Original subtitles

The monsoon...

..the greatest weather system on Earth.

Giver of life...

and the destroyer.

Shaping magical lands

from the Himalayas to Australia.

Its impact felt by giants...

..the exquisite...

and the bizarre -

where spectacular nature meets the planet's most vibrant cultures.

Now, we journey into the tropical heart of the monsoon.

A place of remote islands...

where the monsoon collides with the fires of the underworld...

..creating homes for some of the most wondrous and peculiar

species on the planet.

Sulawesi, a lush island, straddling the equator.

Deep in the forest, there's a new arrival.

He is a crested black macaque.

And he is growing up in an unusual family.

Crested black macaques like to live in extraordinary large groups,

sometimes numbering over 100.

But what sets them apart is their character...

..something that's intimately connected to their home.

Crested black macaques live only in northern Sulawesi,

in rich forests that sit directly in the path of the monsoon.

Torrential rains batter the forest for months on end.

But it is thanks to these monsoon rains

that this baby will develop behaviours

which, more than other monkeys, we might recognise in ourselves.

But first, the youngsters have a lot to learn.

Starting with the monkey basics -

like perfecting their climbing techniques.

But most important for the crested black macaque

is to learn their code of etiquette.

Lip smacking is a request for a hug,

showing a desire to be friends.

Blowing kisses and sharing cuddles

is not only reserved for close family.

Anyone in the troop can join in.

They are amongst the most affectionate monkeys on the planet.

One reason is that with the coming of each monsoon,

the forest presents a banquet.

Over 100 varieties of fruit.

There is more than enough to go round.

So much that they don't need to fight over it.

Instead, they put their energy into the good things in life -

friendships and exploring their forest home.

A discovery draws them all close.

A tiny casualty on the forest floor.

Sometimes, their sensitive behaviour can seem touchingly human.

The monkeys' character is a result

of the riches that the monsoon brings -

life with abundant food.

But in these islands, the effects of this great weather system

are not always so benevolent.

Like a giant letter K,

Sulawesi sits at the epicentre of the monsoon region.

Lying to the south-east is Australia

and far to the northwest is continental Asia.

For much of the year, it seems that Sulawesi is swamped in cloud.

But there is an annual rhythm.

From December, moist winds blow from Asia,

bringing very heavy rain from the north.

Then from June, they blow from Australia,

bringing more rains from the south.

So most islands between the two continents

get monsoon rain not just once, but twice a year.

It's November. The monsoon winds are about to change again.

It's a race against time for another of Sulawesi's unique residents.

BIRD CRIES

A maleo.

They are normally creatures of the forest.

But once a year, they hit the beach.

It's breeding season.

But instead of spending all that time sitting on a nest,

maleos use solar power...

..burying the eggs in sand warmed by the sun.

So eggs can only be laid between monsoons.

And there is not much time left.

One couple has secured a prime spot.

Away from the water and safe from the coming storms.

But two late arrivals spell trouble.

The early birds have to dig fast.

But their new neighbours make the job twice as hard.

It's frustrating work.

At last, the hole is deep enough for her to lay.

A maleo's egg is five times larger than a hen's.

It must provide enough energy for the chick to grow quickly,

fight to the surface

and survive the oncoming monsoon.

Job done.

But is it too late?

As the monsoon clouds arrive, beach temperatures will plummet.

The latecomers may have lost the race against time here.

But Sulawesi's maleos don't rely on solar power alone.

Deep in the forest, the ground stirs.

Hatched from an egg buried a metre deep...

..a maleo chick.

His parents had an ingenious way to beat the monsoon.

They've discovered underfloor heating.

Sulawesi is pocked with hot springs.

Water, superheated by several hundred degrees,

rises up from deep fissures in the Earth.

The island, and hundreds of its neighbours,

sit above great cracks in the Earth's mantle,

and the consequences are explosive.

It's part of what is known as the Ring of Fire.

Five tectonic plates shifting below the sea

in continual collision,

creating island after volcanic island.

All pushed up directly into the path of the monsoon.

When the monsoon winds collide with a large volcanic mountain,

moist air is forced upwards, forming immense clouds.

And the result, arriving in great deluges,

is even more rain.

But this heady combination of volcano and monsoon

has another dramatic effect...

..impacting both wildlife and people.

Java, legendary as one of the most fertile of the Spice Islands.

Yet at its heart lies a mysterious and deadly place.

Each morning, fog drenches the land.

But when the intense sun burns it off, it reveals no rainforest.

This is the Sand Sea.

And once a year, pilgrims risk their lives to come here.

Sarina and her family are Tengger people,

descendants of a great Hindu empire

that once stretched from Sumatra to New Guinea.

Now their traditional culture survives

only around the edges of the Sand Sea.

Today, they are gathering for a time-honoured ritual,

observed for over six centuries.

It's a ritual that for some, in the past, proved fatal.

But Sarina's family, like most Tengger, are farmers,

and believe that the success of their next harvest hangs on this day.

The climb is steep and treacherous.

As many as 3,000 people will ascend to the narrow rim.

This is what Sarina's family have come to honour.

Mount Bromo - a vast and still very active volcano.

Daily, Bromo belches rocks and sulphurous gas.

It could erupt at any time.

The Tengger risk all to bring sacrifices for a Volcano God.

Legend has it that, once, these sacrifices were human.

But these sacrifices aren't made out of fear.

They're made in gratitude for a rich harvest.

Though not much makes it into the Volcano God's belly.

For those who dare to enter the mouth of the volcano,

anything caught is said to be a blessing.

The catchers risk their lives.

The angle of the slope is up to 80 degrees.

One slip, and the sacrifice might be human after all.

The chicken escapes the fire...

..but not the frying pan.

The Tengger are deadly serious about thanking their Volcano God,

and they have good reason.

What seems a desert is not made of sand,

but ash and cinder.

The entire Sand Sea sits within a giant volcanic crater...

..first created by an immense eruption nearly a million years ago,

with Bromo and four other volcanoes nestling at its centre.

Plants are smothered so regularly that little can survive.

But just beyond the crater...

..the Tenggers' farms are lush...

..the result of the volcano's bounty meeting the monsoon.

Volcanic ash is rich in minerals and nutrients, vital for all life.

With each eruption, plumes of ash are scattered far and wide

by the monsoon winds...

fertilising millions of hectares of Javan soil.

Such is the immense yield of food

that 140 million people live on this one island.

That's the same as the whole of Russia.

It's the double dose of monsoon rains

plus an endless supply of nutritious ash

that has driven the evolution of rich and bountiful life

across these tropical volcanic islands...

But there is a strange and wonderful exception.

The island of Borneo.

Home to the oldest rainforests on Earth...

..and yet they seem strangely empty...

Mammals are seldom seen.

Their calls rarely heard.

What life is found

is secretive...

and often, very odd.

A giant Bornean red leech, and it's hungry.

Without mammals to provide a meal,

this forest is like a desert for a bloodsucker.

But the leech has risen to the challenge...

with deadly effect.

The heavy rains trigger the emergence of another giant.

A Bornean blue earthworm, 70 centimetres long.

It follows an irresistible chemical trail...

..to find a mate.

But leaving trails in this forest is dangerous.

The leech has an extremely sensitive mouth.

It tastes its way towards its prey.

Feeling up and down the worm's body,

it searches for an end.

And it starts to suck.

The worm fights back

but there is no escape.

The leech sucks its prey down like spaghetti,

crushing the worm with its muscular throat.

It will be a whole month before this leech needs to hunt again.

The giant leech's evolution from parasite to worm-killer

is just one of nature's answers to the problems of living on Borneo.

Here, life is under extreme pressure.

Despite all appearances, these forests are impoverished.

Starved...by of all things, the monsoon itself.

On Borneo, there are no live volcanoes.

So there are no regular deposits of mineral-rich ash to feed the land.

What there is, in abundance, is rain.

Monsoons have drenched this land for 130 million years,

continually flushing nutrients away.

So without volcanic ash to replenish the goodness,

the monsoon has rendered Borneo's ancient soils infertile.

Yet somehow, the world's tallest rainforest trees grow here.

At first glance, the tall trees suggest abundance.

But this is an illusion.

They have simply evolved to become super-efficient

at gathering minuscule trace amounts of nutrients...

before the monsoon can wash them away.

They lock these nutrients up in giant fortresses

that serve to protect their hard-won gains.

So the challenge for any animal is to break into these fortresses.

Faced with such a monumental challenge,

life on Borneo has responded,

in an explosion of strangeness and beauty.

With the arrival of each monsoon, butterfly numbers boom.

A lifeline for one tiny predator.

The Bornean falconet is the smallest bird of prey in the world,

no heavier than a sparrow.

This pair has three voracious chicks that need small prey in abundance.

Butterflies are just right.

The chicks demand over ten an hour.

Without the monsoonal butterfly glut,

the falconets couldn't raise their young.

But eating butterflies here can be dangerous.

A Nephila spider, joining the monsoon banquet.

For her prey, there is no chance of escape.

Her web is strong enough to hold small birds.

But she recognises this catch.

She snips at her web.

She's caught a tiger butterfly.

And he is utterly toxic.

Butterfly predators need to learn this.

But his poison protection is ultimately due to the way

that the monsoon has starved these forests,

forcing the trees to battle to protect their nutrients.

A minuscule caterpillar, emerged from a butterfly's egg,

laid just after the rains.

Food surrounds him...

..but he faces a formidable problem.

The tree guards its nutrients with fatal poisons.

He begins to chew...

but he's not eating.

He is excavating a trench.

The plant fights back, oozing a noxious sap.

But the caterpillar has created a barrier.

The sap, pumped from the stem, can't reach him.

Finally he finishes his circle.

The heist is complete.

The portion inside is now isolated and safe to eat.

As he grows, he raids the tree's reserves time and again.

Each time, he ingests tiny traces of poison.

And with each dose, his resistance builds.

Until eventually, he achieves complete immunity.

Now the caterpillar can gorge himself.

He has harnessed the tree's defences for himself.

Protected by the poisons in his body,

no predator could safely eat him...

..and his ostentatious warning colours

ensure that they won't even try.

Safe in his cocoon, with poisons coursing through his veins,

the insect is completely protected...

..through his development...

..and into his second life...

as a tiger butterfly.

Across the forest, millions of similar battles rage

in an arms race over nutrients.

With each generation,

the caterpillar armies improve their strategies...

..while the plants constantly refine their chemical weaponry...

..resulting in a poison army of oddities.

And a toxic forest with leaves indigestible to most creatures...

..especially mammals.

But there is one peculiar resident

with extraordinary powers of digestion.

Proboscis monkeys.

They are named after their strange, tumescent noses

but proboscis have also been called the cows of the canopy.

They are the only primate with a digestive system

equipped to chew the cud.

To minimise the level of any poison in their bodies,

no one plant can dominate their diet,

so they are constantly on the move

and then pick only the youngest, less-toxic leaves.

Their immense bellies are packed with a very long, extended gut

and a complex stomach with four separate chambers

that take 50 hours to digest dinner.

And despite all this, most of the forest's foliage

is too difficult to digest.

In this nutrient war, driven by the monsoon,

the trees are runaway winners.

They not only dictate the bodies and lifestyles of these monkeys,

but ensure that the density of mammals is kept low.

But even these fortress trees have one inevitable weakness.

Eventually every leaf must die...

..leaking away precious nutrients...

..drip-feeding them to the forest floor...

..where a voracious horde waits to pounce.

With each monsoon shower,

microbes and fungi burst into action,

bloating on the decay...

..softening the dead vegetation for legions of competing creatures.

The race for nutrients

makes this one of the most competitive environments on Earth.

But there's one creature that's faster and more efficient

at consuming the leaves than anything else.

Processionary termites.

Termites recycle a staggering one-quarter

of all the leaf litter on Borneo.

They tear into the leaves...

..to create tiny food parcels

that are hauled back to the colony

in a tireless relay.

They are amassing a priceless bounty.

Soldier termites flank the column on high alert...

..armed with helmet-like heads that squirt noxious chemicals.

In less than two hours - before anything else can get a look-in -

the leaf has gone.

Marched portion by portion into their underground nests.

A vital supply of nutrients, returned to the soil...

..only to be rapidly sucked back up and locked away again

in the giant fortress bodies of the ancient trees.

The competition for nutrients in this impoverished land,

washed by the heavy monsoons,

has, over millions of years, created a unique array of life.

But there is one place on Borneo

where the monsoon is more extreme than anywhere else...

..where it rains every single day.

Mount Kinabalu.

The highest peak in Borneo.

It towers 4,000 metres high...

..causing immense clouds to form almost continually.

Over millions of years,

the rain has scoured and shaped the rocks of Kinabalu...

..creating an alien landscape,

and washing away any trace of nutrients.

But the bigger the challenge the monsoon presents,

the more ingenious is life's response.

Just below the peaks...

a myriad of unique orchids flourishes.

Their roots reach out into the winds

to catch trace nutrients dissolved in mountain mists.

Over a metre wide, rafflesia is the world's largest flower...

..yet it has no roots, stems or leaves of its own.

It's a parasite - stealing its nutrients from other plants.

And most bizarre of all - the pitcher plants.

Their leaves have evolved to become deep cups,

filled with digestive juices.

The stomach-like vessels hang across the forest...

..waiting for food.

Some have become leaf catchers.

The decomposing soup inside feeds the plant.

Others have become carnivores.

Their colours and scents lure insects

to a sugary nectar that's too tempting to pass by.

But it's a trap.

Insects quickly slip on the wet rim

and tumble into the deadly liquid.

Their drowned bodies decay

in the enzyme-rich juice of the killer plants.

But some pitchers need more than just insects.

A giant amongst carnivorous plants,

the Kinabalu giant pitcher.

It's over 30 centimetres tall

and holds up to two litres of liquid.

It patiently waits for something warm-blooded.

A hungry tree shrew.

The mosses provide moisture for a quick drink

but she needs a meal.

There is something sweet on the air.

The scent of the giant pitcher plant lures her closer.

It's irresistible.

To get a good lick of sugar,

she'll need to climb on to the rim.

One slip and she'll fall.

PLOP!

But the shrew knows what she's doing.

The plant offers its tasty treat

in exchange for an important deposit.

A dose of perfect fertiliser

that the giant pitcher so desperately needs for growth.

Tree shrews are territorial.

By leaving her droppings,

she's signalling to other shrews that this plant is taken.

It is one of the most extraordinary relationships

between plant and mammal anywhere...

..come about only because of the extraordinary evolutionary pressure

from the monsoon here on Mount Kinabalu.

The life found on Borneo

must count amongst some of the most unusual on the planet.

And this is just one of almost 20,000 islands

in the vast archipelago of which Sulawesi and Java also belong.

Each a world of its own,

filled with strange inhabitants and wonderful adaptations to life

trapped in the very heart of the monsoon.

Mount Kinabalu towers more than 4,000 metres

over the island of Borneo.

The monsoon team's goal is to reveal the strange and dynamic world

of this mystical mountain,

and in the ancient forests on its slopes,

they are on the trail of a legendary predator.

One that remains a mystery to science...

..the giant red leech.

To find the leech,

the crew first need to find its prey...

..a giant worm.

We're now at 3,000 metres high.

Apparently, this is where the Kinabalu giant blue worm thrives.

Scientist Alim Biun discovers a telltale clue -

a huge worm cast, surely created by a monster.

That is like an English earthworm. It could be a giant blue.

Yes, yes. It is. It is a giant blue.

How long does it take to get from that...? Nobody knows.

Nobody has studied it. Really? Nobody knows.

Frustratingly, there's no sign of its fully-grown relatives.

So Paul and Richard decide to head for the summit

to capture crucial shots of monsoon clouds

sweeping over the mountain.

It's a 1am start from their camp.

They reach the top, hoping for glorious dawn light.

But all they catch is a fleeting glimpse of the landscape.

One of the problems is that we are here to try and film clouds,

the monsoon,

but actually, for 75% of the time, you are actually in it,

and while you're in it, you can see it.

Hence the wait. Yeah. The big long wait.

Day after day, they scale the rocky peaks

in the hope of striking lucky.

After a week, there's still no sign of a break in the weather.

But their luck is about to change.

Lower down the mountain, they

discover another strange giant -

a pitcher plant, and the tree shrew

that it has a special relationship with.

They're in the last place the crew expected.

Turns out that the best place to film these tree shrews is literally

15 metres from where we were staying.

Shrews are normally incredibly shy

but here they are used to seeing climbers.

Even with the crew watching,

they continue to go about their routine visits

to lick the giant pitcher and make a deposit.

It's an incredible opportunity and Paul wants to attempt

a shot that just wouldn't be possible

with nervous shrews elsewhere.

We have been given special permission

to cut the base of one of these

large pitchers so that I can attach this small camera inside.

So I am just going to stick this on here like this.

With a bit of luck, the tree shrew will poo straight onto my lens.

And he is jumping on.

I can see him looking as well.

PLOP!

Fantastic. Yes.

That's him off. Yes. Got it. Brilliant shot.

It's a world first.

Oh, yes.

With time running out, the team head back to the top.

So once again, we're climbing in the rain.

We have been up and down this mountain ten times.

THUNDER RUMBLES

I just heard some thunder.

The storm is rapidly intensifying,

and the crew have to take cover immediately.

The only shelter is a narrow gully.

Alim, how long do you think this will last for?

It's going to be dark pretty soon so we have decided to abandon some

kit here on the mountain and head back to camp.

It is going to be pretty dodgy

because that is very slippy out there.

Surrounded by thick cloud, it's easy to get lost.

In recent years, people have gone missing

from these slippery slopes.

But for the team, it turns out that this cloud has a silver lining.

Further down the mountain, the heavy monsoon rains

have triggered an emergence of subterranean giants.

Look at this. Yes. Wow.

How many is that that we have collected so far?

More than 10. More than 10? Nice.

And where there are giant worms,

Alim thinks that there should be giant leeches on the hunt.

That's huge!

This is the adult. Wow!

And it's quite hard to determine

whether they're males or females.

Nobody has studied that so far.

Does this suck blood?

No, no, no. That's only looking for earthworms.

It would be impossible to film these animals without the help

of Alim and his team.

In return, the crew help him to gain a valuable insight

into the lives of these mysterious giants,

by filming this rarely seen behaviour for the very first time.

But just as the crew plan to leave the mountain,

there is an unexpected break in the weather.

Dawn reveals a clear morning.

So I've come to the summit of Mount Kinabalu.

I'm the highest person between the Himalayas and Papua New Guinea

and on a day like today, you can really appreciate the beauty

and it just looks absolutely spectacular.

Using time-lapse photography,

the clouds are sped up,

bringing to life to this mountain at the heart of the monsoon.

Next time, the lands of the monsoon

make up one of the busiest and most productive regions on Earth.

This is an epic story of a relationship

between the people who live here

and the bountiful nature that surrounds them...

..from ancient times,

through the challenges of the modern world and into the future.