'Everything on our planet is connected...
'..to our epic journey around the sun.
'Filmed in more than 60 incredible locations...
'..so far, we've shown how animals survive
'in an ever-changing landscape.
'Now... as we enter the last chapter...
'..life braces once more...
'..for what the final season can throw at it.'
If winter is the great equaliser...
..and spring is for new beginnings...
..summer a time of plenty...
..then autumn...
autumn is the season of change.
'For the families we've followed for the last nine months...'
'..change brings opportunity...'
'..but also huge challenges.'
'For many, the last three months
'of our unique annual journey around the sun
'will be their toughest yet.
'It's mid-September.
'And the deciduous forests of North America
'are staging the season's most iconic spectacle.
'This blaze of colour is a last hurrah
'triggered by a drop in temperature.
'The red pigments help the trees extract the last morsels of energy
'before they shed their leaves.
'The forest is preparing to hibernate.
'So, too, are its residents.
'For a chipmunk, it's the busiest time of year.
'He needs to stockpile enough nuts
'to last him through winter.
'Most are rotten.
'But not all.
'One oak tree is still dropping acorns.
'Fresh...
'..nutritious...
'..and plentiful.
'The only problem is...
'..they're in enemy territory.
'And chipmunks don't like to share.
'He'll need to be sneaky...
'..stealthy...
'..and tactical.
'Busted!
'Territorial males...
'..will defend their patch with extraordinary ferocity.
'The little chipmunk puts up a good fight...
'..and has some impressive moves...
'..but knows when he's beaten.
'An injury this late in the year could be risky.
'But going into winter with an empty larder could be fatal.
'Time to do or die.
'Finally, the chipmunk forces his rival to retreat
'and wins access to the tree.
'A determined chipmunk
'can gather 150 nuts a day.
'His stash is building up nicely.
'With a little more work,
'it should be enough to see him through six long months underground.
'As autumn progresses,
'life for those living in the north gets darker,
'colder and much tougher.
'The salmon season is coming to an end.
'But this grizzly bear
'is still desperately trying to catch enough fish
'to feed herself and her family.
'On average, only one in two cubs survives the first year.
'Bears can't stockpile food like chipmunks.
'Instead, they must put on enough weight
'to endure five months of hibernation without eating.
'If Mum can't provide, her cubs won't make it through.'
'A week later, the temperature plummets...
'..and the rivers on which she relies for food freeze over.
'Hopes of these bears surviving the winter
'seem bleaker than ever.
'It's -20 in Northern Canada,
'and this bear family is desperate for food.
'All the fishing rivers are locked in ice.
'But this mum knows one last place.
'Here, warmer water seeping through the bedrock
'keeps the river from freezing...
'..and offers her one last hope.
'As soon as her wet fur is exposed to the freezing air...
'..she becomes an ice bear...
'..one of a unique group of grizzlies
'who know the secrets of this isolated river.
'As long as the water keeps flowing...
'..Mum keeps fishing...
'..up to six weeks later than other bears in the region.
'A little local knowledge
'gives her cubs the best chance of surviving the long winter ahead.
'As the Northern Hemisphere continues to cool,
'hunkering down to hibernate isn't the only option.
'Many animals escape the cold by chasing the sun further south.
'At this time of year,
'billions of animals are on the move.
'From the titanic...
'..to the tiny.
'This little caterpillar
'may not seem very well-prepared for long-distance travel.
'At least not until a miracle happens.
'Squeezed into a tiny cocoon,
'his body turns to soup...
'..then slowly begins to reorganise.
'A magical transformation...
'..from leaf-eating machine
'to migratory marvel.
'The monarch butterfly.
'His wing muscles may be smaller than a grain of rice,
'but incredibly, they'll carry him 2,500 miles
'all the way from Maine...
'..to Mexico.
'Some animals are already enjoying the warmer conditions
'south of the border.
'Sardines come here to breed,
'gathering in large schools, ready to spawn.
'If they live that long.
'A 12 foot-long striped marlin.
'When its stripes begin to glow, it means it's ready to attack.
'The iridescence confuses the sardines.
'To make matters worse,
'marlin rarely hunt alone.
'One of the fastest fish in the sea,
'they can accelerate to 50mph.
'They're so fast,
'they need a special muscle
'to heat their tennis-ball-sized eyeballs
'to sharpen their vision
'and quicken their reaction times.
'The thrashing attracts even more trouble.
'Sea lions join the hunt.
'Up above, pelicans strike from the air.
'Now the sardines are trapped,
'the marlin can clean up.
'Swiping their rapier-like bills
'helps to pick off fish from the school
'and guide them into their mouths.
'Sometimes, they even make a direct hit.
'A school of sardines the size of a house
'is demolished in minutes.
'A month after the equinox,
'the sun's influence has moved far enough below the equator
'for it to be felt deep into the Southern Hemisphere.
'Down here, it's warming up.'
'The change in season
'brings relief for the penguin chick.'
'But also new challenges.
'For ten months, her parents provided all the food she needed.
'But now they've left her...
'..for good.
'At three feet tall, she may be fully-grown,
'but still just a teenager in penguin years.
'And going through a bit of an awkward stage.
'Down feathers may keep her warm, but they won't keep her dry.
'So, before she can join the others at sea,
'she needs to lose them for something more mature.
'At least her friends are suffering the same thing.'
'It's just a phase.
'A couple of weeks later,
'all that fluff is replaced with a sleek coat
'of tightly-packed, waterproof feathers.
'But even a fully-fledged penguin
'can be a little ungainly
'until it reaches the sea.'
'It's a long walk down to the beach.
'Especially when trying to tiptoe past slumbering giants...'
'..without waking them.'
'A three-tonne elephant seal
'could easily crush the little penguin.'
'Thankfully, just a lot of hot air.
'But she now faces her toughest challenge yet...
'..to head out to sea and the unknown.
'Killer whales patrol Marion Island.
'And fledglings make especially easy targets.
'If this little penguin is to avoid starvation...
'..sooner or later, she'll have to take the plunge.
'At this time of year,
'the sun's rays are at their most direct
'over Southern Africa.
'Here, the dry season
'has reached maximum intensity.'
'At nine months old...
'..the most important lesson this young elephant needs to learn
'is how to keep cool.
'Dirt works as sunblock.
'He's experienced dry weather before.
'But this is a drought.
'Our changing climate
'means that rainfall has become more unpredictable.
'Elephants normally drink 200 litres of water every day,
'enough to fill a bathtub.
'Now they must dig deep
'just to get a mouthful.
'It's not enough.
'The calf's two-year-old cousin is struggling.
'If he can't catch up with the rest of the herd...
'..he'll become a target.
'The rains that the elephants so desperately need
'are still 2,000 miles away in the Northern Hemisphere.'
'For the last four months,
'Northeast India has been the wettest place on Earth.'
'Water is a life-giver.
'But months of monsoon can really drag on.
'When the skies finally clear...
'..new visitors arrive.
'This Amur falcon
'has flown a staggering 2,000 miles from Russia.
'Halfway on her mammoth migration to South Africa,
'this is the perfect place for a pit stop.
'Just after the rains, termites take to the air.
'Amur falcons are usually solitary.
'But here, they gather in hundreds of thousands
'for this flying feast.'
'It's the greatest gathering of birds of prey
'found anywhere on Earth.
'By the end of October,
'the sun's intensity has moved further south,
'pulling the tropical rain band that was lodged over India
'across the equator and into the Southern Hemisphere.'
'Eventually, the rains fall
'on a tiny island
'in the middle of the Indian Ocean...
'..waking its most famous residents.
'Red crabs.
'40 million of them.
'They're all heading down to the beach to spawn...
'..clogging up the roads,
'bringing the island to a standstill.
'They wait for months underground
'for the rains to arrive.
'Now it's humid enough
'to breathe in the open air.
'But when the sun re-emerges
'and begins to dry the forest...
'..the race is on.
'They need to reach the sea
'before they dehydrate.
'The females that have mated, like this one,
'carry a precious load.
'Tens of thousands of tiny eggs.
'But many never survive the journey.
'Coconut crabs are ten times her size...
'..and they hunt red crabs.
'And not all of the island's roads are closed.
'She's made it.
'But before she can release her eggs into the sea,
'she must wait for the tide to turn.
'Right now, it's still coming in.
'A few hours later,
'conditions are perfect.
'Now joined by a crowd,
'she enters the shallows.
'Her eggs hatch on contact with water.
'And with a little shake,
'she casts her tiny babies out to sea
'on the outgoing tide.
'The same tropical rain band that passes over Christmas Island
'is now rolling further down into Southern Africa.
'For the elephant herd,
'it can't come soon enough.
'It's now desperately dry.
'But they sense change in the air.
'Using their trunks like a nasal periscope,
'they can sense water 12 miles away.'
'Nightfall brings respite from the heat.'
'But elephants have poor night vision.
'Using the latest camera technology, however...
'..we can see in the dark...
'..much like the lions.'
'The calf knows to stay close.
'But some can't keep up.
'The weakened cousin and his mother
'are lost in the dark.'
'Oblivious to what's happening behind them,
'the yearling and the rest of the herd move on.'
'She won't leave her baby.'
'Her only hope is to guide him away.
'But she's totally outnumbered.'
'The already weak calf
'is now badly injured.
'All the lions need to do is wait.
'By morning,
'her calf has stopped breathing.'
'Elephants are one of the few animals that grieve.'
'They need time to mourn.'
'Calm water in a secluded cove
'seems a good place for the king penguin fledgling
'to take her first-ever swim.
'But nowhere is totally safe.
'She needs to head out to sea
'to find food.
'It's now or never.
'The sooner she reaches the open ocean,
'the sooner she'll be safe.
'Naive to danger...'
'..her hesitation could be fatal.
'Just in time,
'the instinct to escape kicks in.
'A king penguin can't outpace a killer whale.
'But it can outmanoeuvre it.
'Thanks to her agility,
'she finally reaches deeper waters
'and joins the rest of the flock
'to go fishing far out to sea.
'She won't return to land
'for a whole year.
'The monarch butterfly
'is on the final stretch
'of its 2,500-mile journey.
'His destination
'is just around the corner.
'The fact that something so small, so delicate
'has made it all this way
'is nothing short of a miracle.'
Just think what this little butterfly
has flown through to be here.
He's crossed vast deserts,
he's dodged thunderous hailstorms,
he's traversed huge mountain ranges,
and crossed quite a few busy highways.
'He's not the only one to make it.
'Others have found their way here, too.'
When you're in a forest on a windy day,
you can hear the rustle of leaves, and at first,
your ears tell you that's what you're hearing now.
But no, it's the flutter of wings.
Millions and millions of pairs of wings.
'They gather here in this one high-altitude forest
'in Central Mexico
'to escape the freezing temperatures in the north
'and find sun nearer the equator.'
We know they use the sun for navigation,
but perhaps the most remarkable thing of all
is how they know to come here, to these trees.
Why these trees, of all the trees,
of all the forests in all Mexico?
And not one single one of these butterflies
has ever been here before.
'These forests are filled with monarchs every year,
'but each butterfly only lives for a few months.
'With no knowledge passed down between individuals,
'it's only some kind of miraculous, in-built impulse
'that drives them all south here to Mexico.'
He likes me.
What should I call you? Monarch of All You Survey.
Or I should call you Stephen,
after King Stephen, the monarch,
who didn't reign for very long.
God, you're so beautifully-made.
There's no part of you that isn't perfect.
Can't say the same about me.
The other thing which they didn't warn me about...
Goodbye.
..is that, like all living creatures,
they do excrete.
They urinate, and you feel little drops on your head.
I got one on my lip. I couldn't help, and I thought,
"I'll taste monarch butterfly pee."
It is very, very bitter.
Deeply unpleasant.
Nasty.
Otherwise, lovely animals.
'As the Earth nears the end of its epic journey around the sun...
'..it's remarkable to think
'that giant cosmic forces play a role
'in the tiny decisions
'that these little butterflies make every day.
'It's the same for all life on Earth.'
'In Zimbabwe, the band of rain
'that has been pulled south by the sun
'eventually arrives.
'The elephants can spread out,
'finding water holes free from predators.
'In Canada,
'the colder, shorter days
'drive the chipmunk into hiding.
'On an incoming tide,
'the crab babies have returned in their billions.
'Just in time for Christmas.
'And in the sub-Antarctic, the king penguin
'will one day return to the same beach she was born on
'to start a family of her own.'
Our annual journey around the sun is what unites us all
and creates the incredible diversity on our planet,
and great natural wonders like this.
So as another year draws to a close,
it's hard to know what the future holds
in these changing times.
But if one has had the privilege
of witnessing this magical wonder,
then one knows that we have to cherish it.
There can be surely no more spectacular way
to end a year on planet Earth.
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