All language subtitles for BBC.Mexico.Earths.Festival.of.Life.S01E02.Forests.of.the.Maya.720p.HDTV.x264.AAC.MVGroup.org.en

In the heart of the Americas...

..where continents collide...

..there's a land full of natural
riches...

BIRDS HONK

MONKEY GROWLS

..a land of towering giants...

..scorching sands...

..and secret rivers.

Where great civilisations rose...

..and fell.

To succeed here takes passion and
spirit.

This is a country rich in colour and
culture...

..a festival of life.

This is...

In Mexico's far south there's a
forest full of secrets.

It's March, the peak of the dry
season.

This pool is fast disappearing...

..and it draws all the animals from
the forest.

Even the most elusive.

For a young Morelet crocodile,
the pool is also a hunting ground.

There's plenty of potential prey.

Trouble is, most are far too big.

Finally, a realistic target.

Even at his size, sneaking up in
such shallow water isn't easy.

He needs to change his technique.

Perhaps an ambush will work.

Almost.

Success at last.

But he's not the only crocodile
here.

And his taste of victory is
short-lived.

There's a reason water is so scarce
in this corner of Mexico.

This great forest, which stretches
for almost 50,000 square miles,

has no major rivers.

And that's down to the region's
unique geology.

The forest stands upon a vast
peninsula, the Yucatan.

The entire peninsula is a gigantic
slab of limestone.

Limestone is incredibly porous.

Any surface water swiftly drains
away underground.

And this shapes the lives of all who
live here.

For seven months of the year,

virtually no rain falls,

and by April, much of the forest is
barren.

For a mother spider monkey this can
be challenging.

She needs to produce enough milk to
feed her baby.

And that requires plenty of fresh
fruit.

Sometimes, that means travelling
over two miles each day.

But with long, slender fingers
and no thumbs to get in the way

this is child's play for an animal

designed for life in the tree tops.

She's taking her youngster to a
special place...

..where she knows there's fruit all
year round.

The ancient city of Calakmul,

once one of the most powerful in the
Maya civilisation.

In the seventh century, this city
was home to 50,000 people.

The people of Calakmul

cultivated trees that would fruit
throughout the year.

Centuries later, these ancient
gardens have left a lasting legacy.

There's more fruit here than
anywhere else in the forest...

..even at the height of the dry
season.

Over countless generations,

the monkeys have passed this
knowledge on to their youngsters.

MONKEY CALLS

At its peak in the eighth century,

the Maya civilisation grew to almost
13 million people.

Theirs was a highly sophisticated
culture, advanced in mathematics,

language and astronomy.

The huge limestone temples,
built to worship their gods,

are a lasting testament to great
feats of engineering.

Almost every other ancient
civilisation in history

has been built beside a major river.

So how did the Maya
manage without one?

There are almost 1.5 million direct
descendants

of the ancient Maya living
in Mexico today.

Don Roque and his wife Dona Su live
on an isolated farm

in the heart of the Yucatan's
forest.

GOAT BLEATS

This farm has been in Don Roque's
family for generations.

With his children grown up and left
home,

nowadays, it's just him and Dona Su.

They live off the land in a way

little changed since the times of
their ancestors.

But there's more to their farm than
meets the eye...

..a huge natural well, known in
the Yucatan as a cenote.

A cenote is a collapsed cave.

Over thousands of years,
rainwater has eroded

the soft limestone on the surface.

Eventually, the roof weakened
and fell.

This cenote provides Don Roque with
water all year round.

But it's far from unique.

It's one of several thousand cenotes
scattered across the peninsula.

Cenote comes from the Maya word
ts'onot,

meaning holes with water.

It was these mysterious pools

that enabled the Maya civilisation

to flourish without a major river.

And the greatest ancient cities
were founded beside them.

Each cenote is an oasis.

The surrounding forest remains lush,

even at the height of the dry
season.

Filtered through the limestone,
the water is full of minerals.

It supports a unique community
of plants and animals.

Some fish in the Yucatan cenotes
are found nowhere else on Earth.

Within the dense forest,

a cenote can remain hidden,
even when close by.

But the Maya had an almost sure-fire
way of finding them...

BIRD CALLS

..the distinctive call of
the turquoise-browed motmot.

Virtually every cenote has its own
colony.

Elsewhere, motmots prefer to nest
alone,

digging their burrows along river
banks.

MOTMOT CALLS

Here in the Yucatan, they're forced
together,

sharing limited space on the
cenote's soft limestone walls.

Before a male can start looking for
a mate,

he needs to secure a nest site.

But this cenote is already crowded.

17 other pairs are nesting here.

If he's to fit in, this new arrival
must use the right body language.

MOTMOT CALLS

A raised turquoise brow is intended
to intimidate rivals.

The pendulous tick-tock of their
tails

has earned motmots the nickname
clock birds.

This male must persevere if he wants
to breed this year.

At last, he's earned his own little
ledge of limestone.

With a gift of food,

he can get down to the business
of attracting a mate.

There are so many cenotes in the
Yucatan

because of a dramatic event

that changed the history of life on
Earth.

Around 65 million years ago,

a huge meteorite collided with what
is now the Yucatan's north coast.

Its effect was so catastrophic...

..it's believed to have wiped out
the dinosaurs.

In an instant, the impact fractured
the limestone platform,

creating what has become known as
the ring of cenotes.

Satellites have revealed over 200
cluster around its crater.

Satellite technology is also helping
modern-day explorers in the Yucatan.

And new cenotes are still being
discovered today.

It should be about 50 metres
that way. You see anything?

Sam Meacham and Fred Devos are part
of an international community

of cave divers that has
been exploring the Yucatan

since the 1980s.

I started out for the thrill of
being able to explore something.

And from a young age,
I just was imbued

with the desire to go out
and explore this world.

Each new cenote adds another piece
to the puzzle.

Oh, look at this, Sam. Wow.

The moment of discovery, right?
You can't beat it.

In the last 30 years,
cave divers in the Yucatan

have revealed something
extraordinary.

The cenotes are not isolated wells.

Each is connected by an intricate
network of caves and passageways,

spreading like a spider's web
across the peninsula.

Divers have discovered
over 350 caves

and nearly 1,000 miles
of flooded tunnels.

Including the two longest underwater
cave systems on the planet.

Many of these caverns have seen
fewer visitors than the moon.

The great majority
remains uncharted.

For the ancient Maya,
the labyrinth of caves

was out of reach
but not beyond imagination.

This secret underworld
was held sacred.

Home to the 12 gods of Xibalba,

it was a place both feared
and revered.

But the ancient Maya recognised
their link to this unknown world.

Trees.

Always plumbed into the water below,

trees allow life above ground
to flourish.

No tree is better equipped to
do this than the strangler fig.

Its roots can reach 30 metres
into the water below.

Don Roque uses the fig's roots
to enter the underworld...

..navigating his way down steps
carved by his grandfather

over half a century ago.

At the bottom of the cenote,
Don Roque has a secret garden.

Here he cultivates a plant
that wouldn't survive

elsewhere on his farm.

Coffee.

Above ground it's too hot and dry
for coffee to grow.

Down here it's two degrees cooler
and a lot more humid.

Don Roque's cenote is also
a haven for insects.

Food for a colony of resident
cave swallows.

By May the swallows are intent
on one thing.

Breeding.

The cenote provides everything
they need.

Down here they have a ready supply
of soft mud.

They use this to craft their nests

together with fibres plucked
from the hanging fig roots.

All being well,
in around a month's time,

they'll each have a brood
of up to five chicks.

Don Roque's cenote has its own
community of life

thanks to the constant presence
of water.

But the rest of his farm
requires something more.

He plants his land with a mixture
of corn, beans and squash

in a tradition passed down
the generations.

A mix of crops helps maintain
the fragile soil

which lies in a thin layer
on top of the limestone.

But he can't draw enough water
from his cenote

to irrigate an entire field.

For his crops to grow,
Don Roque needs it to rain.

By late May, change is in the air.

The Yucatan relies on
weather systems

that develop thousands
of miles away.

Gathering ever more water
as they cross the Atlantic,

they bring the seasonal rains.

The ancient Maya believed the rain
was a gift from the gods.

For Don Roque, the old gods
are very much alive.

RUMBLE OF THUNDER

The most important of all is Chaac,
the life-giving god of rain.

It is Chaac who determines
each thundercloud.

CRACK OF LIGHTNING

RUMBLE OF THUNDER

Finally letting the rain fall.

1,200 years ago, something happened
that sent the Maya civilisation

into a dramatic decline.

Chaac withheld the seasonal rains.

The Yucatan was gripped by a series
of devastating droughts.

Over 80% of the population vanished.

One by one, the bustling cities
were abandoned

and reclaimed by the forest.

MONKEYS HOWLING

This year the gods have been kind.

By July, it's raining
almost every day.

MONKEYS GRUNT AND HOWL

This brings new growth
to the forest.

Good news for the Yucatan's
noisiest residents.

LOUD HOWL

Howler monkeys.

Their calls carry for over a mile.

MONKEYS HOWL

They howl to let neighbouring groups
know their whereabouts.

This patch of the forest
is worth protecting.

The troop has found a tree
with young, succulent leaves -

a particular favourite.

But a diet of leaves
takes time to digest.

So howlers spend up to 80%
of their time resting...

..making them amongst the most
peaceful of all monkeys

despite their fearsome calls.

Baby howlers feed on their mother's
milk until almost a year old.

This is much easier to digest.

With his mother trying to
sleep off her lunch,

nap time can be a bit dull
for a baby.

RUMBLE OF THUNDER

All life in the Yucatan
benefits from the rain.

Trees burst into fruit.

All the new plant growth

provides food for an explosion
of insect life.

There are over 3,000 different
species on the peninsula.

The insects become food for others.

Almost all the birds in the forest
schedule their nesting to coincide

with this seasonal bounty.

The regular rain is also
good news for Don Roque.

In just six weeks
his corn has shot up.

But the explosion
of plant-eating insects

could cause Don Roque problems.

For his crops to thrive, he needs
the help of a natural ally.

In the heart of the Yucatan,

there's a cave the locals call
El Volcan de los Murcielagos.

The bat volcano.

Every day, an hour before dusk,

it erupts.

More than three million bats
exit the cave.

The ancient Maya associated bats
with death.

This was a swarm
straight from the underworld.

But bats are vital to life
in the Yucatan,

keeping its insect population
in check.

Each can eat its own body weight
in insects every night.

While the bats are focused
on the insects,

others are watching them.

Grey hawks...

..and bat falcons.

These birds are skilled
aerial predators,

their talons perfectly designed
to snatch the bats from the air.

There are other more surprising
hunters here.

Brown jays.

They normally eat insects and fruit.

But the brown jays here
have developed a taste for bats.

The jays don't use talons
to catch their prey.

They use their beaks.

The loss of ten or so bats
barely makes a dent on the swarm.

Tonight, the colony will consume
around 30 tonnes of insects.

A vital service that keeps
the entire forest healthy.

It's late September...

..and it has rained almost every day
for the last three months.

Don Roque's corn is now fully ripe.

In a tradition dating back to the
times of their ancient ancestors,

the first corn of the harvest
serves a special purpose.

Dona Su crushes it to make
a sacred drink called atole.

This is offered to the gods
in a ceremony of thanksgiving.

SPEAKS IN NATIVE LANGUAGE

From June to November, the Yucatan
receives 100 centimetres of rain.

Across the peninsula,
that's over 36 trillion gallons.

The cenotes are refilled.

But most of this water seeps through
the limestone into the underworld.

The work of cave divers like Sam
is furthering our understanding

of the Yucatan's unique
water system.

'We're still exploring here.

'And the more we explore,
the more questions we ask.

'Selfishly, I hope we finish
in my lifetime.

'I don't think we will.'

Metre by metre, the divers are
mapping the underground labyrinth.

It's a painstaking process with
every measurement taken by hand.

But this has revealed
something remarkable.

The water in the caves isn't just
locked within the limestone.

It flows.

The Yucatan's missing rivers
are underground.

Like all rivers, they are compelled
towards the coast.

Here, the fresh water meets salt
water brought by the incoming tide.

This border is called the halocline.

Containing more dissolved particles,

the salt water is heavier
and lies below the fresh water...

..giving the illusion of a surface.

But after months of heavy rain...

..the flow of fresh water prevails.

At the coast, it leaves
the underworld behind.

Mangroves flourish in the mixture
of salt and fresh water.

The roots provide ideal nurseries
for schools of fish.

And gentle giants are drawn
to the Yucatan's shores.

Manatees come to drink
at the outpouring of fresh water.

As the fresh water flows
through the mangroves,

the trees release tannins,
staining it brown.

Eventually the fresh water reaches
its final destination.

It pours out into the Gulf of Mexico
in huge volumes.

DRAMATIC MUSIC

Replenished by billions of gallons
of fresh water,

these vast coastal lagoons
are the ideal home

for a colony of the Yucatan's
most colourful residents.

Caribbean flamingos.

It's been a good year
for the colony,

with nearly 15,000 new additions.

Finding your chick
in such a big crowd isn't easy.

FLAMINGOS SQUAWK

But flamingos have
incredibly good hearing

and her youngster
has his own unique voice.

Just six weeks ago,

the chick was little bigger
than his mother's beak.

These lagoons are full
of brine shrimps.

The beta-carotene in these
tiny crustaceans

gives the flamingos
their distinctive colour.

But it will be another two years
before he starts to turn pink.

Here on the Yucatan's coast,
as elsewhere on the peninsula,

all owe their survival
to the secret underworld.

Without its great hidden rivers,

this would be a hot, dry
and hostile place.

Born of a unique history,

the underworld hidden beneath
this vast forest

gave rise to the ancient
Maya civilisation...

..and it remains the lifeblood
of the Yucatan.

Capturing the beauty
of the Yucatan's underworld

meant sending a film crew into
one of the most alien environments

on the planet.

To do this safely
required expertise.

Between them, this team
has over 50 years' experience

diving on the peninsula.

I want to make sure we get
that right, you know?

Cameraman Mike Madden
was one of the pioneers

of cave exploration here
back in the 1980s.

And Sam Meacham is part of a team
currently mapping

one of the region's
two longest caves.

There's a common misconception
that cave divers are these

adrenaline junkie risk-takers
cheating death on every dive.

Were tarantulas in our
risk management form?

'When, in fact, we're probably
some of the most cautious people

'on the planet.'

There's a very real need
for caution.

All diving carries risks.

But cave diving
heightens these risks.

Surfacing isn't an option
if you run out of air.

This particular cave system,
known as Taj Mahal,

was first explored in 1995.

It has over three miles
of flooded passageways,

some descending almost 30 metres.

Filming here poses
another challenge.

Most of the cave is pitch black.

So the first thing the divers
need to do

is set up a highly specialised
underwater lighting rig.

Four 1,200-watt lights.

100 metres of cable.

All of it has to be carried
into the cave by hand.

Lighting the caves on this scale
is a new challenge for the team

and draws on all their expertise.

Since the 1980s, the dedicated work
of divers like Sam and Mike

has helped put nearly 1,000 miles of
the Yucatan's underworld on the map.

But the vast majority
remains uncharted.

It's pretty amazing that
35 years after the beginning

of cave diving exploration
in this area,

I would say we're still really
beginning to understand

what's going on here.

And now there's an added urgency
to their work.

Over the last 50 years the Yucatan's
population has skyrocketed.

The city of Cancun is one of the
fastest-growing tourist destinations

in the world, with over five million
visitors every year.

This creates jobs,
but the demand for fresh water

is putting pressure on the
peninsula's underground rivers.

The future of this area
is dependent on tourism

and so how do we sustainably manage
these incredible natural resources

so that Mexico can continue
to receive

10-12% of its gross domestic product
through tourism

on a 100-mile strip of beach?

That's important to the future
of Mexico,

not only of this region
but the country as a whole.

Maps of the underground river
systems are far from complete.

New construction work may be
taking place above caves

that are yet to be discovered.

The entire city of Cancun draws its
drinking water from 142 cenotes,

some of which are now at risk
of pollution.

It's a race against time
to reveal the importance

of the Yucatan's hidden underworld.

Back at Taj Mahal,
with the lights in place,

the crew are ready to begin filming.

All our focus is going to be
this direction today.

Every image they film
must be meticulously planned.

Get over. More light.

Less light.

Once the dive begins,

all communication
is through hand signals.

At last the team can capture the
splendour of the hidden underworld.

For most of us,
this flooded labyrinth

remains just as inaccessible
as it was to the ancient Maya.

But for the cave divers
devoted to exploring this world,

the hope is that by opening our eyes
to its beauty and importance,

they will help safeguard its future.

In the next episode, we head
to Mexico's remotest region.

The far north.

A land of great deserts
and rich prairies.

Home to the toughest
of characters...

..secret worlds...

..and some of Mexico's
rarest wildlife.