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The peregrine falcon...

..the fastest animal on Earth.

They live on the edge of what is physically possible,

seeming to challenge the very forces of nature.

They can reach speeds three times faster than a cheetah...

..withstand forces up to 18G...

..twice that of our best fighter pilots.

And can take on prey double their size.

To understand exactly how they're able to do this,

we'll work with the world's top scientists.

Using state-of-the-art technology...

..to put them to the test.

They seem to just live in a

different world of time perception to us. Yeah, absolutely.

Follow a young family of peregrines in downtown Chicago.

And see if one special bird can rise to the ultimate challenge...

..against an Olympic skier.

We'll reveal what it takes to be the world's fastest animal.

Peregrines are birds of prey.

Like their cousins, the hawks and owls,

they've sharp talons and keen eyesight.

But peregrines are in a class apart.

Their prey is among the most difficult to catch...

..other birds.

A successful hunt needs extraordinary agility...

..and above all, speed.

By diving at 200mph,

peregrines can catch even the fastest fliers.

Their hunting prowess has seen them spread across the planet.

They live on every continent, except Antarctica.

From coastal cliffs...

..to Arctic tundra.

And now they've moved into a whole new world...

..ours.

One city in particular provides a perfect window

into their high-speed lives.

Chicago,

home to 2.7 million people,

and over 40 peregrine falcons.

This metropolis is as unnatural as anywhere on Earth.

But the soaring skyscrapers emulate the wild cliff habitats

peregrines are accustomed to.

As many as six nests can be found in one square mile

of downtown real estate.

It's now early May.

In the window box of this 28th-floor apartment,

a male peregrine carefully shelters four eggs.

His partner does most of the incubating,

but she's on a much-needed break.

This is the Perry family.

For the last three years, they've made their home on this balcony,

living alongside its curious residents.

But today is no ordinary day.

A tiny crack on the shell marks the beginning of a new life.

And a rare opportunity to follow

a peregrine family growing up in the wild.

On the other side of the world, in a captive breeding facility,

a more unusual parent is also awaiting an arrival.

The chick inside is well overdue.

You're taking a long time, aren't you?

Are you going to come out and say hello?

I could do with a cup of tea now, though, I tell you. Cor!

But, you know, all I've got to do is sit here and watch and wait.

It's not like the job they've got inside the egg,

which is really tough.

Lloyd Buck has been fascinated with birds since he was a boy.

Good boy! Clever boy!

Now he and his wife, Rose, have a very special family,

including Arnie,

Lily, and Moses, a four-year-old peregrine falcon.

Lloyd and Rose love and care for them all...

Good boys.

Well, this one here is Luna.

..and educate others about the importance

of protecting birds in the wild.

The nice wing feathers are starting to grow now, you can see. Yes!

They also train them to star in films.

But for Lloyd, it's the peregrines that he most loves to fly.

They're my ultimate bird.

I've loved peregrines since I was a young boy.

As much as you fly them, and as much as you get that bond with them,

there's always that little bit of wildness still there.

As Lloyd puts his birds to the test,

they'll reveal the secrets of the peregrine's high-speed world.

And now there's a new addition to their family.

The peregrine chick inside begins to cut a perfect line,

using a tiny bump on its beak, known as an egg tooth.

Finally, 60 hours of waiting.

No sleep, and all of a sudden,

they've just gone crazy.

It's amazing to see.

Wow! Look at that.

He's nearly out.

Already you can see all the little attributes

that are going to help them when they're old enough to fly.

And to think that this little chick,

in about 45 days' time,

will be fully grown,

and have everything it needs to be the fastest animal on the planet.

Over the next few months, with Lloyd's expert guidance,

the tiny chick must learn to master

every skill needed to be a top aerial hunter.

But first, it's got a lot of growing up to do.

In the wild, peregrine parents have just 12 weeks

to raise their young to independence.

The Chicago window-box is now home to three fluffy chicks.

All but one successfully hatched.

Their mother makes a sharp call

to encourage them to open their beaks wide.

While she diligently tends to the chicks,

her partner has his work cut out trying to find their next meal.

But city living has some surprising advantages.

As the sun beats down on Chicago's buildings,

it generates rising thermals of hot air...

..helping him to lift off and soar almost effortlessly.

Chicago's waterfront location attracts migrating birds to prey on.

And street lighting means 24-hour hunting.

A real help with three hungry mouths to feed.

Now, at seven days old,

the chicks have already reached their first milestone,

they've fully opened their eyes.

Peregrines rely on their vision

to spot and track their prey at high speeds.

It's crucial for their survival.

But just how good is peregrine eyesight?

To find out, Lloyd's headed to the Lake District

with his four-year-old peregrine, Moses.

He's enlisted the help of Professor Graham Martin.

First, Moses is fitted with a GPS telemetry device,

which tracks the exact distance he's flying.

He's been trained to catch a bright yellow lure.

Lloyd positions himself one kilometre away.

Will Moses spot the lure?

OK, Graham. The hood is off, the hood is off.

Come on, Mo, come on.

Gone, gone, gone. 200 metres.

A very straight track to you, 400 metres.

A straight track shows he's locked onto his target...

500 metres,

crossing the stream now.

800 metres.

..which is more than can be said for Lloyd.

Where is he? Just crossing over the river.

Oh, there he is, here he is.

Hey, hey, hey! Hey!

I've got him, I've got him.

I had no idea where you were, my boy, till that last second.

Spotting the lure at one kilometre away seems easy enough for Moses.

But how will he fare when Lloyd doubles the distance?

Now... Hood is off. Hood is off.

Even at two kilometres... Come on, Mo. Come on.

..Moses heads straight for his target.

1.6 kilometres, 1.9 kilometres.

Here he is, here he is.

The bird must be with you.

Brilliant. Look at that.

It's actually brilliant.

Well, what do you think? I think we can just go for broke.

Do you want to try the three?

I think that would be a real push,

but we ought to try if he's so easily done 2K.

So, yeah, let's try 3K.

Three kilometres. 1.8 miles.

So Graham's on that track in the very far distance.

It is amazing, though. It's such a small thing, really,

for him to see at that distance.

Peregrine eyesight is twice as sharp as hawks'.

But spotting a lure this far away is an incredible challenge.

No-one is sure he can do it.

Hood is off, hood is off.

He's still looking down the valley, still looking for you.

Still looking, and he's off, he's off.

Keeping quite high.

Moving back towards us.

Coming right overhead now, just gone overhead.

Moses appears to be struggling.

He circles to try and pick out the target.

Come on, my boy, come on.

Moving away from us now.

He's definitely picked up a straight line now.

1.4, 1.8.

Come on. Just going directly away from us.

2.8 kilometres.

He must be very close to you now.

Come on. 2.9 kilometres.

What a boy!

You top man!

He's on the lure, he's on the lure, so he's done it.

You are a mean machine.

Come on. Amazing, Graham. I'm quite impressed with him, to be honest.

Brilliant. Well done.

Excellent. You had a little circle before you came in, didn't you?

Just getting your bearings.

Moses spotted the tennis-ball-sized lure from three kilometres away.

So exactly how is he able to do this?

Peregrines have large eyes,

taking up at least 50% of their skull.

For us, it's only 5%.

The optics of the eye

project an image of the world onto the retina...

..which is packed with light-sensitive cells called cones.

The most important part of the retina is called the fovea...

responsible for ultra-sharp vision or high visual acuity.

But the peregrine's secret is that each eye has two foveas.

The first is for spotting close objects.

Here, the peregrine looks through both eyes using binocular vision.

The second is for spotting things far away.

Now the peregrine looks sideways,

through one eye at a time,

using monocular vision.

So to spot a target three kilometres away...

Moses turns his head

as if staring through a telescope.

The peregrine's superior eyesight gives it a big hunting advantage.

Any of the species that you care to think of that he preys upon,

his vision is so much better.

For something like a pigeon, he's four times better in his acuity.

This means a peregrine can spot its target

and gather speed for an attack,

long before its prey knows it's coming.

So, at three kilometres, say, he can see the prey,

but the pigeon wouldn't see him

until he was only three quarters of a kilometre away.

The vision difference translates into a really important

time difference when you're actually hunting prey.

This hunting advantage is vital

when it comes to feeding a growing family.

And peregrines grow up fast.

The Chicago chicks are now five weeks old,

and about 30 times heavier than when they hatched.

They've been ringed, sexed,

and named by the Chicago Peregrine Program.

This is Tyler,

his sister, Commodore,

and brother, Fred.

Mum's bringing larger prey to satisfy growing appetites.

The three boisterous chicks need up to 11 meals a day.

Tyler is quite happy to feed himself.

He seems to be getting the hang of it.

But his sister may have bitten off more than she can manage.

The bigger they grow, the more they explore.

These lodgers are making quite the mess.

While their landlord cleans up inside...

..these untidy house guests simply sit by and watch.

Their behaviour is becoming more unruly by the day,

but it's all good exercise for their growing flight muscles.

And after all, it's not every day a peregrine comes to stay.

In Somerset, the newest member of Lloyd's family has come home.

It's been 12 weeks since Lloyd watched him hatch.

Good boy.

He's now fully grown, and wearing a hood to keep him calm.

Hello.

Hello. Are you all right?

Oh, he's lovely. He is, isn't he?

He is, he's a real sweetie. Yeah.

There's a good boy. Lloyd's called him Rudy.

There he is, little Rudy.

I don't think we've ever had a falcon so calm so quickly.

Over the next few months,

Lloyd will teach him every skill a young peregrine needs, but first,

it's critical that Lloyd earns his trust.

He must sit quietly and avoid eye contact.

This helps Rudy relax, and he tucks into his first meal.

It's an important step, as now training can begin.

Lloyd will teach Rudy to hunt a yellow lure.

He starts with a line attached for safety.

First, a small hop.

That was brilliant. He's a good boy.

So, he's just building that bond,

and I've got this lure,

and it's a good game.

Then 30 metres more.

Rudy! Rudy!

You didn't brake, Rudy.

That's what your tail's for.

Rudy! Hey!

And a little further, with no strings attached.

Good boy.

So that's his first free flight today.

He's shortcut the whole process by about four days,

because he's progressed at his own speed, which is what you want.

Rudy!

Finally, he needs to catch it in the air.

Good lad. Here, here.

Oh, nearly.

Oh, good boy.

Good lad.

In less than a week, Rudy has learnt the aim of the game -

to catch the lure.

But in the wild, learning to hunt food at high speeds isn't easy.

Less than half of peregrines make it to adulthood.

You couldn't get a better example, really,

of survival of the fittest, than with these guys.

They've got to be at the top of their game all the time.

Once their parents stop feeding them and they're fledged,

they're on their own, literally.

The Chicago peregrine chicks are nearly fully grown.

And their food demands are higher than ever.

It's a good thing their parents are expert hunters.

A city diet can consist of over 100 different species,

many not found in wilder hunting grounds.

But their favourite?

Pigeons.

In a straight chase, a pigeon can reach 50mph,

and weave and dive between the city's buildings for cover.

So one peregrine's strategy is to flush them into open skies.

No luck this time.

But sometimes making the most of an opportune moment

is as good a strategy as any.

A perfect strike at lightning speeds takes precision timing.

So how do peregrines do it?

Lloyd and avian expert Graham want to find out more.

But first, they need something for a peregrine to catch.

Meet the prey drone, designed by gadget guru Chris Watts.

It can perform aerial manoeuvres that mimic bird flight.

And with safety guards and an on-board camera,

it's the perfect device to film a peregrine in hot pursuit.

For the battle arena, a secluded valley in the Lake District.

So, are you set? I'm all set, yeah.

OK. OK, going up now.

Yeah, yeah. Are you happy? Yeah.

It's the prey drone against Lloyd's four-year-old peregrine, Moses.

Start going away.

Go, go, go. Go, my boy.

Wow! Look at that, straight after it.

Not yet, stay as you are, stay as you are, stay as you are...

Climb, climb, climb, climb, climb!

OK. Shall I come back down? No, no, hold your height, hold your height.

Hold it there, hold it there.

Dive, dive, dive, dive, dive!

No matter what the prey drone tries, the result is the same...

He's got it. Oh!

..every time.

Oh! That's it. He got it then.

Just like that.

So how does Moses time these perfect strikes?

He rarely chases directly after the drone.

Instead, he cuts corners to intercept its flight path.

Recent research using prey drones suggests

that adult peregrines use the same method

as missiles to track their targets.

Moses moves to maintain the same line of sight with the drone.

This means he will intercept the flight path of his quarry.

But what happens at the moment Moses strikes?

The drone camera provides a unique view.

Right, let's have a look. Here we go.

Just so you know, this is real time.

OK. This is how quickly it actually happens.

Wow! Whoa!

Wow! That's so fast. Real-time is very fast.

We'll need to see that much, much

slower to understand what's going on.

We should be able to just go through frame by frame.

Here we go. There he is, there he is.

Look at that. He's still absolutely stable.

He lurches forwards. Look at that. The pupils wide open.

He's absolutely locked on, feet well spread.

There, there, look.

From my point of view, it's all under visual control.

I mean, it's just very, very rapid feedback from the eye,

through the brain, back to the feet.

I mean, that's incredible.

They seem to just live in a

different world of time perception to us.

Yeah, absolutely. I think humans can sometimes do this sort of thing.

When you watch a first-class cricketer

doing a fantastic catch and they

get absolute timing and precision just right.

Yeah. It's the same as those talons suddenly going, bang!

And it's literally in no time at all.

The strike took just one-fifth of a second.

But the final component of a perfect catch is a deadly set of tools.

Their feet have warty pads for extra grip,

and talons around two centimetres long, to lock onto their prey.

Their long toes have a ratchet mechanism

to hold their feet locked shut with no muscular effort.

But it's their powerful beak that makes the kill.

A hornlike bump called a tomial tooth

is used to dislocate the prey's neck.

Deadly tools and an elite targeting system combine for a hunting

masterclass above the Chicago skyline.

A perfectly timed strike.

An essential skill for all young peregrines to master.

But first, they need to learn to fly.

And in a city, this is a treacherous task.

The chicks are almost 100 metres above the ground,

with traffic lurking below.

There's no room for error.

It's little wonder this is the most dangerous period in an urban

peregrine's life.

The nest is down to two.

Tyler has made his way onto the ledge above.

His siblings seem more cautious,

but their parents are trying to entice them away from the nest

by taking their next meal out of their reach.

If any chicks want food, they'll need to take a leap of faith.

Tyler tries for the roof of an adjacent building.

But landing is tricky.

A balcony saves the day.

And soon, his courage is rewarded.

A few days later, Tyler is joined by his sister, Commodore.

And finally, Fred leaves the balcony.

The first few days are full of challenges.

They have difficulty dealing with Chicago's famous wind...

..navigating obstacles...

..and they simply don't know which areas to avoid altogether.

Thankfully, their parents are still providing food,

even if sometimes they don't receive much thanks for it.

Time for a more advanced lesson.

The food pass.

Adults share kills this way, and for the chicks,

it's perfect for practising their flying skills.

No luck this time.

So Mum arrives to show how it's done.

Now for another go.

Mastering the food pass is the next step towards fending for themselves.

And no amount of rain is going to stop Lloyd and Rose from teaching

five-month-old Rudy this next lesson.

Apparently there's a bit of rain coming in.

It's time for Rudy to learn the art of the chase.

With Lloyd as the designated back-seat driver,

good communication is essential.

Slower, slower.

Hold it there, hold it there. Quicker, quicker.

Oh, come on!

There he is, here he is! Oh!

OK. Hey!

Are you coming?

We're nearly at the end. Yeah.

Oh! I have to stop. Yeah, stop.

Rudy, hey!

Rudy hasn't quite got the hang of it.

Stop, stop, stop, Rudy.

He's going down. Yeah.

Yeah, he's down. Good lad.

On there. There's a good boy.

Time for round two.

OK, go. There he goes.

Go, go, go, go, go. Quicker, quicker,

quicker, quicker, quicker, quicker.

Faster, faster. Hey, hey!

Let him come in. Slower, slower.

Now speed up, Rose. Go for it!

Go for it! Go for it!

Faster, faster, faster.

Flat out, flat out, flat out, flat out!

Slower. Let him come in.

Hey, hey! Let him come in.

A bit slower.

Not yet. OK.

That's it. Now quicker, quicker, quicker. Go, go, go,

go, go!

Hey, hey!

Slower, slower.

Whenever you're ready, it's yours.

Good lad!

Good boy.

Oh, that was brilliant! There he goes.

In less than ideal conditions,

Rudy has learnt how to chase down his target...

..in his very own food pass.

Back in Chicago, the fledglings have made

their first attempt to catch a bird.

A parrot,

of the plastic variety.

At eight weeks old, they have become far more proficient flyers.

They spend hours chasing each other.

This may seem like fun, but it's essential

to hone their hunting skills.

But in the city, a poorly timed practice

can turn deadly in an instant.

A fledgling tries to grab live prey.

It fails...

..and pulls out...

..leaving its diligent parent to pick up the pieces.

Peregrines can carry their own body weight,

but getting airborne takes time.

A narrow escape.

Their parents won't keep risking their lives for much longer.

And there is still one final skill for the fledglings to learn...

..perhaps the hardest of them all.

It's the peregrine's greatest hunting strategy...

..and the key to being the fastest animal in the world.

When faced with a fast-winged opponent,

peregrines catch rising thermals...

..and soar high above the city.

They judge the right moment...

..fold their wings...

..and dive.

This is called the stoop.

It's how peregrines reach world record speeds of around 200mph,

to catch even the fastest birds.

The stoop is the peregrine's most iconic manoeuvre.

Lloyd has brought six-month-old Rudy

to a hilltop in Somerset to teach him this final skill.

Hey, hey!

Hey!

Hoo-ee! He makes a few false starts.

Hey!

But with Lloyd's encouragement...

Hey, hey!

..instinct kicks in.

Hey!

Rudy performs his first ever stoop.

Just like wild peregrines,

high-speed diving is written in his DNA.

It's perfect conditions today,

a really good updraught up through this gully here behind us,

up onto the hill. He's absolutely really loving it.

The first time today,

I've seen him doing what I would call proper stooping,

where he's really tucking his wings in,

and sustaining it for more than just a fraction of a second.

So, you're getting there, Rudy, aren't you, mate, yeah?

And he's fit and strong now.

He's looking nice and strong and fit on the wing.

He can sustain that speed,

he can tolerate all that pressure on his muscles and just keep it going.

With practice, Rudy will learn to stoop faster and faster.

But what is the secret to reaching such high speeds?

To find out, Lloyd's brought his four-year-old peregrine, Moses,

to one of the highest crags in Britain.

Fleetwith Pike stands a staggering 648 metres above the valley floor.

And to entice Moses down...

..the drone is back.

At the bottom is Professor Christoph Bruecker,

who's recording his speed using GPS telemetry.

Come on. This is it, my boy.

He's looking. He's looking. Keep moving it around, Chris.

He's gone, he's gone, he's gone.

Full stoop, full stoop.

Whoo-hoo!

There he goes.

Holy shmoly!

No, it's already 150 kilometres per hour.

Wow!

Wow, great.

Hi, Christoph. He looked pretty good from up here.

He went off like a little rocket. What kind of speed did we get?

So, the maximum speed that we got was 117 kilometres per hour.

Hoo-hoo! Well done. Superb.

Moses reached over 100mph in just two seconds.

It's hard to imagine, but this is a leisurely pace for a peregrine.

They will only ever go as fast as they need to.

But watching peregrines stoop like this has led Christoph to make some

ground-breaking discoveries about how they reach top speeds.

In a specialist laboratory,

he and his team have created exact replicas of peregrines,

and placed them in wind tunnels.

They reveal how a specific body position called the cupped wing

might help peregrines to reach high speeds.

In this streamlined shape,

drag is reduced and air is directed under the wings,

through a narrow channel.

This squeezes the air, so it flows faster,

increasing the peregrine's speed.

This is the Venturi Effect.

Formula 1 cars use the same principle

to increase grip and go faster.

Using the Venturi Effect,

the peregrine can reach speeds up to 150mph.

To go even faster,

the bird wraps its wings around its body,

and effectively goes into free fall...

..a rare, high-risk manoeuvre, as no wings means no control.

Any error could result in a fatal crash.

Such high speeds exert huge pressures on the body.

So how do peregrines cope?

A nictitating membrane helps protect their eyes during the stoop,

just like a pair of in-built goggles.

Nasal cones are thought to slow air flow,

helping the peregrine to breathe.

And with strong bones and a stiff tail,

they can withstand forces up to 18G in a high-speed turn...

..twice that of our best fighter pilots.

Meaning a stooping peregrine

can pull out of a dive without losing speed.

This is key to catching their prey.

Flying at the very limits of what's possible requires extraordinary

control, skill and experience.

It's a lot to learn for any young bird.

Wow! Look at that.

The journey starts early.

It's all in miniature.

It's just got to grow.

At seven days old, they fully open their eyes.

At five weeks old, they take their first flights.

He's going to be a little pocket rocket, I think.

Before long, they master the food pass.

And finally, they learn to stoop.

The Chicago fledglings have learned all the skills

they need to make it on their own.

And city living will give them the best chance possible,

as urban peregrines have a higher chance

of making it through their first year than their rural cousins.

But for eight-month-old Rudy,

there is still one more milestone up ahead.

It's time to see if he can put all his skills together.

800 miles away...

..in the Swiss Alps.

Lloyd's devised the ultimate test.

A series of hunts in an unfamiliar, extreme environment.

Has Rudy got what it takes?

So this challenge is going to be far from easy for Rudy.

Because with the weather, with the winds, with the terrain...

..it requires incredible focus and determination

from this little falcon.

This is Schilthorn,

altitude 2,970 metres.

Home to golden eagles...

..chamois, and Rudy's opponent...

..Olympic freestyle skier Jonas Hunziker.

For Rudy, this is the toughest opponent imaginable.

Jonas will use world-class tricks,

speed and agility to outmanoeuvre his opponent.

This is my home. This is my environment.

But it's the fastest bird in the world,

and you don't really know what's going to happen.

To succeed, Rudy will have to use

the same key skills any adult peregrine needs to catch its prey.

All of Rudy's training with the lure will now come into play.

OK, three, two, one, go.

OK, he's on you, Jonas, he's on you.

Jonas is faster than anything Rudy's chased before.

To catch him, Rudy needs speed.

He stoops, reaching 86mph in one second.

Strong, narrow wings and a stiff tail help Rudy to twist and turn,

mimicking the skier's agility.

In the snow park, the competition is about to get tougher

as it reaches new heights.

Rudy is struggling to get close,

but his excellent eyesight stays locked onto his target.

As they battle in the air, his reactions are put to the test.

Rudy's trying to use his targeting skills,

but Jonas gives him the slip.

Here we are. Jonas, he's right behind you.

Oh, he nearly hit it there. He's trying again.

Keep going, keep going.

He battles turbulence, but with precision timing, he strikes.

He's got it, he's got it. Whoo-hoo!

I tried to trick him with speed and with tricks, and variety,

and in the end, I had no chance.

Rudy has risen to the challenge and outwitted his opponent.

He's definitely earned his peregrine wings.

The pressure that was going on his little shoulders, you know,

as a young bird,

bringing all those skills that he's learned over the past four months

together, and then trying them out,

but trying them out at a speed I don't think we can even comprehend.

The months of training have all paid off.

He's mastered every skill a peregrine needs

to be a high-speed hunter.

For centuries, the secrets behind

the fastest bird on Earth

remained a mystery.

Peregrines have captured the curiosity of science,

as we look towards them for our aerodynamic answers.

They've conquered the globe, even the newest habitat of all.

But it's their superfast skills that makes them

one of the most successful birds on our planet.

Right, let's have a go.

For me, I've learnt so much during this process

about how they do what they do, how far they can see,

how they achieve those incredible speeds,

but there's also that little bit of mystery left, and I like that.

I don't think I ever want to know completely how they do what they do.