Original subtitles

High flying,

sharp-eyed,

and fierce.

From mountain tops

to river valleys,

eagles rule the skies.

Tenacious and strong.

They are the ultimate bird of prey.

Now, for the first time...

..we'll follow the dramatic story of a wild bald eagle family...

..witness eagles in action...

..and join one man and his feathered friend

to put these icons of the air to the test.

Woohoo! What a girl!

We'll reveal what it takes...

..and even what it feels like...

Wow! We're flying with a golden eagle!

..to be the most powerful bird in the sky.

This is Iowa in the American Midwest...

..and in the midst of a late winter snowfall...

CHIRPING

..a bald eagle is trying to look after her most precious possessions.

These two eggs must be kept at around 37 degrees Celsius

if they are to hatch.

At night, temperatures plummet to minus 25.

By day, it's still cold enough to freeze her eyelashes.

But she'll do whatever it takes to keep these eggs safe.

Over the next few months, we'll follow them around the clock

and see what it takes to become a superpowered eagle.

Bald eagles are just one of 70 different species.

They can look very different...

..but they all share a mesmerising blend of power...

..and beauty.

They've mastered habitats across the planet.

From harpy eagles in the rainforests of South America

to Steller's sea eagles in the icy North Pacific.

And fish eagles in the Great Lakes of Africa.

They live at the top of the food chain...

..but to dominate their world, they must overcome

some significant challenges.

They have to cover hundreds of miles on the wing,

spot their food at vast distances,

and tackle the largest prey of any bird species.

BIRDS CALLING

To find out how eagles achieve this...

..we need to meet a remarkable bird.

This is Tilly.

A golden eagle with a wingspan of almost two metres.

But what makes her unique is the relationship

she has with her lifelong partner.

Bird specialist Lloyd Buck.

Hello!

Hello, my love!

Are you enjoying yourself, eh?

You're the best, ain't ya?

You're a once-in-a-lifetime bird, you are. Eh?

I'll never have another bird like you ever, will I?

Since he was a child,

Lloyd has been obsessed with birds.

Over the years, he's kept and trained many different species.

But one stands out.

Tilly.

They've been together for 20 years,

and have forged an exceptionally close bond.

As far as Tilly is concerned,

Lloyd is her mate for life.

Go on! Go and enjoy yourself, my love.

I wish I was you.

I wish I was you!

Thanks to Lloyd's dedicated work with Tilly,

she acts just like a wild eagle,

but is also comfortable around scientific equipment and cameras.

So this is an extraordinary opportunity to learn

more about these iconic animals.

Eagles are such inspirational birds.

There's so much I think that we don't understand about them,

and that's what I'm hoping to learn here.

A little window into her world, into the world of eagles.

Together, Lloyd and Tilly will take on a series of tests

that will unlock the eagle's remarkable powers.

On the other side of the world, in Iowa,

the adult female seems restless.

One of the eggs is starting to hatch.

From its first moments, the chick must show its strength.

It uses a tiny egg tooth on top of its beak to crack the shell.

CHICKS CHEEPING

Three days later,

it's joined by its sibling.

At this age, they need to eat

almost half their body weight in meat every day.

Thankfully, help is on hand,

and he's bringing fresh supplies.

As with all bald eagles, the male is about 20% smaller than his mate.

It's thought she might be bigger to help produce

and incubate the young.

Bald eagles normally pair for life,

but this female's previous partner disappeared,

so this male is new.

The breeding season can last around ten months,

so rearing these chicks will be a test of their new relationship.

The chicks' weight needs to increase

by a staggering 500% in the first week,

so the adults spend much of the time out hunting.

Bald eagles specialise in catching fish.

They can make up to 90% of their diet.

They're able to pluck them from the water

with remarkable precision.

CHEEPING

But rabbits and squirrels are also delivered to the nest.

For now at least,

this partnership is providing all the food the chicks could need.

Eagles around the world catch a wide variety of prey,

so they have a range of hunting techniques...

..and one species has come up with an extraordinary strategy.

The mountains of Oman.

In this desert realm, food is hard to come by.

But this Verreaux's eagle has a family to feed.

Other birds dive-bomb the predator,

hoping to chase it away.

But this eagle is focused on a terrestrial target.

Rock hyrax.

These small mammals are equipped with special vision.

A shield on their iris cuts out glare,

helping them spot predators,

even in bright sunlight.

But one eagle is just a decoy.

Verreaux's eagles hunt in pairs.

The first flies in plain sight,

distracting the hyrax...

..while the second eagle hugs the contours of the land,

staying hidden...

..until the last moment.

Using teamwork is devastatingly effective.

But catching their quarry is a dangerous task.

There's no room for error.

When eagles hunt airborne prey, if something goes wrong

they usually have space and time to get out of trouble.

They can even escape a glancing blow with the water surface.

But when the prey is on hard ground...

..one wrong move could result in a deadly collision.

Especially when hunting a large, heavy animal.

There's simply no scope to make a mistake.

So how do eagles target and safely catch terrestrial prey?

To find out, Lloyd has come to Scotland

to put his golden eagle Tilly to the test.

But first,

he needs something for her to hunt.

This is Robohare.

Designed and created by tech wizard Chris Watts.

With a fake fur coat

and high-speed motors, it can blend into the undergrowth

or flash across the open.

It's also fitted with an onboard 360 camera to capture all of the action.

OK. She's going to rouse. Get ready.

OK. Go! Go! Go! Fire! Fire!

In a matter of seconds, Tilly locks on to her target.

She's got him. She's done it.

Thank you very much, Tilly.

Good girl!

To challenge Tilly's hunting ability,

they repeat the test

in different conditions.

Go!

From strong winds and overcast skies

to bright sunlight.

But the outcome is the same.

To reveal the secret to her success,

we need to go through the footage frame by frame.

First, Tilly keeps a constant lock on Robohare's position.

Next, she uses her wings to adjust her trajectory

as the wind changes

or the target moves.

She keeps her legs tucked in to stay aerodynamic.

Then, just a quarter of a second before impact,

she swings her feet forwards

so both eyes can see Robohare

AND her talons.

She makes perfect contact.

But in a demonstration of sheer power...

OK, get ready, Chris.

..Tilly's hunting skill is about to reach the next level.

Robohare weighs 5.8 kilos -

one and a half times more than Tilly.

But not only can she catch Robohare...

..she can lift it high into the air.

She even has the strength to carry it with one foot.

A remarkable achievement for a load weighing 150%

of her own body weight.

Yes! Woohoo-hoo!

What a girl!

Good bird! There's a good eagle!

She's able to do this because, like all eagles,

she's armed with highly specialised weapons - talons.

and inflict fatal damage upon their victim...

..while the beak is used to cut up the meal.

The harpy eagle has some of the largest talons in the world,

measuring up to 12 centimetres - twice as long as a golden eagle's.

These weapons can suffocate their quarry

or create puncture wounds and blood loss.

To achieve this, eagles must grip with enormous force

and hold this pressure for a long time, without tiring.

So they rely on some clever mechanics.

Their feet have an in-built ratchet system.

The tendons in their toes are ridged

and so is the tissue around it.

This creates a simple locking mechanism

so the surrounding muscles can relax

without losing any grip force.

Many birds have this adaptation,

but in eagles the ridges are

particularly large, to cope

with the enormous power.

Creating and maintaining such a high force

is a critical part of their success.

And it helps them take down even the largest prey.

But these super-strong weapons have a second essential purpose.

To fight.

Winter in the Alps can be desperately bleak.

Golden eagles soar across the peaks in search of prey.

And when food is scarce,

they have to turn to scavenging.

SQUAWKING

A dead fox.

It could last this female eagle for days.

Such a prized meal is in demand.

This devious mob of crows will try anything to steal a mouthful.

A flash of talons reminds them who's at the top of the food chain.

But the biggest threat

comes from her own kind.

A meal like this is worth fighting for.

In battle, talons are their weapons of choice.

They use their long legs to keep their head, and importantly

their eyes, away from danger.

Using their talons effectively

can make all the difference in who loses

and who survives.

In Iowa...

..our bald eagle youngsters are now one and a half weeks old.

Thanks to the hunting skill of their parents,

they're gaining about 10% in weight each day.

Their talons develop quicker than other parts of their body,

showing how important they are.

But it will be another three months before they have proper control

of these formidable weapons.

For now, they're almost completely defenceless...

..and the slightest thing can pose a threat.

Somehow, one has become tangled in the female's feathers

and it's at risk of choking.

CHEEPING

It's hard to know how this has happened.

And the female seems confused and stressed.

The more she moves around,

the more she pulls on the chick's neck.

A lucky escape,

but now it's stuck on its back

and the male seems distracted by the other chick.

Less than half of all bald eagle chicks survive their first year.

The odds may be against it,

but this time, those powerful talons come to the rescue.

When it comes to growing up,

the gamble of life or death for some eagle species is even greater.

THUNDER RUMBLES

Zambia.

Home to the crowned eagle.

They are known as the most powerful eagles in Africa.

THUNDER AND LIGHTNING

This adult has chosen to nest in a small patch of swamp forest,

and is trying to raise a single chick.

The eaglet needs to eat 30% of its body weight in meat each day.

But right now

there's just not enough food here to support a family.

Nesting here seems like a big miscalculation,

but there's a reason behind taking this risk.

What this forest does hold are fruit trees...

..and the fruit is ripe for harvest.

It's of no use to the eagles,

but it's vital for another animal.

HIGH-PITCHED CALLS

Fruit bats.

Ten million arrive here each year.

It's the largest mammal migration in Africa,

and exactly what the eagles are waiting for.

They target individual bats,

picking them out from the swarm.

Fish eagles and martial eagles join the hunt.

The bats will be here for up to 90 days,

providing food for the chick at its most vulnerable age.

Timing their breeding cycle with the bats' arrival is a risk...

..but for this crowned eagle family, it's paid off.

In Iowa, it's spring.

The adult eagles are delivering

around five fish a day to the nest.

Now four weeks old,

the chicks are changing.

Their fluffy, warm down is peppered with juvenile flight feathers.

But perhaps the most important change is in their vision.

Their eyes open within hours of hatching.

But much like a human baby, they're born with poor sight.

It takes time for it to sharpen

and become one of the most powerful senses in the animal world.

We describe anyone with exceptional sight as eagle-eyed.

But just how good is eagle vision?

To put it to the test,

Lloyd Buck and his golden eagle Tilly

are entering a remote part of Scotland.

They're joined by Professor Graham Martin,

an expert in avian vision.

To compare the basics of eagle and human eyesight,

Graham has a demonstration.

We're going to have some sort of measure of our acuity, how much

detail that we can see, using the black and white stripes, equally

spaced apart, called a grating.

And our task is simply to back away from this and come to the point

when we can't see the stripes any more,

and then that's our threshold for seeing detailed vision.

As they walk further away,

the black and white stripes become less clear,

and then merge to become a grey blur.

I'm just about the limit now.

Yeah, I'm there now.

You're there? Yeah.

I'm still all right.

That's me.

Here I am. Nine metres.

Nine metres? Yep.

I'm just under 13 and a half metres.

Eyesight deteriorates with age,

so it's no surprise that Lloyd has greater visual acuity,

but how do scientists think an eagle like Tilly would fare?

The experiments that have been done

show that they're about five times better than us.

Five times that, it's somewhere right up there.

The end of the tape.

This seems impressive,

but what does it mean for an eagle hunting in the wild?

To find out, Lloyd and Graham have planned a game of hide and seek

on an epic scale.

Tilly must find Lloyd somewhere in this landscape.

Her cage has been covered so she can't cheat,

and Lloyd has found a position 400 metres away.

RADIO: OK, I'm going to release her now. OK.

OK, Lloyd, she's gone.

Tilly immediately scans the landscape in search of Lloyd.

Moving your way now,

at great speed, actually.

She's actually found you in no time at all.

Good girl!

You're beautiful, aren't you?

Tilly spotted Lloyd from 400 metres away,

but Graham thinks that was far too easy.

She was so quickly onto you,

I don't think it was really much of a challenge for her, in a way.

If you wanted to, I think we could push the distance.

What do you think?

OK, that sounds really good.

Lloyd repositions himself for a much bigger challenge.

He's now one and a half miles away

on the opposite side of the glen,

and the weather conditions are not ideal.

Even with a powerful telephoto lens,

it's hard to pick out Graham and Tilly.

It's a long way.

I cannot see you without a pair of binoculars, and even

with the binoculars, there's that much moisture in the air,

so this is a real challenge for Tilly.

OK, then. Well, I'll release her now.

OK?

OK. Good luck.

Come on, Tilly. Come on, Tills.

She's off.

She's looking very hard.

I'm sure she's trying to find you.

Tilly has never faced a challenge like this,

but she starts to make her way to the other side of the glen.

Come on, Tilly! Come on!

HE LAUGHS

Interestingly, she takes an indirect route,

riding a series of strong air currents to reach Lloyd

more efficiently...

..and more quickly.

She's coming in! She's coming in fast! Woohoo!

She's done it, Graham.

Absolutely hammering across the valley!

Yee-hoo! What a bird she is!

You clever bird!

Woohoo!

What an eagle you are, hey?

Hello!

LAUGHS

Graham, she's on my arm.

That is absolutely incredible.

I'm so pleased with her. I've never asked her to find me like that.

That is actually very, very impressive because it took

really very little time at all.

Tilly spotted Lloyd in this vast landscape

from one and a half miles away,

a feat so impressive

it seems almost superpowered.

So how does she achieve this?

Images are projected onto the retina at the back of the eagle's eye.

This area is covered with

light-sensitive cells

known as cones. The more cones,

the sharper the eyesight.

A human eye may have 200,000 cones per square millimetre,

but eagles have over twice as many,

giving them the sharpest eyesight

of any vertebrate animal.

The eagle's supreme visual acuity gives them a significant advantage.

It means they can quickly pick out prey in a vast landscape.

But there's an unexpected downside to having such sharp vision.

The problem is, you don't want to get the sun in your eyes.

It would destroy all the very high acuity it's got.

So they have these big eyebrows. It's like wearing a baseball cap!

That's all designed to keep the sun out their eyes,

so they don't actually ever image the sun.

This brow ridge is what gives eagles their fearsome stare.

But it has a serious drawback.

Of course, if you're keeping the sun out your eyes,

you can't actually see what's up there.

What an eagle wants to do is patrol and look down

at the big terrain below it, and it's bending its head forward.

It's tipping its head down to have a look.

And that means that this blind area,

which is designed to keep the sun out their eyes,

is stopping them actually looking where they're going.

This blind spot isn't usually a problem.

In their natural habitat, they soar high above the trees.

But in a modern landscape,

it can be a fatal flaw.

Across the world, eagles are colliding

with man-made structures.

Wind turbines, often built in wild landscapes,

can be a particular issue.

So at this wind farm in Wyoming,

they've placed observation towers around the site...

..and if an eagle is spotted, they switch the turbines off.

But in bright light, eagles can be hard to spot.

So now they're using artificial intelligence to improve the odds.

This technology harnesses ten cameras to spot

and track flying objects.

It can work out if the object is an eagle in just one second

and temporarily shut down any turbines in its path.

It's over five times more effective than humans,

meaning the eagles here are now far safer.

But elsewhere around the world,

the biggest threat to most eagles is still humans.

In the tropics, deforestation is threatening jungle species...

..like the Philippine eagle

and the harpy eagle.

There are fewer trees for them to nest in

and far less prey for them to hunt.

Many eagles also succumb to lead poisoning,

as hunting ammunition contaminates carcasses.

More than a third of all eagle species are considered

to be endangered or vulnerable.

But conservationists have proved in the past that, with the right help,

some eagles can be saved from the brink of extinction.

During the 1940s, DDT, a potent insecticide,

was considered a wonder chemical.

A solution to pest problems, large or small.

It was even sprayed on people to rid them of parasites.

Colourless and tasteless, DDT seeped into the ecosystems.

At first no-one realised its impact,

but the chemical passed from prey to predator,

and those at the top were hit hardest,

especially bald eagles.

It caused a thinning in eagle egg shells, which meant

they cracked during incubation...

..and it almost wiped them out.

Eventually, DDT was banned

and some heroic conservationists

stepped up.

Eggs were taken from the wild,

hatched safely in captivity...

..and the chicks were returned to the nest to be reared naturally.

And it worked.

There are now thought to be over 140,000 bald eagles in the US.

A truly remarkable comeback.

Today, each new chick is still important to the growing population.

In Iowa, the parents are doing well...

..providing their chicks with enough food to grow at a remarkable rate.

Now eight weeks old,

the eaglets are almost fully grown

and covered with new dark brown feathers.

But they are about to face their biggest survival challenge yet.

FLIES BUZZING

Something seems to be bothering them.

A wet spring has created ideal conditions for an infestation

of bloodsucking blackflies,

and they are attacking the eaglets.

The number of blackflies seems to be getting higher in this region,

and this season is particularly bad.

The chicks are growing weaker from the sheer number of bites.

And, worse still, they're becoming restless.

One youngster is so uncomfortable,

it climbs the tree to get away.

But the chick is 22 metres up,

too young to fledge and too weak to deal with the strong wind.

In sheer desperation, it leaps...

..and falls to the ground.

The nest cameras lose sight of it,

and so do the parents.

This family's future now appears to rest with the remaining chick.

But worryingly, it's also driven from the nest.

CHEEPING

FLIES BUZZING

The parents are helpless.

The chick doesn't yet have full control of its large feet...

..and one mistake is all it takes.

The only hope for the eaglets now

is that they'll be found somewhere beneath the nest.

If the chicks were older they could have flown to safety,

but it takes many weeks for a young eagle to truly master its wings.

In fact, flight is probably the most sophisticated

eagle superpower of all.

Eagles dominate the sky.

They can dive at over 150mph...

..and perform spectacular aerobatics when they fight

or display to a mate.

And one of their greatest aerial abilities is soaring.

Golden eagles can have a home range of up to 2,000 square miles.

To cover these vast distances, they use air currents to push them

high into the air without flapping their wings...

..saving them precious energy.

It's something Lloyd Buck has always wanted to know more about.

So he's come to California,

where paragliding fanatic Michael Vergalla

often flies alongside wild birds of prey.

By learning what it takes to fly a paraglider, Lloyd hopes

he will understand more about how eagles soar.

Bring the wing up in three, two, one...

Wing's coming up.

OK. Walk, walk, walk, walk.

Start running. Run, run, run, run!

Run, run, run, run, run.

All right, Lloyd. OK. Here we go!

We're flying! We're flying, Mike.

Wow!

I've seen Tilly do this so many times, and now I'm doing it.

LAUGHS

When eagles soar, they search

for the strongest air currents to push them higher.

Mike and Lloyd must do the same,

so they look for tiny clues in the air

and movement in the vegetation below.

You're looking for changes.

You're smelling, you're listening.

You're trying to use all of your senses

to figure out what's happening.

Oh, look at the tree moving. Look at the tree moving.

Yep. We're going to get a bump here. Ready?

All right? So you're going to feel...

I can feel it, I can feel it!

There you go. Wow.

And we're going to feel more as we get in here. Yeah.

I can really feel the pressure, the change in it.

Just like an eagle, Mike is trying to gain altitude by harnessing

two common air currents.

Thermals form as the sun heats the earth,

which in turn warms the air above it,

creating a rising column of air.

Updrafts are created when horizontal winds

are deflected skywards by a ridge.

By feeling where these thermals and updrafts are,

they can manoeuvre the wing and climb higher.

This is what Tilly feels. This is what Tilly does.

This is what eagles do. Uh-huh.

One of Mike's favourite ways to find a good thermal is to watch

and follow the local birds.

Got another bird on this ridge here that we can try to join.

Mike can tell how strong a thermal is

by seeing how quickly the birds climb.

And it's not long before he spots a familiar species.

Look out, at the end of the ridge.

You see the birds?

At the end of the ridge, end of the ridge...

Straight out, straight out, straight out.

Straight out. Gotcha! Yeah, yeah, yeah.

That's a goldie. Yeah?

That's a golden eagle. Let's go, let's go.

We're flying with a golden eagle.

Wow!

I've waited my whole life for this, Mike.

THEY CHUCKLE

This is the thing that I've dreamt about since I was a boy.

And my whole life, I've experienced it through my birds. Uh-huh?

But now I'm experiencing it for myself, for real, with you,

and this is just... I can't put that into words.

It's really quite moving, I would say. It's quite emotional.

It's OK, you can cry. I've cried.

I feel quite... I feel very emotional, actually.

This is something, Mike,

I'm never going to forget for the rest of my life.

For Lloyd, soaring on the air currents is pure joy.

But for eagles, it's a critical component of their daily lives.

To be a dominant predator of the sky, they must harness

the wind to cover their territory,

and they make it look easy.

To find out the science behind this superpower,

Lloyd wants to put Tilly to the test.

He's fitting her with a highly accurate GPS tracker to measure

how fast she can gain altitude,

and a 360-degree camera

to see exactly how her wings are adapted to soaring.

We'll know exactly... what you get up to.

Eh?

You're a good girl, yes.

Bop-bop-bop!

Go on, off you go.

Go on.

Tilly soon finds an updraft, and soars high above the glen.

Woohoo-hoo!

You make it look so easy. Eh?

The onboard camera provides a wonderful opportunity

to see the world from an eagle's perspective.

Throughout the flight, the GPS tracker and accelerometer

on her back are collecting important information.

Good girl. Clever eagle!

And Professor Jim Usherwood, a locomotion specialist,

can help interpret the findings.

Well, it's really exciting, especially

having the video next to it.

You can really see what's happening all the way through.

You can see her climbing, circling seven times,

and then reaching quite a height, really very quickly.

She's doing, oh... three, four, five metres a second up

and that's fast. Wow.

That's eight, nine, ten miles per hour...up.

Imagine running up a ladder that fast.

So she's climbing quickly.

Really fast, while hardly travelling across the ground at all.

Tilly climbs without flapping her wings,

saving huge amounts of energy.

Eagles are able to ride the air currents effectively

thanks to their large wing area,

but the shape of their wing

is different to that of many soaring specialists.

Albatross have very long, narrow wings,

which generate a lot of lift for relatively small amounts of drag.

CAWING

It makes them brilliant at gliding,

but this wing shape is no good to eagles.

Long wings are very good for gliding and soaring,

but they're horrible for flapping.

And, of course, this thing at some point will need to flap.

Yeah. She'll need to flap to take off,

carry the weaponry to kill something

and then carry that food back home,

at which point you don't actually want super long wings.

Eagles have to deal with some conflicting tasks.

To soar well, it's best to be lightweight

with extremely long wings.

But to hunt large prey,

it's important to be powerful and heavy

with shorter, broad wings that can flap and take off with big loads.

Eagles manage to achieve both, but how?

The secret is at the end of their wings.

From the onboard camera, it's clear that the feathers on her wing tips

are separated when she flies.

Each one of these primary feathers acts like a tiny aerofoil,

helping air hug the upper surface of the wing.

It means eagles can tilt their wings at very steep angles on takeoff,

generating lots of lift to support a heavy load.

It's also thought these slotted wing tips can reduce elements

of drag, helping them soar with greater efficiency.

It's a clever solution for a wing that has to perform so many tasks,

helping them harness air currents

and dominate the skies.

In Iowa, the nest is still empty.

The parents did all they could to raise their two chicks

and, hopefully, they will breed again next year.

But this isn't the end of the story.

Remarkably, both chicks have been found alive.

The eldest was discovered washed up along the river, five days

after it fell from the nest.

It was later found to have a broken leg.

The other was picked up by local residents,

covered in blackfly bites.

Both chicks were taken

to a raptor rehabilitation centre for treatment,

where they started feeding and putting on weight.

Due to its leg fracture, it's unlikely the eldest chick

will be released, but its future is still bright.

Hopefully it will become an ambassador eagle

to help inspire a new generation of eagle conservationists.

The second chick is making a good recovery

and developing powerful flight muscles.

Paired up with other rescued chicks,

it will soon be strong enough to be released back into the wild.

It's an extraordinary end to a dramatic season,

and a new start to this eagle's life.

By following the journey from egg to eaglet,

we've seen what challenges an eagle must face

to survive its first year.

We've witnessed remarkable dedication

and skill from the parents.

And thanks to a very special eagle called Tilly,

we've uncovered the science behind their superpowers.

I'm so proud of her because,

in her own way, she's brought

much more knowledge and understanding to an eagle's world

about their incredible eyesight...

She's coming in fast! Woohoo!

..that amazing ability to use the air

to soar so well,

and her hunting strategy,

and the power in those feet!

Bring all those things together

and you've got the best aerial predators on the planet.

They really are incredible.

Eagles have long captured our imagination.

Their combination of strength,

elegance,

and skill

make them appear almost...

..superpowered.