Original subtitles

Far away, cut off by vast oceans...

..lie Earth's tropical islands.

Home to remarkable animal castaways...

..that have evolved in isolation...

..and human cultures that have

adapted in extraordinary ways.

From the jungles of Borneo,

with their staggering

wild diversity...

..to Hawaii, the most remote island chain,

colonised by only the hardiest pioneers.

And Madagascar,

the oldest island of all,

where time has given rise

to thousands of unique species.

ANIMALS CALL

These tropical islands

have developed into astonishing

and unique worlds...

..cradling precious life

found nowhere else on Earth.

In the heart of South East Asia...

..lies the tropical island

of Borneo.

Twice the size of the British Isles,

it's the world's third largest island.

Its wide variety of habitats

is home to over 60,000 species of animals

and plants.

Possibly the greatest diversity

of life of any island.

Borneo's shoreline is fringed by

a unique habitat.

A vast flooded forest,

criss-crossed by a network of rivers.

Within this waterlogged jungle,

an extraordinary creature has evolved.

The proboscis monkey.

This male's enlarged nose

serves one key purpose.

To attract a mate.

And his supersized snout...

..has secured him a harem of adoring females...

..and their offspring.

It will take this baby seven long years

to grow a nose to rival his father's.

But for these monkeys...

..it is their pot bellies

that are key to their survival.

There is precious little nutrition

to be found in the bitter leaves of

these flooded forests.

Proboscis have evolved an enlarged gut to extract

any goodness there is.

Still, only the youngest leaves

have enough nutrition

to be worth eating...

..so the male must lead his troop

up to a mile a day

in search of fresh growth.

But their route is often blocked...

..by one of the many rivers that cut through the forest.

Patrolled by giant predators...

..growing to more than five metres long

and weighing up to a tonne.

The saltwater crocodile.

To reach the young, juicy leaves on the other side,

the group will have to cross...

..but the male is hesitant.

Instead, it's the alpha female

who takes the lead.

LOUD SPLASH

The rest of the troop quickly follow.

LOUD SPLASHES

Sounds of their splashes carry

over 200 metres through the water...

..and can draw unwanted attention.

But unlike most other monkeys,

proboscis are excellent swimmers.

To survive here,

they have evolved webbed feet.

Finally, the reluctant male

makes his move.

LOUD SPLASH

SQUEALING

But a mother and baby have been left behind.

The baby must cling on for dear life.

LOUD SPLASH

MONKEYS SQUEAL

This time, the whole family

have made it.

Even the most vulnerable.

At last, they can feed on

the succulent fresh leaves.

With its unique adaptations

for surviving in these flooded forests...

..the proboscis monkey is just one of over 6,000 species

found only on Borneo.

They evolved from ancestors

that were isolated here long ago.

Borneo was once joined to Thailand

and mainland Malaysia,

part of a vast landmass,

home to one of the oldest

forests on Earth...

..but when the last Ice Age ended

10,000 years ago,

sea levels rose, leaving Borneo

and its ancient forests stranded.

The surrounding shallows now host

some of the richest coral reefs in the world.

A single reef

can support more species of coral

than the entire Caribbean Sea.

All this abundance attracted

a remarkable group of seafaring nomads.

The Bajau Laut.

People of the Sea.

Over generations of diving,

their bodies have transformed.

Their spleens are 50% larger than average.

It's believed this provides their

blood with more oxygen for diving.

They can hold their breath

for over three minutes,

and spend 60% of their day hunting underwater.

Longer than almost any other human being.

The Bajau Laut settled on Borneo's coasts around a thousand years ago.

Villages like Tatagan may only be 20 miles from the nearest town...

..but the 200 or so people

who live here still rely on the sea

for nearly all their needs.

Rajamil and his son, Fidel,

are traditional fishermen...

..but they're having to adapt to the modern world.

Plastic is the scourge of today's oceans,

but for Rajamil and Fidel, it provides an opportunity.

Rajamil is teaching his son

how to turn this plastic

into something useful.

The lure will have to be convincing

if it's to trick the reef's

most intelligent resident.

The reef octopus.

With his new fishing technique,

Rajamil can catch enough octopus

to support his whole family.

Adapting to change, the Bajau continue to live off

one of the richest coral reefs in our seas.

But Borneo's exceptional diversity

only increases as you head inland...

..and enter one of the last surviving fragments

of a tropical rainforest

dating back 48 million years.

Covering an area larger than Germany, a single square kilometre

can hold more species of tree than the whole of Europe.

But one group of giants dominate.

The Dipterocarpus.

Towering up to 100 metres high,

they are the tallest rainforest trees in the world.

A single fruiting tree

can support over a thousand different species of animals.

This leads to intense competition

for food and space.

To survive in these crowded canopies...

..life has evolved in wondrous ways.

Borneo has over 20 species of gliding reptile.

More than any other island on Earth.

With nightfall, the competition in the jungle intensifies...

..as many of Borneo's 180 species

of frog now burst into song.

FROG CALL

All singing for a mate.

CALLING CONTINUES

The bigger the frog,

the louder the call.

But this male tree-hole frog

is barely bigger than a fingernail.

He'll need to do something special

if he wants to be heard by

a nearby female.

She may only be metres away...

..but the chorus from the other frogs is deafening.

This tiny male, however, has a trick.

He searches for a tree hole.

The size and shape of the hole

are critical.

He then does something remarkable.

FROG CALLS It begins with a soundcheck.

CALLING CONTINUES

Too low.

He changes pitch.

HIGH-PITCHED CALLING

Too high.

SLIGHTLY DEEPER CALLING

That's it.

CALLING CONTINUES

CALLING CONTINUES

At this specific frequency,

the tree-hole resonates,

amplifying the sound and broadcasting the call

more than 50 metres across the forest.

CALLING CONTINUES For a female,

it's music to her ears.

CALLING CONTINUES

With superb directional hearing...

..she can home in on his calls.

CALLING CONTINUES

Finally, the tiny couple meet.

Hidden from predators,

the tree-hole will go on to make

an ideal nursery for their tadpoles.

Compared to the abundance of life in the treetops...

..on the forest floor, it's an impoverished world.

Here, the roots of the giant trees

suck up most of the nutrients...

..leaving the soil poor.

With little to eat down here,

many of Borneo's terrestrial mammals

are smaller than on mainland Asia.

Confined to her protected forest sanctuary...

..the exceedingly rare

Bornean Sun Bear.

Just over a metre long,

it's the smallest bear in the world.

This fallen branch

is a valuable treat.

Filled with wood grubs and beetles,

nothing is wasted.

Even a foul-tasting millipede.

But it's not enough to sustain even this little bear.

The real prize sits high above.

Guided by her exceptional sense of smell...

BUZZING

..it's the sweet scent of honey.

For larger bears, this beehive

may be out of reach...

..but being small helps defy gravity.

With sharp claws and rough pads on her feet,

she can ascend 40 metres,

higher than any other bear.

BUZZING

To make it in Borneo's jungle treetops...

..this miniature acrobat

has become more monkey than bear.

For those confined to the depleted

forest floor, survival requires innovative solutions.

Here, mysterious signs

line pathways through the jungle.

Left by indigenous hunters...

..that have inhabited this island's jungles

for over 4,000 years.

Etat and Geran are Penan, native Borneans,

and still reliant on their intimate knowledge

of the forest to find food.

A common fairy-bluebird.

It's a meagre kill.

Not enough to feed themselves, let alone their families.

But the Penan have an ingenious way of reaching out to others.

Along the path, they plant sticks on which they leave messages.

A single feather signifies they have caught a small bird

and a folded empty leaf shows that they are hungry and in need of food.

It's an ancient sign language known as Oroo.

With more than 50 different symbols...

..the Penan can communicate across 100 square miles of forest.

Etat and Geran have found a welcome note left by fellow hunters.

With their unique sign language and strong communal bonds,

the Penan have overcome the challenge of finding enough food

on Borneo's forest floor.

In the heart of the island, looming above the rainforest,

lies another of Borneo's diverse habitats.

Mountains.

Conditions may be tougher here, but they are still rich in life.

Their range runs over 500 miles through the centre of the island.

At over 4,000 metres,

Mount Kinabalu is one of the highest peaks in South East Asia.

Moist air from below cools and condenses

into a thick veil of cloud.

It rains here almost every day...

..the water washing away any goodness in the soil.

Sheltering in ravines lie dwarf forests,

the trees stunted from the lack of nutrients.

These extreme conditions have pushed one group of plants

to extraordinary lengths to survive.

Pitcher plants.

They have become carnivores.

With the promise of nectar...

..the plant lures in its victims...

..onto its slippery edge.

Below lies a pool of deadly digestive enzymes...

..from which there is no escape.

The captives' bodies slowly dissolve

in the pitcher's stomach-like vessel...

..providing the plant with the nutrients so lacking in the soil.

Borneo holds over 40 species of pitcher plant,

the greatest collection in the world...

..including the Hemsleyana pitcher.

It's after something much bigger than insects.

SCREECHING

A woolly bat.

Rather than using nectar as bait...

..the pitcher's flat lid is perfectly shaped

to reflect the bat's sonar...

..drawing it in.

But the woolly bat is safe.

After a night's hunting, this bat needs a place to shelter.

Rather than fall into its lethal pool,

the bat fits snuggly into the pitcher's tapered cup.

In the heat of the day,

the pitcher's waxy walls even keep its guest cool.

How the plant benefits only becomes apparent at dusk.

The nocturnal guest awakens...

..leaving behind its payment.

Nutrient-rich bat droppings, known as guano.

This plant has tapped into one of the greatest sources

of nutrients on the island.

One that has created a world of remarkable diversity

in the most surprising place of all.

The deluge of rain has carved out one of the largest cave chambers

in the world.

Known as Deer Cave,

at places it's almost 200 metres wide.

Big enough to fly a jumbo jet through.

SCREECHING

As the sun sets, a great exodus begins.

Emerging from caves across the island,

millions of bats spread out over the forest.

They are the most numerous mammal on Borneo,

and their impact is immense.

The bats from Deer Cave alone are thought to catch

up to 36 tonnes of forest insects every night.

At dawn, they return to the cave to roost,

where their excrement falls like rain...

..building, over centuries, mountains of guano

more than 15 metres high.

Feeding on it is one of the largest concentrations of cockroaches

in the world...

..as well as a wealth of other creatures.

Foot-long centipedes.

Giant cave spiders.

Even a cave crab.

Thanks to the bats, even in this extreme habitat,

Borneo harbours an extraordinary array of life.

For 10,000 years,

this remote island's astonishing biodiversity

has been protected by its isolation.

MONKEY HOWLS

CHAINSAW ROARS

But with the arrival of industrial logging and farming

in the last 50 years, all this has changed.

Today, over half of its ancient rainforests have been cleared.

Felled for timber, much of the land has been turned

into vast plantations for crops such as palm oil.

With the destruction of the forests,

researchers like Twentinolosa are increasingly concerned

about the future of Borneo's most iconic resident.

The orangutan.

His work has helped us understand

just how clever these great apes really are.

Many of the forest leaves are poisonous,

but a mother can identify around 500 species that are safe to eat.

Vital knowledge that she will pass on to future generations.

One particular orangutan has led researchers

to a breakthrough discovery.

Years of carrying a heavy baby have taken their toll.

It appears Indah is suffering from aching joints.

The medicinal paste she creates contains powerful

anti-inflammatories, thought to ease her pain.

Indah's vast knowledge of these ancient forests

includes a treatment for arthritis.

But as their rainforest homes are destroyed,

their future, along with Borneo's other unique plants and animals,

are under threat.

In under 20 years, half of all Borneo's orangutans

have been lost.

An average of 100 killed every week.

Over thousands of years,

Borneo's wide variety of habitats...

..from its bustling coral reefs...

..ancient forests...

..and remote mountain peaks...

..have been the birthplace of thousands of unique species.

But with the continued destruction of their home,

how much longer can these remarkable animals survive?

Filming Borneo's staggering wild diversity presented the team

with many challenges.

These jungles are designed for pain.

There's scorpions, spiders, snakes, bees, leeches. It's horrible.

Ow, ow. Fire ants.

Ooh, ow... Ow, ow, ow.

Are you OK?

But their greatest challenge was capturing the moment

proboscis monkeys make their dramatic leaps across rivers

patrolled by crocodiles.

One of the proboscis monkey's last strongholds

is a 150-square-mile area of flooded forest known as the Kinabatangan.

The only way for the crew to find and film these semi-aquatic monkeys

is by boat.

For the next two weeks, director Georgie Ward

and cameraman Neil Anderson must navigate

its intricate network of waterways,

guided by naturalist Cede Prudente,

who has worked on these rivers for over 20 years.

His extensive experience quickly pays off...

There it is.

..as he tunes in to the monkeys' calls.

Yeah.

There's no visual, but we can hear them further inland.

Hearing the monkeys is one thing, but following them through

the impenetrable jungle is near impossible.

We're not finding anyone yet.

Confined to the river's edge,

the crew must wait patiently for the proboscis to come to them.

Oh, there's a group here. See, this is the male.

After several days of searching,

Cede tracks down a troop of monkeys perched on the river bank.

So we've just stopped and I've got my first glimpse of a proboscis,

which is really exciting.

For Georgie, there's one individual that really stands out.

Oh, he's huge.

The male's got this massive nose

and these eyes that just kind of stare at you.

The crew ready themselves for the monkeys to jump.

Oh, there's a few of them on there now.

But the troop change their minds.

The monkeys have literally just turned

and gone back into the forest.

While the proboscis retreat,

Cede gets news of another troop also close to the river's edge.

OK, OK. Chien, let's go.

So the other boat has seen monkeys, so hopefully we haven't missed it.

OK, OK.

There's a bit of movement in the trees so it looks like

they could jump, so Neil's just getting his camera ready.

OK, Neil? Neil? Yeah, I've got them. Wow, there's the big male.

Keep an eye, because I think that's going to just jump in the river.

Just focus on the tree.

But once again, the monkeys take fright.

And this time, it's clear to see why.

No wonder they're nervous about crossing the river.

We've spotted a massive crocodile.

It is huge.

I'm pretty happy that we're still a good 20 metres

away from it, to be honest.

For today at least, the troop has lost its appetite

for the new leaves across the river,

and eventually the monkeys bed down for the night.

Dawn the next day, and the crew head back to the troop...

..only to be caught out by one of Borneo's tropical downpours.

THUNDER

Six inches of rain can fall here in a single day.

More than the UK gets in a month.

But the downpour continues, giving the crew little choice

but to beat a hasty retreat back to base.

With less than a week's filming left, they're running out of time.

We just want to get out there. It's quite frustrating.

Finally, with a break in the weather,

the team can head out again.

This time, Cede leads them to a new part of the flooded forest.

They find a troop crossing the river.

But they're taking the easy route across.

It's good to see the monkeys out in the open eventually,

but if they're going to keep using these bridges,

we'd better go a bit, maybe, further downriver.

Although these rope bridges provide safe passage for the proboscis,

they are designed to help Borneo's biggest primate.

Just somewhere behind the big tree to the right.

We've got this tiny little intimate view of an orangutan

feeding on termites, which is quite rare to see.

Borneo's orangutan is critically endangered.

The rope bridges give these great apes access

to the last strips of forest that line the river banks...

DRONE WHIRS

..which are all that remain of their habitat here.

Literally 20 metres behind the trees is a huge palm oil plantation.

When I say huge, it just goes on and on to the horizon.

That is unbelievable.

In the old days, when I was here 25 years ago,

a lot of this was forest - natural forest.

With so much of their natural vegetation destroyed,

proboscis monkeys are also highly endangered.

Still, Cede remains hopeful.

It's not too late, so whatever we have now, I think we just need to

improve the management, and I guess the oil palm plantation

has to work with NGOs and government,

so they play a big role.

Returning to the heart of the flooded forest,

they receive news of another proboscis troop

poised to cross the river.

With the shoot almost out of time,

this could be the crew's last opportunity

to capture the monkeys' elusive river crossing.

This is the closest we've got to seeing them jump.

I hope this is it. My heart is racing.

OK, OK, OK. Ready, ready, ready. Ready, ready.

One, two, three....

Go!

Wow.

OK, ready? OK.

Wow.

Oh, my gosh.

Ah, the big male.

But a mother and baby have been left behind.

All the rest of the group have already crossed.

The wary female may have spotted a crocodile.

Oh, my gosh, she's jumped.

Oh, my gosh.

Ah, it's just her head, just her head,

out the water, holding her nose up.

Come on, come on. Come on, go.

I'm so happy. I'm so happy and relieved.

Great work, team. Amazing.

Excellent. Yes. High fives all round, guys.

That was brilliant. Wow, well done. That was great.

We've been here for weeks but that is the moment,

that leap, that jump, that crossing of the river

for them to get to the other side, get away from those crocs,

so, yeah, quite a special moment to actually experience that.

This dramatic footage provides fresh insight

into the lives of these remarkable monkeys...

..but as their forest home continues to be destroyed,

even greater challenges lie ahead on this rapidly changing island.

Next time, Hawaii.

The most remote island chain on Earth.

From its lush forested peaks

to its low-lying sandy atolls,

its varied islands are home to extraordinary wildlife,

thriving against the odds.