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STEPHEN FRY: As a new year starts,

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a new life begins.

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After nearly two months
of careful incubation,

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this king penguin chick

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is ready to face the world.

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A world she'll soon discover

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keeps changing all the time.

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In the far south,

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the days will soon get shorter...

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..the weather will worsen.

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And this little chick
must learn to adapt

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

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In 365 days from now,

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the Earth will have come
full circle round the sun.

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As we journey through space,

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around this ball of fire,

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it fuels extraordinary change...

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..creating the seasons
that alter the worlds

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of almost every animal
on our planet.

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Determining when they move...

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..fight...

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..and when they raise a family.

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In this programme...

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..we'll see how animals
use incredible strategies

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to cope with
their ever-changing world...

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..as we travel full circle
through every season

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in a year on planet Earth.

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Nowhere in the Northern Hemisphere

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is winter as extreme

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or felt more harshly

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than in the High Arctic.

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This polar bear mum and cub

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

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A night that will last
another 45 days.

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At the start of the year,

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the Northern Hemisphere is tilted

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

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It's cold and dark.

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Food is thin on the ground.

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And not everyone will survive
long enough to see the sun

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when it eventually rises again.

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But even in these darkest months,

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the sun's presence
is still evident.

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

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they create a light show

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that's truly out of this world.

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The northern lights.

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This spectacle

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is hundreds of kilometres
above the Earth's surface.

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

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In February,

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the Northern Hemisphere
begins to face towards the sun.

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Days start to get longer
and warmer...

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..and winter
in these wooded valleys

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begins to lose its grip.

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But until it's gone for good,

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food for this red squirrel
is hard to come by.

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Squirrels don't hibernate.

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So, to get through winter,

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he relies on forward planning

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and a very good memory.

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

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..carefully grouped
according to type.

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Now he must remember
where he left them.

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To help him, his hippocampus,

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the part of the brain
concerned with memory,

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has expanded.

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It's the same part of the brain

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that's first affected
with Alzheimer's,

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and researchers are hoping
we can learn more about it

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from studying squirrels.

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Whatever he's doing, it's working.

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Erm, mostly.

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

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In late winter,

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most squirrels' stashes are empty,

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so thieves
are always on the lookout...

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

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Finally, he can finish
his breakfast in peace.

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In these bitterly cold months,

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competition for food
is at its fiercest.

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Nowhere more so
than on the east coast of Japan.

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Steller's sea eagles

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are one of the most powerful raptors
in the world.

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And with a wingspan
of over two metres,

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one of the largest.

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Now that much of the sea
is frozen solid,

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these big bruisers

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resort to underhand
means to get fish.

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SCREECHING

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SCREECHING

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Harmony will only be restored

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when the temperature rises,

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sea ice melts

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and fishing gets easier again.

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

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As days in the Northern Hemisphere

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continue to get longer and warmer...

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

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The king penguin chick is
now four months old,

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and beginning to spread her wings.

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To adapt to the cold,

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

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and is already
50 times her birth weight...

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

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To keep their not-so-little one fed,

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Mum and Dad
are falling over backwards

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with constant trips to the sea.

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

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But the chick's months
of being waited on

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are coming to and end.

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As the days continue to get shorter
this far south,

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the water is getting colder.

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Currents are shifting

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and prime feeding areas
are moving further away.

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

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and the chick
will be left to fend for herself.

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As life in the Southern Hemisphere
gets harder,

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in the Norther Hemisphere,
it's getting easier.

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Spring is in full flow.

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Day length
is now longer than night...

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..and solar energy
reaching the ground has increased.

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A splash of rain,

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and the north transforms
into a sea of colour.

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New growth.

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New life.

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And new opportunities.

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On the largest, highest plateau
in the world,

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the locals
have never had it so good.

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Thanks to the new spring growth,

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these pikas are having a feast...

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..and a baby boom.

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

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SQUEAK

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This season
is enough to put a very big smile

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on one hungry resident's face.

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The Tibetan fox
has the widest gape of any fox.

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All the better to eat pika with.

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SQUEAK

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

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SQUEAK

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When she can catch one.

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Pikas have hundreds of boltholes,

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

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SQUEAK

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SQUEAKING

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SQUEAK

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Teamwork keeps them one step ahead.

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SQUEAK

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SQUEAK

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But not everyone's paying attention.

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The fox hunts
every morning and evening,

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not just for her,

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but for her three
eight-week-old cubs.

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Usually the father helps
to feed his cubs.

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But he has disappeared,

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leaving Mum
to bring them up on her own.

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Not easy.

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

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the cubs have a good chance
of making it.

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Across the Northern Hemisphere,

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this is the time to start a family.

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Though one animal
is a little slow to get going.

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Up here at 2,000 metres,

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it can feel more like winter.

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But at last,

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the sun has pushed the temperature
up to five degrees,

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making all the difference
to one cold-blooded creature.

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A common European frog.

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He's been hibernating
in an underground stream

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for over six months.

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Now he's desperate to get a mate.

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

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So, he had better hop to it.

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He needs to move in daylight

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to make the most
of the sun's warmth.

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But his muscles are slow to warm up.

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Hot-blooded in passion,

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cold-blooded in body.

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A frustrating combination.

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Other males have emerged.

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The first to the pond

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will have the pick of the females.

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

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The others are pairing up.

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

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As the sun's powerful rays
beam down,

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slowly his body
starts to warm again.

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The last five metres

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takes all he's got.

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He may be late...

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

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It's not just his world

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that's hotting up.

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We are now halfway through
our annual orbit...

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

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Summer has begun.

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As we enter
the hottest season of the year,

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life prepares to adapt again
to the changes it brings.

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For some, this is a time to feast

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and a chance to store energy...

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..as food becomes more abundant.

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Nowhere more so
than in Southwest China.

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Here, the landscape is dominated

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by the fastest-growing plant
on the planet.

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Bamboo.

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

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Giving one animal
the vital chance it needs

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to pile on the pounds.

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The giant panda.

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

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But now she can eat
as many nutritious shoots

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as she can manage.

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As her diet changes,

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so too do her gut bacteria,

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helping her lay down fat
for leaner months ahead.

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While she tucks in,

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

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

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The cub will be independent
in just five months,

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and is starting to test
how it feels.

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Although shoots
are higher quality than leaves,

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

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to get enough nutrients.

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

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

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

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Her meal could stretch on
for 14 hours.

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

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he can afford to take it easy.

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Mum has four months to fatten up
before winter.

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But some things in life

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are even more important than bamboo.

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PANDA WHINNIES

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WHINNIES

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This is the pair's
last summer together.

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WHINNIES

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

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Until then, Mum will do all she can

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to help him
stand on his own four feet.

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Summer here
is the wettest time of year.

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Over 70cm of rain

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can fall in a single month.

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While in the south,

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in Australia's Northern Territory,

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there is serious drought.

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

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Months without rain,

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and dry grasslands,
are like a tinderbox.

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00:27:14,960 --> 00:27:17,960
It only takes a tiny spark

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to set
these flammable plants alight.

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Add wind...
and the woodland is ablaze.

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Those that can flee for their lives.

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But not everyone has the nerve.

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Or the know-how.

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These hooded parrot chicks

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are one month old.

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

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SCREECHING

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As well as the flames,

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00:28:09,960 --> 00:28:13,160
deadly fire hawks
are on the prowl...

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..looking for creatures
flushed out by the fire.

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The chicks have missed their chance.

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00:28:48,960 --> 00:28:54,640
Bush fires kill billions of animals
every year...

265
00:28:59,960 --> 00:29:04,960
..which is why the chicks' parents
have planned ahead.

266
00:29:13,960 --> 00:29:16,480
The home they've chosen,

267
00:29:16,480 --> 00:29:19,960
this termite mound
made of sand and clay,

268
00:29:19,960 --> 00:29:21,960
is fireproof.

269
00:29:30,480 --> 00:29:35,960
And this scorched ground is,
in fact, what the chicks need

270
00:29:35,960 --> 00:29:37,960
to tempt them out.

271
00:29:41,640 --> 00:29:45,160
The grasses
have dropped their seeds,

272
00:29:45,160 --> 00:29:50,800
just in time for the parrots'
first meal out as a family.

273
00:29:53,960 --> 00:29:56,960
In less than a week,
the chicks will leave home...

274
00:29:58,960 --> 00:30:01,960
..and the parents
will be empty-nesters

275
00:30:01,960 --> 00:30:04,960
until they breed again next year.

276
00:30:09,960 --> 00:30:12,960
The winds that gave fuel
to these fires

277
00:30:12,960 --> 00:30:15,960
are the south-easterly trade winds.

278
00:30:16,960 --> 00:30:18,960
Vast currents of air

279
00:30:18,960 --> 00:30:22,640
that are carried west
as the Earth rotates,

280
00:30:22,640 --> 00:30:25,960
and pulled north
towards the heat of the sun.

281
00:30:28,960 --> 00:30:31,960
As they sweep over the Indian Ocean,

282
00:30:31,960 --> 00:30:34,960
they change the direction
of the currents beneath...

283
00:30:36,960 --> 00:30:38,800
..creating conditions

284
00:30:38,800 --> 00:30:43,000
for the sea's most important
food source to thrive.

285
00:30:44,640 --> 00:30:46,480
Plankton.

286
00:30:46,480 --> 00:30:49,480
Microscopic plants and animals.

287
00:30:50,480 --> 00:30:54,480
The staple food
of almost every marine ecosystem.

288
00:31:00,960 --> 00:31:03,160
The miniature plants

289
00:31:03,160 --> 00:31:06,960
produce over half of the oxygen
that we breathe.

290
00:31:18,320 --> 00:31:20,960
On this coral reef,

291
00:31:20,960 --> 00:31:22,960
they feed fish.

292
00:31:24,480 --> 00:31:25,960
From the smallest...

293
00:31:29,960 --> 00:31:30,960
..to the largest.

294
00:31:46,960 --> 00:31:49,800
Reef manta rays,

295
00:31:49,800 --> 00:31:51,960
with a four-metre wingspan,

296
00:31:51,960 --> 00:31:55,960
make a seasonal migration
around these atolls,

297
00:31:55,960 --> 00:31:57,960
following the plankton.

298
00:32:16,960 --> 00:32:21,960
Swimming one behind the other,
they catch plankton

299
00:32:21,960 --> 00:32:24,960
from the slipstream
of the manta in front.

300
00:32:26,960 --> 00:32:29,960
And as the leader turns,

301
00:32:29,960 --> 00:32:33,000
they form what's known as
a feeding cyclone...

302
00:32:34,960 --> 00:32:37,960
..channelling
the tiny plants and animals

303
00:32:37,960 --> 00:32:40,800
into their super-sized mouths.

304
00:32:46,960 --> 00:32:49,960
These gentle giants

305
00:32:49,960 --> 00:32:53,960
need a constant flow of water
to breathe.

306
00:32:56,960 --> 00:32:59,960
So, with their wing-like fins,

307
00:32:59,960 --> 00:33:02,480
these birds of the sea

308
00:33:02,480 --> 00:33:04,960
are always on the move...

309
00:33:05,960 --> 00:33:09,960
..returning to this bay
year after year

310
00:33:09,960 --> 00:33:13,320
in numbers up to 5,000 strong

311
00:33:13,320 --> 00:33:17,960
for the biggest manta feeding
aggregation in the world.

312
00:33:23,960 --> 00:33:28,480
While the mantas
are free to follow their food...

313
00:33:29,960 --> 00:33:31,960
..in the same ocean,

314
00:33:31,960 --> 00:33:34,640
6,000km south...

315
00:33:35,960 --> 00:33:40,000
..the king penguin chick
is close to starving.

316
00:33:56,960 --> 00:33:59,480
It's been four months

317
00:33:59,480 --> 00:34:02,960
since her parents left
to find food,

318
00:34:02,960 --> 00:34:06,960
and she hasn't eaten
in all that time.

319
00:34:16,960 --> 00:34:20,960
Most parents have returned
with bellies full of fish.

320
00:34:25,960 --> 00:34:29,320
But hers
have yet to make an appearance.

321
00:34:35,960 --> 00:34:37,960
In response to fasting,

322
00:34:37,960 --> 00:34:41,960
her metabolism and growth rate
have slowed.

323
00:34:43,960 --> 00:34:45,960
Beneath all that fluff,

324
00:34:45,960 --> 00:34:49,960
she's lost 70% of her body weight...

325
00:34:50,960 --> 00:34:54,160
..and is now just 4kg.

326
00:34:58,960 --> 00:35:02,960
King penguin chicks
can survive without food

327
00:35:02,960 --> 00:35:04,960
longer than any other bird.

328
00:35:07,960 --> 00:35:13,960
But each year, half starve to death
waiting for their parents to return.

329
00:35:34,960 --> 00:35:39,960
But her mum and dad
aren't going to let that happen.

330
00:35:41,960 --> 00:35:45,960
They arrive in the nick of time.

331
00:36:03,960 --> 00:36:05,960
With her parents' help,

332
00:36:05,960 --> 00:36:09,800
this chick
has made it to eight months.

333
00:36:11,960 --> 00:36:12,960
The time it's taken

334
00:36:12,960 --> 00:36:17,960
for our planet to journey
two thirds of its way round the sun.

335
00:36:22,960 --> 00:36:24,960
By the time it's gone full circle,

336
00:36:24,960 --> 00:36:28,640
this chick must be ready
to go it alone.

337
00:36:44,160 --> 00:36:48,320
As we enter
the final leg of our journey,

338
00:36:48,320 --> 00:36:53,960
in the north,
the sun's rays become less intense.

339
00:36:55,960 --> 00:36:57,960
Temperatures fall.

340
00:36:58,960 --> 00:37:02,960
And this triggers
a season of spectacular change.

341
00:37:10,960 --> 00:37:12,000
Autumn.

342
00:37:18,320 --> 00:37:21,960
And it's not only the leaves
that are changing colour.

343
00:37:24,960 --> 00:37:26,960
In Northeast India,

344
00:37:26,960 --> 00:37:29,160
heads are turning.

345
00:37:38,960 --> 00:37:44,960
Because the one and only male
in this group of golden langurs

346
00:37:44,960 --> 00:37:47,960
has never looked so good.

347
00:37:50,960 --> 00:37:54,960
For most of the year,
he's creamy-white in colour.

348
00:37:54,960 --> 00:38:00,960
But in the breeding season,
his coat turns a stunning gold,

349
00:38:00,960 --> 00:38:02,960
making him irresistible

350
00:38:02,960 --> 00:38:05,960
to the troop's six females.

351
00:38:11,960 --> 00:38:13,960
These shy langurs

352
00:38:13,960 --> 00:38:15,960
are becoming
increasingly endangered.

353
00:38:17,960 --> 00:38:20,960
As their habitat has fragmented,

354
00:38:20,960 --> 00:38:25,800
their numbers have halved
in the last 30 years.

355
00:38:29,960 --> 00:38:33,960
There are only 6,500 left
in the world.

356
00:38:41,640 --> 00:38:43,960
But this male is doing his best

357
00:38:43,960 --> 00:38:45,960
to get those numbers rising.

358
00:38:53,960 --> 00:38:57,960
And he's not the only one
feeling hot-blooded right now.

359
00:39:04,960 --> 00:39:07,960
As temperatures continue to fall,

360
00:39:07,960 --> 00:39:12,960
in Northern Norway,
this alpha male musk ox

361
00:39:12,960 --> 00:39:15,480
prepares to breed.

362
00:39:18,960 --> 00:39:23,960
He's responsible
for all the youngsters and females

363
00:39:23,960 --> 00:39:24,960
in his harem.

364
00:39:24,960 --> 00:39:28,960
And autumn is when it's hardest
to defend them.

365
00:39:44,960 --> 00:39:48,960
To prepare for the hardship
of winter to come,

366
00:39:48,960 --> 00:39:52,960
these 400kg herbivores

367
00:39:52,960 --> 00:39:55,960
have gown an extra layer
of insulation

368
00:39:55,960 --> 00:39:58,960
beneath their long, shaggy
outer coats.

369
00:39:58,960 --> 00:40:03,960
One of the warmest natural fibres
in the world.

370
00:40:09,960 --> 00:40:12,000
But for the alpha male,

371
00:40:12,000 --> 00:40:15,960
there's a much more pressing
problem than the cold.

372
00:40:19,960 --> 00:40:22,000
GRUNTING

373
00:40:22,000 --> 00:40:24,800
Lone males

374
00:40:24,800 --> 00:40:28,960
that come here to steal his harem.

375
00:40:32,960 --> 00:40:36,960
It's the alpha's job
to fight them off.

376
00:40:40,640 --> 00:40:43,960
He sidesteps
to make himself look bigger.

377
00:40:46,960 --> 00:40:49,480
But his rival is an equal match...

378
00:40:51,960 --> 00:40:54,960
..and is not backing down.

379
00:41:06,480 --> 00:41:11,960
Running head-on towards each other
at 50kph

380
00:41:11,960 --> 00:41:14,960
is like driving towards
an oncoming car.

381
00:41:24,960 --> 00:41:26,960
If the alpha's defeated,

382
00:41:26,960 --> 00:41:29,960
he'll lose all his females.

383
00:41:32,160 --> 00:41:35,960
Ten-centimetre skulls and horns

384
00:41:35,960 --> 00:41:39,160
protect them
from fatal brain injury.

385
00:41:46,320 --> 00:41:48,960
GRUNTING

386
00:41:55,000 --> 00:41:58,480
The challenger
is finally chased off...

387
00:42:00,960 --> 00:42:03,960
..leaving the alpha free to mate

388
00:42:03,960 --> 00:42:06,960
with all the females in his harem.

389
00:42:08,960 --> 00:42:10,960
For this season, at least.

390
00:42:15,960 --> 00:42:18,960
It's now almost 12 months

391
00:42:18,960 --> 00:42:22,960
since our journey
round the sun began.

392
00:42:25,960 --> 00:42:28,960
But before the Earth
comes full circle...

393
00:42:30,000 --> 00:42:34,960
..the penguin chick
has one final challenge to overcome.

394
00:42:38,960 --> 00:42:41,960
It's time for her to leave home.

395
00:42:44,960 --> 00:42:48,960
She's now sporting
a fully-waterproof adult coat...

396
00:42:50,960 --> 00:42:54,960
..having gone through
that awkward teenage stage

397
00:42:54,960 --> 00:42:56,960
and shed her fluffy down.

398
00:43:03,160 --> 00:43:04,960
SQUAWK

399
00:43:06,480 --> 00:43:09,960
She must now swap
the safety of her island home

400
00:43:09,960 --> 00:43:12,960
for the big blue beyond.

401
00:43:19,960 --> 00:43:22,640
But her path to adulthood...

402
00:43:25,320 --> 00:43:27,960
..is full of killer whales.

403
00:43:39,960 --> 00:43:45,960
Up ahead, less cautious penguins
take the plunge.

404
00:43:50,960 --> 00:43:54,960
And their commotion
distracts the predators.

405
00:43:59,960 --> 00:44:01,960
It's her chance!

406
00:44:10,960 --> 00:44:13,960
She's almost through
the danger zone.

407
00:44:20,960 --> 00:44:22,960
But she's been spotted.

408
00:44:22,960 --> 00:44:26,960
These six-tonne killers are faster.

409
00:44:35,960 --> 00:44:38,960
But only in a straight line.

410
00:44:45,960 --> 00:44:47,960
The penguin may be young...

411
00:44:52,960 --> 00:44:55,960
...but she's already agile enough
to get away.

412
00:44:59,960 --> 00:45:03,960
Not bad for her first-ever swim.

413
00:45:09,000 --> 00:45:11,960
For the next three years,

414
00:45:11,960 --> 00:45:15,960
this ocean will be her home...

415
00:45:16,960 --> 00:45:21,960
..until she returns
to this exact same spot

416
00:45:21,960 --> 00:45:24,160
to raise a family of her own.

417
00:45:31,480 --> 00:45:34,800
Our planet has now completed

418
00:45:34,800 --> 00:45:39,960
its 940 million-kilometre orbit
around the sun.

419
00:45:41,480 --> 00:45:46,960
And the penguin has completed
her first year of life.

420
00:45:46,960 --> 00:45:51,000
But the journey doesn't end here.

421
00:45:51,000 --> 00:45:55,960
As one year draws to a close,

422
00:45:55,960 --> 00:45:59,320
the next is already beginning.

423
00:46:00,960 --> 00:46:02,960
Across the globe,

424
00:46:02,960 --> 00:46:07,960
life will continue to be shaped
by the sun's influence.

425
00:46:11,000 --> 00:46:13,960
It drives seasonal changes...

426
00:46:14,960 --> 00:46:17,960
..nurtures incredible diversity...

427
00:46:18,960 --> 00:46:20,480
..and unites us all...

428
00:46:23,960 --> 00:46:25,960
..as we journey together

429
00:46:25,960 --> 00:46:30,960
through another year
on planet Earth.

430
00:46:38,960 --> 00:46:40,960
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