Defying Gravity Life in the Air

The sky is one of the most challenging places to live.

But all across the world,

extraordinary animals do something we can only dream of.

Take to the air.

Some spend their whole lives up here.

Others only visit for a moment.

We'll discover how many incredible animals thrive in the sky...

..and what clever tricks they use to get airborne.

With the help of some specially trained animals,

the latest technology

and special effects techniques,

we'll reveal brand-new discoveries

that explain how animals take to the skies.

This is Life In The Air.

So, how do animals take to the air in the first place?

In this episode, we'll meet incredible creatures,

each with their own special techniques.

But they must all overcome one of our planet's

most powerful and universal forces.

Gravity.

It takes a very special animal to defy gravity.

But in Namibia, Southern Africa,

there's one that's mastered it like no other.

The caracal.

A cat with a unique ability to leave the earth.

It does something remarkable.

It catches birds in flight.

What looks like a misplaced haystack

is the largest nest in the natural world.

Home to 100 sociable weavers.

An irresistible target for a hungry cat.

CARACAL GROWLS

You could forgive a bird for believing it was safely out of reach.

But the caracal is perfectly designed to catch it.

Its front is smaller and lightweight

But its back legs are built as a booster rocket -

30% longer and with twice the muscle mass.

This design maximises the caracal's speed on takeoff.

And the faster it's travelling when it leaves the earth,

the higher it will get.

Caracals are built for a vertical launch.

DRAMATIC MUSIC PLAYS

But what goes up must come down.

And come down in the right way.

We know that cats always land on their feet,

but how?

This mystery kept scientists arguing for over a century.

It needs to turn around,

but to do that, it has to push against something else.

But there's nothing there.

This caracal is about to do something that would seem impossible.

All cats have a remarkable design.

A flexible spine which allows them to rotate their front and back ends

in different directions at the same time.

As it falls back to earth,

the caracal creates a clockwise rotation

in the front half of its body,

but the back spins in the opposite direction.

By spinning in two different directions at the same time,

the caracal is effectively pushing against itself.

But it does even more.

Like a spinning ice-skater,

it pulls its front legs close

which makes the front half of its body spin faster.

This creates a twist in its spine

allowing it to swing the back legs round...

..and prepare for landing.

NEIL ARMSTRONG: Houston, The Eagle has landed.

This cat not only defies gravity

but lands again safely,

and it all happens...

..in under a second,

something all cats can do.

Catching food is just one of the many reasons

why animals leap into the sky.

Gazelles leap to show predators that they are too difficult to catch.

Tree-living lemurs leap to move quickly

across dangerous open ground.

The perfect way to make a rapid escape.

But while all leaping animals must overcome gravity,

there's one that uses the power of gravity itself to take to the skies.

The Australian outback is one of the toughest places to live.

Temperatures can reach 50 degrees centigrade.

A kangaroo can only survive by wetting its body to stay cool.

An extravagant use of water in one of the driest continents on the planet.

They need a constant supply of water to replace what they lose.

In a desert over a million kilometres square...

..how does a kangaroo travel huge distances

without breaking a sweat?

They've developed the most efficient form of travel found on land.

And it all relies on the unique design of those enormous legs.

FAST-TEMPO MUSIC PLAYS

The secret lies in the tendons at the base of the ankle

which connect muscle to bone.

Normally tendons are tough and strong.

But a kangaroo's are curiously weak and stretchy.

So when gravity brings it back to earth

their special tendons act like huge elastic bands

absorbing the energy but then releasing it again.

Almost half the power for the next leap

comes not from the muscles...

..but from the energy recycled by these tendons.

By taking to the air,

kangaroos have evolved the most efficient way

of travelling on earth.

But it only works because they take to the air.

When we run, our legs have to move faster,

and we use more energy.

But hopping, like this, is unique.

When a kangaroo speeds up

its legs don't move faster.

Simply by altering the angle of takeoff,

it can increase the distance it flies with each hop.

It means no matter how fast

a cruising kangaroo decides to travel,

its muscles do almost exactly the same amount of work.

They can fly along at the speed of an Olympic sprinter,

ten metres every second,

over 4m with every stride

and never get tired.

For mile after mile,

after mile, after mile, after mile, after mile...

..to reach this.

A sheep station oasis.

Where there's always water.

SHEEP BAA

While the sheep could never leap their fence,

the kangaroo still has enough energy to tackle it with ease.

It's only because of their energy-recycling tendons

and their ability to take off at the perfect angle

that kangaroos can not only survive

one of the most hostile environments on the planet,

but make it look easy.

But if you thought kangaroos had the ultimate launch mechanism,

you'd be wrong.

Early spring in an English field.

It looks empty, but down in the grass,

something extraordinary is about to happen.

One of the greatest acrobatic acts in nature.

Meet the planthopper.

Barely 4mm long.

This one is not yet fully grown,

but even though it has no wings,

it has an incredible ability to get airborne.

And it's going to need it soon.

This field won't be empty for long.

COWS MOO

Cows have spent the winter sheltering in barns.

For months, they wait to be out in the fields again.

MUSIC: The Blue Danube by Johann Strauss II

But in early spring,

the day finally arrives

when they are let loose once again.

They're so excited, they gambol like lambs.

COWS MOO

Not so exciting for the hoppers.

Now they have potentially lethal neighbours.

But when in danger,

this incredible little insect does something which looks impossible.

They simply...disappear.

Rewinding then slowing the action 700 times reveals the truth.

Fleas may be known as the greatest leapers,

but plant hoppers rewrite the record books

when it comes to one of the fastest takeoffs in the natural world.

Having the ultimate ejector seat

means they need something found nowhere else in nature.

Cogs.

COGS CLANK Just before takeoff,

between their legs rows of tiny teeth intermesh,

locking them together.

It's quite literally a clutch in their crotch.

These cogs ensure that when one leg moves

the other has to

within 30 millionths of a second,

accelerating the hopper to 700g.

If you were in that rocket,

you'd be pushed into your seat with a force of 56 tonnes.

But this record-breaking leap has one major flaw.

If it fires those legs on unstable ground,

that much power can spin the hopper hopelessly out of control.

Each launch is a leap of faith into the unknown.

MUSIC: The Blue Danube by Johann Strauss II

Hoppers, kangaroos and caracals defy gravity

with an incredible launch,

and they're not alone.

The animal kingdom is full of fabulous leapers.

But even the greatest leap inevitably ends

with gravity bringing you crashing back to earth.

A moment's lapse in concentration...

..and it can catch you completely unawares.

You might be the world's greatest leaper,

but you can't let it go to your head.

If you want control in the air and to manage your fall,

you need another strategy.

And in the flooded forests of North Carolina, USA,

there's an animal that does just this.

This is a world unchanged for thousands of years.

But we're here to meet the swamp's newest arrivals

who are about to be born.

Their proud-looking father is considered by some

the most attractive bird in North America.

But it still took time to win his partner's affection.

And this is the most important day since they paired up six months ago.

When they decided to start a family,

they had no choice but to make their nest high in the trees...

..to protect their 12 eggs.

Not only from alligators...

..but from deadly snakes.

The height that kept eggs safe

now creates huge problems

on day one.

Jump day.

Until now, they've kept their nest a secret.

With all 12 noisy chicks hatching at once,

they will soon be discovered by predators.

Their mother has to get them down in minutes.

But they can't fly.

There's only one thing to do.

Jump for it.

On the day they hatch, these tiny ducklings must confront

the force that all flying animals must conquer.

Gravity.

Now the clock is ticking.

Every splash could attract a predator.

If the fall doesn't injure them first.

You might think the water saves them...

..but hit that too fast and it's like falling onto concrete.

The ducklings save themselves

by altering the invisible air that surrounds us all.

A falling duckling encounters air resistance

caused by having to push invisible air molecules aside.

Even at a day old,

it's using airflow in two important ways.

First, the duckling instinctively angles its webbed feet and tiny wings

to make sure it's the right way up.

Like a free-falling parachutist.

Secondly, its fluffy body makes it hard for that air to get past.

It's known as drag and slows its fall.

Without this air resistance, after little more than 30 seconds,

a falling duckling would break the sound barrier.

By using the air around it,

the duckling ensures it can control its fall...

..hit the water upright and at a survivable speed.

In under a minute, all 11 - make that 12 - ducklings are down,

allowing the mother to lead them to safety

before they attract the attention of lurking predators.

These ducklings show that you can start to beat gravity

by controlling your body in the air

and altering the way air flows around you.

Surviving a free fall is one thing,

but what if you need more control to get yourself out of danger?

It's winter in the far north of America.

Temperatures nose dive to minus 40 degrees centigrade.

Colder than the average at the North Pole.

It brings big problems for the animals that live here.

Squirrels.

In the day, there are too many predators.

Night is the only time they dare venture out.

But in the winter, food is scarce.

And deep snow makes it impossible to move on the ground.

They need to find a short cut between the trees.

Their only option is to jump for it.

DRAMATIC MUSIC PLAYS

This is the moment that most squirrels would start to worry.

But these ones have something special tucked up their sleeves.

And that's really big sleeves.

They are flying squirrels.

When climbing trees, muscles retract their flying gear,

but once airborne, a wriggle reveals a simple wing.

Two layers of fur-lined skin stretched between wrists and ankles.

Just imagine a normal squirrel inside a furry, elastic duvet cover.

Flying squirrels have long limbs to create big wings.

A flattened tail adds more surface area

and steers the squirrel in the air.

And each hand has a second thumb, giving the wing an upturned tip.

These winglets can reduce drag by up to 20%

and are now found on most aircraft...

..a few million years after they first appeared on squirrels.

But how does this furry wing help the squirrel glide?

The squirrel's body diverts oncoming air...

..forcing the air downwards.

This generates a force in the opposite direction

known as lift,

which pushes the squirrel up.

It sounds complicated,

but if you've ever stuck your hand out of a car window,

you know how this works.

Using this simple wing,

flying squirrels can glide the length of a football field,

but rarely do.

And the reason is a major predator.

The great horned owl.

For the owl, the ice is an asset.

It freezes its kills,

then thaws out its frozen ready-meals...

..as and when it's hungry.

In the air, owls are silent killers.

Their feathers evolved to absorb every sound.

A squirrel is unlikely to hear an oncoming owl,

so its safest strategy is to always imagine one might be closing in.

Compared to the owl,

the squirrel's simple wing makes it a sitting duck.

That's why, whether an owl is there or not,

these squirrels feel a need for speed.

Flying up to 30km/h.

But high-speed flying gives them a new problem.

Hurtling fast towards solid wooden objects.

Thankfully, emergency stops are second nature.

Just before landing, the squirrel tilts backwards.

Its wing becomes a parachute.

The elastic skin billows out...

..trapping air to reduce speed.

An arched back absorbs impact like a curved suspension spring.

And all four limbs contact at once for a textbook landing.

The simple wing has enabled the squirrel

to not only control the air around it,

but reduce the impact of landing at speed.

Allowing the flying squirrel to escape predators

and feed safely,

even in the depths of winter.

But what if you need to glide like a squirrel from tree to tree

but you don't have any wings?

Your body would need to be a very special shape.

One, we'll find here.

The tropical rainforests of Borneo.

Home to the paradise tree snake.

When it comes to flying,

you've got to feel sorry for snakes.

Not a leg to stand on, let alone a wing to flap.

But its body shape can teach us a lot about how to fly.

Living high in the trees presents a huge challenge.

If you want to travel across the jungle...

..you've a long journey ahead.

All the way down one tree

before you can climb the next.

And the forest floor is no place to linger.

ANIMAL GROWLS

It's full of predators just waiting for animals passing through.

Perhaps that's why, here in Borneo,

so many things take to the air.

Frogs...

..lizards...

..even flying plants.

Well, seeds.

But how does a snake get around with so many gaps to be crossed?

This snake has an ingenious solution.

The bendy snake becomes a rigid rod.

Its body, a bridge.

By holding on with their tail,

tree snakes can cross gaps with 90% of their body unsupported.

But not even this incredible core body strength

can prepare them for gaps like this.

Jungle trees in Asia can be unusually tall.

The distance between them bigger.

There's no way a snake can bridge gaps like these.

Instead, it does something different.

There are 3,500 species of snake in the world.

But only one like this.

This is a snake that flies.

What is the secret to this unique gliding ability?

Remarkably, just after launch,

the snake throws its ribs forward,

flattening its body into a very special shape.

It's called an aerofoil.

This shape changes the way air flows around the snake.

Oncoming streams of air passing over the top

are suddenly forced to change direction

and speed up.

This faster moving air is strung out,

so the air pressure above drops.

With low pressure air above and high pressure air below,

the snake is pushed up and is now gliding.

The snake's flight path reveals another important way

the aerofoil shape works.

On takeoff, the snake plummets,

gravity takes hold

and the snake picks up speed.

But as it falls faster, it begins to fly forward.

That's because the faster

that the air flows over the aerofoil's surface,

the more lift it generates.

And the snake starts to glide.

Inevitably, all gliders come to earth

because they're using gravity to pick up speed.

They have to drop in height to fly forward,

so if you want to stay airborne for longer...

..you need to power your flight.

To discover how animals do that,

we're heading to the middle of the Atlantic.

This ocean stretches over 12,000km from pole to pole.

And is almost as deep as Everest is high.

In this vast wilderness,

even a single palm frond floating miles from tropical shores

can suddenly find itself the centre of considerable attention.

In an empty ocean, it offers shelter.

And inevitably, life begins to gather.

It's a haven, not just for these fish

but soon for their eggs.

For a handful of days each year...

..thousands of fish meet to give life to their next generation.

Quite how they choose the perfect moment is still a mystery.

But once the first fish spawns, the rest soon follow.

Each female can lay 20,000 eggs.

And before long, the sea turns milky as males rush in to fertilise them.

In the haze, it's hard to see approaching predators.

TENSE MUSIC PLAYS

Rapid escape is critical.

And this is when these amazing fish reveal their true identity.

Flying fish.

Fins become wings.

Unlike the snake, they can't use gravity to pick up speed...

..which is why their tail is unique amongst all fish.

The lower half is longer than the top.

So even with its body in the air,

the tip of the tail remains submerged.

Thrashing it side to side provides forward momentum,

and as the fish speeds up,

the aerofoil-shaped pectoral fins generate lift.

Until, eventually, the force is enough to send them flying.

Once their special tail has got them started,

flying fish can glide over 100m

at speeds of 60km/h.

Their fins, shaped for high-speed flight,

are a match for the fastest falcon.

But that's not all.

Flying fish are held up by a cushion of air

compressed between their bodies and the water's surface.

And when they lose height,

their powerful tail can accelerate them skyward once again.

This is powered flight.

By pushing themselves forward, the fish create more lift

and can spend longer in the air.

Now we're really flying.

Powered flight opens up the skies to many animals.

Most do this by flapping their wings.

But it's hard work.

Flapping requires more power than any other form of movement...

..increasing an animal's energy costs by up to 20 times.

To stay active, a hovering hummingbird needs to drink

two-thirds of its body weight in nectar every day.

But what if an animal could stay airborne for hours...

..with no effort at all?

It sounds impossible.

But in Africa there are those that can.

There is one species which needs to travel hundreds of kilometres

to find and follow their migrating food.

In this case, the wildebeest herds

travelling across the African continent.

This animal's great skill is taking advantage of the fact

that air is constantly in motion.

Meet the vulture.

A vulture's huge wings generate so much lift

that in a glide they lose height at less than a metre per second.

So, in theory, if they can find air

that's rising faster than they are falling,

they could fly forever without flapping a wing.

In the early morning, impatient birds take test flights.

They wait for the air to start moving.

And as the land warms up, that's just what happens.

Although we can't see it,

moving air flows through a landscape like water.

As the sun heats the cliff face,

warming air rises

dragging cool air up from the valley floor.

When this air collides with the cliff,

just like the sea hitting a harbour wall...

..it's driven further upward.

Across the plains,

an area of land that absorbs more heat

creates columns of warm rising air above it,

thermals.

These are the skies' elevators,

and the vultures ride them in their hundreds.

It's the need to capture rising air

that explains the shape of a vulture's wing.

They need to be huge like a sail

to catch as much rising air as possible.

But big wings can create problems.

As an animal flies,

the higher pressure air below a wing is sucked over the tip to the top,

creating spirals of unstable air that slow the vulture

and would make it lose height faster.

Broad wings generate more of this drag

as there's a wider wing tip for the air to spill over,

and that's why vultures have those long single feathers

at the end of their wings.

They effectively turn one wide wing into several thin ones,

which helps stop those negative spirals of air from forming.

This unique design makes the vulture a true record-breaker...

and when conditions are right, hundreds gather...

..using a thermal to gain height...

..and those incredible wings to effortlessly glide onward

in search of the next thermal.

Hopping across the African plains between islands of rising air,

they can fly hundreds of kilometres a day in search of food,

and reach altitudes of over 11,000m,

making them the world's highest-flying bird.

The vulture is just one of the many extraordinary animals

we've seen that take to the air to survive.

These animals have some incredible adaptations

for launching into the skies.

Some have mastered control in the air.

Others generate forces like drag to protect them from impact,

and lift to allow them to glide.

Those that go further

take advantage of a special aerofoil shape,

and by increasing the airspeed over its surface

can stay in flight for longer.

But only the very best combine all of these skills...

..to effortlessly beat gravity...

..and truly master life in the air.

In this series, the team's mission

was to reveal the incredible abilities of airborne animals

in more detail than ever before.

Weeks of patient filming

allowed the team to capture real-life events,

like the leaping ducklings, which only occur once a year.

Revealing the science behind how these animals master the skies

required additional filming tricks and some incredible individuals

who would allow the team to capture their unique behaviour -

impossible to achieve in any other way.

Of all the animals in the programme

none presented more of a challenge than the flying snake.

They glide effortlessly,

but capturing their natural behaviour would have been impossible

without the world's leading expert

and some ingenious film-making techniques.

To film them, the crew heads to Tenom Agricultural Park in Borneo -

a known hotspot for flying snakes.

Director Simon Bell is excited by the prospect.

So, we've got this site that gives us a beautiful backdrop.

We've got some lovely jungle in the background,

some mountains in the distance.

It's going to look great.

Cameraman Pete McCowen prepares.

The success of the shoot relies on a high-speed digital camera

that slows the action 60 times.

Director Simon is aware of the challenges ahead.

It's really hard to see these snakes in pristine forest.

They're not uncommon,

but you're never going to see them in the jungle

unless you work with a guy who knows them like Jake knows them.

Professor Jake Socha - the world's expert on flying snakes.

He's studied them for over 15 years,

and for him, the chance to observe them

in their native habitat is an opportunity

to record new behaviour.

He's brought more cameras than the crew.

Before his studies, flying snakes had been the stuff of legend.

The literature goes back into the late 1800s.

What's in there is foreigners talking to locals

who describe a flying snake,

and the scientists think the locals are making things up.

Some people say they're straight in the air,

some people say they're wiggling around.

I found it compelling to solve this mystery.

What is the snake doing and then how does it do it?

With his years of experience,

Jake is realistic about how the crew can film the snake's behaviour.

To put a camera in the trees

and hope that you have an animal glide on by,

that's impossible to do.

If you really want to see what they do in the air,

you have to set up an experimental situation.

The crew's best hope for filming snake flight

is to use a technique Jake pioneered

with a few modifications for the jungle.

They need three things.

A tower for the snakes to fly from, a target for them to aim at,

and of course, the snakes themselves.

This clearing is the perfect spot,

and with some help from the crew,

rope access specialists begin construction on a 50-foot tower,

carrying everything into the jungle by hand.

There's a lot that could go wrong.

You know, we've got some really good guys,

but that tower's only halfway up right now.

It's going to be twice that height.

The steel cable at the top

will help to compress the tower, giving it rigidity.

The problem with that is you then have a potential

for sort of...snaking, we call it.

So, what we then do is we put in half-height cables

to try and prevent that sort of S-shape developing within the tower.

That'll hold it nice and straight

and once they're there, it's a bomber.

While the rope team worked on Jake's safety,

Simon ensured the ground was covered in dry grass

for the softest of snake landings.

For his research, Jake needs to control

the exact height of the snake's flight,

so a tower is the only option.

Without him, the crew have little hope

of bringing snake flight to the screen.

So, we're kind of in his hands in a way.

You know, this is all his design, this whole set-up.

When that snake's gliding from that scaffold tower,

it's going to look spectacular.

Although Simon now feels more confident,

there's still one vital thing missing.

There are tens of thousands of this particular snake on Borneo,

but to tell you the truth, they're not easy to find.

I've never been in the forest and spotted one

and been able to catch it.

As day one ends, success is far from certain.

Day two, and as the crew put the finishing touches to the tower,

they get some good news.

Snakes have been found closer to home than anyone had imagined.

-What do you think?

-Ah, they're beautiful.

But seeing them up close gives cameraman Pete new concerns.

They're beautiful little snakes, but like the one Jake's got,

it's a very small little snake,

so trying to capture that is going to be interesting.

You're going to have a hard time keeping track,

or maybe not cos you're a pro, right?

Yeah. That's the impression I try to give.

Filming worries aside, it's time to get Jake's experiment underway.

Trees in Borneo can be well over 75m high.

For a flying snake, a 15-metre tower is child's play.

If only it were the same for the scientists.

I'm generally bad with heights.

I don't like 'em.

I think that's a good place to be, right?

It's keeps you away from tall things

that you might fall off.

I'm a bit concerned about Jake.

He has revealed that he is a little bit afraid of heights.

It should be perfectly safe, but there will be a bit of a sway

when you get to the top of that thing.

I'm not utterly frightened.

I'm just frightened.

Hey, I'm almost there, right? Thank God.

It's a nice view, though.

Well done!

With over 15 years of experience,

Jake knows that hoisting snakes slowly in a soft bag

they can comfortably curl up in

is the best way to ensure they arrive relaxed and raring to fly.

Snake arrival by pulley.

At least, that's the theory.

He is not having any of it,

so I'm not going to force him to do anything.

To film natural behaviour,

you can't rush one of the world's most impressive flying stars.

All right.

The crew are ready...

Come on, baby. Thank you.

..and they must stay alert,

because when a snake decides to fly, you don't get much warning.

Going right away. Now.

Oooh! Ooh!

Phenomenal. Just phenomenal.

Just as Jake predicted,

from this height the snakes are landing safely

and reaching the target tree.

They're flying. They're absolutely flying.

It's a great relief, and all eyes turn to cameraman Pete.

Ready? Now.

HE MUMBLES

Yeah, that was really great. I couldn't even see it.

The snakes are really taking to the experimental set-up.

Dropping now.

All the pressure is now on Pete.

-Pete, there are some bits where it's going this way.

-Yeah.

-Did you get any of that?

-No.

But with the snakes flying so well,

Pete is learning to keep up with them.

Woo!

Well done, Pete. Well held.

That's amazing.

Whoa!

I think that's the first time I've ever seen this,

where you see a phenomenal glide

and then she landed on the tree there.

This is brand-new data and it tells us that

when the snake lands on a natural substrate

that its body is flat.

This is beautiful. I'm really excited to get this.

With the shots captured, there's only one thing left to do -

release the stars of Jake's research back to where they came from.

This is my favourite snake.

It's ready, it's looping down.

OK.

After nearly 20 years of study,

Jake is still discovering new things about the animal that he loves.

What I got out of this trip is a new appreciation for this animal.

Some people look at me and think that I'm insane.

They say, "Why would you want to do that?"

Any time you can learn something that is new to science

and new to the world, you know, that's pretty exciting.

This is fantastic.

The team had revealed the remarkable flight

of flying snakes in more detail than ever before,

capturing the beauty of an animal once thought of as only a myth.

Next time, we discover how nature

has pushed the basic flying body plan to the limit.

How do the heaviest animals take off,

the fastest use speed as a weapon

and half a million avert air traffic disaster in total darkness?