Original subtitles

[narrator] Earth is a restless place.

[Thunder rumbling]

Its seasons driven by the orbit around our sun.

An epic journey that sets the rhythms of all life.

Humans honour this passage through ritual and celebration.

[Fireworks blasting]

Nature marks the cycle with its own patterns.

Over the course of a year,

the planet's most spectacular events of migration,

rebirth and transformation unfold.

[Roaring]

Moment by moment,

month by month,

throughout a wild year on Earth.

The first third of the year has already passed,

as the Earth continues in perpetual motion around the sun.

It maintains a steady pace,

hurtling at 107,000 kilometres an hour through space.

In May, seasons are in transition.

It's a volatile time.

In the heart of North America, trouble's brewing.

Late spring is a time when hot and cold air collide.

[Lightning striking]

Humid air from the tropics

sweeps up the plains of central United States.

It meets with dry, frigid air rushing from the Arctic.

This clash creates a superstorm, whose winds stir into tornadoes.

[Intense music playing]

Each year, over a thousand twisters

menace the United States.

[Dramatic music playing]

Although they can occur throughout the year,

spring is when tornadoes are at their most mighty.

Thundering across the plains of North America,

is another force of nature.

Wild mustangs.

Each spring, they arrive from all directions,

converging at the foot of the Sierra Nevada Mountains.

They form a mega-herd, hundreds strong.

[Neighing]

What brings them together is fresh springtime pasture.

Winter's snow cover is now lush meltwater,

irrigating thick, nutritious grass.

For mustangs,

this seasonal feast provides rocket fuel for breeding.

Females are on heat.

[Neighing]

And bachelors are feeling extra frisky.

One moves closer to the females, testosterone racing.

A pretty grey mare catches his eye.

But standing in his way, is the stallion.

The bachelor can't suppress his urges any longer.

The old stallion responds, and the rivals draw close.

[Battle music playing]

[Battle music continues playing]

Stamping the ground, the challenger claims victory.

He is now boss.

The old, defeated stallion is exiled.

He will live out his days on the fringes,

in the company of the castaways.

The new leader eyes a young colt,

the son of the old stallion.

He, too, will be exiled when he reaches maturity.

But for now, in the plentiful time of spring,

all are welcome to run with the herd.

As spring advances into summer in North America,

another turning point approaches South East Asia.

Indochina is parched.

In this ancient land of temples and tombs,

many months have passed with little to no rain.

Heat envelopes the devotees of ritual and prayer,

as all wait for the heavens to break.

Falling barometric pressure and rising humidity

signal the monsoon is on its way.

Snakes are sensitive to atmospheric changes.

This is crucial for the king cobra,

whose life cycle is timed around the coming rains.

For this queen of the kings,

May and June are critical months.

She mated just over a month ago and is now heavy with eggs.

Using the coils of her body to collect leaves,

she builds a mound.

The rotting leaves create the perfect humidicrib,

to incubate her eggs over the coming months.

She must build her leafy tower high enough,

so it won't be flooded by the imminent monsoon.

[Thunder striking]

[Growling]

The king cobra is the only snake species

to build a nest like this.

And she will guard it ferociously,

come hell or high water.

Above her, elemental forces stir.

By late May,

the region experiences the most intense direct sunlight of the year.

Heat builds, sucking moisture from the Indian Ocean.

A thick rain band forms,

sweeping across a vast area from Indochina

to the Indian subcontinent.

This is the largest seasonal movement of rain on the planet.

The monsoon is here.

[Rain pouring]

The deluge will continue for four months.

[Rain pouring]

In parts of India,

one metre of rain can fall in a single day.

Over a billion people,

one sixth of the world's population,

rely on these rains for food and economy.

The monsoon is the most dramatic annual weather event

to shape the lives of the region's creatures.

In Sri Lanka,

the monsoon revitalizes the waterways

that carve through the cloud forest.

Water levels rise.

Ponds swell in size.

There's no better aphrodisiac for tree frogs.

Not surprisingly,

monsoon triggers their mating season.

The strapping female attempts to carry her smaller suitor

to a slippery nest site.

[Chirping]

Spot chosen, she regains her balance

and excretes sticky proteins,

which her back legs froth into a lather.

Into this foam ball, she lays up to 300 eggs,

which the hitchhiker male eagerly fertilizes.

Their mating is by no means private.

This tree, overhanging the perfect pond

is a hotly contested hook-up place for many other pairs.

Dozens of lusty bachelors

are looking for any opportunity to join in.

More than one male can fertilize a foam ball,

so it's always worth a shot.

The couple stays single-mindedly engrossed with each other,

ignoring the voyeurs.

Half an hour later, the deed is done.

Left alone, the female extracts herself from the hardening foam,

a tricky, sticky business.

The ball hardens,

forming a protective casing,

where the eggs will safely develop for the next week.

Then, mirroring the rain that inspired their creation,

tiny tadpoles drop to the awaiting nursery below.

The foam nest falls, too, providing sustenance

for their magical metamorphosis into frogs.

It's mission accomplished for the mother tree frog.

She perfectly timed her work to the season.

Floodwaters will flush her progeny far and wide,

as the monsoon rolls onwards.

By June,

the rising floodwaters present challenges

for the young and old across Asia.

[Grunting]

[Bellowing]

Every struggle is monitored from above.

Any drowning is another banquet

for the resident griffon vultures.

While this vulture species scans the sodden landscape

for water-softened carrion,

their cousins on a different continent

do best in the extreme dry.

In stark contrast to Asia,

June is winter in South Africa

and the driest time of year.

Cape vultures are on patrol.

For optimum height and distance,

they rely on riding the thermals.

In winter,

the sun's intensity weakens and thermals slacken.

They can't travel as far.

But when it's this dry, they don't need to.

[Heroic music playing]

Food is everywhere.

Almost no rain has fallen for two months

and both land and creatures are stressed.

Each death summons the aerial undertakers.

This bird of prey never kills.

Instead, vultures rely on scavenging for food

and affectionately known as 'the clean up crew.'

[Screeching]

Their grisly work is essential health of the whole ecosystem,

clearing death and disease with each mouthful.

There aren't many animals

that can scatter this feeding frenzy.

In the dry, lions are spoiled for choice.

There's no point wasting energy on a chase,

when food is strewn across the plain.

[Roaring]

The vultures can only watch.

And wait for the leftovers.

Finally,

the lions are so bloated they can barely move. The vultures pluck up the nerve to reclaim the table.

One lion's trash is a vulture's treasure,

and worth fighting for.

[Screeching]

[Dramatic music playing]

The bird's highly acidic stomachs

are able to digest skin and sinew.

And bone.

At this time of year,

returning home with a belly full of bone

is the highest priority of all.

Its calcium strengthens the vulture's light flight bones

And its minerals help produce strong eggs.

Which is the most important thing in May and June.

The peak months

in the cape vulture's breeding season.

High on the sheer cliffs

of South Africa's Waterberg Mountains,

dozens of vultures tend their nests.

Pairs bond for life,

produce one egg each year and take turns on the nest.

The calories from the giraffe meal

will sustain this vulture for days,

as he settles in for his shift.

Which frees his mate to head out on her own undertaking duty.

Travelling up the central coast of South Africa,

the dryness endures.

Although winter brings cooler days,

rainfall is sporadic.

But on the arid Eastern Cape, an oasis exists.

And the world's largest land animal,

the African bush elephant, thrives here.

In the dry season,

drinking and bathing are both important.

Mud protects against sun and insects.

Elephant calves love applying their sunscreen

and can't seem to get enough.

Although quenched,

the elephants need much more than water to sustain them.

To live in this desert,

they rely on a plant

that has adapted to life here too.

The prolific bacon tree is a hardy succulent plant,

whose leaves retain water, even on the driest of days.

But despite the elephants' year-long access

to good water and food,

they are still not immune to the dry season's cruelty.

A young mother signals her loss to the herd.

She has been standing vigil for several days,

unable to leave her calf, even now.

Scavengers give the mother no chance to grieve.

[Sombre music playing]

[Trumpeting]

Guarding the corpse may be futile,

but her instinct to stay is too strong.

She was supposed to raise her calf for 14 years

and isn't ready to walk away.

[Sombre music playing]

But as the day wears on,

she grows more exhausted.

Something has to give.

[Ominous music playing]

It's said elephant memories are long.

[Bellowing]

Although she finally leaves this place,

it's unlikely she will forget what happened here.

The calf's body offers life after death

for the other dry season survivors.

The mother re-joins the herd.

She will live for decades and have many more calves.

Each time, a little wiser

to the merciless ways of the dry season.

As May ends,

the Earth approaches the midway point

on its journey around the sun.

In the southern hemisphere, days are nearing their shortest.

Ocean currents also respond to volatile seasonal forces.

Strong winds in northern Australia

trigger a torrent of water to rush down the west coast.

In May and June,

the world's longest boundary current,

the Leeuwin Current, is at its peak strength.

And rushing to meet it are Australian salmon.

Tens of thousands of them.

They converge off south Western Australia to spawn.

Predators follow.

[Inspirational music playing]

Some salmon die.

But their precious larvae are whisked away by the current

to nursery grounds, thousands of kilometres away.

On their journey,

they pass by another underwater spectacle.

Each winter, as sea temperatures fall,

giant cuttlefish rise from the depths

to converge in a protected bay in southern Australia.

It's the only known mass aggregation

of cuttlefish in the world.

They've come here for courtship.

Cuttlefish speak through their skin.

The males loudly communicate their strength in patterns

and colours to attract the attention of females.

Having made his attentions clear,

a large alpha male corrals his chosen female.

He separates her from the others.

Then escorts her

to a private corner of the reef to mate,

taking her in his eight-arm embrace.

She chooses a safe crevice to lay her fertilized eggs.

Her mate blocks the entrance to her lair,

guarding both her and his paternity rights.

His vigilance is justified.

Other males want access to his female.

One plucky hopeful dives in.

Bad idea.

[Intense music playing]

It's an attack that would deter most rivals.

But not this one.

He's either desperate to mate, or a sucker for punishment.

Either way,

the alpha male has run out of patience.

[Dramatic music playing]

Ink is usually expelled to confuse predators.

Now, it's a sign of pure panic.

With the rival finally banished,

the alpha male rests easy,

as his female finishes laying,

undisturbed.

Despite all this passion,

neither will experience parenthood.

At the end of their breeding season,

both male and female will die.

Their precious progeny will hatch without supervision,

and make their way back to the depths of the Southern Ocean,

to await their own signal to breed.

In mid-June,

the sun's zenith reaches its most northerly point

on the globe.

The southern hemisphere

is tilted furthest from the sun's rays,

while the northern hemisphere is fully exposed.

For 24 hours,

Earth sits at a magical tipping point.

At dawn of June 21st,

people gather at the ancient pagan site of Stonehenge

to watch the sun break through the stones.

In the northern hemisphere,

the year's longest day begins.

The summer solstice.

[Uplifting music playing]

Festivities are celebrated across Europe.

Fire pays homage to the sun.

And sets alight the year's shortest night.

[Uplifting music playing]

Near the North Pole, in the land of the midnight sun,

the summer solstice means a never-ending day.

When the northern hemisphere awakens on June 22nd,

it's officially summer.

Across Europe,

long days are filled with the sound of cicadas.

And in the south of France,

fields of lavender bloom with the sun's strong rays.

Sun scorches the mediaeval walls of Carcassonne Castle.

Since the Dark Ages,

this hillside fortress in France has housed royalty

and hosted war.

Where armies once clashed,

a kestrel now hunts.

In summer,

the grasslands around the castle are full of seed

and running with rodents.

The kestrel's favourite prey.

If anyone can see them, he can.

He is one of the few birds of prey capable of hovering.

Hanging suspended in the air,

he holds his head completely still.

[Intense music playing]

Perfect for lining up his target.

The kestrel's kill isn't for him.

He's on a tour of duty

and quickly heads back home to base.

He's met at the door and hands over the spoils.

[Chirping]

June is mid-nesting time for kestrels.

The female remains with the chicks

until they are two weeks old,

so relies on the male for home delivery.

He won't stay long.

Duty calls.

The kestrel chicks need constant food.

So it's back to the killing fields.

[Triumphant music playing]

Beyond the crumbling castles,

and down in a warming river,

a very different European parent

is also answering the call of nature.

This female crayfish is heavy with eggs,

cradling approximately 200 beneath her body.

She mated last winter,

so has carried this weight for six months.

Now, season helps her complete the task.

June's warmer water

speeds up the development of the eggs.

Exhausted,

all she needs to do now is wait and stay hidden.

Her river is in racoon territory.

Racoons were introduced from North America,

and they love dining on European crayfish.

The crayfish larvae hatch in unison

and remain attached via tiny stalks.

Over two weeks,

the youngsters moult, detach from Mum and drift away.

Finally unencumbered,

the depleted mother is free to rest,

forage and rebuild her strength.

But she doesn't get a chance.

The racoon detects her presence,

using his most powerful sense.

Touch.

The crayfish has sight and flight on her side,

but the invader persists.

The crayfish uses claws to defend herself,

but the racoon has claws, too.

As the mother is devoured,

her hatchlings scatter.

They may live for 20 years,

so will fight many a battle of their own in future summers.

By late June,

summertime has embraced much of the northern hemisphere.

At the equator,

the wet season has left its mark.

In the Llanos of Colombia,

the landscape is more water than earth.

And the nesting trees of egrets are islands.

The birds are nearing the end of their breeding season,

and still wear their fancy seasonal plumage.

The seasonal flood helps these fish eaters with parenting.

More fish, right on the doorstep.

Predators, too.

Caimans are cousins of the alligator,

and normally fish eaters.

But in the wet season,

they turn their sights skyward.

Stirring their appetites are the clumsy antics

of the fledgling egrets.

They are four weeks old.

And preparing for their first flight.

But if they can't go up, they risk falling down.

[Dramatic music playing]

It's a welcome change of diet for the caimans

and they can't get enough of it.

[Dramatic music playing]

Whether a fallen chick survives,

is up to willpower and pure luck.

It's a rare miss for the caiman.

And a heart-stopping start at life for the escapee.

June comes to an end.

The volatility of the past two months

is etched in the skies.

A time of seasonal gear-shifting and unpredictable forces.

The planet reaches the mid-point

in its annual voyage around the sun.

And completes the first half of the human calendar year.

The second half promises to be just as wild a ride

in this wild year on Earth.