A Year on Planet Earth (2022-…): Season 1, Episode 5 - Full Circle - full transcript

As a new year starts,

a new life begins.

After nearly two months
of careful incubation,

this king penguin chick

is ready to face the world.

A world she'll soon discover

keeps changing all the time.

In the far south,

the days will soon get shorter...

..the weather will worsen.

And this little chick
must learn to adapt



if she's to survive
her first year on Earth.

In 365 days from now,

the Earth will have come
full circle round the sun.

As we journey through space,

around this ball of fire,

it fuels extraordinary change...

..creating the seasons
that alter the worlds

of almost every animal
on our planet.

Determining when they move...

..fight...

..and when they raise a family.

In this programme...

..we'll see how animals
use incredible strategies

to cope with
their ever-changing world...



..as we travel full circle
through every season

in a year on planet Earth.

Nowhere in the Northern Hemisphere

is winter as extreme

or felt more harshly

than in the High Arctic.

This polar bear mum and cub

are seeing the new year in...
in darkness.

A night that will last
another 45 days.

At the start of the year,

the Northern Hemisphere is tilted

almost as far away from the sun
as it can be.

It's cold and dark.

Food is thin on the ground.

And not everyone will survive
long enough to see the sun

when it eventually rises again.

But even in these darkest months,

the sun's presence
is still evident.

As solar winds collide
with the Earth's magnetic field,

they create a light show

that's truly out of this world.

The northern lights.

This spectacle

is hundreds of kilometres
above the Earth's surface.

But it's only visible
when the sky is at its darkest.

In February,

the Northern Hemisphere
begins to face towards the sun.

Days start to get longer
and warmer...

..and winter
in these wooded valleys

begins to lose its grip.

But until it's gone for good,

food for this red squirrel
is hard to come by.

Squirrels don't hibernate.

So, to get through winter,

he relies on forward planning

and a very good memory.

In autumn,
he buried about 3,000 nuts...

..carefully grouped
according to type.

Now he must remember
where he left them.

To help him, his hippocampus,

the part of the brain
concerned with memory,

has expanded.

It's the same part of the brain

that's first affected
with Alzheimer's,

and researchers are hoping
we can learn more about it

from studying squirrels.

Whatever he's doing, it's working.

Erm, mostly.

Do you ever get that feeling
you're being watched?

In late winter,

most squirrels' stashes are empty,

so thieves
are always on the lookout...

..and will steal anything
they can get their paws on.

Finally, he can finish
his breakfast in peace.

In these bitterly cold months,

competition for food
is at its fiercest.

Nowhere more so
than on the east coast of Japan.

Steller's sea eagles

are one of the most powerful raptors
in the world.

And with a wingspan
of over two metres,

one of the largest.

Now that much of the sea
is frozen solid,

these big bruisers

resort to underhand
means to get fish.

Harmony will only be restored

when the temperature rises,

sea ice melts

and fishing gets easier again.

Our planet is now three months into
its annual journey around the sun.

As days in the Northern Hemisphere

continue to get longer and warmer...

..in the Southern Hemisphere,
they're getting shorter and colder.

The king penguin chick is
now four months old,

and beginning to spread her wings.

To adapt to the cold,

she's become the proud owner
of this fine feather coat,

and is already
50 times her birth weight...

..thanks to plenty of fish takeaways
from her parents.

To keep their not-so-little one fed,

Mum and Dad
are falling over backwards

with constant trips to the sea.

As parents, it can sometimes
feel like you're doing all the work.

But the chick's months
of being waited on

are coming to and end.

As the days continue to get shorter
this far south,

the water is getting colder.

Currents are shifting

and prime feeding areas
are moving further away.

Soon, her parents will be gone
for months on end,

and the chick
will be left to fend for herself.

As life in the Southern Hemisphere
gets harder,

in the Norther Hemisphere,
it's getting easier.

Spring is in full flow.

Day length
is now longer than night...

..and solar energy
reaching the ground has increased.

A splash of rain,

and the north transforms
into a sea of colour.

New growth.

New life.

And new opportunities.

On the largest, highest plateau
in the world,

the locals
have never had it so good.

Thanks to the new spring growth,

these pikas are having a feast...

..and a baby boom.

And pikas aren't the only
ones to thrive in spring.

This season
is enough to put a very big smile

on one hungry resident's face.

The Tibetan fox
has the widest gape of any fox.

All the better to eat pika with.

In fact, over 90% of
this wily predator's diet is pika.

When she can catch one.

Pikas have hundreds of boltholes,

and are quick to warn each other
when they spot danger.

Teamwork keeps them one step ahead.

But not everyone's paying attention.

The fox hunts
every morning and evening,

not just for her,

but for her three
eight-week-old cubs.

Usually the father helps
to feed his cubs.

But he has disappeared,

leaving Mum
to bring them up on her own.

Not easy.

But with so much food around,
and a hard-working mum,

the cubs have a good chance
of making it.

Across the Northern Hemisphere,

this is the time to start a family.

Though one animal
is a little slow to get going.

Up here at 2,000 metres,

it can feel more like winter.

But at last,

the sun has pushed the temperature
up to five degrees,

making all the difference
to one cold-blooded creature.

A common European frog.

He's been hibernating
in an underground stream

for over six months.

Now he's desperate to get a mate.

And there, in that pond,
is where the party is.

So, he had better hop to it.

He needs to move in daylight

to make the most
of the sun's warmth.

But his muscles are slow to warm up.

Hot-blooded in passion,

cold-blooded in body.

A frustrating combination.

Other males have emerged.

The first to the pond

will have the pick of the females.

But our guy has... run out of steam.

The others are pairing up.

Try as he might, he just can't move.

As the sun's powerful rays
beam down,

slowly his body
starts to warm again.

The last five metres

takes all he's got.

He may be late...

..but things have turned out
pretty well after all.

It's not just his world

that's hotting up.

We are now halfway through
our annual orbit...

..and the Northern Hemisphere
is tilting towards the sun.

Summer has begun.

As we enter
the hottest season of the year,

life prepares to adapt again
to the changes it brings.

For some, this is a time to feast

and a chance to store energy...

..as food becomes more abundant.

Nowhere more so
than in Southwest China.

Here, the landscape is dominated

by the fastest-growing plant
on the planet.

Bamboo.

In summer, it can grow
a staggering one metre a day.

Giving one animal
the vital chance it needs

to pile on the pounds.

The giant panda.

In winter, this mum has to eat
poor-quality bamboo leaves.

But now she can eat
as many nutritious shoots

as she can manage.

As her diet changes,

so too do her gut bacteria,

helping her lay down fat
for leaner months ahead.

While she tucks in,

her 11-month-old cub
takes the chance to explore.

Apart from when they're little,
all giant pandas live alone.

The cub will be independent
in just five months,

and is starting to test
how it feels.

Although shoots
are higher quality than leaves,

Mum still needs to eat
up to half her body weight a day

to get enough nutrients.

Her cub, on the other hand,
isn't yet weaned.

And although he's old enough
to eat solid food,

for him, it's...
take it or leave it.

Her meal could stretch on
for 14 hours.

But on a diet
of Mum's fat-rich milk,

he can afford to take it easy.

Mum has four months to fatten up
before winter.

But some things in life

are even more important than bamboo.

This is the pair's
last summer together.

Soon, this little bear
must learn to live on his own.

Until then, Mum will do all she can

to help him
stand on his own four feet.

Summer here
is the wettest time of year.

Over 70cm of rain

can fall in a single month.

While in the south,

in Australia's Northern Territory,

there is serious drought.

Out here, bush fires
can spread 25km each day.

Months without rain,

and dry grasslands,
are like a tinderbox.

It only takes a tiny spark

to set
these flammable plants alight.

Add wind...
and the woodland is ablaze.

Those that can flee for their lives.

But not everyone has the nerve.

Or the know-how.

These hooded parrot chicks

are one month old.

They're getting ready to fledge,
but they've left it too late.

As well as the flames,

deadly fire hawks
are on the prowl...

..looking for creatures
flushed out by the fire.

The chicks have missed their chance.

Bush fires kill billions of animals
every year...

..which is why the chicks' parents
have planned ahead.

The home they've chosen,

this termite mound
made of sand and clay,

is fireproof.

And this scorched ground is,
in fact, what the chicks need

to tempt them out.

The grasses
have dropped their seeds,

just in time for the parrots'
first meal out as a family.

In less than a week,
the chicks will leave home...

..and the parents
will be empty-nesters

until they breed again next year.

The winds that gave fuel
to these fires

are the south-easterly trade winds.

Vast currents of air

that are carried west
as the Earth rotates,

and pulled north
towards the heat of the sun.

As they sweep over the Indian Ocean,

they change the direction
of the currents beneath...

..creating conditions

for the sea's most important
food source to thrive.

Plankton.

Microscopic plants and animals.

The staple food
of almost every marine ecosystem.

The miniature plants

produce over half of the oxygen
that we breathe.

On this coral reef,

they feed fish.

From the smallest...

..to the largest.

Reef manta rays,

with a four-metre wingspan,

make a seasonal migration
around these atolls,

following the plankton.

Swimming one behind the other,
they catch plankton

from the slipstream
of the manta in front.

And as the leader turns,

they form what's known as
a feeding cyclone...

..channelling
the tiny plants and animals

into their super-sized mouths.

These gentle giants

need a constant flow of water
to breathe.

So, with their wing-like fins,

these birds of the sea

are always on the move...

..returning to this bay
year after year

in numbers up to 5,000 strong

for the biggest manta feeding
aggregation in the world.

While the mantas
are free to follow their food...

..in the same ocean,

6,000km south...

..the king penguin chick
is close to starving.

It's been four months

since her parents left
to find food,

and she hasn't eaten
in all that time.

Most parents have returned
with bellies full of fish.

But hers
have yet to make an appearance.

In response to fasting,

her metabolism and growth rate
have slowed.

Beneath all that fluff,

she's lost 70% of her body weight...

..and is now just 4kg.

King penguin chicks
can survive without food

longer than any other bird.

But each year, half starve to death
waiting for their parents to return.

But her mum and dad
aren't going to let that happen.

They arrive in the nick of time.

With her parents' help,

this chick
has made it to eight months.

The time it's taken

for our planet to journey
two thirds of its way round the sun.

By the time it's gone full circle,

this chick must be ready
to go it alone.

As we enter
the final leg of our journey,

in the north,
the sun's rays become less intense.

Temperatures fall.

And this triggers
a season of spectacular change.

Autumn.

And it's not only the leaves
that are changing colour.

In Northeast India,

heads are turning.

Because the one and only male
in this group of golden langurs

has never looked so good.

For most of the year,
he's creamy-white in colour.

But in the breeding season,
his coat turns a stunning gold,

making him irresistible

to the troop's six females.

These shy langurs

are becoming
increasingly endangered.

As their habitat has fragmented,

their numbers have halved
in the last 30 years.

There are only 6,500 left
in the world.

But this male is doing his best

to get those numbers rising.

And he's not the only one
feeling hot-blooded right now.

As temperatures continue to fall,

in Northern Norway,
this alpha male musk ox

prepares to breed.

He's responsible
for all the youngsters and females

in his harem.

And autumn is when it's hardest
to defend them.

To prepare for the hardship
of winter to come,

these 400kg herbivores

have gown an extra layer
of insulation

beneath their long, shaggy
outer coats.

One of the warmest natural fibres
in the world.

But for the alpha male,

there's a much more pressing
problem than the cold.

Lone males

that come here to steal his harem.

It's the alpha's job
to fight them off.

He sidesteps
to make himself look bigger.

But his rival is an equal match...

..and is not backing down.

Running head-on towards each other
at 50kph

is like driving towards
an oncoming car.

If the alpha's defeated,

he'll lose all his females.

Ten-centimetre skulls and horns

protect them
from fatal brain injury.

The challenger
is finally chased off...

..leaving the alpha free to mate

with all the females in his harem.

For this season, at least.

It's now almost 12 months

since our journey
round the sun began.

But before the Earth
comes full circle...

..the penguin chick
has one final challenge to overcome.

It's time for her to leave home.

She's now sporting
a fully-waterproof adult coat...

..having gone through
that awkward teenage stage

and shed her fluffy down.

She must now swap
the safety of her island home

for the big blue beyond.

But her path to adulthood...

..is full of killer whales.

Up ahead, less cautious penguins
take the plunge.

And their commotion
distracts the predators.

It's her chance!

She's almost through
the danger zone.

But she's been spotted.

These six-tonne killers are faster.

But only in a straight line.

The penguin may be young...

...but she's already agile enough
to get away.

Not bad for her first-ever swim.

For the next three years,

this ocean will be her home...

..until she returns
to this exact same spot

to raise a family of her own.

Our planet has now completed

its 940 million-kilometre orbit
around the sun.

And the penguin has completed
her first year of life.

But the journey doesn't end here.

As one year draws to a close,

the next is already beginning.

Across the globe,

life will continue to be shaped
by the sun's influence.

It drives seasonal changes...

..nurtures incredible diversity...

..and unites us all...

..as we journey together

through another year
on planet Earth.