All language subtitles for z03

Over 1,000 kilometres northwest
of Australia's mainland,

a speck of an island
rises out of the Indian Ocean.

A tiny refuge to plants
and creatures

found nowhere else in the world.

Birds rule its skies,

magnificent, bullying,
and strange,

while hungry giants
patrol its seas.

And its land is the stage for a
miracle migration of millions.

A spectacular red army
marches to the sea...

under attack by monsters both
big and small...

bound for amorous assignations

and a midnight moon dance
to ensure their future.

This is the fantastic story
of Christmas Island.

[♪]

Deep in the island's
central rainforest

a season of waiting has begun
for its most famous species.

[♪]

The flashy red crab.

Its ancestors were sea crabs.

As they slowly moved inland
over 10 million years ago,

taking advantage of new habitats
with few predators,

their gills gradually shrank and
they evolved modified lungs.

Though now a dedicated
land creature,

the plate-sized crab
must still keep its lungs moist

in order to breathe.

So it's trapped here, in the
deep humidity of the forest,

by its ocean heritage.

Dry days and sunshine are
its great enemies.

It sticks to streams and its
moist burrows in the rainforest.

In this muggy haven,
the red crab has thrived.

There are tens of millions
of them.

The rainforest floor is
pockmarked with their burrows.

They are like the
forest's gardeners,

constantly excavating,

tilling and aerating the soil.

A keystone species,

they eat the damp litter
from the forest floor,

excreting it as
nutrient-rich fertilizer,

enriching and propagating
their comfy home.

But the red crab has a dilemma,
and it's a big one.

They want to reproduce,

but their young can
only develop in the ocean

five kilometres away.

An immense journey
for a critter used to moving

only a few metres a day.

And the rainforest
isn't uniformly wet.

The crabs must run a
deadly gauntlet

of dry, rocky stretches.

Their only chance: the monsoon.

The season of drenching rains

will provide a temporary wet
highway to the ocean,

and a future generation.

But the monsoon is weeks away.

For now, they wait.

Christmas Island itself,

all 135 square kilometres of it,

is just the very tip of
an enormous volcano

that erupted out of the sea
floor some 60 million years ago,

with a limestone cap formed
by aeons of coral growth.

The island juts dramatically
out of the sea,

steep cliffs rising to a plateau
of rich rainforest.

Because it formed in the
middle of an ocean,

every living thing here

is an immigrant that flew,
blew, floated, or rafted in

over the millennia.

Isolated hundreds of kilometres
from the nearest land mass...

[Birds chirping]

...it's become a vital breeding
site for seabirds.

Some 60,000 of them come
to nest here each year.

[Birds chirping]

Boobies, frigate birds, and
magnificent tropic birdscan all
be seen feeding together just offshore.

Diving, wheeling, and plunging
into the rich currents.

Three different species of booby
nest on Christmas Island,

but only the brown boobies
nest here all year-round.

Graceful gliders and
powerful fliers,

their webbed feet are
good for paddling

and even
incubating their eggs,

but not ideal for running
take-offs or landings.

That's why they prefer
to nest on cliffs,

where they can launch directly
into strong updrafts.

Both parents are dedicated to
taking care of their young.

While most couples lay two eggs,

this firstborn chick

will have pushed its younger,
weaker sibling out of the nest

to its death long ago.

Now it has all the food
to itself.

Its mother has just returned

with a cropful of
fish and squid,

which she regurgitates
directly into the greedy beak

of her youngster.

At almost three months old,

he's nearly the same size
as his mother.

In another month, he'll be ready
to fly on his own.

But it will be a further
five months

before the chick stops
pestering its parents for food

and leaves the nest for good.

Such devoted parenting
is made easier

thanks to the bountiful
waters of Christmas Island.

Since their parents don't
have to travel far to feed,

the hungry chicks
still scan the skies

for the arrival of
their next meal.

[Thunder rumbling]

With the first rains,

the restlessness in the
interior rainforest intensifies.

At first, only a few crabs stir.

But soon, there are millions,

making a determined march
toward the edge of the forest.

The males leave first,
creating great traffic jams

with their synchronized departure.

Red crabs join the
march to the sea

when they reach four or five
years of age.

They will continue
marching annually

during their 20- to 30-year
lifespan.

But the journey is long and
full of enemies.

An armoured giant lurks
along their path.

The largest land crab species on
the planet: the robber crab.

Like something straight out of
a sci-fi movie

or your worst nightmare.

Just its midsection can be
over one metre wide.

But they may take an
amazing 50 or 60 years

to reach their largest.

They're called robber crabs here

for their penchant for
stealing shiny objects

and taking them
to their lairs.

That pair of constantly
moving antennae

are some of the most
sensitive sniffers in the world,

able to smell hundreds of times
more keenly than a dog.

The smell of carrion or
rotting coconuts

especially grabs
their attention.

And with those massive claws,

they can shred the tough
coconuts with ease.

They'll also drag the
tough husk fibres home

to use as bedding
in their burrows.

In other places, they're known
as coconut crabs.

Christmas Island has the largest
and densest population

of these monsters in the world.

There are around 10,000,

though their numbers can't touch
those of the red crab.

And while coconuts may be on
the menu, given the chance,

these omnivores won't
turn down a meal of red.

Usually, the smaller reds

are too agile for
the robber crabs to catch,

but in the crowded
melee of the migration,

it's much easier
picking them off.

Even if the little reds can
evade the colossal robber crabs,

they're just the first of many
nightmares they'll encounter

on their long march to the sea.

Christmas Island is truly
ruled by crabs.

There are 14 different species
of land crab here,

more than anywhere
else in the world.

They arrived here as sea crabs,
like the scaly rock crab...

but evolved over the millennia

to take advantage of
just about every nook and cranny

on the island.

The blue crab
moved up the cliffs

and in toward the interior

by becoming a
freshwater specialist.

It haunts streams and seepages

like a beautiful
blue-white ghost.

Both sexes have hairy legs and moustaches,

dense mats of hair on either
side of their mouth parts

that help them
filter their food.

Once thought to be a subspecies
of a crab

found throughout
the Indo-Pacific,

it has now been discovered
to be its own species,

found only on
Christmas Island.

Once nearly wiped out by islanders

who harvested it
for its delicate meat,

the blue crab
is now protected.

Not everything the red crabs
pass on their migration

is a threat.

In the treetops above

is one of the island's
other permanent residents:

the endemic
Christmas Island goshawk.

This clever predator has an
extensive menu,

feeding on other birds,

small mammals, reptiles,
and insects,

and is a specialist
forest hunter.

There may be only 50
breeding pairs on the island,

and this is the only
place they're found.

Its smaller, lighter cousin,
the nankeen kestrel,

also hunts here.

While the goshawk is agile
enough to hunt in the forest,

the kestrel prefers to use its
extraordinary hovering ability

in the more open areas.

It can remain almost
motionless in the sky,

looking for the slightest
signs of movement

of its favourite prey:

giant grasshoppers.

Once the insect is in sight,

the kestrel makes a silent
but pinpoint-accurate descent.

Another great master
of the skies

is the Christmas Island
flying fox.

Named for its fox-like face,
it's actually a bat,

one of the few species that
is active during the day.

This 350-gram mammal feeds
on native fruit and flowers,

and plays an important role
in pollination on the island.

Papaya, recently
introduced here,

is also a particular favourite.

Unlike insectivorous bats,

these fruit-eaters
have no sonar.

Feeding during the day,

they rely on sharp eyesight and
a keen sense of smell instead.

Their roosts are close
to the coast,

for easy take-off and
access to updrafts

that carry
them across the island

in search of fruits and flowers.

While Christmas Island itself

supports many species found
nowhere else on the planet,

its strategic position
between great ocean currents

means it's also a Grand Central
Station for ocean travellers.

The south-flowing powerful
South Equatorial Current

acts like a conveyor belt
for plankton and fish eggs.

One of the world's most
endangered fish,

the southern bluefin tuna,
spawns here,

at the western edge of
its breeding ground

in the path of the current,

which then carries
their tiny young south

into temperate waters.

But it's the east-flowing
South Java Current

that has the greatest impact
on the island.

It brings the rains that trigger
the crab migration.

It may also play a role in
another great migration

that is under way,

one that could not be more
different than that of the crab,

but their destinies are
on a collision course.

The whale shark,

the largest fish in the world
reaching 20 metres in length

and weighing 20 tonnes,

makes its way from the reefs off
western Australia

to the waters of
the Indian Ocean

and Christmas Island,

a 1,600-kilometre journey.

They arrive at Christmas Island
at a very specific time,

one that experts think

is directly tied to
the annual ritual

taking place right now
on the tiny island.

The monsoon season has triggered

one of the greatest
migrations on earth.

The red crabs of
Christmas Island

are on their perilous
march to the sea.

If there is a break in the rain,
they risk dehydration.

But there's no turning back once
committed to the march.

They keep to the shade,

moving in the morning
and evening if they can.

But now they're approaching
the most treacherous part

of their journey.

A killing field unlike anything
their kind has faced

over the aeons their ancestors
have made this arduous journey.

An invader against which
they are nearly defenseless.

The most insidious threat
on the island:

yellow crazy ants,

named for
their frenetic movements.

Having hitched a ride
to the island

on cargo ships decades ago,

these aliens have proceeded
to wreak ecological havoc.

They've created super-colonies
of billions,

and they show no mercy
to the unfortunate creatures

they encounter.

When a red crab enters
their territory,

they swarm it,

spraying it with corrosive
formic acid from their abdomens.

Any single ant can spray
only a tiny amount,

but they work in concert,

finding the chinks in
the crab's armour,

eyes, mouth, joints,

blinding it and rendering
it helpless.

The crab responds by foaming moisture

out of its mouth parts,

which does little

but waste their precious
internal supply of water.

It's a slow, torturous death.

The merciless ants won't
even wait for them to die

to begin
eating them.

The crazy ants' toll on
the red crabs

is almost unimaginable.

It's estimated that they've cut
the population

from 50 million to half that
in just a few decades.

Ant control programs

have only managed to reduce the
ant numbers and slow the decline
of the red crabs.

The yellow crazy ant
killing fields

don't stop them all.

Millions still make it through,

driven on by instinct to an
appointment with destiny.

Not all creatures here
have such trouble

with the yellow crazy ants.

The golden orb-weaver
weaves an impressive web

that glistens like gold
in the sunlight.

The orb-weaver's silk is
strong, flexible, and sticky.

As the spider produces its silk,

it covers it in a
layer of spider glue,

ensuring its prey sticks fast.

But it's what's actually
within the silk itself

that protects the spider
from the angry ants.

It comes complete

with a compound called
pyrrolidine alkaloid,

a built-in ant repellent.

While she is a formidable
defender of her web

and will attack any invaders,

the ant deterrent is
enough to keep the crazy ants

at a safe distance.

It turns out that the big spider
has tiny groupies,

literal hangers-on who hover
at the edges of her web,

alert for any insect

that's too tiny for the
queen to be bothered with.

These little thieves,
called dewdrop spiders,

are commonly found on
the outskirts

of most golden
orb-weavers' webs.

Fortunately for them, she has
a larger meal in mind.

And quickly sets upon
a grasshopper

ensnared in
the filaments of the web.

She injects it with venom

then carefully wraps her dinner
for safekeeping

to eat when she's in
the mood.

[♪]

Within a week, the surviving
front lines of the red army

have nearly reached
their destination:

the beaches where
they were born.

But this final leg of the
journey won't be an easy one.

Craggy, treacherous cliffs
ring the island.

The only way to the water
is down.

They cling for dear life,
sometimes upside-down.

A fall could crack a shell,
a death sentence.

Finally, they reach the
waters of their birth.

Here, they can take a
refreshing dip,

cleaning up, hydrating, and
filling up on salts and minerals

they've used up
on the long journey.

They need it after
their marathon,

and to face another
odyssey ahead.

The females are already arriving

for one of the most remarkable

breeding spectacles
in the world,

and they're expecting the
males to be ready for them.

The red crab's distant cousins,
hermit crabs,

are year-round beach dwellers,

and pay little attention to
the march unfolding around them.

Unlike most crabs,

hermits have soft abdomens
instead of hard shells.

To protect their vulnerable
underparts from predators,

they take up residence
in abandoned seashells,

usually snail shells.

As they grow, they need to find
larger and larger shells,

and spend endless hours
on the beach

inspecting
potential new homes.

Sometimes trying them
on for size.

The best shells are at a premium,

and it's common to
see hermit crabs

tussling over a
particularly appealing shell.

Almost unbelievably,

these little hermits are
closely related

to the
giant robber crabs,

which also begin their
lives in hermit fashion,

carrying their shell homes
around with them.

It's only when the robber crab
is about a year old

that it sheds its hermit ways,

abandons life in
its borrowed shell,

and hardens its body
with layers of calcium.

Only then to they begin to grow
to their enormous size.

Returning to their cliffside
homes with full bellies

to feed their chick,

the brown boobies
seem completely oblivious

to the massive scarlet
migration going on around them

as crabs shuttle
up and down the beach.

While crabs and boobies

don't always make getting
around look easy,

one bird, unique to
Christmas Island,

is known for its elegance:

the golden bosun.

The island's beautiful,
yellow-tinged variation

on the more widely distributed
white-tailed tropic bird.

With its long yellow tail streamers,

it is the angel of
the island's skies.

They prefer to nest inland
in the forest trees,

away from the hustle and bustle
of the crowded cliffs.

After their reviving dip
in the sea,

the males have clambered back up
the cliffs of Christmas Island

to the terraces above

to prepare their welcome
for the ladies.

Using their claws
as earth-movers,

they methodically dig burrows.

They will serve as enticement
to the females.

They're shallow and only
about 30 centimetres long,

but a lot depends on them.

With limited real estate
to work with,

staking out claims can become
quite competitive.

Some crabs would rather steal
than build.

There's a lot more bluster
than violence involved,

with smaller males usually
backing down

before any damage
can be done.

Still, this is serious business.

Without a suitably impressive burrow,

a male is unlikely to
seduce a female,

and his long trek

from forest to sea

will have been in vain.

In the end, the terraces become
crowded beach condo complexes,

with a burrow or two
in each square metre.

With the real estate
tussles settled,

some of the males retreat to
the moisture of their burrows.

They're only a cliff away
from the refreshing ocean,

but hormones bid them to stay,

guarding their hard-won homes

and waiting to welcome
the females.

[♪]

Up above the fray,

another booby species makes
its home in the treetops.

Clinging with their big pink
webbed feet to the branches,

the red-footed boobies
have just returned

from a long journey out
to sea to feed.

Preening is the order
of the day.

These seabirds travel
great distances

and dive hard into the
ocean for food,

both of which require
their feathers

to be kept in perfect shape.

An unwelcome visitor sits
too close for comfort.

A Christmas Island frigatebird,

the bane of the
boobies' existence.

As the boobies head out to feed,

the frigatebirds often provide
an unwanted escort.

Described by some as
muggers and thieves,

they're sometimes
called pirate birds.

The boobies are plunge-divers,

folding back their wings and
daggering into the water

at speeds of up to
50 kilometres per hour

to catch fish up to 50 metres
deep in the water.

All that plunging is hard work.

Gullets full, they head
home for the terraces,

all too often with a
frigatebird on their tails.

It's now that these pirates
live up to their name.

Why do all that work of
diving and fishing

when the booby is
doing it for you?

It harasses the
booby relentlessly,

hoping to force it to
regurgitate what it's caught.

But this booby is not so easily intimidated,

and returns to the terraces
with its crop still full.

It's been 10 days

since the monsoon rains

touched off the red crab migration,

and the rear-guard of
the red army is picking its way

over the steep cliffs
to the beach.

Now it's the females' turn
to dip in the ocean

to refresh and replenish.

[♪]

The sea is not always
gentle with them.

Because millennia of evolution
in the forested interior

have turned them
into land animals

with lungs and only
remnants of gills,

these crabs can drown
if dragged under.

They can also fall prey
to large fish,

like this giant trevally
patrolling the shallows.

[♪]

The survivors turn their
backs on the sea.

They have an appointment up
in the terraces,

a strenuous climb away.

[♪]

In the village of burrows
above the sea,

it's a buyer's market
in the real estate game.

The females busily inspect the
males' architectural offerings.

There's urgency now.

They're responding to the cycles
of the moon,

urging them to mate
and brood their eggs now

while there's still time.

A female who finds a male

with a well-appointed
burrow engages with him.

They mate face-to-face
in clenches

that can last 25 minutes
or more.

[♪]

Then she moves into
her new home.

She'll produce up to 100,000
eggs within the next three days,

brooding them in a pouch
slung under her abdomen.

She'll incubate them
for 12 or 13 days.

Having finished his annual
mating duties,

the male
immediately turns for home,

starting on the
long and dangerous trek

back into the interior.

Once again, the red army will
face the implacable crazy ants,

and the hungry robber crabs,

as they run the gauntlet
in reverse.

If they don't make it back,

at least they'll have
made a heroic effort

to pass their genes onto
the army's next generation.

Many of Christmas Island's
creatures take advantage

of opportunities at sea
and on land.

[♪]

A female great frigate bird
flies inland.

Unlike most seabirds,
which drink salt water,

frigate birds will take
advantage of freshwater

when it's available.

And when they do,

they use their graceful diving
skills to drink on the wing.

[♪]

Back at the coast,
the waning moon

announces that the
time has come.

The female red crabs,

having brooded their eggs
for about two weeks,

begin to emerge
from their burrows.

Each carries in her brood pouch
some 100,000 eggs.

Slowly, carefully,
they make their way

from the forest terraces
above the beach to the cliffs,

carrying their precious
and cumbersome burdens.

They're not so agile now,
and some will pay the price.

Robber crabs can smell
them coming.

Their caviar is an
added bonus,

and the robbers prey on
them mercilessly.

[♪]

The lucky survivors pick their
way back down the cliffs.

When they reach the shore,

they dip again to
rehydrate and refresh.

And then they wait.

On beaches all
around the island,

they redden the coast

with their urgent need
to reproduce,

and timing is everything.

Tonight will be the neap tide,

when the waning
moon's tug is the gentlest

and the difference between high
and low tide is smallest.

[♪]

As each female enters the water,

she raises her claws
and does a big of a jig,

releasing her eggs.

A moon dance on which the future
of her kind depends.

Soon the shallows are darkened,
saturated with billions of eggs.

[♪]

The eggs hatch immediately
into larvae

on contact with the seawater,

before being swept out
to sea.

In just one month, they'll morph
through several life stages

until they're ready to return
to land as baby crabs.

That is, if they survive.

Dawn reveals a beach full of
females, their pouches empty,

setting off on the long
march home.

There's no way to predict

how many of their offspring
will return.

At the mercy of the weather,
currents, and predators,

their fate is yet
to be determined.

Whale sharks arrive just
in time for the spawning,

when billions of tiny crab
larvae fill the waters.

Other ocean giants also seem
in on the secret.

Manta rays fly through the
plankton, filling up as they go.

With each mammoth mouthful,

it seems more likely the
red crabs' incredible migration

will have been in vain.

This is why it's a numbers game.

It has been a month

since the dancing red crab mothers

released billions of
eggs into the ocean

and returned to the rainforest
at the centre of the island.

By the time they return here to
the shores of Christmas Island,

they have morphed into another
life stage known as megalops.

In some years, just a handful
of them return,

and other years
it's a bonanza.

This year is one of
the miracle years

for this most amazing
of migrations.

Millions of tiny crablings
scrabble up the beach,

turning the shoreline pink
with the promise of life.

After three to five days
at the water's edge,

they have molted and transformed

into their
air-breathing crab stage.

Instinct drives them to follow
their journey up the cliffs,

through the terraces,
the gauntlet of predators,

and into the interior rainforest.

There's no way to predict

how many will fall
victim along the way,

but survivors will spend
four or five years

in their forest home

before they'll hear the call
of their ocean origins.

Then they too

will join the yearly march
to the sea

to burrow

and fight

and mate

and dance,

carrying on the ancient
tradition etched in their genes.

A spectacle of reproduction
unlike anything else on earth.

Here, on the remarkably
restless sanctuary

of Christmas Island.