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.
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