Amazon Flooded Forests The Dark: Nature's Nighttime World

As night creeps across the planet...

..and our familiar daytime world is plunged into darkness,

strange creatures are beginning to stir.

This is when most animals are active.

But the drama of their nocturnal lives is hidden from our eyes.

These are specialized beasts, all adapted for the dark.

It's a world we know almost nothing about.

Now, a team armed with specialist cameras is travelling

to the remotest corners of Central and South America...

That's unbelievable!

..to uncover the secret lives of animals after dark.

-WHISPERING:

-Wow!

It's a journey into the unknown.

WHISPERING: Look at him. He can smell me.

-WHISPERING:

-Don't...run.

-Holy

-BLEEP.

WHISPERS: Get me out of here.

For six months, a team of biologists and film makers

is exploring Central and South America...

..home to many of the most diverse habitats on Earth.

They aim to discover why animals come out in the dark,

and how they survive in a world with no light.

They started in the jungles of Costa Rica.

Now, the team is moving South for the second leg of the expedition.

The team has split to follow three separate missions,

in three very different habitats,

across the dark heart of South America.

Insect specialist Dr George McGavin is in Venezuela

to explore a place of permanent darkness.

A cave that no biologist

has ever entered.

There are caves here which have formed over millions of years

and haven't seen the sun - any animals in there

have been there evolving in total darkness for millions of years,

and we might be the first people to ever see them.

The cave was discovered in 2009

by international exploration team La Venta.

George has joined them as they prepare

to return for the first time.

These places have been isolated for so long that

there's a very high chance anything we find here is completely new.

Their base is the top of this remote tepui -

a giant table top mountain.

The cave entrance is far below them,

hidden in thick jungle at the base of this cliff.

It's about 110 metres from where I am to the end of the rope.

That is a very long way down. A very long way down, indeed.

The cave has been cut off from the light for millions of years -

enough time for new species to evolve.

What creatures live here?

And how have they adapted to permanent darkness?

George hopes to find out.

1,700 miles south,

at the edge of the Amazon basin,

wildlife filmmaker Gordon Buchanan is heading into the Pantanal -

the largest wetland on Earth, and the richest.

The Pantanal is one of the most

bio-diverse places on the planet.

There's life everywhere, but most of those animals

that you see during the day are absent at night,

and they're replaced by a whole set of other creatures.

Almost nothing is known about what goes on here at night-time.

Gordon wants to find out more.

Top of his list is one of South America's most bizarre animals.

The giant anteater.

Elsewhere, they come out in the day.

But here, scientists have reported them emerging after dark

to escape the relentless heat.

In the shade, it's 42.

Out here in the sun, I don't know what it'll go up to,

but it is blisteringly hot.

How does a daytime animal function in the dark?

Gordon will use the latest night vision cameras to find out.

He hopes to learn what the giant anteaters are up to at night.

In Venezuela, George has reached the cave entrance.

This will be his last glimpse of daylight.

That's not coming through.

For the next four days, the team will follow the river

three miles through the cave, looking for life in the darkness.

Only a few steps inside...

Ho-ho! Look at this.

..and George finds something interesting.

Now, that is one of a cave's most spectacular insects.

Now, all of these threads are produced by a fly larva.

You can just see it there.

And it makes these vertical threads,

and on the threads are very sticky blobs of goo.

There, you see? That's fantastic. Now, that is a prey item.

It's still alive, look!

This predator takes advantage of the dark.

It sets its traps close to the cave entrance.

Insects from the outside stray in.

Unable to see the threads, some, inevitably, are caught.

So, that tiny little midge has flown along here in the pitch darkness,

it can't see anything, of course, and it's stuck fast.

Vibrations on the thread tell the larva

that a new meal has been snared.

The larva then oozes its way along, down the vertical thread,

consumes the prey, and then goes back up.

And these threads are all over here.

So, for a small, flying insect like this,

this cave is just full of hazards, and there it's come to a sticky end.

HE LAUGHS

In every sense of the word!

Even in this twilight zone, creatures are adapted to the dark.

George and the team head further underground in search of life.

To the South, the third and final team

will push deep into the Peruvian rainforest

at the headwaters of the mighty Amazon.

Base Camp is an old river steamer.

On board are tropical biologist Bryson Voirin,

and camerawoman Sophie Darlington.

It's sort of a wildlife filmmaker's dream to come to the Amazon.

It's rammed full of the world's most exciting animals.

Bryson is an expert on the large mammals in this region.

During the day, I know what to expect.

But at night-time, it's going to be a whole different ball game.

The forest floor here is covered by several metres of flood water

for most of the year.

It's a unique habitat for the team to explore.

With little dry land, many animals live in the canopy.

Sophie is here to find a very special monkey.

There are over 100 different species in the Amazon,

but only one kind comes out at night.

Owl monkeys.

It would just be amazing to see these owl monkeys

and how they move about the trees at night.

Like us, monkeys all over the world are completely reliant on daylight.

All except the owl monkey,

which is uniquely adapted for life in the dark.

Sophie will stake out a fruiting tree,

where she hopes the monkeys will come to feed.

She will have to perch on a small platform

30 metres above the water.

OK...

This is a new challenge for her.

She has 20 years' experience, but all of it at ground level.

I'm not enjoying this.

SHE PANTS

I'm finding it very hard.

It's an amazingly odd feeling, being up above the forest.

OK, it's solid.

Catching the monkeys on film will take luck and persistence.

The reward will be a unique glimpse into canopy life after dark.

While Sophie stakes out the treetops,

Bryson searches at water level.

He's looking for nocturnal animals in the undergrowth

and in the waters of this flooded forest.

My plan is to do a survey of species in the river at night-time.

So we're going to go out and try to go into the forest

with the little boats, with bright torches or spotlights

and hopefully see some of the nocturnal species

that are out here in this part of the Amazon.

Across South America, night approaches.

In the Pantanal, Gordon leaves camp and heads out onto the plains

in search of the giant anteater.

As the sun sets, the Pantanal changes.

Night is when most predators come out to hunt.

Animals of the day hide as best they can and sleep.

The countless species that have lain hidden during daylight

gradually emerge.

The night shift begins.

Armed with a thermal camera that detects body heat,

it doesn't take Gordon long to spot something.

Right...

Oh!

On his camera, warm-blooded animals glow brightly

against the cool background.

-WHISPERS:

-It's a rhea. It's a flightless bird.

This is the biggest bird in South America.

-HE CHUCKLES

-Look at that!

Oh, that's really nice. It has a whole heap of chicks with it.

Rheas ferociously protect their young.

During the day, most predators stay clear of these giant birds.

They stand one-and-a-half metres tall,

and their heavily muscled legs pack enough punch to break bones.

But in the dark, the tables are turned.

With poor vision, they are vulnerable to surprise attack.

At night-time, they do the sensible thing and just keep a low profile.

With a second specialist camera

that films using light invisible to animals,

Gordon can take a more detailed look.

These chicks are just mini versions of the adult.

And that big bird is not the mother, that's the father.

The female lays the eggs and the male broods them.

The female swans off.

But he's doing an incredibly good job of looking after these chicks.

He's taking that one under his wing.

Sitting still is a surprisingly effective strategy

to hide from predators in the dark.

This rhea is sitting out there in the pitch black,

it can't see anything. Probably doesn't even know that I'm here.

If we just switch the light off,

you will see what I can see without the equipment.

Like us, rheas are virtually blind in the dark.

But they have very good hearing.

CHIRPING

At the first sound of danger, they scatter.

The male finds his chicks in the dark by calling.

CHIRPING

They will regroup in a safe place to wait out the hours of darkness.

Rheas survive the dark by hunkering down.

But the giant anteaters Gordon is searching for

are always on the move.

To find them, he, too, must keep going.

In Venezuela, George has journeyed deeper into the cave.

No light reaches here at all.

It's the perfect place to find strange, dark-adapted creatures.

The team are getting ready to spend their first night underground.

It's not long before George finds something

sharing their sleeping quarters.

My bed is about five yards from here.

HE LAUGHS

So I didn't have to come very far to find an amazing beastie.

I'm going to stick out my neck here

and say that this is a new species

of harvestman.

I'll bet you this is the first time

anyone's seen this thing.

And I'll bet you any money

that it's unique to this tepui.

Harvestmen are ancient relatives of spiders.

And this one is very unusual.

It's not reacting to my torch at all,

so I'm assuming it may not have any eyes. I can't see any eyes.

For animals here, it's all about touch.

Eyesight is of no importance whatsoever.

And so it seems very odd to us, who are dependent on our eyesight.

But for them, their main sense is touch.

Over millions of years, these harvestmen have evolved

to live in complete darkness.

For George, it's an exciting taste of what lies ahead.

It's been a long day,

and the team bed down for their first night in the cave.

I have absolutely no idea what time it is.

I don't know if it's morning, noon or night.

One of the things that hits you

is when you switch off all your torches

and it just gets totally, profoundly dark...

But it is very scary.

Away from the cave's oppressive darkness, Gordon's still searching

for clues that may lead him to the giant anteater.

He's stumbled across something strangely out of place

in the Pantanal's wild plains.

This building up ahead...

Definitely abandoned, no sign of light or life at all.

Places like this, when the human inhabitants move out,

become homes for other creatures.

And if there's any access to it,

I'm sure there will be animals coming and going.

This goes against my better judgement...

OK.

God, I don't really want to go in there.

I'd rather be walking about out in the forest

than being anywhere near this house.

-WHISPERS:

-This place has been taken over by animals,

there's crap all over the floor.

I'm not sure what's left that, maybe a fox.

Oh, it stinks!

It really stinks in here.

Jeez!

CONTINUOUS HIGH-PITCHED SCREECHING

Look at that. This looks like blood that's dripping down the walls.

HE EXHALES

There's just a kind of stench wafting out of this room.

It's a really strong, animal-y smell.

Right, I'm going to look.

-SCREECHING

-What is that noise?!

Definitely something in there.

Oh, my God.

Oh, my God.

-That is a

-BLEEP

-nightmare.

-WHISPERS:

-It's full of bats... Oh, they're vampire bats.

Hundreds of them.

Eugh, God.

That stuff coming down the walls is blood.

Vampire bats, they feed entirely on blood.

And when they roost, during the day when they defecate,

they're just defecating blood.

So it's just blood that is fuelling them,

blood that's passing through them, and all these streaks

down the walls, it's just...

It's blood from

other living animals.

That is gross.

Under cover of darkness, vampire bats sneak up on large mammals,

using their acute hearing to home in on the sound of breathing.

Then, with special thermo receptors on their noses,

they detect hot blood flowing

close to the skin.

This is where they bite and feed.

It's official. I've found the most disgusting toilet on the planet.

These hideouts are safe places for the vampire bats

to take refuge during daylight hours.

When they return to the roost, they regurgitate blood to share

with the young and other hungry bats in the colony.

I know they're just animals doing what they do,

-but it's disgusting!

-HE CHUCKLES

Eugh! God... Get me out of here.

I have never been so glad to leave a place in all my life.

It's an unsettling encounter, and not what Gordon is looking for.

With no signs of giant anteaters, he heads back to camp.

The Amazon team, Sophie and Bryson, are coming to the end

of a long night.

On the river, Bryson has spotted something colourful.

Look at that. A sleeping kingfisher.

The majority of birds down here are going to be sleeping at night-time,

cos flying at night-time is kind of risky behaviour,

or a dangerous thing to do. You crash into a tree, you'll die.

But while most birds don't have the vision to operate at night,

their prey, insects, come out in their millions.

INSECTS BUZZ INSISTENTLY

I'm getting attacked by these night wasps.

You get about a three-second warning once they land on you

before they sting you. Ow!

HE COUGHS

They keep going into my nostrils and I just ate one.

HE SPLUTTERS Agh!

I can feel it crawling in my throat.

At night, biting insects are everywhere.

INSECTS BUZZ

In the canopy, Sophie is a sitting target.

She's been stuck on a one-metre square platform all night,

waiting for owl monkeys to visit the fruiting tree.

(I've never, ever been around so many mosquitoes.)

It's hell on Earth at the minute.

Mosquitoes, like vampire bats, hunt for blood

under the cover of darkness.

They home in on the carbon dioxide from every breath

that Sophie exhales.

When you're being bitten this much,

staying still and concentrating is really quite hard.

I'm fairly knackered.

I'm quite looking forward to a bit of sleep...

..and no mosquitoes.

Day brings a change in the flooded forest,

as a new set of animals emerge.

The light makes the jungle seem a friendlier place.

BIRDS HOOT

And it gives the team a chance to rest.

In the Pantanal, Gordon washes off the stench

of last night's bat encounter

and relaxes after his long hours exploring the plains.

Oh, God, I've got these mosquito bites all over my legs,

it's just so nice to be in the water.

As the day wears on, deep in the heart of this Venezuelan mountain,

George's mission into perpetual darkness continues.

Up on the surface,

it takes special technology to uncover the secrets of the dark.

Down here, for George, it is old-fashioned exploration.

They have reached a deeper area of river.

And the caving team are keen to show George what they think

is a very significant find.

What we're hunting for is this little pale catfish.

The catfish would almost certainly be a new species

and the only fish to be found anywhere in these mountains.

Why is it here?

And how does it survive in the dark?

George!

Have you got one?

Well done, guys. Oh, wow, look at that. Well, here it is.

That is fantastic, look at it!

I'm holding in my hand the only species of fish

that's been found anywhere on any tepui.

It only lives inside this cave stream

and it just found its way into the cave system.

This is a truly extraordinary discovery.

With no other fish for miles around,

how its ancestors found their way into this cave

is a complete mystery.

Isolated in the dark for millennia,

these catfish have started to lose the skin pigment

that camouflages them.

Without light, it has no use.

Generation by generation, these fish are adapting to the dark.

I'm not sure if it's completely blind.

There are eyes there, but a million years from now,

it will be completely blind,

because it's evolving in the total darkness of this cave

and so eyes have no value at all for it.

Instead of eyes, this fish relies on other senses.

The large barbels around its mouth are sensory organs,

similar to the whiskers of a cat.

Its skin is also covered in taste buds,

meaning that this fish can taste its way to a meal in the dark.

There is heaps of food material that gets washed in from the top

with all the rains, silt, algae, bits and pieces

and eventually ends up here. It doesn't have to go anywhere else,

all the food arrives on its patch.

Well, it's time for our little star...

..to go back...

..into the wild.

Beautiful.

In the Pantanal, Gordon has struggled to find

the giant anteaters that are reportedly coming out at night.

Perfect tree here.

To improve his chances of studying them, Gordon sets up camera traps

in an area where the animals have been seen in the past.

Switched on, ready to go.

If anything visits these trees during the night,

an infrared motion sensor will trigger the cameras,

and the animal's activity will be recorded.

Wow, look at this!

This big tree is covered in lots of interesting marks.

It looks as if somebody's hacked it with a machete,

but there's way too many of them for it to have been made by humans.

You've got one big score there.

Whatever animal left these marks,

it is enormous. The highest scratches go beyond my reach.

A great place to set up a camera trap, and if this animal comes back,

we'll get a clear shot of it. It's a little bit of a mystery,

because I haven't seen anything like this before.

The area covered with camera traps,

Gordon moves on to search for the giant anteater.

As the sun sets,

the Amazon team prepare for another night in the jungle.

Bryson is pushing further into the flooded forest.

HE CALLS OUT IN FOREIGN LANGUAGE

Wow, look at that!

A huge three-toed sloth just sleeping right there. Look at that!

Despite their reputation for laziness,

sloths spend more time awake than asleep.

They are polyphasic, active for periods during both day and night.

Oh, look, she's starting to climb.

Climbing around the canopy in the dark is risky.

One wrong move could mean a fatal fall.

For Bryson, it's a chance to witness

some of the sloth's special adaptations.

She's smelling the branch before she crawls on it.

They never will crawl on a dead branch, cos if they do,

they'll fall out of the tree.

They've got an amazing sense of smell.

Sloths can detect a dangerously weak and rotten branch in the darkness

by smell alone.

To help them move around the canopy at night,

they also create a mind map of trees.

They have an amazing memory of the canopy connections,

so she probably knows exactly where she's going.

This sloth is low enough that I think I can get a closer look at it.

It's just on the other side of these vines.

Right up there.

Sloths spend most of their lives high up in the canopy.

Finding one so low in the tree is rare.

Bryson has studied them for many years.

This is a great opportunity to examine one.

Ooh!

Hey. Wow.

Wow, she is beautiful, look at her.

HE CHUCKLES She's absolutely gorgeous.

Hey. So, I've been working with sloths for ten years now.

This doesn't stress them out at all. They're pretty comfortable with it.

They're so strange looking when you see them up close.

They are also surprisingly comfortable with the insects

in their fur.

Sloths have a special relationship with a moth called the sloth moth.

And you can see them crawling all over her right now.

And these moths spend their entire life on the back of the sloth.

Living in the sloth's fur helps the moths avoid predators.

What the sloth gains from the relationship, if anything,

is a mystery.

Oh, taking my headlamp.

I think she's ready to go home. I'll put her back in her tree.

All right. Back home.

Out on the Pantanal,

Gordon's anteater search continues.

He has heard movement in a small patch of forest.

Not the giant anteater he's hoping for, but one of its cousins.

Isn't that just the weirdest-looking animal you've ever seen?

A lesser anteater.

Just metres in front of me.

Amazing.

Lesser anteaters spend up to 60% of their time in trees.

(OK, it's moved down. Let's see if I can follow it.)

However, they often leave the branches

to move between patches of forest, or to forage on the ground.

(There it is, right there.)

And look at this fella. Now, that is one bold little creature.

This is incredible, to be so close to a wild animal like this.

Anteaters are distant relatives of sloths and, like them,

they forage for food during the day and at night.

Still here. He's about to open a little bit of this log.

There's probably some ants or termites in there.

They have poor eyesight,

relying on smell and hearing to avoid predators and detect prey.

You can see here exactly what he was after - these termites.

Now, he's just pulled back the bark, and underneath this rotten log,

there are millions and millions of termites.

He just starts probing his tongue in there and lapping them up.

There's clearly plenty of food here for anteaters.

Even enough for giants.

It's a promising sign.

In the canopy of the Amazon,

Sophie is still staking out the fruiting tree,

waiting for any sign of the owl monkeys.

So far, she has had no luck at all...

..and things are about to get worse.

THUNDERCLAP

They are really large clouds. Very, very foreboding.

Not great, really, to be up a tree...

in the middle of a tropical rainstorm, on a metal platform.

The thunderstorm is really nearly here, and I'm in two minds.

I want to stay, and I really want to see the monkeys,

but I also don't want to get caught in a storm.

Here it comes.

THUNDER RUMBLES

Here it is, here it is. Go! Go!

Oh, I can't believe we pushed it.

Please, don't leave me up here.

It's quite unnerving up there,

the tree's moving around an awful lot.

OK, clear.

We need to get out of the forest. It's dangerous.

The one place you don't want to be in a tropical rainstorm

is in a flooded forest,

in a metal boat with loads of deadwood,

and that's why we're trying to get out of here

as quickly and safely as possible.

BOAT ENGINE STARTS

The storm brings high winds and lightning.

The biggest danger to Sophie is falling trees.

They must pick their way

back through the forest to the main river fast.

That is... That's lovely.

Even though we're now out and you can now see the lightning

and the rain's heavier, we're away from the woods. That is very good.

The Amazon team take shelter in the old steamer.

Sophie and Bryson will have to wait for the storm to subside

before they can head back out into the flooded forest.

George is now two miles into the cave.

Few creatures can survive this far into total darkness.

Oh, my God!

I don't believe what I'm seeing!

This is a swimming cricket.

Whoa! Look at it! Look!

It's using its little legs

in a sort of breaststroke.

Look at it, it's a proper breaststroke.

Oh!

Oh! Oh, my God!

It's a female, it's an adult female.

This is one of the weirdest

cave animals I've ever seen.

Crickets are common around the world,

but this one is entirely different.

In mastering this environment, using only touch and taste,

this strange-looking animal has become the apex predator.

There is an animal perfectly adapted

for life as a hunter in pitch-darkness.

It's got everything it needs -

it's got long antennae,

it's got these very sensitive palps

here for feeling its prey,

and these amazingly spiny legs.

So as soon as it meets something, feels it, the legs come in,

the spines are there,

and then grab them between these ENORMOUS great jaws.

This is the lion of the cave.

This is something you don't want to meet if you're a bug.

Look at her, look at her! Ooh, she's big!

Ooh, God, she is strong, and she's trying to bite my finger. Agh!

She is trying to slice through my thumb. Agh!

Ooh! Argh.

Look, I'm not even holding you, just go away, please.

This is the only way she is going to let go. Argh! Agh!

Gah! Oh!

Oh!

Isolated for millions of years in a cave with limited prey,

this animal has evolved to hunt both on land and underwater,

making the most of its uniquely demanding habitat.

HE LAUGHS

Oh, man! Just the perfect animal for a cave.

Animals could live in the dark as easily as we live in daylight.

They just need the right senses - touch, smell and hearing.

As Bryson pushes into the very depths of the flooded forest,

he comes across a creature that takes hearing to an extreme.

CREATURES SCREECHING

There's dolphins swimming around my boat right now.

They're actually pretty loud at night-time.

They kind of come by and you hear them breathe, going...

-HE MIMICS BREATHING NOISE

-..right next to the boat.

DOLPHIN EXHALES LOUDLY

Thousands of miles from the sea, these pink river dolphins

have evolved for life in the fresh water of these flooded forests.

They use sound to navigate and hunt, sending out clicks,

and listening for echoes from their surroundings.

I never realised that the forest floods this much, that the dolphin

can actually feed in the middle of the forest, miles from the river.

That's weird.

And they do it at night-time.

With their highly tuned sonar,

dolphins operate superbly in the pitch-black.

High up in the canopy, Sophie's vigil has finally paid off.

(I think I've just heard an owl monkey.)

SCREECHING

(Oh, do you hear that? That's an owl monkey.)

(Did you see it thrashing around in the bushes?)

SHE GASPS

After days of frustration,

Sophie is able to capture footage of these wild monkeys in the canopy.

(There's another one just come in.)

(And they're feeding.)

(That's very cool.)

(It's just a pure example of an animal)

(beautifully adapted for the night.)

(They're out there on their own, all the other primates are asleep,)

(and so they have the trees to themselves.)

Unlike many nocturnal animals, owl monkeys still rely on eyesight.

(Big glowing eyes. It's the main feature.)

Their eyes are 50% larger than other monkeys,

and perfectly adapted for the dark.

They have sacrificed colour and sharpness for sensitivity.

Their retinas are crammed with cells that detect even the dimmest light.

For a fuller picture of how these monkeys function in the dark,

Sophie must switch to thermal imaging.

(It's extraordinary, the way he's moving around.)

(Just bouncing through the trees. It's just incredible.)

Sophie's images show how the monkeys' ultra-sensitive eyes

help them see branches and judge distances in the darkness.

(This is the first time they've ever been filmed in the canopy)

(with the thermal cameras,)

(and it just gives you a whole new view.)

(He's going to jump!)

(He's going to jump! Oh!)

(That's incredible.)

(This creature has just leapt)

(ten foot through the air.)

(I've just watched them leaping through the forest)

(as if it was broad daylight, and it's not.)

(It's dark.)

(They are so well adapted, it takes your breath away.)

(You don't expect to see monkeys leaping through the forest at night.)

(You just don't.)

(Owl monkeys have very distinct territories,)

(which means if they're visiting this fruiting tree,)

(their nest could very well be close-by.)

Sophie has recorded unique footage

of these remarkable animals at night.

Her final challenge is to film them at their nest in the day.

On the plains of the Pantanal,

Gordon's thermal camera has picked up something large.

Oh, my God.

Look, look, look, look!

The unmistakable outline of the elusive giant anteater.

That's great.

This is the first time I've ever seen a giant anteater,

and I'm not disappointed.

It is an INCREDIBLE beast.

Like the lesser anteater, this giant has poor eyesight.

It uses a strong sense of smell to navigate in the dark.

He's got that big long nose.

SNIFFING

I think it's safe to say that the giant anteater

is one of the strangest animals that roams the planet.

I wonder if I can get closer?

(Yeah, I'm going to try and get a bit closer.)

Now, this animal is after the exact same prey

as the lesser anteater that I saw -

ants and termites -

but obviously, a monster like this

needs many, many more of them.

The giant anteater is not truly nocturnal.

In other parts of South America, it forages during the day.

But its powerful sense of smell

means it's equally at home in the dark.

In very hot areas like the Pantanal,

they make the most of the cool night air

and sleep during the heat of the day.

He's still on the move, so I'm going to try and keep up with him.

Giant anteaters can move quickly.

With his heavy cameras, Gordon is unable to keep up.

I completely lost it. Even with all this technology,

it's still quite easy to lose stuff in the dark.

Gordon gives up the chase, after a disappointingly short encounter.

His hope is that the camera traps

will reveal more nocturnal behaviour.

As soon as it's light enough, Gordon checks his traps.

With luck, their footage will reveal

what these giants are doing at night.

Right, here we go.

Oh, look at this!

The traps have done their job.

Oops, he's having a sniff.

He's having a stiff at the tree.

The cameras have recorded over 15 hours of footage.

Surprisingly, several different individuals have visited this spot.

Ooh, look, this one's got a baby on its back. You can just see it.

They seem drawn to the tree

where Gordon found mysterious scratch marks.

Oh, wow!

That's what it is!

Whoa!

That anteater's actually off the ground.

He's technically climbing.

Giant anteaters are ground-dwellers and are not known to climb.

This animal isn't reaching. He's not standing up on his back legs.

He's actually climbing the tree.

So, all these marks way up the tree have been left

by that mysterious creature - the giant anteater.

The big question is, why is the anteater climbing the tree?

I think it may well have something to do with marking a territory,

that different anteaters come here and they scratch and leave a scent.

Smell is incredibly important to these giants.

The camera trap images suggest that they use scent to communicate,

and to map each other's movements in the dark.

There's not that much known about giant anteaters,

but one thing that is in every publication

is that they do not climb trees, and here's an anteater climbing a tree.

Oh, wow! Wow, look at him.

Gordon has done more than just film these animals.

He has documented a completely new behaviour.

This is the first place it's EVER been filmed.

In the flooded forests of the Amazon,

Sophie has found the owl monkeys' nest.

In daylight, the eyes that are so vital at night

seem even more striking.

The little one is yawning.

And it's obviously night-time. He's meant to be asleep.

But he's so curious, he can't resist just peeking out the hole.

By adapting for life after dark,

these owl monkeys avoid competition for food

and can shelter from daytime predators.

I've never filmed anything quite so gorgeous.

Seeing these monkeys at rest during the day

is a perfect end to Sophie's mission.

She has achieved a wildlife first.

Her remarkable thermal images show how freely these monkeys are able to

move around the canopy in the dark.

Working through the night in the flooded forest

has been an extreme challenge for the Amazon team.

However, both Sophie and Bryson leave with new insight

into how animals survive here in the dark.

In Venezuela, after four days in total darkness,

and following the underground river for three miles,

George can go no further.

We're now exactly at the end of the underground stream.

And it sinks down... Ooh!

..through a big choke of boulders which have fallen down.

HE GRUNTS

Oh! Look, sunlight! That's the most amazing colour to see

after being in darkness for so long.

Ah, we're there.

Oh, look at it, it's getting brighter and brighter!

God, that almost hurts your eyes, actually.

And the other thing that really hits you is the fresh air.

HE BREATHES IN DEEPLY

Ah! What a view!

Ah!

This is the world I am part of down here.

Fascinating though the darkness is

and amazing as the animals are, we're not creatures of the dark.

We should be out there in the sun, and that's where I belong.

It's the end of an extraordinary journey.

From night in the flooded forest

to the perpetual darkness of the cave,

incredible creatures and new species

have evolved to live in an alien world.

Adapting their senses and behaviour

to survive...in the dark.

Next time, the team head to the very bottom of the continent...

..for the final phase of the expedition...

..at the wild southern tip of South America...

Look at that.

It's scary as hell!

..where more nocturnal mysteries await.

What is that?

Subtitles by Red Bee Media Ltd