flock of juvenile bar-tailed godwits crashed into a radar dome on a military base near Cold Bay, on the Alaska Peninsula. The birds had only just set out on their epic flight to the Southern Hemisphere. Two died on impact; seven were badly injured and subsequently euthanised.
Luckily, one of Gill’s colleagues worked at the military base and had the wherewithal to not only collect and measure the birds but preserve them in a freezer. Subsequent compositional analysis revealed that they had an average total body mass of 367 grams – 55% of which was fat. This didn’t surprise Gill; from field observations, he knew the birds were gorged with fat prior to departing Alaska. What did surprise him was the abnormally small size of the birds’ stomachs, gizzards and livers – and the abnormally large size of their wing muscles and hearts, compared to those of non-migrating bar-tailed godwits.
Unsure of what to make of these results, Gill shared them with a colleague.
Although it was nearly 30 years ago, Theunis Piersma, professor in Global Flyway Ecology at the Conservation Ecology Group at the University of Groningen, in the Netherlands, still remembers the moment that Gill handed him a yellow manila folder with the results of the analysis.
“It was like boom,” Piersma tells me on a video call from his second office at the NIOZ Royal Netherlands Institute for Sea Research, where he can watch migratory birds flying over the Wadden Sea. “It opened my mind.”
The research showed that migratory shorebirds aren’t, as US biologist Eugene Odum had previously argued, like planes that have a constant structure but variable fuel load. Rather, not only are the birds able to gain huge amounts of fat to use for fuel, but their bodies undergo a significant restructure to ensure this fuel is used most efficiently.
As Piersma and Gill wrote in their 1998 paper “Guts Don’t Fly”: “The small size of the nutritional organs of extremely fat bar-tailed godwits…is consistent with the suggestion that it is unprofitable and energetically too expensive to carry a digestive machinery over thousands of kilometres of open ocean.”
Piersma, Gill and colleagues gathered more evidence to support the idea that bar-tailed godwits fly nonstop across the Pacific by examining large-scale weather maps; building flight simulation models; and trawling through more historical observations of the birds across the world. In 2005 they published this evidence in a landmark paper titled “Crossing the ultimate ecological barrier”. It prompted disbelief – and some scepticism – within the scientific community. But new technology soon provided indisputable proof.
On 17 March 2007, an adult female known as E7, who was carrying a surgically implanted 26-gram battery-powered satellite transmitter roughly the size of a 20-cent coin, departed the Firth of Thames in Aotearoa New Zealand. After flying continuously for seven days and nights across 10,200km, she arrived at the Yellow Sea. Five weeks later, she took to the skies again, flying 7,200km over five days to her breeding grounds on the Yukon–Kuskokwim Delta in Alaska. Then, in the early hours of 29 August, she departed Alaska and spent the next eight days travelling nonstop over the Pacific Ocean to a bay south-east of Tāmaki Makaurau/Auckland.
The last leg of this 29,000-km migration was 11,680km. At the time, this was the longest known continuous flight of any bird – and although it didn’t surprise godwit researchers, it did catapult E7 to global fame.
“In 2012, we went to China to do an exchange,” explains Lee Tibbitts, a long-time wildlife biologist at the USGS’s Alaska Science Centre and frequent colleague of Gill’s, including for the tracking of E7. “And folks there knew about E7; there were posters all around town about her.”
Tracking these birds isn’t easy research to conduct. Indeed, one of the most remarkable discoveries of recent times was the result of hours of arduous field work and a good dose of “sheer dumb luck”, according to Daniel Ruthrauff, also at the Alaska Science Centre.
In July 2022, he and Jesse Conklin from the University of Groningen’s Conservation Ecology Group travelled to Nome, a small town on the Seward Peninsula in western Alaska. Neither of the experienced wildlife biologists expected to succeed in their unprecedented mission: to find bar-tailed godwit chicks – which leave their mossy nests and begin roaming only days after hatching – and fit them with satellite transmitters to try to learn more about juvenile movements.
After several fruitless days hiking through the tundra, being feasted on by mosquitoes, these “two 54-year-olds with creaky knees” – in Ruthrauff’s words – found three tiny balls of fluffy feathers in the shrub. While the chicks’ parents flew around screeching and swooping them, Ruthrauff and Conklin caught and glued onto each one a radio transmitter weighing half a gram and measuring 15 millimetres in length, minus the antenna.
But even with the radio signal, the biologists struggled to follow the brood over the next couple of days. “We thought families would stay within a few hundred metres – maybe a kilometre – within this period. But we were hiking up to a kilometre in just one day,” Conklin says.
On 15 July, Ruthrauff and Conklin managed to relocate and recapture the rapidly growing chicks. While the parents mobbed them once more, they replaced the radio transmitters with slightly larger solar-powered satellite ones in loose-fitting harnesses to allow for growth. Then they went home, hoping that the trio of chicks – and the transmitters – would survive.
Not long afterwards, the signal from two of the chicks stopped moving – a sign that they’d died, or that the transmitters had fallen off or stopped working. All attention was on the remaining bird.
This roughly three-month-old male – dubbed B6 – didn’t seem like a migration candidate. For one thing, after leaving the tundra, B6 travelled to a site around 100km north of the regular staging ground for bar-tailed godwits on the Yukon–Kuskokwim Delta. For another, he was still in this place in mid-October, long after the majority of his kin had left the soon-to-be-frozen Arctic. But finally, on 12 October, just five months after he’d hatched, B6 took off, heading out over the Aleutian Islands and beyond for the first time.
Eleven days after his departure, he touched down near Ansons Bay, a small holiday village on Tasmania’s north-east coast. Over the roughly 250 hours B6 had been continuously flapping his wings in the air, he’d covered a total distance of 13,560km – close to the maximum range of an Airbus A380. And, given most adult bar-tailed godwits migrate separately to juveniles, it’s likely that he completed his maiden migration without the guidance or supervision of his parents or any other elders.
Although Ruthrauff celebrated B6’s accomplishment, which made news headlines around the world, he couldn’t help but laugh about how it was framed. “If calling it a new world record makes people pay attention, that’s cool – but these birds are just going about their business. They don’t care about records.”
24 January 2023
The boat glides across glassy water that reflects the blue sky and wisps of cirrus cloud. Robert Dixon drives while Elisabeth Dark – a Birdlife Southern NSW committee member, and the only other person on today’s survey – and I hold onto our hats. The air is muggy, the summer Sun hot and bright even though it rose less than two hours ago. Botany Bay is crowded with fisherman and recreational boaters enjoying the last of their holidays.
Dixon cuts the motor when we arrive at Towra Spit Island. Roughly the same number of bar-tailed godwits are roosting on the sand as during my visit a month ago, with a few eastern curlews and masked lapwings mixed in amongst them. But there are no little terns today. “They’re usually here and quite active now, darting in and out,” Dixon says.
Some of the godwits are restless, stretching wings and calling softly – a high-pitched, sharp kwee-kee-kwee-kee – as small waves wash over the island. Many scuttle away from the encroaching tide but others don’t pay it much heed, letting the water ripple halfway up their long legs. They haven’t yet changed into their deep orange breeding plumage, and although most are plumper than last month, they still need to build up their fat reserves before they’re able to fly without stopping to the Yellow Sea.
Habitat loss through rapid industrialisation is one of the main challenges confronting migratory shorebirds. In 2012 (opposite), bar-tailed godwits staging en route back to Arctic nesting grounds roosted on an active dredge-dumping site near Donggang, in Liaoning Province, China. Rich mudflats such as these on the Yellow Sea shoreline are critical to many species’ migration success, but in recent decades they’ve shrunk by millions of hectares. This dredging project was designed to improve access to a fishing port; the infilled area – excised from the Yalu Jiang National Nature Reserve – was re-purposed as industrial land. Credit: David S. Melville.
“Shorebirds are an acquired taste,” Dark says, as Dixon navigates back to the jetty. “They might not look very interesting, but once you know their story you can’t help but feel inspired by them, feel empathy for them.”
It’s easy to overlook bar-tailed godwits and other avian wanderers, because their presence in one location is fleeting. And because they aren’t dependent on just one place, it can be easy to think that they’ll always have somewhere else to go. But their continued existence is fragile, reliant on a handful of irreplaceable locations. Remove or disturb a single link in the chain of a species’ migratory pathway, and the consequences can be catastrophic.
For decades, migratory shorebird numbers have been rapidly declining globally. This has been particularly acute among the 50 million birds that, like the bar-tailed godwit, traverse the East Asian-Australasian Flyway (EAAF), which covers an area of 85 million sq. km, from the Russian Far East and Alaska, through East and South-east Asia, to Australia and New Zealand. It’s the most threatened of the nine major flyways – essentially huge migratory bird highways – that crisscross the globe.
A 2016 study used 20 years of continent-wide citizen science data to assess population trends of 10 shorebird taxa that use the EAAF. It found that numbers of two bar-tailed godwit subspecies – baueri and menzbieri – and five other taxa had declined at rates of up to 8% per year.
“Remove or disturb a single link in the chain of a species’ migratory pathway, and the consequences can be catastrophic.”
The primary driver of this steep decline is habitat loss and degradation, especially at the flyway’s beating heart: the rich mudflats of the Yellow Sea. For at least 240 bird species, these serve as a one-of-a-kind service station where they can refuel before continuing their migration. But over the last few decades, millions of hectares have been replaced with urban and agricultural land reclamations as population and industry have grown.
One 2014 study found that over a 4,000km strip of coastline between China and South Korea, 28% of tidal flats that existed in the 1980s had disappeared by the late 2000s, and up to two-thirds had been lost over the past five decades.
When Theunis Piersma first visited the area a decade ago, the Yellow Sea situation was so severe that his first thought was that he and his colleagues would soon be describing the extinction of a great number of shorebird species.
Thankfully, this future appears to have been avoided – for now. In January 2018, for example, the Chinese government announced a moratorium on all “commercial-related” coastal wetland reclamation along its coastline, and the following year, a large portion of China’s Yellow Sea coastal wetlands secured an even stronger layer of protection in the form of World Heritage status.
Other countries in the region are now following suit, substituting development policies with ones of protection. This change is driven by the tireless international advocacy of the very same group of people who revealed so many of the bar-tailed godwits’ secrets. That advocacy has taken them to some surprising places.
In 2009, for example, Adrian Riegen was part of a small team that travelled to North Korea to set up a migratory shorebird monitoring project. He’s been back several times since, each time building up more trust and rapport with the authorities. “We hope to survey the entire coast of North Korea on the Yellow Sea,” he says. “I often say under my breath, ‘The things we do for shorebirds.’”
But the future for bar-tailed godwits and other migratory shorebirds remains precarious. Throughout their entire migratory pathway, many places they depend on and are deeply attached to continue to be destroyed by development – and even those that are protected are now at risk from one of the major impacts of climate change.
“In the case of the Yellow Sea, you have mudflats that go right up to dykes and garages and things like that,” Robert Gill explains. “There’s not the luxury of habitat being created further inland if sea level rises. And it’s the same problem on the Yukon delta and elsewhere.”
It’s a fundamental contradiction: as Riegen says, “One of the most important things to remember is how vulnerable they are – despite how robust they are.”
Migration: innate instinct, or something more? Since unearthing that bar-tailed godwits restructure their entire bodies for their migration, researchers have discovered some of the birds’ other remarkable talents. Recent satellite tracking has shown that some birds select favourable winds to depart all of the sites along their migratory route, and the days they select ensure the greatest possible overall wind assistance throughout the entirety of their flights. The implication of this is as profound as the birds’ migration is astonishing: that they are able to detect and respond to wind and weather conditions in distant atmospheric regions. They’re “pretty decent meteorologists”, says Gill.
But so many mysteries remain about their epic migration.
The implication of this is as profound as the birds’ migration is astonishing: they are able to detect and respond to wind and weather conditions in distant atmospheric regions.
How, for example, are they able to perceive distant weather conditions? Why do they develop such strong site fidelity, returning not just to the same general area but to the very same bay, beach or portion of tundra, year after year to feed and breed? Why do adults and juveniles migrate in two separate waves?
How are they able to orientate themselves so accurately that when, for instance, they fly from the Yellow Sea to Alaska, they will track well south of the direct route for about 4,500 kilometres to benefit from favourable winds, before abruptly turning north-east towards their destination while over the middle of the ocean? How can godwits navigate so precisely that, as Piersma says, “it’s like they have a GPS on board”? Do they use the stars and Sun, in conjunction with wave patterns and the Earth’s magnetic field, or do they possess tools beyond our comprehension?
“[D]espite decades of research, we remain unable to satisfactorily explain these feats of endurance,” Piersma and his colleagues write in a 2022 literature review of shorebird migration.
This statement implicitly rejects an explanation for bird migration that has satisfied some scientists in the past – but is, according to Piersma, “plain stupid”. The idea is a product of a kind of scientific thinking that “ignores all of this consciousness around us” and considers Homo sapiens to be in possession of uniquely complex ways of being, behaving and thinking.
“Migratory birds, like most animals, have historically been looked at like machines that are all just genetically programmed to do all of these fantastic things,” Piersma says. “But that, for sure, is a big mistake.”
While he accepts that genes, by their encoding of proteins, probably influence avian behaviour – much as they do human behaviour – there is no doubt in his mind that bar-tailed godwits are, like us, “learning entities. And we’re only at the start of understanding what that really means.”
Jesse Conklin echoes this sentiment. Study and observation over many decades has made him realise that these birds are not “like robots” controlled by an identical genetic blueprint. They are “sentient creatures” that possess individual personalities, learn from trial-and-error, and are capable not only of extreme feats of flying but also extreme feats of communication, memory and intelligence.
“I don’t know whether this all gets me closer to understanding bird migration,” Conklin says. “But it’s certainly fascinating. We just find more and more possibilities the more we look. We’re not finding the unified theory of migration” – because, he adds after a brief pause, “that doesn’t really exist”.
21 February 2023
It’s a scorching, windless morning and Dixon is back out on the boat in Botany Bay – this time with the help of Deb Andrews, a retired National Parks and Wildlife Service natural heritage officer, and Dr Michael Fleming, a research ecologist.
We find a flock of 24 bar-tailed godwits roosting on a small beach near the Taren Point Shorebird reserve, and a solo male perched on a post in the middle of the water. The feathers on his breast are a deep cinnamon colour and he is so fat that he looks like a mini soccer ball about to pop.
As we approach Towra Spit Island, a large flock of birds takes flight, heading north-east. They rapidly gain height, spreading out and coming together as if they are a single, breathing organism. Silhouetted against the sky, the trace of their flight resembles calligraphy on pastel blue paper. They wheel around to the west; in a couple of seconds they’re directly above the boat. It’s then we see that they are bar-tailed godwits.
For a moment, the 50 or so birds are so close that we can hear the sound of their sharp, powerful wings above their calls to each other. Then they wheel back towards the island in a tight formation and land on the sand. But not a second later they take off again – and for the next 30 minutes, we watch as they perform this same dance four more times, perhaps a sign of a disturbance or predator we cannot detect, or perhaps a sign of their Zugunruhe. When the flock finally re-joins the bar-tailed godwits on the island, we’re able to get a better look at them through our binoculars and count roughly 200 birds in total. All are plump with fat for their upcoming flight to the Yellow Sea, and the males are in near-full breeding plumage.
“I don’t think it’s long now until they fly back north to breed,” Andrews says. “They’re already dressed for the party.”