Original subtitles

[narrator] Earth is a restless place.

[thunder]

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.

Nature marks this cycle with its own patterns.

[dolphins clicking]

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.

As the sun rises on 1 September,

it marks Day 244 of Earth's annual journey.

The planet is two thirds of the way through its orbit,

and the seasonal swings across the globe

activate change in the natural world.

Over Southern Africa,

the heat is rising.

Rain won't fall for another two months.

The dry will only deepen.

In the Rift Valley of Zambia,

herbivores are at breaking point.

Desperate for water,

creatures big and small converge where the last pools exist.

The Luangwa River.

Their arrival is closely monitored.

The dry activates a change in hunting strategy for the lions.

Instead of roaming far and wide,

they become laser-focused on the river's edge

and what it entices.

[spitting]

[boar grunting]

Despite their best efforts,

only a third of all attacks end in a kill.

They can't afford to waste more energy in this heat.

Hungry,

the pride waits for something more worthwhile.

Every day, the buffalo herd stampedes to the river.

The lions size them up.

One adult buffalo

offers the pride over half a tonne of prime meat.

[dramatic music playing]

But a meal must be selected very carefully.

If the lions get it wrong,

they risk being trampled or gored to death.

The safest targets are the elderly, weak or alone.

This one is all three.

[tense music playing]

The big cats are totally satisfied by this big meal.

Even on the hottest days,

they don't need to drink water

if they can quench their thirst on blood.

The moisture in the buffalo's body

is also a magnet for butterflies.

The half-digested grass spilling from the stomach

contains salt,

which gives an essential mineral boost.

[calming music playing]

In the dry season, nothing goes to waste.

Across the border in Zimbabwe,

watercourses evaporate by the day.

And lagoons shrink by the hour.

Two elderly brothers face the worst hippo nightmare.

They instinctively stay in their pool,

but as it dries, the mud threatens to entomb.

The old bull decides to act

while he still has a chance,

leaving his brother behind.

To live, he must find water.

[chirping]

Sun damaged and dehydrated, he reaches relief.

But it's far from ideal.

Hundreds of hippos are forced into close confines

in the last deep waterholes.

Stress and aggression are high.

And every private business is public.

But this beggar can't be choosy.

Any water is bliss.

It's also a heavily guarded resource.

The pool is the territory of an alpha male.

He has no intention

of making room for this stranger.

[intense music playing]

The warning is clear,

but the old bull doesn't leave.

He has nowhere to go.

Instead, he displays his willingness to fight.

The alpha needs no further encouragement.

[dramatic music playing]

The pod can barely move out of the way

as the 2-tonne bulls go head to head.

[dramatic music continues playing]

The old bull is forced to do the last thing he wants to do...

leave the water.

His search resumes anew for a place to call his own.

Zimbabwe will remain locked in the dry season

for another two months.

But to the south-west, reprieve comes sooner.

Early rains have reached the fringes

of the Kalahari Desert.

[rain pouring]

It's the change of fortune

a meerkat family's been waiting for.

Nothing escapes their gaze

as the shower unlocks the desert's food larder.

[chattering]

[joyful music playing]

For the matriarch, it's the excuse needed

to coax her litter out of their underground den

for the very first time.

[joyful music playing]

[playful music playing]

They're only a few weeks old,

and until now have only been milk-fed.

But while there's a flush of food,

it's an opportunity for their first foraging lesson.

[chattering]

Tackling live prey is daunting.

Especially when it's almost your size.

To know what to do,

they need to watch and learn.

At first, the pups are presented with easy meals.

Injured or dead.

As their confidence grows,

the lessons get harder.

They observe the mastery

and mistakes.

The rain's bounty encourages the whole troupe

to stay out in the open, feasting.

It's noted.

A sentinel's call relays the threat

and urgency.

[sentinel calling]

When to run for cover

isn't something a meerkat pup needs to be taught.

It's deep in its DNA.

[tense music playing]

[chattering]

As the danger passes,

a quick head count assures the matriarch

everyone's accounted for.

With more rain in the air, lessons will resume tomorrow.

Just like in the Kalahari,

September and October are months of renewal in Australia.

Across the continent, spring has sprung.

[buzzing and squawking]

The warmth activates termites

to come out of the woodwork.

In hot pursuit is the numbat.

One of Australia's rarest marsupials.

Mirroring the meerkats in Africa,

numbat babies also venture out at this time of year.

Spring rains flush the landscape.

An echidna rouses from hibernation, hungry.

On the other side of the swollen river

is her favourite foraging site.

[calming music playing]

On the grassy plains of Eastern Australia,

springtime's arrival means a breeding boom for kangaroos.

The boss of a mob flexes his muscles.

This spring he's at the top of the hierarchy,

and doesn't like the way

a subordinate is prepping his boxing gloves

and drooling over his harem of females.

[tense music playing]

The boss reminds them all of his dominance,

by marking his territory.

Paying no heed,

the lower-ranked male inches closer to the females.

There's only one thing to do.

The boss must put him in his place.

[dramatic music playing]

Authority affirmed,

the boss focuses on wooing the females.

Although kangaroos breed all year round,

spring's fresh, protein-rich grass

activates a production line of babies.

[gentle music playing]

Mother kangaroos can fall pregnant

while still nursing joeys.

The buck knows it well.

And will fight for their favours all spring.

Young males start boxing practice early.

It takes a while to refine moves.

And to learn to fight fair.

[playful music playing]

They kick and claw their way to the top of the hierarchy.

Each full of ambition

to be the top buck in a future spring.

Just as kangaroos rely on spring's grass

to kickstart family,

humans also time their lives around growing seasons.

In south-west China,

the world's most important crop is ready for harvest.

Monsoon rains irrigated the paddy fields.

Summer's sun ripened the grain.

Now in September,

the rice is ready.

The rice pickers are part of a 10,000-year-old tradition.

Filling the food bowls of the world.

China dedicates an area as big as Italy to rice fields,

while agriculture takes up over a third

of the planet's land surface.

But most of the earth is ocean.

And it's the oceans

that are key drivers of our climate and weather.

During September,

changes in sea temperature

in the eastern equatorial Pacific intensify the wind.

This wind charges towards South America

collecting huge quantities of moisture as it goes.

Welcoming the water is the Choco Rainforest.

September is the start of the wet season,

in what is already

one of the wettest places on Earth.

And someone is singing in the rain.

It's a male golden dart frog.

[singing]

He sings to activate female admirers

to come to his territory.

[singing]

It's an anxious wait.

Finally, a female fan.

But does she like his serenade?

[male dart frog singing]

With her at close range,

he offers her a final heartfelt reprise of his love song.

[singing]

Success.

The male escorts her through his territory,

as they choose a suitable nest site.

He gives her space while she lays her eggs.

Then she's gone for good.

The male fertilises the eggs externally.

Then, over the two weeks it takes the eggs to hatch,

he's their dedicated guardian.

As tiny tadpoles, they are vulnerable to predation

and can't stay in their leaf-litter cradle for long.

But they haven't got legs yet to hop to the nearest stream.

So their father

comes to the rescue.

In an evolutionary brainwave,

he piggybacks them through the forest.

Safely in the stream,

the tadpoles will take two or three months

to morph into frogs.

The male dart frog wastes no time

on long goodbyes.

Before another downpour drowns him out,

it's time for a repeat performance.

[male dart frog singing]

As calendar days pass,

the sun reaches a point where it's positioned

directly above the equator.

[triumphant music playing]

Between 21 September and 24,

the planet's terminator line, visibly dividing day and night,

runs in perfect parallel to the axis from pole to pole.

For 24 hours,

the northern and southern hemispheres

experience the same length of daylight and night-time.

This is called the Equinox.

It marks the start of autumn in the northern hemisphere.

Days progressively shorten,

inspiring a terrestrial wardrobe change.

As the sun's rays weaken,

deciduous trees withdraw nutrients from the leaves.

[triumphant music playing]

This seasonal fall

turns the landscape

into a kaleidoscopic oil painting.

Humans are bewitched by the colours,

then bothered by the debris.

In wilder places,

where leaf litter is left to lie,

magic spawns.

Fungi are quintessential autumn species.

October's coolness, wetness and decay

activate their fruiting bodies,

which break the surface in the form of mushrooms,

toadstools, puffballs and moulds.

Fungi speed up rot,

providing rich nutrients for other plants.

Without their work processing the dead,

the living world would grind to a halt.

Millions of species of fungi exist and occupy every habitat.

They're a favourite food

for autumn foragers.

Hedgehogs are also on the prowl,

ensuring they're fat enough to survive winter's hibernation.

If not, it may be a never-ending sleep.

And for red deer, a war cry means one thing.

[crying]

The start of autumn's rutting contest.

Males clash antlers

to gain access to females and breeding rights.

Every battle counts.

Thousands of kilometres away, in the north of Canada,

a distant relative of the red deer

is also activated by autumn.

October's declining weather

acts like a starter gun for caribou.

It's time to run

racing winter,

to warmer pasture 600 kilometres south.

[triumphant music playing]

So begins the longest land migration on Earth.

They move as one, like schooling fish.

Each guided by a built-in compass.

Females lead the charge,

accompanied by new calves born four months ago.

Males bring up the rear, heads held high

despite the heavy weight of antlers.

Their path is well-worn,

traversed for thousands of years.

This older female

has made the return trip for over a decade.

She knows the perfect pace to keep up with the herd

as well as care for her calf.

Her youngster was born to run.

When only a day old,

he was already faster than an Olympic sprinter. He will need to run his personal best now.

Grey wolves are expert caribou hunters.

And this migration is their gravy train.

[dramatic music playing]

The calf's natural fitness

and instinct to stay close to his mother,

saves his life.

Other calves are not so lucky.

The wolf pack divides to conquer.

[dramatic music playing]

The herd press on.

The unforgiving rocky terrain is perilous.

But it's not just the earth

that mars their marathon with danger.

Rivers cross their migratory route,

forcing the herd to become waterborne.

For the calf,

the crossing is proving more challenging than a wolf chase.

He's had no practice

and can't keep up with his mother.

[sad music playing]

[crying]

She hears his calls and turns back.

S he keeps upstream from him,

shielding him from the pull of the current.

Each river crossing brings them closer to their destination,

but it's three months of running to get there.

The promise of forest,

food and rest spurs the great deer onwards.

With winter biting at their heels.

Across the Atlantic Ocean,

temperatures are also starting to fall.

In the British Isles, a chill is in the air.

Summer fields fall fallow.

October's crisp weather

is the best growing time for apples.

Orchards hang heavy with fruit.

While the windfall attracts all sorts of insects.

It's just rewards for the honey bee,

whose springtime flower duties help pollinate the trees.

But their buzz of excitement

attracts unwanted attention.

Hornets are Europe's largest social wasp and carnivorous.

Although they like a sugar hit once in a while,

they haven't come for the apples.

In autumn, the hornets are more murderous than ever.

Winter will kill most of them.

Before it does, they have mouths to feed.

[buzzing]

[tense music playing]

Their queen has produced a new generation of rulers.

Before now,

she sired only asexual workers to do her bidding.

But in autumn,

she creates sexually active drones and future queens.

They are fattened in haste.

Before autumn ends,

these special larvae must develop,

reproduce and disperse.

The threat of winter activates autumn preparations

throughout the animal kingdom.

Human kingdoms, too.

Across Europe,

castles were built to be both war and weatherproof.

Most critical

as conditions deteriorate into winter.

The ability to adapt to season

shaped a fiefdom's destiny as much as battle.

But castles aren't just built with bricks and mortar.

In Catalonia,

the most celebrated towers rising from the ground

are made with human limbs.

[triumphant music playing]

The art of the castells

is a UNESCO recognised cultural tradition.

October is the main competition month for castell teams,

requiring hours of practice.

Strength, balance, courage and wisdom' is their motto,

pushing them to new heights.

By the end of October,

Europe becomes colder and darker by the day.

But in the South Pacific,

each day brings more sunlight and warmth.

Things are heating up.

The warm tropical seas surrounding Tonga

inspire romance.

And it starts with a song.

A female humpback whale

hears it loud and clear.

It's the tell-tale melody of a male,

travelling through the abyss.

[underwater calling]

Requiring no further introduction,

the balladeer arrives.

The two titans are now so close, they can eyeball each other.

For two months, they have swum from Antarctica

to reach this Polynesian paradise.

October is the humpback's breeding season.

Which means the pair isn't alone for long.

Other males have also heard the song.

For them,

it's a call to action.

[underwater calling]

The female is suddenly pursued by half a dozen virile hopefuls.

[dramatic music playing]

The 'heat run' is on.

[dramatic music playing]

The chase is a test of strength and endurance.

And becomes increasingly aggressive.

[dramatic music playing]

Finally, the competitors fall away.

Leaving the balladeer as victor.

After mating,

the female turns her sights back south again.

When she returns here next year,

she will birth her fist calf.

With male harmonics once again her background music.

[whale singing]

October comes to an end.

It's closure for two months of intense activation.

In the southern hemisphere, summer's in the air.

In the northern hemisphere, winter waits in the wings.

Without a moment to spare,

the planet's inhabitants prepare for the final chapter

of this wild year on Earth.