♪♪ FULLER: I love Eastern curlews.

They're majestic.

They're stately.

They are powerful fliers.

They have a purpose.

LINSCOTT: The way a group of godwits looks when it takes to the air, the way they move together... move with the wind, give this embodied shape to the wind.

It is remarkable.

NARRATOR: Shorebirds are Earth's most global citizens, crossing from one end of the world to the other each year.

Yet below them, once familiar landscapes are giving way to development, drought, and rising seas.

Scientists are doing their best to map their epic journeys and the dangers they face as they follow the flights of these heroic birds.

LINSCOTT: I hope I might even catch up with her in a couple of weeks in a very different part of the world.

I wish her the best.

She's got a really long way to go.

♪♪ ♪♪ ♪♪ ♪♪ ♪♪ NARRATOR: On beaches and tidal mudflats all around the world, you'll see them in their thousands... ...shorebirds.

There are more than 200 species on the planet... ...feeding on the teeming life between the tidelines.

♪♪ ♪♪ Then, from one day to the next, they'll be gone on an extraordinary journey.

They're heading for their breeding grounds, up to 9,000 miles away, following ancestral flyways that wrap around the globe.

♪♪ Shorebirds, like this little Western sandpiper, are supreme endurance athletes.

They can fly for days and nights without landing... over cities... and deserts... and trackless oceans.

[ Thunder rumbling ] ♪♪ The bogs and tundra of the Arctic north.

Here, in the endless summer daylight, their chicks can feed on clouds of insects.

And in just a few weeks, they'll gain the weight to follow their parents south again.

♪♪ But the world beneath their wings is changing.

Shorebirds are among the most threatened birds on the planet.

♪♪ We're going to fly with three of these adventurers and share the elation and the anxiety of the men and women who track their migrations from three separate continents.

From the far south of South America... from the desert beaches of West Africa... and from Australia, in a place called Moreton Bay... FULLER: See that curlew up there flying?

JACKSON: Yeah!

NARRATOR: ...around 500 square miles of mudflats and sandbanks on Australia's east coast.

Every March, biologist Richard Fuller and his colleague Micha Jackson come here to watch the shorebirds fatten up for their journey north.

JACKSON: Couple of hundred birds there, I think.

NARRATOR Richard's special interest -- the largest migratory shorebird in the world -- the Far Eastern curlew.

FULLER: I love Eastern curlews.

They're majestic.

They're stately.

They are powerful fliers.

They have a purpose.

They're on a mission.

And although they're a brown bird, but the intricacy of their plumage and the patterning on them is just fascinating and beautiful.

NARRATOR: These magnificent birds fly more than 7,000 miles to their breeding grounds in north Asia and back again.

Over the course of its 20-year lifespan, an Eastern curlew travels the distance from the Earth to the Moon.

To make these prodigious flights, it must have fuel.

It needs to gain up to half its bodyweight in fat.

FULLER: A curlew's diet is comprised almost completely of crustaceans.

But they have a particular predilection for crabs.

They love crabs.

The curlew will probe into the ground, you know, often 20 centimeters down, grab a crab, and when it's successful, you'll see a curlew rip its bill out of the sediment, and it will be kind of manipulating the crab in its bill, sometimes tossing it up into the air, to get it in the right position, and then it goes in, in one gulp.

♪♪ NARRATOR: But the curlew's feeding grounds in Moreton Bay are shrinking.

Human encroachment has been going on for decades.

FULLER: There's every chance the Eastern curlew could be extinct within a few decades, and that's a terrifying thought.

♪♪ NARRATOR On the other side of the world, where the Sahara meets the Atlantic, huge flocks of hungry birds are jostling for a spot on the beach.

Busy and beak-down in the mud is our West African migrant -- the red knot.

GILS: They are so pretty!

NARRATOR These plucky little birds must double their weight in just a few weeks to power their 6,000-mile migration from Mauritania to Siberia, where they breed.

But red knots, too, are struggling.

GILS: We had a half a million red knots in the 1980s, and nowadays it's only 100,000.

So a loss of 80% in just 40 years.

♪♪ NARRATOR Dutch ecologist Jan van Gils has been studying the red knot for 30 years.

It's not just the red knot population that's declining.

The individual birds are shrinking, too.

GILS: The bill is getting shorter, the wing is getting shorter, the legs are getting shorter.

And you can say, "Well, who cares?

Smaller red knots?"

But what is important, if you come here as a smaller red knot in Mauritania, you have a big problem.

NARRATOR Jan and his colleagues from the University of Nouakchott take samples of the mud the bird feeds in.

GILS: Oh, yeah!

Oh!

Look at that.

[ Indistinct conversations ] So, this is the food that the red knots really, really like.

They ingest these bivalves whole, and they crush these bivalves in their stomach.

So, they have a very strong stomach.

They need good food.

They need the bivalves like this in order to make it to Northern Siberia.

But these birds are becoming smaller, so maybe all these bivalves are actually way too deep for the knots to reach.

NARRATOR So what are they eating instead?

GILS: The birds were roosting here this morning and we see signs of where they were roosting, we see tracks.

Here it is.

NARRATOR: The red knots' droppings provide the evidence.

GILS: A normal knot dropping is full of fragments of shellfish.

They have switched diets from their favorite bivalves to sea grass.

So, it is, in a way, a very sad story because this shows they are fueling up for Siberia on very poor-quality food.

♪♪ ♪♪ NARRATOR: In Chiloé Island, more than halfway down the long coast of Chile, our South American voyager dances on the wind.

LINSCOTT: The way a group of godwits looks when it takes to the air, the way they move together... move with the wind, give this embodied shape to the wind.

It is remarkable.

NARRATOR As long-distance athletes, Hudsonian godwits outperform almost every other shorebird.

Each year they fly 9,000 miles, from Chile to Alaska.

Most make just one or two refueling stops.

But their options are narrowing by the year.

Jennifer Linscott has joined an international network of scientists studying the migration of Hudsonian godwits.

LINSCOTT: We really don't know how many of those sites exist, and we don't know how they are changing over time.

We know that it's now a landscape that's been completely re-engineered for agriculture.

Godwits, like many other migratory shorebirds, are in decline.

And we think that that likely has a lot to do with what's happening during migration.

♪♪ NARRATOR The best way to get answers, the scientists all agree, is to attach GPS trackers to individual birds.

FULLER: Tracking goes to the heart of what conservation is.

You can describe the migration of the species by mapping it, by understanding the places it visits and crucially by understanding what threats they're facing along the flyway.

NARRATOR: But to attach a tracker on a bird, first, you have to catch it.

In Australia... ...in South America... and in West Africa, the nets are being set.

Jan is hoping to catch some red knots as they fly in to roost at night.

FULLER: Oh, this is great.

There's birds coming in to the catching area.

NARRATOR: But Richard and his team must wait for the curlews to gather in precisely the right spot.

FULLER: Eastern curlews are exceptionally difficult birds to catch.

They're very, very wary.

[ Sighs ] Come on, birds.

[ Wind whistling ] NARRATOR So must Jennifer in Chile.

[ Birds chirping ] LINSCOTT: This is the part we can't control.

We just have to wait, wait for the tide to come in, wait for the birds to move.

Wait for them to move to the right spot.

NARRATOR: In Australia, the moment arrives.

MAN: Everybody ready.

3, 2, 1, fire.

NARRATOR: But for Team Curlew, it's a miss.

♪♪ Will Team Godwit in Chile have better luck?

MAN: Tres, dos, uno.

¿Bolsa?

WOMAN: Bolsa.

Tal vez nos vemos un poco estresadas pero es para apurarnos y que las aves lleguen pronto.

MAN: Dos.

LINSCOTT: We got about, hmm, 30... 30 birds?

♪♪ ♪♪ NARRATOR: Jan and his team have also netted some red knots.

GILS: So... it seems we have 13 red knots.

So, that's really awesome.

♪♪ NARRATOR: In Mauritania... and in Chile, the satellite trackers are fitted.

♪♪ Despite months of trying, Richard and his team in Moreton Bay have failed to catch a single curlew.

♪♪ But there is one bird that they tagged back in 2017 that is still transmitting her location.

Her name is AAD.

She's a tough, successful traveler.

Richard has already tracked her twice, all the way to northern China and back here to Moreton Bay.

FULLER: I have a high sense of anticipation right now, an excited expectation.

But I'm also apprehensive, I think, and deeply concerned.

Will she find what she needs along her migration journey?

NARRATOR: As March draws the curtain on the southern summer, shorebirds start to stir with yearning for the north.

The scientists call it migratory restlessness.

♪♪ FULLER: You can see them getting excited; calling to each other, maybe taking short flights.

But then, eventually, a group will decide, "This is the moment."

NARRATOR: AAD spreads her wings.

FULLER: The first bird of the expedition in the air.

♪♪ NARRATOR: And in Chile, Jennifer and the team send the godwits on their way.

LINSCOTT: I hope, you know, I'll be in the same area where she's likely to stop along the way.

So there's a chance I might even catch up with her in a couple of weeks in a very different part of the world.

I just wish her the best.

She's got a really long way to go.

♪♪ ♪♪ NARRATOR: Thousands of miles of ocean lie between the shorebirds and their first hope of rest.

[ Thunder rumbling ] A migrating shorebird may not need to sleep.

It rests half its brain while the other half remains alert.

♪♪ It's thought that pigments in its eyes let it perceive the Earth's magnetic field and stay on course.

♪♪ At night, it can navigate by the stars.

♪♪ The godwits fly over 5,000 miles of open ocean.

They can't glide or swim, so must beat their wings continuously... ...crossing over Central American and the Gulf of Mexico.

After six days and nights without food, water, or rest, they reach the coast of Texas.

But the land below is in severe drought.

Tracking shows the birds are slowing down and making turns, searching perhaps for a refuge that isn't there.

And so, they press on.

Shorebirds burn fat for water as well as energy.

They can even digest parts of their own organs to stay hydrated.

And when their bodies are pushed to their utmost limit, they burn the very muscle that beats their wings.

At last, the godwits find a place to rest and feed in South Dakota.

LINSCOTT: South Dakota is filled with wetlands.

They're just divots in the landscape that were carved out by the movement of a glacier, and now they fill with snowmelt and rainwater every spring.

♪♪ As soon as summer rolls in and the temperatures climb, that water's going to evaporate, but for now, it's perfect.

It's exactly the kind of habitat that's gonna help them find the fuel that they need to keep migrating.

♪♪ NARRATOR: Every spring, Jennifer spends weeks scouring South Dakota, searching for the birds she tagged in Chile.

LINSCOTT: They have been migrating through this ephemeral landscape for thousands of years, so they're evolved for that.

But the rates at which things are changing are much faster than they've ever been.

We don't know if godwits can cope with this kind of variability now in the way that they've coped with it in the past.

♪♪ Looks like it's right back here.

Oh, yeah, that's a godwit.

KYLIE: Godwit?

Nice.

[ Birds chirping ] LINSCOTT: Looks like there's more than one.

KYLIE: Ooh.

Wait, is that a whole group of godwits, do you think?

LINSCOTT: Yeah, I think so.

KYLIE: Yeah?

Cool.

LINSCOTT: One, two, three.

You can feel, in a way, just watching them, how long of a journey it's been and how hungry they are.

It's incredible.

You know, we spend so much time out here looking and looking and looking.

And then to finally see one out in the middle of a -- of a cornfield, you know, a godwit that we might have seen in Chile not that long ago... ...it's a great feeling.

NARRATOR: In Western Europe, the red knots also need to refuel on their journey from West Africa to Siberia.

They flock to the vast tidal mudbanks that stretch along the Dutch and German coasts -- the Wadden Sea.

♪♪ ♪♪ GILS: This is the westernmost part of the Wadden Sea.

It's a major staging site for the birds on their way to the Arctic.

♪♪ They stay here for, like, two, three weeks in order to gain strength again to travel all the way to Siberia.

♪♪ Yes, we have, currently two birds that we caught in Mauritania just a few weeks ago.

When you see birds that you have tagged yourself and they arrive here in the Wadden Sea, ahh, that's so cool.

NARRATOR: But at this moment, Jan's elation turns to bitter disappointment.

GILS: We have a new problem, and it's the war in Ukraine.

And, ahh, we actually just heard from the Ministry that we cannot go to Siberia.

We are forced to ban our connections to Russian scientists right now from this moment.

And we just heard we cannot go.

It's a huge frustration.

♪♪ These birds are going to Russia.

They're crossing borders that we cannot cross this year and maybe next year, and God knows for how long.

♪♪ NARRATOR: From Moreton Bay, Richard watches his curlew's journey north.

FULLER: We've tracked AAD crossing over the Great Barrier Reef, Cape York, Papua New Guinea, still flying, over some of the highest mountains in Southeast Asia pushing north, over the Philippines, and she's touched down in Taiwan.

♪♪ NARRATOR: In Taiwan, birdwatching is a national passion.

WOMAN: [ Speaking native language ] FULLER: We immediately notified birdwatchers in Taiwan and the messages went out on social media, hundreds of people began searching for AAD.

ZHENG-FENG: [ Speaking native language ] NARRATOR: It is retired vet Li Zheng-Feng who scores the jackpot.

♪♪ WOMAN: [ Speaking native language ] ZHENG-FENG: [ Speaking native language ] FULLER: We can track birds with satellite transmitters, but when you see one on the ground, it's really the holy grail.

That's an on-ground confirmed observation of the bird that's just been a dot on a computer screen up until that point.

So, I'm super excited about that, and I'm excited to learn where she goes next.

♪♪ NARRATOR: Where AAD goes next is northern China, where she and her forebears have been nesting for generations.

But Richard fears that, year by year, her chosen breeding ground is less likely to bring her success.

FULLER: This region of China has undergone massive transformation.

Those wonderful grassy, forested, mosaic, wilderness and swamplands have been converted into rice paddies.

So, now some of our curlews, they're literally using the last remaining patches of that original habitat, and we see birds making forays out into the rice paddies, perhaps forlornly looking for food.

There won't be much for them.

Yet we see them still searching there.

The birds that traditionally breed in China, I think are now under immense threat and likely to be declining really fast.

NARRATOR: Many other shorebird species nest farther north, in the marsh and tundra of the Arctic.

As the snows melt and the air warms, the godwits arrive in the boglands of Alaska's Beluga River.

In their 5-week journey, they've demonstrated a mastery of navigation, as well as extraordinary stamina.

Astonishingly, many of them land within a hundred yards of where they were born.

Jennifer's colleague Nathan Senner leads the godwit research here in Alaska.

SENNER: All of Jenny's birds have made their way back to Alaska and are hopefully finding each other as quickly as they can and getting on with the breeding season because, you know, they've got only 10 weeks here.

What we've found is that they're remarkably able to, in some cases, lay their first egg within five days of getting here.

NARRATOR: The researchers need to know how many chicks will survive this year to fly south.

SENNER: So, we have to find the nest and then, once the eggs hatch, put tracking devices on the chicks and follow their movements and their survival over the course of their development here in the bog.

NARRATOR: On the other side of Alaska, Jan is on the trail of a different population of red knots.

The birds he tagged in Mauritania are on their way to Siberia without him.

So now, he and his team are searching for nests without any tracking devices to guide them.

♪♪ They play red-knot calls over a speaker, hoping to attract adult birds that they can follow to their nests.

[ Bird calls playing ] GILS: But knots in the Arctic are very, very cryptic.

They have feathers with the color of the lichens on the rocks here.

So there are thousands of rocks, and they all look like red knots.

NARRATOR: After two weeks of fruitless hunting, Jan's team tries out a new approach -- a drone with an infrared camera they hope will detect the warm-blooded red knots nesting in the frozen tundra.

GILS: Oh, my God.

NARRATOR: And at last, they spot one.

GILS: Ah, I feel excited.

I feel really excited.

It heats me up in the cold.

♪♪ NARRATOR: Back in Beluga, Nathan knows the godwits' breeding area intimately, but it's no less of a wonder each time he finds a nest.

♪♪ ♪♪ [ Bird chirping ] SENNER: You can see the bill of the chick starting to poke out.

This bird is gonna hatch tomorrow morning.

NARRATOR: Nathan marks the location of the nest so his team can return tomorrow.

SENNER: If we're not there when the chick actually hatches, we're never likely to see them because they are moving away from the nest within a couple of hours of hatching, and it's incredibly difficult to find them in the bog after they've actually left the nest.

NARRATOR: And scientists aren't the only ones searching for nests.

♪♪ Hidden cameras reveal a variety of predators.

♪♪ ♪♪ ♪♪ SENNER: Uh-oh.

That's not good.

I found an egg with some, like, an open egg with some blood in it that looks to me more like it was eaten than, like, it hatched.

That another one?

Alright, well, let's leave these parents to their anguish.

Yeah, not good.

You're rooting for the birds.

That's why we're here.

I mean, it is part of the whole process, but as -- Yeah, when you've watched a nest for a long time, it's not a good ending.

♪♪ NARRATOR: It's June in the Arctic.

The warm air buzzes with insects.

Summer is here and from those hollows in the scrub emerges... life.

♪♪ ♪♪ ♪♪ ♪♪ ♪♪ Nathan and his team have returned to one of their godwit nests, searching for newly hatched chicks.

♪♪ ♪♪ [ Birds chirping ] SENNER: Can I hand you the first one?

WOMAN: Gosh, they are really cute, kinda goofy.

SENNER: There we go, 25.

WOMAN #2: Look at those floppy legs.

SENNER: When they come out of the egg, some parts of them are more developed than others and so that they can run across the bog as quickly as they're out of the egg, they've got really developed legs, whereas their bill, you can see, is nothing like the adult bill yet.

It's quite short because they just preen insects off the vegetation.

They're not probing into anything.

And then the wings, of course, they're not anywhere near being ready to fly.

So those are the least developed of all.

NARRATOR: And yet, those wings are going to carry the young bird 9,000 miles.

SENNER: The fact that this chick in two months is gonna go from 22 grams to over 300 grams, and it's gonna fly all the way to southern South America, that's a phenomenal -- phenomenal growth rate.

♪♪ ♪♪ NARRATOR: In the tundra to the north, Jan's infrared drone reveals that one of his red knots' clutches has hatched.

♪♪ ♪♪ WOMAN: Oh!

Another chick.

MAN: Wow, nice!

GILS: Nice!

MAN: Tarsus is 28.3.

NARRATOR: For the red knot chicks, the first few weeks of life are especially perilous.

Only about a quarter of them will live long enough to make the journey south.

GILS: He's going.

Here he is.

There we go!

Do your best, man!

NARRATOR: But Jan's main concern is that even those that survive will be smaller than they ought to be.

GILS: Three weeks after the snow has melted, there's the insect peak on which the chicks can feed.

With the rapid warming of the Arctic, the summer has already started.

These insects are emerging earlier from the soil.

But what the birds do not do is adjust their travel schedule.

So nowadays, these birds in the Arctic arrive too late for the chicks to make use of this burst of insects.

And so, they don't have good growing opportunities and that makes these birds smaller than they actually should be.

NARRATOR: For the godwit chicks, too, it's a race against time.

SENNER: Once the chicks hatch, both parents take care of the chicks for at least the first three weeks or so that they're around.

But then at some point, the female will actually take off and it'll just be left up to the male, and the male will see the chicks through to fledging before he too takes off.

And then the chicks are left all alone.

♪♪ [ Wind whistling ] NARRATOR: As the days shorten in the Arctic, the young shorebirds embark on their first, and most dangerous, migration.

Their maiden flight is a miracle and a mystery.

They're going home... a home they've never seen but somehow, always known.

SENNER: The first southward migration, to me, just seems epically difficult.

You're making these incredible flights, having never done it before, and that alone, if you didn't survive that, it wouldn't surprise me.

And then when you throw on top of it the threats that the birds are facing, at each and every point during the course of their migration -- hurricanes... droughts in the midcontinent... hunting... [ Gunshot ] ♪♪ NARRATOR: Shorebirds are hunted all along their flyways.

In France alone, thousands of red knots are killed each year.

GILS: These mainly juveniles, because they are a bit more naive than adults, they're shot on their migration.

FULLER: Curlews are shot at just as they leave breeding grounds and are subject to hunting pressure all the way through their southbound migration.

♪♪ ♪♪ NARRATOR: Curlews that dodge the hunters in Northern China face other perils as they head southward to refueling grounds in the Yellow Sea.

Among them is AAD.

♪♪ On the outskirts of Shanghai, in Rudong County, the birds scour the shoreline for somewhere to feed.

FULLER: Thousands of kilometers of seawall have replaced the natural coastline along much of eastern China, taking out more than two-thirds of the habitat that Eastern curlews use when they're on migration.

NARRATOR: Over 2 million acres of shorebird habitat have been lost to development in the Yellow Sea.

♪♪ The hope of finding safe harbor here gets slimmer every year.

But AAD gets lucky.

FULLER: AAD found a patch of remaining habitat at Rudong, which is great-quality habitat, that thousands of shorebirds congregate on during migration.

NARRATOR: This intertidal flat is an oasis of mud amidst the concrete.

Jing Li is the co-founder of a conservation group that campaigns to protect this vital shorebird refuge.

She's seen firsthand how coastal development and local industries have put pressure on shorebirds like the curlew.

Few shorebirds actually eat the clams.

But they're competing for space on the mudflat.

Grassroots activism and international collaboration are turning the tide in the Yellow Sea.

Recently, development on the Rudong County mudflats has been stopped.

♪♪ NARRATOR: On the Americas flyway, young southbound godwits are arriving in the prairie potholes of the Dakotas.

♪♪ LINSCOTT: The wetlands out here we know are less numerous today than they used to be.

We don't really know how many of those wetlands we've lost, but, by some estimates, maybe as many as 90%.

♪♪ We don't have to make a choice between farming and shorebirds.

There are ways that these two things can co-exist.

These wetlands don't need to be there permanently.

They just need to be there for the couple of weeks a year that birds really need them.

NARRATOR: The godwits continue south, stopping in Panama... ♪♪ ...where thousands of shorebirds congregate... ♪♪ ...a vision of grace amidst the degradation of their flyway.

♪♪ ♪♪ ♪♪ ♪♪ On the far side of the Pacific, AAD is winging her way home over the Philippines... ...when a typhoon strikes.

[ Thunder rumbling ] [ Wind howling ] The massive storm, with winds topping 80 miles an hour... [ Lightning crashes ] ...rips across the flyway.

AAD is blown into a corner of Southeast Asia she has never seen before.

Richard can only watch from Moreton Bay, hoping she finds her way home.

FULLER: She ended up on a track going southwest and managed to find a large river mouth in Borneo that had suitable habitat... ♪♪ ...and spent time actually kind of stopping and regrouping and refueling there.

♪♪ And then really in an incredible turn of events, she took off in exactly the right orientation to bring her all the way back to Australia, entering Australia just over Darwin and actually stopping in the wetlands in the Gulf of Carpentaria for a few days.

♪♪ ♪♪ NARRATOR: Gangalidda-Garawa people are custodians of an area in northern Australia the size of France.

They've watched over it for many thousands of years.

MAN: [ Speaks indistinctly ] YANNER: Right on the edge of the water.

A flyway, you know, is like a string of pearls, interconnected.

And you're only as strong as your weakest link.

And it's only from standing back you see the whole thing.

And it's the same here.

If each person along the flyway is sharing information, you see the bigger picture, and only then do we understand, see the full painting, the beauty of it.

NARRATOR: Thanks to its traditional owners, this vast wetland is now a protected site.

YANNER: There's one bird in particular that impressed us -- the Far Eastern curlew, comes all the way from China and Siberia and places and then he travels for days and nights nonstop.

Pound for pound, he's a little world champion and we wanna dedicate a bit of our country to looking after him.

[ Birds chirping ] ♪♪ ♪♪ NARRATOR: After two more days of flying, AAD is home... landing in Moreton Bay, just yards from where she left five months earlier.

She and her fellow curlews have logged over 13,000 miles.

♪♪ ♪♪ FULLER: One of the great causes for hope is the sheer number of good people around this flyway arguing passionately for the conservation of these birds.

And these arguments are gaining traction and causing change.

♪♪ ♪♪ GILS: Oh, my God, do you guys see it?

Oh, it's a transmitter bird!

It's back from Siberia.

It's a female that spent three and a half weeks in Siberia, just enough time to show us that she was successfully reproducing.

Oh, this is so great!

Yah!

NARRATOR: All across the southern hemisphere, shorebirds are coming home.

♪♪ GILS: We can learn from the birds because they tell a global story.

They tell a story that the world has troubles.

And we should actually listen to them.

♪♪ LINSCOTT: Shorebirds are incredibly well evolved for these flights.

But the world that they're doing this in is changing very quickly.

If we don't change the way we see ourselves and the land that we live in, we'll lose them.

In a sense, we're kind of a flock, we're all part of the same thing.

♪♪ ♪♪ ♪♪ ♪♪ ♪♪ To learn more about what you've seen on this "Nature" program, visit PBS.org.

♪♪ ♪♪