Episode 1 Lost Land of the Volcano

On the far side of the world is an island carved by waterfalls

and forged by volcanoes.

Look at that! It's being thrown a kilometre into the air.

New Guinea, home to ancient cultures,

the last great frontier of jungle exploration in the world.

For a nine-month period, a team of scientists, film-makers and cavers

have been exploring the most remote parts of this island.

The terrain looks a total nightmare!

This is what we do expeditions for, places like this.

Unimaginably beautiful and totally unexplored.

They've witnessed the birth of new mountains

and explored ancient craters.

To find something that's never before been seen by science,

this has got to be one of the most incredible moments of my life.

That is just fantastic.

They've discovered animals found nowhere else.

Wow, wow, wow! Jeepers.

Look at that.

Their aim?

To search for species new to science and find the evidence to help preserve these forests for ever.

We can't save everything, but we have to save the richest places,

and the richest places on Earth are forests like this.

New Guinea.

A huge tropical island on the edge of the South Pacific Ocean.

This rugged jungle hides a network of deep, isolated valleys.

They're the most promising places in the world to find rare animals.

The creatures that have evolved here are truly strange.

Kangaroos that live in trees,

exotic birds of paradise...

..giant cassowaries with their armoured crests,

and the shy and secretive cuscus.

At the heart of the island is Mount Bosavi, a giant volcano long since

extinct, and the team's home for this phase of the expedition.

On their way in is a team of experts on the animals of New Guinea.

But for wildlife cameraman Gordon Buchanan, it's his first time here.

This is a very, very difficult terrain.

You've got these steep gullies, riverine valleys and very, very thick forest.

Very much the unknown and somewhere that I'm really quite nervous about.

They're heading for a base camp in the foothills of Mount Bosavi.

George McGavin is head of the science team.

He's already in camp, with some of the tribe who own this ancient land.

They'll be working with the scientists and filmmakers to find the forest creatures.

The heart of this camp is the jungle lab.

We have assembled a team of specialists, world experts

in their groups - birds, reptiles, amphibians, bats, insects - and they're going to be working in here.

That helicopter kicks up quite a blast, but that's all the scientists coming in.

Hi, there's lots of work for you here!

Each expert has their own special skill for finding rare animals.

They'll be exploring for new species in a forgotten corner of our planet.

It's a task more vital today than ever, as this ancient forest has an uncertain future.

Steve Backshall is the last member to arrive.

How we're going to move around in here and go about actually trying to find wildlife,

I have no idea.

It's the third time that Gordon, George and Steve have been on jungle expeditions together.

George is the scientist. He'll go anywhere in his search for strange insects.

Gordon is the wildlife cameraman.

Nothing will stop him getting the perfect picture.

Steve is the adventurer and climber.

Whether it's up mountains or down waterfalls,

the bigger the challenge, the better it is.

Day one in the New Guinea base camp.

As they prepare the gear, something bizarre arrives in camp.

George, you come here. I've got one thing for you.

It's been caught by boatman Nick Awaiyo

and expedition photographer Ulla Lohmann.

There's no rest in this place.

Oh, my God, that is absolutely incredible.

A thing that folks don't often think is that stick insects can fly.

I can just take it off the camera lens.

The front wings are quite short,

little tiny...little winglets there,

but the hind wings are just beautifully fan-like,

like a big pleat.

That is the biggest stick insect I have ever seen in the wild.

Working with a team of skilled boatmen, Steve is keen to head downstream.

He'll be exploring the fast-flowing rivers that pour down these mountains.

It really is spectacular, if a little bit up and down.

There's an awful lot of water flowing through here.

It's a fantastic opportunity for us to get somewhere that is just almost totally unknown.

These rivers are the roads of the rainforest, eventually taking Steve into uncharted territory.

In New Guinea, the rivers roar not just over the ground,

but also underground, through caves deep within these limestone mountains.

Steve's journey will ultimately lead him to follow a river deep into this underworld.

He'll be exploring where no human has ever been,

living and sleeping under a million tonnes of rock.

Back in base camp, Gordon's preparing to trek into the forest.

He'll be working with a team of trackers to capture on camera the secretive animals of this jungle.

There's no point of reference in Papua New Guinea.

There are no cats, there are no rhinos, there are no elephants, there are no monkeys.

There is nothing familiar about the creatures that live in this forest.

So in some ways, I feel as if I'm starting from scratch.

It's quite daunting, the prospect of going into this forest and starting to look for things.

But New Guinea does have the most spectacular and strange birds in the world.

From now on, Gordon will be out searching for them.

Hornbills.

You never, ever see them from the ground.

One of the largest birds of New Guinea, the hornbill.

But he soon finds signs of a real giant of a bird.

Ooh! There's something there, hang on.

This is the first thing that I've found. It's a cassowary footprint.

And this is an enormous bird.

That footprint is the size of my hand,

so we're talking about a bird that's about kind of four, five feet tall.

I'd love to be able to find one of them.

In the jungle lab, the experts sort their equipment, before starting their hunt for animals.

The team has come from all over the world and is working with some of New Guinea's leading scientists.

They're led by Dr George McGavin, a specialist in insects from Oxford University.

He's set an ambitious target.

This whole area is completely unexplored and as head of the scientist team,

I want to find at least 30 new species right here.

This goal isn't just for the sake of science.

Proving this forest is rich can be a powerful reason to protect it.

Just 20 miles south, the jungle is disappearing.

If we're to have any chance of saving it,

we have to be able to tell everybody this is a very rich area.

Hopefully, we'll find some new species to keep people aware of

the fact that these habitats still exist and are worth saving.

If the forests go, we will lose the majority of species on Earth without even knowing they were there.

Steve and the river team are five miles downstream.

Around them, waterfalls pour down from Mount Bosavi.

Oh, wow, this is a monster!

These tracks here...

..are croc tracks.

This is quite clearly the hind foot of a croc.

It's been coming in from this direction.

It's come up to check something out.

The tracks lead back into the forest.

Crocodile nest!

But it's been... You can see it's been dug up.

This one's still got amniotic fluid inside it, look.

This has happened very recently, possibly last night.

Well, this isn't the hatchlings breaking out of their own accord.

They have an egg tooth, which is on the end of their nose, which they use to break out of the egg

and they make a very clean departure, whereas this has just been shredded.

And I am 99% sure these have been taken by a monitor lizard.

That's one of the biggest predators of nests like this.

What a shame. This forest does feel prehistoric to me.

It feels like a place where you could see a dinosaur around every corner.

And crocodiles have been around since the time of the dinosaurs and this is

exactly the way that a Velociraptor, or a T Rex, would have laid its eggs, buried in the vegetation.

There's an art to finding the creatures that hide in these forests.

Scientists put up survey nets to find birds and bats,

fishing nets are placed in the creeks...

..and George walks quietly, searching for insects.

Deep in the forest, Gordon's found a tiny nest.

It looks like it belongs to a curiosity of nature,

one of the smallest parrots in the world.

Oh, wow - here, right here.

As you can imagine, a pygmy parrot is pretty small, that's how it got its name.

They're tiny, they're only about...not much bigger than my thumb.

It's actually quite a big hole for a small bird and what they do on these rock-solid termite mounds,

they'll dig in - probably using their beaks and their claws -

and burrow down into it and lay their eggs there.

But this is all quite, all fresh stuff, it's just been excavating this morning.

I'm kind of concerned that it might not come back,

but it's definitely worth setting up the hide and just waiting it out.

To have any chance of filming these tiny birds, he must blend into the background

and settle down for a long wait.

George is taking a more active approach to finding his insects.

Wood like this is an incredibly useful food material for loads of insects.

I mean, it's eaten by beetles and termites and lots of stuff.

There isn't anything wasted in the jungle, it's all recycled.

There's over one million species of insects known to be living in jungles,

and scientists estimate there's another five million waiting to be discovered,

if you know where to look.

Ooh, there's a nice beetle! I've got to work very carefully now, cos...

I don't want to hurt them. There we are, look at that.

There she is. A bess beetle.

They are fantastic.

That's a reward and a half.

She's got fantastic little red hairs all round the thorax here.

What a find.

His first discovery is from a group of obscure and odd animals - talking beetles.

They live in groups with their young ones and they call to each other as well.

They make squeaks.

If you can get the boom down, I'll just try to make it squeak.

BEETLE CHIRRUPS

I can hear it from here.

In the dark, in logs, you can't see each other, but if you can make squeaking noises,

then you know where each other are.

An extraordinary find.

New Guinea is THE place for the weird and wonderful.

These forests are the most diverse and complex habitats that have ever evolved on Earth.

There's a huge store of species here about which we know nothing at all.

If you lose these forests, from being a very rich planet, we would instantly become a very poor one.

So that is absolutely...gorgeous, absolutely gorgeous.

Steve's on the river survey with fish expert Phil Willink.

They're trying to get to a jungle creek to check the nets.

In just the wrong place, the engine fails.

-You OK?

-Yeah.

Don't think we want to go in that.

They're caught in a whirlpool.

Why is this...not...starting?

Whoa!

-It's chucked us out.

-Hang on.

The whirlpool throws them free, but then they're trapped in a vicious current and the engine's dead.

Here, you want to paddle? Switch it off.

I'm not sure we're gonna make it.

Gordon's still patiently watching the nest of the pygmy parrot.

There's simply no way round this.

If you want to film animals in the wild, most of the time,

you've got to do a stakeout.

Sit tucked away in a hide and just sit and wait.

You can't really switch off in a hide,

you can't read a book or pick your toenails, you've got to stay alert

and try and tune in to the sounds and the changes in the sounds

and anticipate the arrival of the animal that you're after.

After a struggle with the current, Steve and Phil make it to the bank.

Well, that's our first warning of what this river can do.

This river's a beast.

It just creates incredible currents.

And you saw the boat there just being span round in a whirlpool.

It's very difficult to do anything about it really.

MOTOR STARTS

With the boat bailed out and the engine sorted, they're off again.

That's the creek mouth straight ahead.

There's a rock right here, go left.

Whoa, cut the engine.

SPLASHING

Ooh, I heard something splosh up ahead.

Ooh! That's a venomous catfish.

-No way!

-Yeah. Let's be a little careful here.

-It's probably best to grab it from the head.

-If I get whacked, how bad a day will I have?

It's basically the same as getting hit by a stingray spine.

What an extraordinary looking fish! That is a true alien mouth, isn't it?

-Look at that.

-They're covered with taste buds, it's actually tasting its environment all the time.

Its eyes are not particularly large, so it has to use other senses

to find things, particularly in these muddy rivers here.

Look at the dorsal spine coming erect there, and at the end of it, you can see the sharp tip to it.

And, you know, it's living in the same river with giant crocodiles, so it needs a defence.

These spines also can go up and then lock into place,

so if a crocodile tried to grab it,

it would go through the roof of its mouth.

It's amazing to think that a fish like this can actually defend itself

against a three, four-metre long crocodile.

If it's going to hurt one of those, it's sure as heck going to hurt one of us.

Oh, yeah, so you've got to be really careful.

Gordon is still crouched in his hide,

and he's found absolutely nothing.

The heat I can contend with,

but the heat combined with the kind of infestation

of bees and mosquitoes,

that's when it gets very unpleasant.

George is finding it a lot easier to uncover his creatures.

This place is full of surprises.

Millipedes are normally quite tough animals,

but this one is incredibly tough. Very, very armoured.

It has these little spines that point backwards

all the way along it,

which must help it as it drives under logs and soil and stuff,

cos that's where it lives.

It's absolutely weird.

Very strange-looking animal.

And there's an even more bizarre find.

These ants have been infected by the spores of some fungal disease.

And the fungus infects them in such a bizarre way that it causes them

to crawl upwards, and it glues them onto a leaf.

As the fungus eventually breaks out through the shell at the end,

it grows this little stalk here,

and there's some little balls there which contain spores.

From those balls will erupt the spores, which will blow as far

as they can and infect a whole new group of ants.

So it's a really smart trick. And underneath every leaf here

are those ants just pinned onto the leaf,

dead husks, sucked dry by the fungal disease which has infected them.

Absolutely amazing.

At last, Gordon gets his reward.

The pygmy parrots have returned to their nest.

Look, there they are.

They're on the nest.

Oh, my word,

they are tiny.

Oh, wow! That is the weirdest thing.

We've got a parrot here that is significantly smaller

than many of the insects that live in this forest.

And they're very much a parrot.

His feet are true parrot feet,

two toes facing forward, two facing back.

They seem very affectionate with each other,

which is quite typical of parrots.

Parrots have a strong bond between male and female,

sidling up to each other, beak-rubbing

and constantly reinforcing their relationship.

They move so fast, it's very jerky,

it looks as if it's almost speeded up.

You shouldn't say that animals are adorable in the wild,

but they are simply adorable.

Stop.

Pretty pleased with that.

Back at camp, it's been a good day for the scientists.

Already, it seems this forest is incredibly rich.

Jack Dumbacher is searching for the birds of the jungle,

and investigating the diseases they carry.

One of the things that's very interesting to me here is that we have a very pristine environment,

and birds and other wildlife carry natural diseases,

and so understanding these diseases, how they're spread, how they're moved around by birds and humans,

is very, very important, for conservation as well as for basic biology.

The birds are recorded by the expedition photographer.

And then they can fly home.

Alan Allison is passionate about frogs.

He's been studying them in New Guinea for over 30 years,

but he's never seen this one before.

Interestingly enough, they call when it first gets dark -

just about seven o'clock - and they call for about an hour.

Seven o'clock frog.

You can tell the time by it.

It's a different species here than elsewhere.

-That's added one new species to our vertebrate list.

-That's right.

To be finding new species already bodes very well for the expedition.

For the moment, the scientists are hidden in the foothills of Mount Bosavi.

But in a few weeks, the team will head higher

up the steep mountain slopes

and down into the heart of this extinct volcano.

This giant crater is trapped from the outside world by walls half a mile high.

They will be the first scientists ever to travel into this lost world.

They believe it could hide truly spectacular new creatures.

Mount Bosavi is a huge mountain - large enough to generate its own weather system.

And mostly, that means rain.

I do love it when it's like this, when the rain really comes down.

That's the real force and power of this place.

It's what makes everything work.

If there wasn't this amount of rain,

you wouldn't have this amount of life.

Ugh! Very refreshing.

Jack has been collecting birds away from the rest of the team,

and has a surprise for Gordon.

-What have you got, Jack?

-You'll never believe it.

-Oh, wow!

-This is your little buff-faced pygmy parrot.

Oh, goodness me!

So if you can just hold your fingers as close as you can to his body...

-Let me grab his legs again...

-Ow! That's a parrot's beak.

Yeah, it's pointy...

He can't do that much damage.

Oh, man!

That is just the cutest thing.

So now you can really see how tiny he is, like, compared to your thumb.

-Yeah. He is just a parrot in miniature.

-Yup.

You cannot believe that a parrot can be this small.

This tiny bird weighs less than half an ounce.

Oh, my word.

In the forest, actually, the feather... Ow!

Oh!

And actually, one of the things I wanted to do was get a little bit of DNA.

I wasn't gonna take blood from him, cos he's a little bit too small.

So we did get one feather he left us, so we can use that.

That evening, the pygmy parrot is the butt of all the jokes.

You can guarantee that somewhere in these forests, there'll be a tiny little pirate.

Just the way that nature works.

-"Who's a tiny boy, then?"

-"Pieces of two!"

THEY LAUGH

-There's a fully grown larva there.

-The jungle lab is filling with new and curious creatures.

I'll bet you any money, that wasp right there, that's walking along that leaf, is a new species.

I'll bet you any money.

42mm long.

Alanna Maltby is a bat expert from the Zoological Society of London.

Oh, he's tiny!

Yeah, he's really small and really cute.

-What is it?

-It's a bent-winged bat. And I'll show you why.

Most bats, they just have their fingers,

and when they fold their wings, they just fold them straight up.

But this one folds them doubly...

-Oh, right!

-..because they're really long.

But I can't figure out which bent-winged bat it is.

It doesn't quite match with any of the descriptions.

-Which means?

-Which means it could be a new species.

A new species of furry animal. A mammal! Absolutely brilliant!

-Which is quite rare, to find a new species of mammal.

-Yeah, it is, very rare.

A small creature, but a big discovery.

No-one expected this success so soon.

Rainforests come alive at night.

Gordon treks out to find what's hiding there.

Rainforests are very difficult places to work at the best of times.

But this forest in particular is extra tough, because the animals

that live here are very secretive and they're incredibly well hidden.

He has an infrared camera for filming in the dark.

There's something moving in the undergrowth.

Wow!

It's pretty big. It's about a metre and a half, maybe.

And really, I daren't go any closer than I am to it.

I think it's a small-eyed snake.

These things lurk about in the leaf litter, and they...they kill people.

Very, very, very dangerous snake.

It would be very bad news if you were to stand on one of these.

Oh...

He's just opened his mouth right up.

That's a sinister-looking snake.

It really does freak me out,

seeing something as dangerous as this in the forest at night time.

It'd be so easy to stand on a snake like this.

They need a positive identification.

Steve is the team's snake specialist.

He thinks it might be one of the most venomous snakes round here.

Hello, guys.

Oh, wow!

Look at that! Gordy...

-Is that a small-eyed snake?

-It looks almost definitely like one.

The only way you can really tell is to get up close and look at the amount of scales around the eye.

The snake's obviously hunting.

Ooh!

Striking quite vigorously.

Ooh!

Where's the head?

Need to pin the head to get control of the snake.

So, now that I've got it up close, you can see although it does have

that tiny, beady, black, recessed eye that you'd expect

from the small-eyed snake, it also has a couple of extra scales between the eye and the nostril.

It's a ground snake,

not venomous, but very aggressive and always ready to strike.

So, Gordy. Fantastic, mate!

So it's not a small-eyed snake?

It's not a small-eyed snake.

-And it'll eat rodents, frogs, lizards, sort of...?

-Yeah.

All the things you're trying to film.

And he's off. None the worse for wear.

This phase of the work is based in the foothills of Mount Bosavi.

But there's a series of trips in this expedition.

Steve's embarking on another quest.

He's heading east, to an island off the coast of New Guinea

called New Britain.

The forests here on New Britain are some of the most spectacular I've ever seen anywhere in the world.

We're flying through a very deep, steep-sided gorge,

with a whitewater river flowing right down through the middle of it.

He's on his way to join a world class team of adventure cavers.

These limestone hills are hollow.

Under here is a honeycomb of caves which may stretch for miles.

Their job is to explore them.

There's just one problem -

this is the only way into the caves.

A whitewater river thunders from the entrance.

And it's halfway up a jungle cliff.

Oh, my life! Look at this!

This must be it, this must be Mageni Cave.

That's where we're going.

The local village have turned out to meet Steve.

Hello. Hello.

Hello. Hee!

This is the village of Ora,

which is as close as we can get in the helicopter to the caves.

So I guess we're gonna try and rouse some support here,

try and get a few people to help us carry our stuff in, cos we've got an awful lot of it.

We'd like to meet the head man,

and get permission to be wandering around on what essentially is their land.

Every piece of forest in New Guinea belongs to a local tribe.

-Steve can't go anywhere without the consent of the chief.

-Hello, hello.

Have you ever been to the cave, Mageni Cave?

-Yes.

-And what do you think is inside the cave?

HE SPEAKS IN LOCAL DIALECT

It seems that there's a feeling, perhaps even a local myth,

that there's a huge snake inside these caves.

It would be very nice if it wasn't a local myth!

If it was true, that would be great!

One week in, and everyone at base camp has settled into a routine.

But there's nothing regular about the animals coming in.

It's a blue-tongued skink. He's beautiful.

Every animal they find is recorded.

Some of them are bright and beautiful. Some shy and camouflaged.

What do you think it is?

Little striped thrush.

Little striped thrush.

They've catalogued hundreds of animals.

And at least seven of them are brand new species.

Gordon has a new goal. Together with Muse Opiang, he'll be searching for the secretive mammals of the forest.

To give us an overall view of the animals that live in this forest,

we can't just use legwork,

we have to put these traps out and find out what's living here.

And we've got some kind of forest rat in here.

I'll get him out and Muse can tell me exactly what it is.

Do you like all the rats?

-I like them.

-Do you think they're ugly?

-No, no, they're not ugly.

Muse knows where to set the traps.

And Gordon uses his tracking skills to search for signs.

There's quite a kind of musky smell around here.

Some big holes down there.

I'm just gonna check it out.

You're not only using your eyes and your ears to find animals,

and quite often some animals give themselves away by their smell.

There's definitely something around here or something that's been here.

Have a look at this.

Whooo!

Spooky!

It's almost a cave.

Erm, there's a bit of a jump down.

Luke, you might want to hand me the camera.

Got it.

He's found the entrance to a tunnel.

Yeah. Cos they're a long way...

Here, there's animal tracks.

And see this muddy area? It's all smoothed down.

You look around other areas,

it doesn't have any of this surface mud that's just been smoothed over.

Oh, there's a nut, kind of chewed fruit in there.

This is a really good place to set up a little camera trap.

Because without a doubt, there are animals coming and going from here.

Muse helps to train a remote camera on the tunnel.

-That's the right height.

-OK.

-You think that's good here?

-Yes.

Switch it on. OK, arming it in ten seconds.

OK, I think we should just get out. It's running.

Throughout the forest, remote cameras are placed to catch any mammals passing by.

It's vital they find what lives here.

They're surrounded by pristine forest,

but the front line is getting closer.

Just 20 miles south, the loggers have moved in.

Every day, more trees disappear.

George is pulling together all the evidence from the scientists.

This report will be sent to government officials here,

in the hope that it'll add into a plan for conserving the wildlife here.

This is a critical issue now.

This whole area in the foothills of Bosavi is a very special forest.

The evidence is beginning to confirm that these forests are unique.

And not only above the ground.

To the east, the preparations for the underground exploration are well under way.

Steve sets out on his trek to the cave entrance,

with a little help from the villagers.

They're heading to meet the team at their camp above the waterfall.

The rest of the cavers have been there for a couple of days, preparing the gear.

They've brought state-of-the-art equipment to map the river that flows through these caves.

-..more cave out there?

-Exactly, it gives you an idea of what we're up against.

As the only naturalist on the team,

Steve's job is to search for any animals in the caves.

We've got a remarkably strong team here.

We have three members of the original expedition that came here just a couple of years ago.

What's clear is that this is a gigantic cave system.

This is a cave that goes on for a lot further than they managed to explore.

That's our real aim, to push on into areas

where they thought there might be the chance of something special, and try and find what's there.

It's supposed to be the dry season. Heavy rains will flood the caves.

This is really bad at the moment. The whole reason we planned to do this trip now

is because the rains aren't due for at least another month.

And if this carries on, it's gonna be more of a discomfort.

There'll be no way we would get down the caves. And if we do, it would be very, very dangerous.

At the moment, the worst thing we have to worry about is mud.

The fact that all the kit is gonna die.

Back at base camp, an injured bat's been brought in.

Alanna's nursing it back to health.

This is a common blossom bat.

And it eats nectar with a very long tongue.

And because it eats sugar, it needs sugar every 24 hours.

-Will you do the honours?

-Yeah, absolutely.

I think if we can get a good meal into her now,

and release her before it gets too warm, then she'll be fine.

This bat is specially adapted to feeding on flowers.

This fantastic tongue...

-Look at that!

-..is rolled up inside its mouth and then it sticks it out

down between the petals of a flower so that it can get to the nectar.

Which is exactly what it's doing here,

-it's going straight down the syringe tip.

-Yup.

Look at that.

It's just gone from being nearly unconscious to really perky.

That is... That is really nice.

There we go, some strength back.

We should release it as soon as possible,

and then it won't be too hot for it to fly back to its day roost.

It's day nine, and already the scientists have found ten species that are completely new to them.

They're kept busy, day and night.

Muse and Gordon have found a creature in one of their traps.

It's a striped possum.

Striped possum.

They're famously feisty creatures,

that are more than a match for bigger foe.

Oh, wow! He's a beauty!

They're marsupials, raising their babies in a pouch.

And for defence, can let out very strong smells.

He's black and white like a skunk, and he actually smells like a skunk - very strong, musty odour.

You can see that finger, it's quite extraordinary.

There are few animals in the world that have that kind of adaptation.

The long finger is for winkling grubs out of holes.

We'll weigh him, measure him and then take him back to exactly where we found him.

Let's measure the tail first.

330.

For the base, left to the tip.

With the vital statistics taken, it's time to release him.

Right, this is the tricky part.

You can see how sharp his teeth are.

I really want to avoid getting bitten.

Owww!

Oh!

That's a bit of a nip. OK, can I nick that other glove just in case?!

This glove is made from the same material

that bullet-proof vests and stab jackets are made from.

And he's actually causing quite a bit of pain so I'm gonna take him out and release him.

OK, I reckon as soon as his feet touch, he's gonna be off.

OK, pal. There you go.

Oh, look at that!

Yeah, that's good. He's much happier now.

700 miles to the east, Steve and the team are abseiling down to the mouth of the cave.

We've seen the cave from the air.

But to stand here and for the first time really be able to hear

the sound of it raging beneath us is something else.

It's an 80-metre drop to the entrance.

Oh, wow!

It's not a very usual view, hanging above a waterfall.

And below it there's this majestic drop down to the pool beneath.

I'm not liking where these ropes are bringing me down though.

I'm gonna be right in the waterfall.

Whoa!

Just hope I can find somewhere

to get my footing on here.

Ho-ho!

I just do not wanna slip now.

Out there, everything's green and magical.

In there, it's all frankly a little bit frightening.

In the lab, George has been distracted from his job of writing the report.

Somebody brought me back these in a little bag.

I'm not sure what they are... Oh, wow. Look!

Long-horned beetles.

And they're mating!

Oh, my God! That's the male and the female.

-Alanna? Have you seen these?

-Yeah?

-I found them for you, George.

-It was you who found them?

Oh, thank you very much. They're absolutely gorgeous.

Actually, I should be slightly anxious about this, because they have got very, very sharp jaws

and if it happens to sink it into my earlobe,

you will hear...

Ooh, squeaking.

Oh, they're squeaking.

This being the land of squeaking beetles.

BEETLES SQUEAK QUIETLY

The cavers are pushing their way up the white-water river.

The current is strong.

They can't afford to put a foot wrong.

Oh, this is unbelievable!

They're now half a mile into the cave and face a huge obstacle,

a waterfall swollen by heavy rains.

This is the largest waterfall that we know of

in the whole of the Mageni cave river system.

The entire volume of the river is flowing over this waterfall,

and it's a real crux point in the cave.

If you can't get beyond this, then you really have been stymied,

you know, you can't get any further.

Back at camp, Gordon starts to sort through the thousands of pictures

captured by the remote cameras.

The thing about this system is you can't review it in the field, so it's quite exciting.

There's a Christmas morning moment.

You come back with this little memory card,

put it in the computer and then you find out exactly what you've got.

Sometimes it's a pair of socks and sometimes it's a Scalextric.

Hmm.

At first it looks like socks.

Any movement triggers the camera.

One of the curiosities of New Guinea is there are hardly any large mammals living on the jungle floor.

A rat.

You've got giant rats here.

Rats that are bigger than domestic cats.

The last camera trap to check is from the tunnel entrance.

Another rat. I think that's a different species.

Hmm.

Then something very special,

one of the most secretive creatures in New Guinea.

Look! That is a cuscus.

I knew it! Look, look, look. I do not believe that.

He's just having a good old root around.

These images were taken at five in the morning.

Cuscus are only active at night.

This one's returning to the cave, where it must spend the day.

Oh, goodness me.

I would have absolutely have loved to have been there.

It's an important find for the team.

Cuscus are so shy they're rarely seen.

At dusk, Gordon heads out to try and capture one on camera.

During the day, they'll either be asleep in the trees,

and more often than not they'll be in a hole,

whether that's a hole in a tree,

a hole in the ground or underneath these big boulders.

I've got lots of different camera systems that we can pretty much

check out every option at night time and try and get some shots of them.

At the waterfall, Steve's putting his skills as a climber to good use.

He's leading the way up.

An old rope has been left by the previous expedition.

It feels pretty good.

But it's been battered by the waterfall for the last two years

so I can't really afford to risk my life on it.

A camera is attached to Steve's helmet.

All I can see is spray.

Can't see anything. Rocks.

Yeah! That's it!

Lots of loose rock.

Whoa!

I have a feeling this is going to be the crux.

That overhanging right in the waterfall.

It's now pitch black and Gordon is pushing into unknown territory

to find and film the elusive cuscus he'll use only infra-red light.

Got lots of noise up in the top of this tree.

Not the cuscus, but giant fruit bats.

We've got these fruit bats feeding on figs.

It's a long way up.

You can see the way that they're using their wings,

their claws, to clamber about in the tree tops.

Because he's using infrared light, the bats are completely undisturbed.

Oh, look at them squabbling!

Oh, oh! Fight, fight! There's two fighting there.

It's amazing that there's actually fisticuffs up there,

you'd think there'd be enough to go round,

but evidentially not.

Everyone's just defending their little patch of figs.

Oh, look, he's just testing with his mouth to see how ripe that is.

But what these bats have that I haven't seen on other fruit bats

is this enormous thumb, this big hook,

and they're using those hooks

to clamber about in the tree tops.

Incredibly agile.

These are key animals in the ecology of the rainforest,

feeding on fruit and dispersing the seeds up to 30 miles away.

It does mean filming them has its down sides.

I was thinking that a fig on the head was the worst thing that we could get,

but probably bat poo is a bit worse.

Oh! There you... Ugh! Ugh!

Seems that figs have the same effect on fruit bats as they do on humans.

At last Steve has made it up the jagged rocks of the waterfall.

That's more like it!

The water-sodden team haul themselves up.

At the top of the falls they start the painstaking work of mapping the underground river.

Lasers measure to a millimetre the size of the ancient chamber.

-How's that?

-Yeah.

Then it's on again.

They must find a place to sleep before they get exhausted.

Oh, it's cold!

It's now very late, and Gordon's pushing deeper into the jungle on the track of the cuscus.

There's something in the trees.

I just got some eye shine directly above me.

I think it's round about here.

Power on. Oh, there you go, right in the middle there.

At last, Gordon's found his animal.

You little beauty!

It's a cuscus.

And there he is just happily sitting on the branches a long, long way up.

The size of a domestic cat, cuscus are nocturnal,

moving high in the canopy with their babies secure in their pouches.

And you get ground cuscus

and its hands are less well developed for climbing,

but this one is very, very comfortable in the trees.

It's such an unusual animal. It doesn't really bear any resemblance

to any animals that we would commonly know.

You can see he's got this big, long tail.

It not only helps him balance as he moves through the trees,

but it's a prehensile tail, he can use that as an extra limb.

And you can just make out that the end of his tail is naked,

so he can wrap that tail around branches and use it as a fifth arm.

They're quite a bit like teddy bears with a big long tail.

They're quite beautiful. They're really nice animals.

A first small glimpse of the cuscus, but a great success for Gordon.

-Oh, there he goes!

-Then it's off, disappearing into the forest.

All right, Steve?

The cavers are now two miles into the mountain,

under a hundred million tonnes of rock.

It's like being inside the home of some massive alien,

the walls all dripping with slime.

And they're not alone.

Look at that.

It's a very bizarre little crab.

It's evolved in isolation here in this cave.

These are the kind of creatures

that turn out to be absolutely new to science.

The eyes have faded away to almost nothing.

They're of no use whatsoever in a place like this.

In fact,

this will be the first light that this crab will ever have experienced.

I really wasn't expecting to find any life much past the first hundred metres of the cave.

So this is... This is quite a find.

They can't stop for long.

Although they're now very tired they must push further into the cave

to find a dry spot to make camp.

Getting anywhere is tough.

In the calm of the jungle lab,

George tallies up the remarkable discoveries they've made.

We're a third of the way into the trip and so far

we've got one new species of bat,

we've got certainly two new species of frog

and two more that are potentially new species.

We've got three species of fish new,

insects and spiders, five to eight, possibly ten.

A lot more to come.

The list expands quicker than he expects.

Hi, Alan. What are you doing?

Alan's come across something just a stone's throw from the lab.

Well, I just caught a very pretty gecko.

Oh, that's gorgeous!

Is that the first one you've got of those here?

Now, I've got to ask you this, have you seen that before here?

-We have not.

-Have you seen it anywhere?

No, I'm almost certain this is a new species.

-Not only that, but it's a girl.

-How do you know?

-Well, you can see the eggs.

-That's the eggs, is it?

-Yeah, you can see them right through the body.

Transparent? That is absolutely gorgeous!

Oh, my goodness. That's amazing.

Feels absolutely lovely, doesn't it?

It's like velvet.

The tail is quite strikingly banded

and you can see how well they blend in.

Alan's gecko is like icing on the cake for the team.

Two weeks in and the expedition's exceeded all expectations.

For the cavers, there's no celebrations.

They're now deep in the bowels of the mountain

and there's no place to stop.

The river is as strong as ever, sapping their energy.

Exhausted, they struggle on into the darkness.

Later in the expedition, the team enlists the help of a local tribe

in the search for exotic birds of paradise...

Jeez, there's two of them! There's two of them. Wow!

-They witness an exploding volcano...

-Grief!

Enter the lost world of the jungle crater...

Oh, soaking!

And Steve discovers a new flooded cave

in the depths of the underworld.

Subtitles by Red Bee Media Ltd