0:00:02 > 0:00:04As night creeps across the planet...
0:00:05 > 0:00:09..and our familiar daytime world is plunged into darkness,
0:00:09 > 0:00:12strange creatures are beginning to stir.
0:00:14 > 0:00:17This is when most animals are active.
0:00:19 > 0:00:23But the drama of their nocturnal lives is hidden from our eyes.
0:00:25 > 0:00:29These are specialized beasts, all adapted for the dark.
0:00:34 > 0:00:38It's a world we know almost nothing about.
0:00:40 > 0:00:43Now, a team armed with specialist cameras is travelling
0:00:43 > 0:00:47to the remotest corners of Central and South America...
0:00:48 > 0:00:50That's unbelievable!
0:00:50 > 0:00:54..to uncover the secret lives of animals after dark.
0:00:55 > 0:00:57- WHISPERING:- Wow!
0:00:57 > 0:01:00It's a journey into the unknown.
0:01:00 > 0:01:04WHISPERING: Look at him. He can smell me.
0:01:05 > 0:01:07- WHISPERING:- Don't...run.
0:01:07 > 0:01:09- Holy- BLEEP.
0:01:09 > 0:01:11WHISPERS: Get me out of here.
0:01:21 > 0:01:25For six months, a team of biologists and film makers
0:01:25 > 0:01:28is exploring Central and South America...
0:01:29 > 0:01:32..home to many of the most diverse habitats on Earth.
0:01:33 > 0:01:38They aim to discover why animals come out in the dark,
0:01:38 > 0:01:42and how they survive in a world with no light.
0:01:51 > 0:01:54They started in the jungles of Costa Rica.
0:01:54 > 0:01:58Now, the team is moving South for the second leg of the expedition.
0:02:00 > 0:02:03The team has split to follow three separate missions,
0:02:03 > 0:02:05in three very different habitats,
0:02:05 > 0:02:08across the dark heart of South America.
0:02:12 > 0:02:16Insect specialist Dr George McGavin is in Venezuela
0:02:16 > 0:02:18to explore a place of permanent darkness.
0:02:22 > 0:02:23A cave that no biologist
0:02:23 > 0:02:25has ever entered.
0:02:31 > 0:02:35There are caves here which have formed over millions of years
0:02:35 > 0:02:38and haven't seen the sun - any animals in there
0:02:38 > 0:02:43have been there evolving in total darkness for millions of years,
0:02:43 > 0:02:46and we might be the first people to ever see them.
0:02:50 > 0:02:53The cave was discovered in 2009
0:02:53 > 0:02:56by international exploration team La Venta.
0:02:56 > 0:02:58George has joined them as they prepare
0:02:58 > 0:03:00to return for the first time.
0:03:00 > 0:03:04These places have been isolated for so long that
0:03:04 > 0:03:09there's a very high chance anything we find here is completely new.
0:03:10 > 0:03:14Their base is the top of this remote tepui -
0:03:14 > 0:03:16a giant table top mountain.
0:03:17 > 0:03:20The cave entrance is far below them,
0:03:20 > 0:03:24hidden in thick jungle at the base of this cliff.
0:03:29 > 0:03:35It's about 110 metres from where I am to the end of the rope.
0:03:36 > 0:03:42That is a very long way down. A very long way down, indeed.
0:03:46 > 0:03:50The cave has been cut off from the light for millions of years -
0:03:50 > 0:03:53enough time for new species to evolve.
0:03:54 > 0:03:55What creatures live here?
0:03:55 > 0:03:58And how have they adapted to permanent darkness?
0:03:58 > 0:04:00George hopes to find out.
0:04:12 > 0:04:141,700 miles south,
0:04:14 > 0:04:17at the edge of the Amazon basin,
0:04:17 > 0:04:22wildlife filmmaker Gordon Buchanan is heading into the Pantanal -
0:04:22 > 0:04:26the largest wetland on Earth, and the richest.
0:04:37 > 0:04:39The Pantanal is one of the most
0:04:39 > 0:04:41bio-diverse places on the planet.
0:04:44 > 0:04:47There's life everywhere, but most of those animals
0:04:47 > 0:04:49that you see during the day are absent at night,
0:04:49 > 0:04:52and they're replaced by a whole set of other creatures.
0:04:52 > 0:04:56Almost nothing is known about what goes on here at night-time.
0:05:08 > 0:05:10Gordon wants to find out more.
0:05:10 > 0:05:15Top of his list is one of South America's most bizarre animals.
0:05:17 > 0:05:19The giant anteater.
0:05:21 > 0:05:24Elsewhere, they come out in the day.
0:05:24 > 0:05:29But here, scientists have reported them emerging after dark
0:05:29 > 0:05:31to escape the relentless heat.
0:05:31 > 0:05:33In the shade, it's 42.
0:05:33 > 0:05:36Out here in the sun, I don't know what it'll go up to,
0:05:36 > 0:05:38but it is blisteringly hot.
0:05:40 > 0:05:44How does a daytime animal function in the dark?
0:05:44 > 0:05:48Gordon will use the latest night vision cameras to find out.
0:05:50 > 0:05:53He hopes to learn what the giant anteaters are up to at night.
0:05:58 > 0:06:01In Venezuela, George has reached the cave entrance.
0:06:03 > 0:06:06This will be his last glimpse of daylight.
0:06:10 > 0:06:12That's not coming through.
0:06:14 > 0:06:17For the next four days, the team will follow the river
0:06:17 > 0:06:22three miles through the cave, looking for life in the darkness.
0:06:25 > 0:06:27Only a few steps inside...
0:06:27 > 0:06:30Ho-ho! Look at this.
0:06:30 > 0:06:32..and George finds something interesting.
0:06:36 > 0:06:40Now, that is one of a cave's most spectacular insects.
0:06:42 > 0:06:48Now, all of these threads are produced by a fly larva.
0:06:48 > 0:06:50You can just see it there.
0:06:53 > 0:06:56And it makes these vertical threads,
0:06:56 > 0:07:01and on the threads are very sticky blobs of goo.
0:07:03 > 0:07:07There, you see? That's fantastic. Now, that is a prey item.
0:07:07 > 0:07:08It's still alive, look!
0:07:10 > 0:07:13This predator takes advantage of the dark.
0:07:14 > 0:07:17It sets its traps close to the cave entrance.
0:07:18 > 0:07:22Insects from the outside stray in.
0:07:22 > 0:07:26Unable to see the threads, some, inevitably, are caught.
0:07:28 > 0:07:34So, that tiny little midge has flown along here in the pitch darkness,
0:07:34 > 0:07:37it can't see anything, of course, and it's stuck fast.
0:07:38 > 0:07:41Vibrations on the thread tell the larva
0:07:41 > 0:07:43that a new meal has been snared.
0:07:47 > 0:07:51The larva then oozes its way along, down the vertical thread,
0:07:51 > 0:07:54consumes the prey, and then goes back up.
0:07:54 > 0:07:56And these threads are all over here.
0:07:56 > 0:07:59So, for a small, flying insect like this,
0:07:59 > 0:08:04this cave is just full of hazards, and there it's come to a sticky end.
0:08:04 > 0:08:06HE LAUGHS
0:08:06 > 0:08:08In every sense of the word!
0:08:10 > 0:08:14Even in this twilight zone, creatures are adapted to the dark.
0:08:16 > 0:08:19George and the team head further underground in search of life.
0:08:22 > 0:08:25To the South, the third and final team
0:08:25 > 0:08:27will push deep into the Peruvian rainforest
0:08:27 > 0:08:30at the headwaters of the mighty Amazon.
0:08:35 > 0:08:38Base Camp is an old river steamer.
0:08:40 > 0:08:43On board are tropical biologist Bryson Voirin,
0:08:43 > 0:08:45and camerawoman Sophie Darlington.
0:08:46 > 0:08:50It's sort of a wildlife filmmaker's dream to come to the Amazon.
0:08:50 > 0:08:54It's rammed full of the world's most exciting animals.
0:08:56 > 0:09:01Bryson is an expert on the large mammals in this region.
0:09:01 > 0:09:03During the day, I know what to expect.
0:09:03 > 0:09:07But at night-time, it's going to be a whole different ball game.
0:09:09 > 0:09:13The forest floor here is covered by several metres of flood water
0:09:13 > 0:09:14for most of the year.
0:09:17 > 0:09:20It's a unique habitat for the team to explore.
0:09:29 > 0:09:33With little dry land, many animals live in the canopy.
0:09:35 > 0:09:38Sophie is here to find a very special monkey.
0:09:40 > 0:09:43There are over 100 different species in the Amazon,
0:09:43 > 0:09:45but only one kind comes out at night.
0:09:45 > 0:09:48Owl monkeys.
0:09:48 > 0:09:51It would just be amazing to see these owl monkeys
0:09:51 > 0:09:53and how they move about the trees at night.
0:09:53 > 0:09:58Like us, monkeys all over the world are completely reliant on daylight.
0:10:00 > 0:10:01All except the owl monkey,
0:10:01 > 0:10:05which is uniquely adapted for life in the dark.
0:10:10 > 0:10:12Sophie will stake out a fruiting tree,
0:10:12 > 0:10:15where she hopes the monkeys will come to feed.
0:10:17 > 0:10:19She will have to perch on a small platform
0:10:19 > 0:10:2130 metres above the water.
0:10:23 > 0:10:24OK...
0:10:24 > 0:10:26This is a new challenge for her.
0:10:28 > 0:10:33She has 20 years' experience, but all of it at ground level.
0:10:33 > 0:10:36I'm not enjoying this.
0:10:40 > 0:10:43SHE PANTS
0:10:43 > 0:10:44I'm finding it very hard.
0:10:51 > 0:10:55It's an amazingly odd feeling, being up above the forest.
0:10:56 > 0:10:57OK, it's solid.
0:11:00 > 0:11:04Catching the monkeys on film will take luck and persistence.
0:11:07 > 0:11:11The reward will be a unique glimpse into canopy life after dark.
0:11:13 > 0:11:15While Sophie stakes out the treetops,
0:11:15 > 0:11:18Bryson searches at water level.
0:11:20 > 0:11:23He's looking for nocturnal animals in the undergrowth
0:11:23 > 0:11:26and in the waters of this flooded forest.
0:11:28 > 0:11:31My plan is to do a survey of species in the river at night-time.
0:11:31 > 0:11:34So we're going to go out and try to go into the forest
0:11:34 > 0:11:37with the little boats, with bright torches or spotlights
0:11:37 > 0:11:39and hopefully see some of the nocturnal species
0:11:39 > 0:11:42that are out here in this part of the Amazon.
0:11:46 > 0:11:49Across South America, night approaches.
0:11:54 > 0:11:58In the Pantanal, Gordon leaves camp and heads out onto the plains
0:11:58 > 0:12:00in search of the giant anteater.
0:12:11 > 0:12:15As the sun sets, the Pantanal changes.
0:12:15 > 0:12:17Night is when most predators come out to hunt.
0:12:17 > 0:12:23Animals of the day hide as best they can and sleep.
0:12:32 > 0:12:35The countless species that have lain hidden during daylight
0:12:35 > 0:12:37gradually emerge.
0:12:39 > 0:12:42The night shift begins.
0:12:48 > 0:12:52Armed with a thermal camera that detects body heat,
0:12:52 > 0:12:56it doesn't take Gordon long to spot something.
0:12:56 > 0:12:57Right...
0:12:57 > 0:12:59Oh!
0:13:00 > 0:13:04On his camera, warm-blooded animals glow brightly
0:13:04 > 0:13:06against the cool background.
0:13:06 > 0:13:08- WHISPERS:- It's a rhea. It's a flightless bird.
0:13:08 > 0:13:12This is the biggest bird in South America.
0:13:17 > 0:13:19- HE CHUCKLES - Look at that!
0:13:20 > 0:13:26Oh, that's really nice. It has a whole heap of chicks with it.
0:13:28 > 0:13:30Rheas ferociously protect their young.
0:13:31 > 0:13:35During the day, most predators stay clear of these giant birds.
0:13:35 > 0:13:38They stand one-and-a-half metres tall,
0:13:38 > 0:13:42and their heavily muscled legs pack enough punch to break bones.
0:13:42 > 0:13:45But in the dark, the tables are turned.
0:13:45 > 0:13:49With poor vision, they are vulnerable to surprise attack.
0:13:51 > 0:13:55At night-time, they do the sensible thing and just keep a low profile.
0:14:03 > 0:14:04With a second specialist camera
0:14:04 > 0:14:08that films using light invisible to animals,
0:14:08 > 0:14:11Gordon can take a more detailed look.
0:14:12 > 0:14:15These chicks are just mini versions of the adult.
0:14:15 > 0:14:20And that big bird is not the mother, that's the father.
0:14:20 > 0:14:23The female lays the eggs and the male broods them.
0:14:23 > 0:14:26The female swans off.
0:14:26 > 0:14:30But he's doing an incredibly good job of looking after these chicks.
0:14:30 > 0:14:33He's taking that one under his wing.
0:14:36 > 0:14:39Sitting still is a surprisingly effective strategy
0:14:39 > 0:14:41to hide from predators in the dark.
0:14:43 > 0:14:45This rhea is sitting out there in the pitch black,
0:14:45 > 0:14:49it can't see anything. Probably doesn't even know that I'm here.
0:14:49 > 0:14:52If we just switch the light off,
0:14:52 > 0:14:55you will see what I can see without the equipment.
0:15:00 > 0:15:04Like us, rheas are virtually blind in the dark.
0:15:04 > 0:15:07But they have very good hearing.
0:15:08 > 0:15:10CHIRPING
0:15:10 > 0:15:13At the first sound of danger, they scatter.
0:15:17 > 0:15:20The male finds his chicks in the dark by calling.
0:15:20 > 0:15:23CHIRPING
0:15:25 > 0:15:29They will regroup in a safe place to wait out the hours of darkness.
0:15:33 > 0:15:36Rheas survive the dark by hunkering down.
0:15:37 > 0:15:40But the giant anteaters Gordon is searching for
0:15:40 > 0:15:42are always on the move.
0:15:42 > 0:15:45To find them, he, too, must keep going.
0:15:50 > 0:15:54In Venezuela, George has journeyed deeper into the cave.
0:15:55 > 0:15:57No light reaches here at all.
0:15:59 > 0:16:03It's the perfect place to find strange, dark-adapted creatures.
0:16:08 > 0:16:13The team are getting ready to spend their first night underground.
0:16:17 > 0:16:19It's not long before George finds something
0:16:19 > 0:16:21sharing their sleeping quarters.
0:16:23 > 0:16:27My bed is about five yards from here.
0:16:27 > 0:16:28HE LAUGHS
0:16:28 > 0:16:33So I didn't have to come very far to find an amazing beastie.
0:16:35 > 0:16:37I'm going to stick out my neck here
0:16:37 > 0:16:40and say that this is a new species
0:16:40 > 0:16:41of harvestman.
0:16:41 > 0:16:43I'll bet you this is the first time
0:16:43 > 0:16:45anyone's seen this thing.
0:16:45 > 0:16:47And I'll bet you any money
0:16:47 > 0:16:49that it's unique to this tepui.
0:16:51 > 0:16:55Harvestmen are ancient relatives of spiders.
0:16:58 > 0:17:00And this one is very unusual.
0:17:04 > 0:17:08It's not reacting to my torch at all,
0:17:08 > 0:17:13so I'm assuming it may not have any eyes. I can't see any eyes.
0:17:13 > 0:17:16For animals here, it's all about touch.
0:17:16 > 0:17:18Eyesight is of no importance whatsoever.
0:17:18 > 0:17:22And so it seems very odd to us, who are dependent on our eyesight.
0:17:22 > 0:17:25But for them, their main sense is touch.
0:17:32 > 0:17:35Over millions of years, these harvestmen have evolved
0:17:35 > 0:17:37to live in complete darkness.
0:17:46 > 0:17:49For George, it's an exciting taste of what lies ahead.
0:17:51 > 0:17:53It's been a long day,
0:17:53 > 0:17:56and the team bed down for their first night in the cave.
0:18:01 > 0:18:04I have absolutely no idea what time it is.
0:18:04 > 0:18:09I don't know if it's morning, noon or night.
0:18:10 > 0:18:12One of the things that hits you
0:18:12 > 0:18:15is when you switch off all your torches
0:18:15 > 0:18:20and it just gets totally, profoundly dark...
0:18:20 > 0:18:23But it is very scary.
0:18:34 > 0:18:38Away from the cave's oppressive darkness, Gordon's still searching
0:18:38 > 0:18:41for clues that may lead him to the giant anteater.
0:18:44 > 0:18:48He's stumbled across something strangely out of place
0:18:48 > 0:18:50in the Pantanal's wild plains.
0:18:52 > 0:18:55This building up ahead...
0:18:55 > 0:18:59Definitely abandoned, no sign of light or life at all.
0:18:59 > 0:19:03Places like this, when the human inhabitants move out,
0:19:03 > 0:19:07become homes for other creatures.
0:19:07 > 0:19:09And if there's any access to it,
0:19:09 > 0:19:12I'm sure there will be animals coming and going.
0:19:12 > 0:19:16This goes against my better judgement...
0:19:16 > 0:19:17OK.
0:19:19 > 0:19:22God, I don't really want to go in there.
0:19:28 > 0:19:31I'd rather be walking about out in the forest
0:19:31 > 0:19:33than being anywhere near this house.
0:19:38 > 0:19:40- WHISPERS:- This place has been taken over by animals,
0:19:40 > 0:19:43there's crap all over the floor.
0:19:43 > 0:19:46I'm not sure what's left that, maybe a fox.
0:19:48 > 0:19:50Oh, it stinks!
0:19:50 > 0:19:52It really stinks in here.
0:19:52 > 0:19:54Jeez!
0:19:54 > 0:19:57CONTINUOUS HIGH-PITCHED SCREECHING
0:19:58 > 0:20:03Look at that. This looks like blood that's dripping down the walls.
0:20:05 > 0:20:06HE EXHALES
0:20:06 > 0:20:09There's just a kind of stench wafting out of this room.
0:20:09 > 0:20:14It's a really strong, animal-y smell.
0:20:16 > 0:20:18Right, I'm going to look.
0:20:18 > 0:20:20- SCREECHING - What is that noise?!
0:20:20 > 0:20:22Definitely something in there.
0:20:28 > 0:20:30Oh, my God.
0:20:30 > 0:20:32Oh, my God.
0:20:38 > 0:20:41- That is a- BLEEP- nightmare.
0:20:42 > 0:20:46- WHISPERS:- It's full of bats... Oh, they're vampire bats.
0:20:46 > 0:20:49Hundreds of them.
0:20:49 > 0:20:51Eugh, God.
0:20:55 > 0:20:58That stuff coming down the walls is blood.
0:20:58 > 0:21:03Vampire bats, they feed entirely on blood.
0:21:03 > 0:21:07And when they roost, during the day when they defecate,
0:21:07 > 0:21:09they're just defecating blood.
0:21:09 > 0:21:12So it's just blood that is fuelling them,
0:21:12 > 0:21:14blood that's passing through them, and all these streaks
0:21:14 > 0:21:17down the walls, it's just...
0:21:20 > 0:21:22It's blood from
0:21:22 > 0:21:24other living animals.
0:21:24 > 0:21:25That is gross.
0:21:30 > 0:21:35Under cover of darkness, vampire bats sneak up on large mammals,
0:21:35 > 0:21:39using their acute hearing to home in on the sound of breathing.
0:21:40 > 0:21:44Then, with special thermo receptors on their noses,
0:21:44 > 0:21:47they detect hot blood flowing
0:21:47 > 0:21:48close to the skin.
0:21:48 > 0:21:51This is where they bite and feed.
0:21:53 > 0:21:57It's official. I've found the most disgusting toilet on the planet.
0:22:02 > 0:22:05These hideouts are safe places for the vampire bats
0:22:05 > 0:22:08to take refuge during daylight hours.
0:22:09 > 0:22:13When they return to the roost, they regurgitate blood to share
0:22:13 > 0:22:17with the young and other hungry bats in the colony.
0:22:18 > 0:22:21I know they're just animals doing what they do,
0:22:21 > 0:22:24- but it's disgusting! - HE CHUCKLES
0:22:28 > 0:22:31Eugh! God... Get me out of here.
0:22:32 > 0:22:35I have never been so glad to leave a place in all my life.
0:22:36 > 0:22:41It's an unsettling encounter, and not what Gordon is looking for.
0:22:42 > 0:22:46With no signs of giant anteaters, he heads back to camp.
0:22:51 > 0:22:56The Amazon team, Sophie and Bryson, are coming to the end
0:22:56 > 0:22:57of a long night.
0:22:59 > 0:23:02On the river, Bryson has spotted something colourful.
0:23:04 > 0:23:07Look at that. A sleeping kingfisher.
0:23:07 > 0:23:11The majority of birds down here are going to be sleeping at night-time,
0:23:11 > 0:23:13cos flying at night-time is kind of risky behaviour,
0:23:13 > 0:23:16or a dangerous thing to do. You crash into a tree, you'll die.
0:23:18 > 0:23:23But while most birds don't have the vision to operate at night,
0:23:23 > 0:23:26their prey, insects, come out in their millions.
0:23:26 > 0:23:30INSECTS BUZZ INSISTENTLY
0:23:30 > 0:23:33I'm getting attacked by these night wasps.
0:23:33 > 0:23:35You get about a three-second warning once they land on you
0:23:35 > 0:23:37before they sting you. Ow!
0:23:37 > 0:23:39HE COUGHS
0:23:39 > 0:23:41They keep going into my nostrils and I just ate one.
0:23:41 > 0:23:44HE SPLUTTERS Agh!
0:23:44 > 0:23:46I can feel it crawling in my throat.
0:23:49 > 0:23:52At night, biting insects are everywhere.
0:23:52 > 0:23:55INSECTS BUZZ
0:23:55 > 0:23:58In the canopy, Sophie is a sitting target.
0:23:58 > 0:24:02She's been stuck on a one-metre square platform all night,
0:24:02 > 0:24:05waiting for owl monkeys to visit the fruiting tree.
0:24:07 > 0:24:11(I've never, ever been around so many mosquitoes.)
0:24:12 > 0:24:14It's hell on Earth at the minute.
0:24:18 > 0:24:21Mosquitoes, like vampire bats, hunt for blood
0:24:21 > 0:24:23under the cover of darkness.
0:24:23 > 0:24:26They home in on the carbon dioxide from every breath
0:24:26 > 0:24:28that Sophie exhales.
0:24:30 > 0:24:32When you're being bitten this much,
0:24:32 > 0:24:38staying still and concentrating is really quite hard.
0:24:42 > 0:24:44I'm fairly knackered.
0:24:44 > 0:24:46I'm quite looking forward to a bit of sleep...
0:24:50 > 0:24:52..and no mosquitoes.
0:25:01 > 0:25:05Day brings a change in the flooded forest,
0:25:05 > 0:25:07as a new set of animals emerge.
0:25:09 > 0:25:13The light makes the jungle seem a friendlier place.
0:25:13 > 0:25:14BIRDS HOOT
0:25:17 > 0:25:20And it gives the team a chance to rest.
0:25:23 > 0:25:26In the Pantanal, Gordon washes off the stench
0:25:26 > 0:25:28of last night's bat encounter
0:25:28 > 0:25:32and relaxes after his long hours exploring the plains.
0:25:35 > 0:25:38Oh, God, I've got these mosquito bites all over my legs,
0:25:38 > 0:25:41it's just so nice to be in the water.
0:26:02 > 0:26:07As the day wears on, deep in the heart of this Venezuelan mountain,
0:26:07 > 0:26:10George's mission into perpetual darkness continues.
0:26:17 > 0:26:19Up on the surface,
0:26:19 > 0:26:23it takes special technology to uncover the secrets of the dark.
0:26:23 > 0:26:27Down here, for George, it is old-fashioned exploration.
0:26:32 > 0:26:34They have reached a deeper area of river.
0:26:36 > 0:26:39And the caving team are keen to show George what they think
0:26:39 > 0:26:41is a very significant find.
0:26:43 > 0:26:49What we're hunting for is this little pale catfish.
0:26:51 > 0:26:55The catfish would almost certainly be a new species
0:26:55 > 0:26:58and the only fish to be found anywhere in these mountains.
0:27:02 > 0:27:04Why is it here?
0:27:04 > 0:27:07And how does it survive in the dark?
0:27:07 > 0:27:09George!
0:27:09 > 0:27:11Have you got one?
0:27:11 > 0:27:16Well done, guys. Oh, wow, look at that. Well, here it is.
0:27:16 > 0:27:18That is fantastic, look at it!
0:27:21 > 0:27:25I'm holding in my hand the only species of fish
0:27:25 > 0:27:29that's been found anywhere on any tepui.
0:27:29 > 0:27:31It only lives inside this cave stream
0:27:31 > 0:27:34and it just found its way into the cave system.
0:27:36 > 0:27:40This is a truly extraordinary discovery.
0:27:42 > 0:27:45With no other fish for miles around,
0:27:45 > 0:27:48how its ancestors found their way into this cave
0:27:48 > 0:27:50is a complete mystery.
0:27:54 > 0:27:57Isolated in the dark for millennia,
0:27:57 > 0:28:01these catfish have started to lose the skin pigment
0:28:01 > 0:28:03that camouflages them.
0:28:03 > 0:28:06Without light, it has no use.
0:28:13 > 0:28:18Generation by generation, these fish are adapting to the dark.
0:28:22 > 0:28:25I'm not sure if it's completely blind.
0:28:25 > 0:28:28There are eyes there, but a million years from now,
0:28:28 > 0:28:30it will be completely blind,
0:28:30 > 0:28:34because it's evolving in the total darkness of this cave
0:28:34 > 0:28:36and so eyes have no value at all for it.
0:28:40 > 0:28:44Instead of eyes, this fish relies on other senses.
0:28:46 > 0:28:50The large barbels around its mouth are sensory organs,
0:28:50 > 0:28:53similar to the whiskers of a cat.
0:28:53 > 0:28:57Its skin is also covered in taste buds,
0:28:57 > 0:29:01meaning that this fish can taste its way to a meal in the dark.
0:29:05 > 0:29:09There is heaps of food material that gets washed in from the top
0:29:09 > 0:29:13with all the rains, silt, algae, bits and pieces
0:29:13 > 0:29:16and eventually ends up here. It doesn't have to go anywhere else,
0:29:16 > 0:29:20all the food arrives on its patch.
0:29:20 > 0:29:25Well, it's time for our little star...
0:29:26 > 0:29:28..to go back...
0:29:29 > 0:29:31..into the wild.
0:29:35 > 0:29:37Beautiful.
0:29:42 > 0:29:44In the Pantanal, Gordon has struggled to find
0:29:44 > 0:29:48the giant anteaters that are reportedly coming out at night.
0:29:48 > 0:29:50Perfect tree here.
0:29:50 > 0:29:55To improve his chances of studying them, Gordon sets up camera traps
0:29:55 > 0:29:59in an area where the animals have been seen in the past.
0:29:59 > 0:30:02Switched on, ready to go.
0:30:08 > 0:30:10If anything visits these trees during the night,
0:30:10 > 0:30:15an infrared motion sensor will trigger the cameras,
0:30:15 > 0:30:18and the animal's activity will be recorded.
0:30:26 > 0:30:28Wow, look at this!
0:30:28 > 0:30:35This big tree is covered in lots of interesting marks.
0:30:35 > 0:30:38It looks as if somebody's hacked it with a machete,
0:30:38 > 0:30:42but there's way too many of them for it to have been made by humans.
0:30:42 > 0:30:44You've got one big score there.
0:30:44 > 0:30:47Whatever animal left these marks,
0:30:47 > 0:30:51it is enormous. The highest scratches go beyond my reach.
0:30:51 > 0:30:55A great place to set up a camera trap, and if this animal comes back,
0:30:55 > 0:30:59we'll get a clear shot of it. It's a little bit of a mystery,
0:30:59 > 0:31:01because I haven't seen anything like this before.
0:31:09 > 0:31:12The area covered with camera traps,
0:31:12 > 0:31:14Gordon moves on to search for the giant anteater.
0:31:17 > 0:31:19As the sun sets,
0:31:19 > 0:31:22the Amazon team prepare for another night in the jungle.
0:31:30 > 0:31:34Bryson is pushing further into the flooded forest.
0:31:43 > 0:31:45HE CALLS OUT IN FOREIGN LANGUAGE
0:31:46 > 0:31:48Wow, look at that!
0:31:50 > 0:31:54A huge three-toed sloth just sleeping right there. Look at that!
0:32:00 > 0:32:03Despite their reputation for laziness,
0:32:03 > 0:32:06sloths spend more time awake than asleep.
0:32:08 > 0:32:13They are polyphasic, active for periods during both day and night.
0:32:16 > 0:32:19Oh, look, she's starting to climb.
0:32:21 > 0:32:25Climbing around the canopy in the dark is risky.
0:32:28 > 0:32:31One wrong move could mean a fatal fall.
0:32:34 > 0:32:36For Bryson, it's a chance to witness
0:32:36 > 0:32:39some of the sloth's special adaptations.
0:32:39 > 0:32:42She's smelling the branch before she crawls on it.
0:32:43 > 0:32:46They never will crawl on a dead branch, cos if they do,
0:32:46 > 0:32:47they'll fall out of the tree.
0:32:47 > 0:32:50They've got an amazing sense of smell.
0:32:54 > 0:32:59Sloths can detect a dangerously weak and rotten branch in the darkness
0:32:59 > 0:33:01by smell alone.
0:33:02 > 0:33:05To help them move around the canopy at night,
0:33:05 > 0:33:07they also create a mind map of trees.
0:33:09 > 0:33:12They have an amazing memory of the canopy connections,
0:33:12 > 0:33:14so she probably knows exactly where she's going.
0:33:16 > 0:33:20This sloth is low enough that I think I can get a closer look at it.
0:33:20 > 0:33:23It's just on the other side of these vines.
0:33:25 > 0:33:27Right up there.
0:33:27 > 0:33:30Sloths spend most of their lives high up in the canopy.
0:33:30 > 0:33:34Finding one so low in the tree is rare.
0:33:34 > 0:33:36Bryson has studied them for many years.
0:33:36 > 0:33:39This is a great opportunity to examine one.
0:33:40 > 0:33:42Ooh!
0:33:43 > 0:33:45Hey. Wow.
0:33:45 > 0:33:47Wow, she is beautiful, look at her.
0:33:49 > 0:33:53HE CHUCKLES She's absolutely gorgeous.
0:33:54 > 0:33:57Hey. So, I've been working with sloths for ten years now.
0:33:57 > 0:34:01This doesn't stress them out at all. They're pretty comfortable with it.
0:34:01 > 0:34:05They're so strange looking when you see them up close.
0:34:07 > 0:34:10They are also surprisingly comfortable with the insects
0:34:10 > 0:34:13in their fur.
0:34:13 > 0:34:16Sloths have a special relationship with a moth called the sloth moth.
0:34:16 > 0:34:19And you can see them crawling all over her right now.
0:34:19 > 0:34:23And these moths spend their entire life on the back of the sloth.
0:34:23 > 0:34:27Living in the sloth's fur helps the moths avoid predators.
0:34:30 > 0:34:33What the sloth gains from the relationship, if anything,
0:34:33 > 0:34:35is a mystery.
0:34:42 > 0:34:44Oh, taking my headlamp.
0:34:44 > 0:34:47I think she's ready to go home. I'll put her back in her tree.
0:34:52 > 0:34:55All right. Back home.
0:35:05 > 0:35:07Out on the Pantanal,
0:35:07 > 0:35:10Gordon's anteater search continues.
0:35:12 > 0:35:15He has heard movement in a small patch of forest.
0:35:17 > 0:35:22Not the giant anteater he's hoping for, but one of its cousins.
0:35:24 > 0:35:27Isn't that just the weirdest-looking animal you've ever seen?
0:35:29 > 0:35:30A lesser anteater.
0:35:32 > 0:35:35Just metres in front of me.
0:35:35 > 0:35:38Amazing.
0:35:46 > 0:35:50Lesser anteaters spend up to 60% of their time in trees.
0:35:50 > 0:35:53(OK, it's moved down. Let's see if I can follow it.)
0:35:53 > 0:35:56However, they often leave the branches
0:35:56 > 0:36:01to move between patches of forest, or to forage on the ground.
0:36:01 > 0:36:03(There it is, right there.)
0:36:04 > 0:36:08And look at this fella. Now, that is one bold little creature.
0:36:08 > 0:36:12This is incredible, to be so close to a wild animal like this.
0:36:21 > 0:36:25Anteaters are distant relatives of sloths and, like them,
0:36:25 > 0:36:29they forage for food during the day and at night.
0:36:31 > 0:36:36Still here. He's about to open a little bit of this log.
0:36:36 > 0:36:40There's probably some ants or termites in there.
0:36:42 > 0:36:44They have poor eyesight,
0:36:44 > 0:36:48relying on smell and hearing to avoid predators and detect prey.
0:36:50 > 0:36:54You can see here exactly what he was after - these termites.
0:36:54 > 0:37:00Now, he's just pulled back the bark, and underneath this rotten log,
0:37:00 > 0:37:03there are millions and millions of termites.
0:37:03 > 0:37:08He just starts probing his tongue in there and lapping them up.
0:37:14 > 0:37:18There's clearly plenty of food here for anteaters.
0:37:18 > 0:37:21Even enough for giants.
0:37:21 > 0:37:23It's a promising sign.
0:37:28 > 0:37:30In the canopy of the Amazon,
0:37:30 > 0:37:33Sophie is still staking out the fruiting tree,
0:37:33 > 0:37:36waiting for any sign of the owl monkeys.
0:37:36 > 0:37:39So far, she has had no luck at all...
0:37:42 > 0:37:43..and things are about to get worse.
0:37:43 > 0:37:46THUNDERCLAP
0:37:46 > 0:37:51They are really large clouds. Very, very foreboding.
0:37:51 > 0:37:54Not great, really, to be up a tree...
0:37:54 > 0:37:58in the middle of a tropical rainstorm, on a metal platform.
0:38:06 > 0:38:09The thunderstorm is really nearly here, and I'm in two minds.
0:38:09 > 0:38:12I want to stay, and I really want to see the monkeys,
0:38:12 > 0:38:15but I also don't want to get caught in a storm.
0:38:18 > 0:38:20Here it comes.
0:38:20 > 0:38:21THUNDER RUMBLES
0:38:26 > 0:38:29Here it is, here it is. Go! Go!
0:38:29 > 0:38:30Oh, I can't believe we pushed it.
0:38:32 > 0:38:34Please, don't leave me up here.
0:38:38 > 0:38:40It's quite unnerving up there,
0:38:40 > 0:38:42the tree's moving around an awful lot.
0:38:44 > 0:38:45OK, clear.
0:38:45 > 0:38:49We need to get out of the forest. It's dangerous.
0:38:52 > 0:38:55The one place you don't want to be in a tropical rainstorm
0:38:55 > 0:38:57is in a flooded forest,
0:38:57 > 0:39:00in a metal boat with loads of deadwood,
0:39:00 > 0:39:02and that's why we're trying to get out of here
0:39:02 > 0:39:04as quickly and safely as possible.
0:39:04 > 0:39:05BOAT ENGINE STARTS
0:39:05 > 0:39:09The storm brings high winds and lightning.
0:39:10 > 0:39:13The biggest danger to Sophie is falling trees.
0:39:14 > 0:39:15They must pick their way
0:39:15 > 0:39:18back through the forest to the main river fast.
0:39:32 > 0:39:34That is... That's lovely.
0:39:34 > 0:39:36Even though we're now out and you can now see the lightning
0:39:36 > 0:39:41and the rain's heavier, we're away from the woods. That is very good.
0:39:45 > 0:39:47The Amazon team take shelter in the old steamer.
0:39:48 > 0:39:51Sophie and Bryson will have to wait for the storm to subside
0:39:51 > 0:39:53before they can head back out into the flooded forest.
0:40:05 > 0:40:10George is now two miles into the cave.
0:40:10 > 0:40:14Few creatures can survive this far into total darkness.
0:40:17 > 0:40:18Oh, my God!
0:40:23 > 0:40:25I don't believe what I'm seeing!
0:40:27 > 0:40:29This is a swimming cricket.
0:40:29 > 0:40:34Whoa! Look at it! Look!
0:40:34 > 0:40:37It's using its little legs
0:40:37 > 0:40:38in a sort of breaststroke.
0:40:38 > 0:40:41Look at it, it's a proper breaststroke.
0:40:41 > 0:40:43Oh!
0:40:43 > 0:40:47Oh! Oh, my God!
0:40:48 > 0:40:52It's a female, it's an adult female.
0:40:52 > 0:40:54This is one of the weirdest
0:40:54 > 0:40:56cave animals I've ever seen.
0:40:59 > 0:41:02Crickets are common around the world,
0:41:02 > 0:41:04but this one is entirely different.
0:41:07 > 0:41:10In mastering this environment, using only touch and taste,
0:41:10 > 0:41:16this strange-looking animal has become the apex predator.
0:41:19 > 0:41:23There is an animal perfectly adapted
0:41:23 > 0:41:26for life as a hunter in pitch-darkness.
0:41:27 > 0:41:29It's got everything it needs -
0:41:29 > 0:41:31it's got long antennae,
0:41:31 > 0:41:33it's got these very sensitive palps
0:41:33 > 0:41:35here for feeling its prey,
0:41:35 > 0:41:37and these amazingly spiny legs.
0:41:37 > 0:41:40So as soon as it meets something, feels it, the legs come in,
0:41:40 > 0:41:41the spines are there,
0:41:41 > 0:41:44and then grab them between these ENORMOUS great jaws.
0:41:48 > 0:41:50This is the lion of the cave.
0:41:50 > 0:41:54This is something you don't want to meet if you're a bug.
0:41:54 > 0:41:57Look at her, look at her! Ooh, she's big!
0:41:57 > 0:42:02Ooh, God, she is strong, and she's trying to bite my finger. Agh!
0:42:02 > 0:42:05She is trying to slice through my thumb. Agh!
0:42:05 > 0:42:07Ooh! Argh.
0:42:07 > 0:42:11Look, I'm not even holding you, just go away, please.
0:42:12 > 0:42:17This is the only way she is going to let go. Argh! Agh!
0:42:18 > 0:42:21Gah! Oh!
0:42:24 > 0:42:25Oh!
0:42:27 > 0:42:31Isolated for millions of years in a cave with limited prey,
0:42:31 > 0:42:35this animal has evolved to hunt both on land and underwater,
0:42:35 > 0:42:40making the most of its uniquely demanding habitat.
0:42:48 > 0:42:50HE LAUGHS
0:42:52 > 0:42:55Oh, man! Just the perfect animal for a cave.
0:42:58 > 0:43:04Animals could live in the dark as easily as we live in daylight.
0:43:04 > 0:43:10They just need the right senses - touch, smell and hearing.
0:43:15 > 0:43:18As Bryson pushes into the very depths of the flooded forest,
0:43:18 > 0:43:23he comes across a creature that takes hearing to an extreme.
0:43:23 > 0:43:26CREATURES SCREECHING
0:43:26 > 0:43:29There's dolphins swimming around my boat right now.
0:43:29 > 0:43:31They're actually pretty loud at night-time.
0:43:31 > 0:43:34They kind of come by and you hear them breathe, going...
0:43:34 > 0:43:37- HE MIMICS BREATHING NOISE - ..right next to the boat.
0:43:37 > 0:43:39DOLPHIN EXHALES LOUDLY
0:43:42 > 0:43:47Thousands of miles from the sea, these pink river dolphins
0:43:47 > 0:43:51have evolved for life in the fresh water of these flooded forests.
0:43:54 > 0:43:58They use sound to navigate and hunt, sending out clicks,
0:43:58 > 0:44:01and listening for echoes from their surroundings.
0:44:05 > 0:44:08I never realised that the forest floods this much, that the dolphin
0:44:08 > 0:44:13can actually feed in the middle of the forest, miles from the river.
0:44:13 > 0:44:14That's weird.
0:44:16 > 0:44:18And they do it at night-time.
0:44:27 > 0:44:29With their highly tuned sonar,
0:44:29 > 0:44:33dolphins operate superbly in the pitch-black.
0:44:43 > 0:44:47High up in the canopy, Sophie's vigil has finally paid off.
0:44:49 > 0:44:52(I think I've just heard an owl monkey.)
0:44:52 > 0:44:55SCREECHING
0:44:55 > 0:44:58(Oh, do you hear that? That's an owl monkey.)
0:45:00 > 0:45:03(Did you see it thrashing around in the bushes?)
0:45:20 > 0:45:21SHE GASPS
0:45:22 > 0:45:25After days of frustration,
0:45:25 > 0:45:30Sophie is able to capture footage of these wild monkeys in the canopy.
0:45:36 > 0:45:38(There's another one just come in.)
0:45:39 > 0:45:41(And they're feeding.)
0:45:41 > 0:45:43(That's very cool.)
0:45:49 > 0:45:53(It's just a pure example of an animal)
0:45:53 > 0:45:55(beautifully adapted for the night.)
0:45:55 > 0:45:58(They're out there on their own, all the other primates are asleep,)
0:45:58 > 0:46:01(and so they have the trees to themselves.)
0:46:03 > 0:46:07Unlike many nocturnal animals, owl monkeys still rely on eyesight.
0:46:09 > 0:46:12(Big glowing eyes. It's the main feature.)
0:46:15 > 0:46:18Their eyes are 50% larger than other monkeys,
0:46:18 > 0:46:21and perfectly adapted for the dark.
0:46:23 > 0:46:27They have sacrificed colour and sharpness for sensitivity.
0:46:31 > 0:46:35Their retinas are crammed with cells that detect even the dimmest light.
0:46:39 > 0:46:43For a fuller picture of how these monkeys function in the dark,
0:46:43 > 0:46:46Sophie must switch to thermal imaging.
0:46:56 > 0:46:59(It's extraordinary, the way he's moving around.)
0:46:59 > 0:47:02(Just bouncing through the trees. It's just incredible.)
0:47:03 > 0:47:07Sophie's images show how the monkeys' ultra-sensitive eyes
0:47:07 > 0:47:12help them see branches and judge distances in the darkness.
0:47:17 > 0:47:21(This is the first time they've ever been filmed in the canopy)
0:47:21 > 0:47:22(with the thermal cameras,)
0:47:22 > 0:47:25(and it just gives you a whole new view.)
0:47:27 > 0:47:28(He's going to jump!)
0:47:28 > 0:47:30(He's going to jump! Oh!)
0:47:33 > 0:47:35(That's incredible.)
0:47:35 > 0:47:37(This creature has just leapt)
0:47:37 > 0:47:39(ten foot through the air.)
0:47:43 > 0:47:46(I've just watched them leaping through the forest)
0:47:46 > 0:47:50(as if it was broad daylight, and it's not.)
0:47:50 > 0:47:51(It's dark.)
0:47:53 > 0:47:57(They are so well adapted, it takes your breath away.)
0:47:57 > 0:48:00(You don't expect to see monkeys leaping through the forest at night.)
0:48:00 > 0:48:01(You just don't.)
0:48:19 > 0:48:23(Owl monkeys have very distinct territories,)
0:48:23 > 0:48:26(which means if they're visiting this fruiting tree,)
0:48:26 > 0:48:29(their nest could very well be close-by.)
0:48:29 > 0:48:32Sophie has recorded unique footage
0:48:32 > 0:48:35of these remarkable animals at night.
0:48:35 > 0:48:39Her final challenge is to film them at their nest in the day.
0:48:54 > 0:48:57On the plains of the Pantanal,
0:48:57 > 0:49:01Gordon's thermal camera has picked up something large.
0:49:02 > 0:49:04Oh, my God.
0:49:04 > 0:49:06Look, look, look, look!
0:49:08 > 0:49:13The unmistakable outline of the elusive giant anteater.
0:49:15 > 0:49:17That's great.
0:49:19 > 0:49:24This is the first time I've ever seen a giant anteater,
0:49:24 > 0:49:28and I'm not disappointed.
0:49:28 > 0:49:31It is an INCREDIBLE beast.
0:49:31 > 0:49:36Like the lesser anteater, this giant has poor eyesight.
0:49:36 > 0:49:40It uses a strong sense of smell to navigate in the dark.
0:49:43 > 0:49:46He's got that big long nose.
0:49:46 > 0:49:48SNIFFING
0:49:51 > 0:49:54I think it's safe to say that the giant anteater
0:49:54 > 0:49:58is one of the strangest animals that roams the planet.
0:50:00 > 0:50:02I wonder if I can get closer?
0:50:02 > 0:50:04(Yeah, I'm going to try and get a bit closer.)
0:50:13 > 0:50:18Now, this animal is after the exact same prey
0:50:18 > 0:50:21as the lesser anteater that I saw -
0:50:21 > 0:50:22ants and termites -
0:50:22 > 0:50:24but obviously, a monster like this
0:50:24 > 0:50:26needs many, many more of them.
0:50:32 > 0:50:36The giant anteater is not truly nocturnal.
0:50:36 > 0:50:40In other parts of South America, it forages during the day.
0:50:40 > 0:50:42But its powerful sense of smell
0:50:42 > 0:50:45means it's equally at home in the dark.
0:50:46 > 0:50:49In very hot areas like the Pantanal,
0:50:49 > 0:50:51they make the most of the cool night air
0:50:51 > 0:50:53and sleep during the heat of the day.
0:50:55 > 0:50:59He's still on the move, so I'm going to try and keep up with him.
0:51:02 > 0:51:05Giant anteaters can move quickly.
0:51:05 > 0:51:08With his heavy cameras, Gordon is unable to keep up.
0:51:11 > 0:51:15I completely lost it. Even with all this technology,
0:51:15 > 0:51:18it's still quite easy to lose stuff in the dark.
0:51:19 > 0:51:23Gordon gives up the chase, after a disappointingly short encounter.
0:51:23 > 0:51:25His hope is that the camera traps
0:51:25 > 0:51:28will reveal more nocturnal behaviour.
0:51:31 > 0:51:36As soon as it's light enough, Gordon checks his traps.
0:51:39 > 0:51:41With luck, their footage will reveal
0:51:41 > 0:51:44what these giants are doing at night.
0:51:49 > 0:51:51Right, here we go.
0:51:53 > 0:51:56Oh, look at this!
0:51:56 > 0:51:59The traps have done their job.
0:52:06 > 0:52:08Oops, he's having a sniff.
0:52:08 > 0:52:10He's having a stiff at the tree.
0:52:14 > 0:52:17The cameras have recorded over 15 hours of footage.
0:52:18 > 0:52:23Surprisingly, several different individuals have visited this spot.
0:52:23 > 0:52:28Ooh, look, this one's got a baby on its back. You can just see it.
0:52:30 > 0:52:32They seem drawn to the tree
0:52:32 > 0:52:35where Gordon found mysterious scratch marks.
0:52:38 > 0:52:40Oh, wow!
0:52:41 > 0:52:43That's what it is!
0:52:49 > 0:52:51Whoa!
0:52:52 > 0:52:55That anteater's actually off the ground.
0:52:56 > 0:53:00He's technically climbing.
0:53:03 > 0:53:08Giant anteaters are ground-dwellers and are not known to climb.
0:53:12 > 0:53:15This animal isn't reaching. He's not standing up on his back legs.
0:53:15 > 0:53:17He's actually climbing the tree.
0:53:21 > 0:53:25So, all these marks way up the tree have been left
0:53:25 > 0:53:28by that mysterious creature - the giant anteater.
0:53:34 > 0:53:38The big question is, why is the anteater climbing the tree?
0:53:39 > 0:53:44I think it may well have something to do with marking a territory,
0:53:44 > 0:53:48that different anteaters come here and they scratch and leave a scent.
0:53:48 > 0:53:52Smell is incredibly important to these giants.
0:53:52 > 0:53:56The camera trap images suggest that they use scent to communicate,
0:53:56 > 0:53:58and to map each other's movements in the dark.
0:54:00 > 0:54:03There's not that much known about giant anteaters,
0:54:03 > 0:54:06but one thing that is in every publication
0:54:06 > 0:54:11is that they do not climb trees, and here's an anteater climbing a tree.
0:54:11 > 0:54:14Oh, wow! Wow, look at him.
0:54:16 > 0:54:19Gordon has done more than just film these animals.
0:54:19 > 0:54:22He has documented a completely new behaviour.
0:54:24 > 0:54:27This is the first place it's EVER been filmed.
0:54:34 > 0:54:37In the flooded forests of the Amazon,
0:54:37 > 0:54:41Sophie has found the owl monkeys' nest.
0:54:41 > 0:54:43In daylight, the eyes that are so vital at night
0:54:43 > 0:54:46seem even more striking.
0:54:48 > 0:54:52The little one is yawning.
0:54:52 > 0:54:54And it's obviously night-time. He's meant to be asleep.
0:54:55 > 0:54:58But he's so curious, he can't resist just peeking out the hole.
0:55:00 > 0:55:02By adapting for life after dark,
0:55:02 > 0:55:05these owl monkeys avoid competition for food
0:55:05 > 0:55:08and can shelter from daytime predators.
0:55:08 > 0:55:11I've never filmed anything quite so gorgeous.
0:55:15 > 0:55:17Seeing these monkeys at rest during the day
0:55:17 > 0:55:20is a perfect end to Sophie's mission.
0:55:23 > 0:55:26She has achieved a wildlife first.
0:55:26 > 0:55:31Her remarkable thermal images show how freely these monkeys are able to
0:55:31 > 0:55:33move around the canopy in the dark.
0:55:36 > 0:55:39Working through the night in the flooded forest
0:55:39 > 0:55:42has been an extreme challenge for the Amazon team.
0:55:44 > 0:55:48However, both Sophie and Bryson leave with new insight
0:55:48 > 0:55:50into how animals survive here in the dark.
0:55:55 > 0:56:01In Venezuela, after four days in total darkness,
0:56:01 > 0:56:04and following the underground river for three miles,
0:56:04 > 0:56:06George can go no further.
0:56:09 > 0:56:12We're now exactly at the end of the underground stream.
0:56:12 > 0:56:15And it sinks down... Ooh!
0:56:15 > 0:56:18..through a big choke of boulders which have fallen down.
0:56:20 > 0:56:23HE GRUNTS
0:56:23 > 0:56:27Oh! Look, sunlight! That's the most amazing colour to see
0:56:27 > 0:56:30after being in darkness for so long.
0:56:30 > 0:56:32Ah, we're there.
0:56:38 > 0:56:40Oh, look at it, it's getting brighter and brighter!
0:56:40 > 0:56:42God, that almost hurts your eyes, actually.
0:56:44 > 0:56:46And the other thing that really hits you is the fresh air.
0:56:46 > 0:56:49HE BREATHES IN DEEPLY
0:56:51 > 0:56:53Ah! What a view!
0:56:57 > 0:56:59Ah!
0:57:00 > 0:57:03This is the world I am part of down here.
0:57:03 > 0:57:06Fascinating though the darkness is
0:57:06 > 0:57:11and amazing as the animals are, we're not creatures of the dark.
0:57:11 > 0:57:15We should be out there in the sun, and that's where I belong.
0:57:20 > 0:57:23It's the end of an extraordinary journey.
0:57:25 > 0:57:28From night in the flooded forest
0:57:28 > 0:57:30to the perpetual darkness of the cave,
0:57:30 > 0:57:34incredible creatures and new species
0:57:34 > 0:57:37have evolved to live in an alien world.
0:57:40 > 0:57:43Adapting their senses and behaviour
0:57:43 > 0:57:47to survive...in the dark.
0:57:47 > 0:57:52Next time, the team head to the very bottom of the continent...
0:57:54 > 0:57:57..for the final phase of the expedition...
0:57:58 > 0:58:02..at the wild southern tip of South America...
0:58:05 > 0:58:08Look at that.
0:58:11 > 0:58:12It's scary as hell!
0:58:12 > 0:58:16..where more nocturnal mysteries await.
0:58:16 > 0:58:19What is that?
0:58:42 > 0:58:45Subtitles by Red Bee Media Ltd