Every year, spectacular seasons transform our planet.
They're the driving force of all life on Earth...
..bringing opportunities and huge challenges.
Spring bursts with new life...
..but it's a race to grab fleeting chances.
Summer brings glorious abundance,
but the heat can push animals to their limits.
Autumn is nature's great gold rush...
..but competition is fierce.
Winter creates a frozen wonderland...
..but only the most resourceful will survive.
In every corner of the planet,
animals rise to overcome the seemingly impossible...
..to thrive against the odds...
..as the seasons create the greatest shows on Earth.
Autumn - the season when nature puts on its most flamboyant displays.
It's as generous with its bounty as it is with its beauty.
But the good times won't last. The clock is ticking.
For many animals, it's their last chance to get ready before the cold
closes in.
And the first challenge is to fatten up and fill the larder.
The great Northwoods of North America...
..26 million acres of forest.
In autumn, as the days get shorter and the light fades...
..the trees go through a stunning transformation.
They draw all the goodness out of their leaves...
..and then they let them go.
In a Canadian forest, along with the falling leaves,
the trees are releasing a seasonal feast...
..acorns.
For a chipmunk, it's manna from heaven.
He's stockpiling acorns for winter,
and the quickest way to carry them is cramming as many into his mouth
as possible.
He can get six in, at a push.
There's no time to waste.
Within a couple of weeks, the forest could be under half a metre of snow.
He needs to gather at least 100 acorns
to see him through the lean months ahead.
A chipmunk keeps his store of nuts hidden away in his winter burrow,
a metre underground, and for good reason.
There are thieves around.
As soon as the coast is clear,
a light-fingered neighbour takes his chance.
With winter coming, pinching someone else's supplies
is a serious business.
The precious pile is starting to look very thin...
..and that could mean starvation for the rightful owner.
The honest chipmunk is still slogging away, gathering acorns...
..but, when he returns, he's in for a shock -
there's almost nothing left of the store.
Retribution is swift.
CHATTERING AND SQUEAKING
With the thief sent packing, it's straight back to work.
When winter comes, every nut will count.
Autumn's abundance will be a lifeline.
Chipmunks aren't the only ones getting ready.
In Yellowstone in North America, the trees are turning gold.
This moose has spent the summer fattening up on greenery.
She'll stand up to her knees in water for hours at a time,
feasting on pond weed.
When there's good food underwater, a long nose comes in useful,
and she can close her huge nostrils to keep the water out.
But the good times are coming to an end.
Once winter takes hold, the lake will freeze
and she'll be reduced to eating bare twigs from trees.
So she's packing away more than 10kg of greens a day...
..while she still can.
But there's another animal in this neck of the woods with a more
radical approach to gathering food.
TREE CRACKS
A beaver - the only animal capable of chopping down an entire tree.
He'll fell a cottonwood in a couple of hours, using only his teeth.
He chews away just enough to make it unstable...
..and lets the wind do the rest.
TREE CRACKS
And then the real hard work starts.
He chops the branches into manageable chunks to eat later...
..and the best way to get them back home is by water.
So he and his partner have built a network of waterways
especially for the job.
While he's busy bringing in the supplies,
she's doing some maintenance to the dam.
In a couple of weeks, their canal system will freeze up,
so they're gathering food now, while they still can.
They'll survive all winter eating nothing but these branches.
He drags them one at a time to his underwater larder.
He might bring in several hundred of them...
..so even when the pond has frozen over,
there will still be plenty of food.
All this industry has caught the attention of a young moose.
A beaver's pond could be the perfect place to find something to eat.
But he can forget that idea.
This is no time for sharing.
Autumn might be the season of glorious colour,
but it can be a wild time, too.
THUNDER RUMBLES
As the temperature starts to fall,
changes in air pressure cause massive storms.
THUNDER RUMBLES
In the river in southern Alaska,
the storms are about to bring in one of autumn's biggest feasts,
and on the river bank, a hungry crowd is gathering...
..grizzly bears.
If they're going to survive the coming winter,
they need to build up their weight by more than half in just a few weeks.
It's the wettest time of the year
but all this rain is good news for the bears.
It's flooding the rivers...
..opening the way for millions of fish to start heading their way.
Pacific salmon.
They've travelled thousands of miles of sea and now they're swimming
inland to spawn.
They're returning to the very rivers where they were born.
And the bears are lining up to meet them.
They're gathering at a waterfall.
They know that the salmon must pass through this bottleneck in the river.
It will be the best fishing for miles around.
BEARS GRUNT
The biggest males start to fight over the prime spots.
BEARS ROAR
The salmon are starting to collect in a whirlpool at the bottom of
the falls.
With one almighty push, the first fish starts its ascent.
It uses its whole body to leap more than two metres in the air...
..and if it's lucky, past the waiting bears.
But eventually, the migration hits its peak.
There are so many salmon, the bears can hardly miss.
A big male bear can catch as many as 30 fish a day.
But it's not always as easy as it looks.
This is a tough neighbourhood.
A female with three young cubs nervously approaches the river.
She's desperate to fish, but these big males could attack her family...
BEARS ROAR
..so it's dangerous.
BEARS ROAR
After a long summer nursing three cubs, she's skin and bone.
Unless she can eat soon, she'll struggle to get them through winter.
The big males carry on bingeing...
..but one by one, they haul themselves out of the river for an afternoon nap.
They're so full, they can hardly move.
It's the young mother's big chance.
She climbs to the top of the falls, but she'll have to be quick.
SHE GROWLS
Finally!
The salmon run is vital to every bear on the river.
They'll sleep for six months, all through the bitter Alaskan winter...
..so the fat they lay down now will help guarantee
their survival.
If this young mother can keep fishing...
..she'll give her family the best chance of making it through till spring.
But not everywhere offers such rich autumn pickings.
For animals across the planet, sometimes, the only option is to leave home
and look for better times elsewhere.
In North America every autumn,
hundreds of pronghorn trek across Yellowstone...
..to escape the advancing snow.
They leave their summer pastures and race to the safety of the lowlands,
where they can graze all winter.
In the Arctic, birds that came here in spring are starting to make
an exit.
The seas have provided a bounty all summer, but as autumn creeps in,
food is getting harder to find.
The bonanza is over.
Hundreds of thousands of birds are heading south.
SQUAWKING
Snow geese spend the short summer in the Canadian Arctic,
raising their families,
but in autumn, they travel 3,000 miles south
to the warmth of the Gulf of Mexico.
The birds fly together in enormous flocks.
There may be more than five million of them,
all making this vast round trip.
But for some animals, these journeys are fraught with danger.
On the Norwegian island of Svalbard,
100,000 Brunnich's guillemots have been here since spring,
nesting on the safety of the sea cliffs.
Now their food's running out
and it's time for these young families to go.
But these parents face the worst possible mission.
SQUAWKING
Each pair have one precious chick
and they've spent all summer looking after it.
Now they must persuade it to jump off the cliff, down to the sea.
It's a drop of 150 metres.
The chicks are only three weeks old...
..and they can't fly properly.
It's a terrifying leap of faith.
And there's worse.
There's a family of hungry Arctic foxes waiting on the beach.
The chicks must make it all the way to the sea without touching land.
The first dad encourages his chick over the edge.
Not far enough.
He makes a desperate dash for the sea.
FOX GROWLS
CHICK SQUEAKS
The next family step up to take their turn.
Anxious to save his offspring from the same fate,
his dad goes with him.
But they both fall short.
So close and yet so far.
FOX BARKS
A third family has witnessed the grim fate of the neighbours,
but there's no other way down.
SPLASHING
It may not be the most graceful landing, but they're all down safe.
When parents fly with their chicks,
they have a much better chance of survival.
THEY CHIRP
But this is only the start of their journey.
Now they have to travel south to the coast of Greenland,
where they will spend the winter.
And because they're not strong enough to fly,
the chicks are going to have to swim there...
..and it's 600 miles.
But Mum and Dad will be with them all the way.
Even when you can fly, these autumn journeys are an enormous challenge.
In the skies above Central Asia,
it's the start of one of the toughest migrations on the planet.
THEY SQUAWK
Demoiselle cranes.
They've spent the summer in Mongolia and Kazakhstan, but now winter is
breathing down their necks, so they're flying south to India.
But first, they must cross the world's highest mountain range,
the Himalayas.
In places, these peaks tower five miles high.
The cranes can't go round them
because this mountain range spans five countries.
They have to find a way through.
And to make things worse,
autumn brings treacherous storms to this part of the world.
The cranes gain height, trying to break through the clouds,
but strong headwinds force them back.
They're beaten, for now...
..so they set up camp for the night.
SQUAWKING
But they dare not linger.
There'll be more storms on the way.
SQUAWKING
At dawn, there's a window of clear weather.
SQUAWKING
It's now or never.
But to get any further, the cranes must cross Sniper Alley.
The golden eagles that live here have been expecting them.
The eagles know the cranes will be coming this way in autumn.
Normally, they'd be too fast to catch...
..but, right now, they're flying tired...
..and the eagles work in pairs.
One eagle picks out a young bird and sets up an ambush.
BIRD SQUAWKS
He drives it into the talons of his partner.
The exhausted crane never stood a chance.
One man down, the rest of the flock pushes on.
They use rising columns of air to help them gain height.
They may reach altitudes of 26,000 feet.
And finally, they're across this vast mountain barrier and heading
south towards India.
Many of them won't make it, but this monumental journey is the only way
to stay ahead of a brutal winter.
They'll fly a distance of more than 1,000 miles and, in spring,
they'll fly all the way back.
For another animal, autumn starts a migration
of a totally different kind...
..and it happens under the sea.
The oceans cool more slowly than the land,
but as the temperature starts to change,
it triggers an unusual autumn spectacle.
In the Southern Ocean of South Australia,
there's a big crowd starting to gather.
Giant spider crabs are marching in unison across the sea floor.
They spend most of the year offshore...
..but, in the autumn, these big orange crabs head to the shallows.
They're getting ready to moult.
They've outgrown their shells and they need to grow a new one.
It can take them up to an hour to crack open their old armour plating
and wriggle out.
But it takes a couple of weeks for their new shells to develop...
..and waiting naked on the sea floor...
..is dangerous.
A stingray.
The crabs scatter in a panic.
There may be 250,000 to choose from, but the ray is particular.
The softer the crabs, the easier they are to swallow.
But the ray barely makes a dent in the population.
There's safety in numbers.
And with so many crabs gathered together,
some take the opportunity to look for a partner.
With the party over,
the crabs step over the discarded remains of their old wardrobe
and head back to the deep.
For lots of animals, autumn is the season for finding a mate.
But it's an intense time of year.
And with winter round the corner,
the search for a partner is full of challenges.
Only the toughest will succeed.
Male wild ass, fuelled with testosterone,
tear up the Tibetan plains as they compete for mares.
Timing is critical.
They need to mate now so their foals will be born next summer,
when there is plenty to eat.
Off the coast of Britain, grey seal bull fights are a bloody affair.
Only the biggest and bravest will get to breed...
..and he'll mate with every female on the beach.
In North America, male elk live quiet lives until autumn,
when they come together for the rut.
They grow a new set of antlers every year,
weighing almost 20kg.
The bigger the antlers, the stronger the bull.
ELK GRUNTS
But for one animal, the battle to breed is not only about brute force,
it's also about technique.
Patagonia, South America.
Autumn is approaching
and a male Darwin's beetle is looking for a partner.
His success will be down to the size of his jaws...
..and how he uses them.
He heads off to the forest to start his search.
The females will be in the trees,
probably feeding somewhere on the trunk.
They should be easy enough to find.
But when the trees are more than 25 metres tall,
it's a long way to climb.
There she is.
Unfortunately for him,
all the other males in the neighbourhood are also after her.
He has no choice but to fight them off.
But it's not just about strength.
It's about...
grappling.
He reaches over the rival's head and hooks his enormous jaws under
his wing covers.
He gets a grip,
lifts...
..and chucks.
He climbs onwards.
There are other males standing in his way,
but nothing will stop him now.
They meet at last.
She doesn't appear to be totally smitten.
But she finally allows him to wrap his great big jaws around her...
..and they get intimate.
But then,
he throws HER out of the tree.
Beetle armour is tough and, luckily,
she's just where she needs to be to lay her eggs on the forest floor,
among the roots.
For many animals, these fights to breed
are triggered by the shortening days.
It's a race to get ahead of your rivals before time runs out.
In Alaska, the tundra is turning red
and the stage is set for an almighty showdown.
A musk ox.
He's spent the last few weeks
fighting to keep control of a harem of females.
Over the few weeks that they are in season, he'll mate with all of them.
But he needs to be on his guard
because he has competition.
Another bull is trying to muscle in.
The dominant bull is going to have to fight him off.
The interloper turns his back
and the king charges.
These bulls have a layer of horn across their heads
ten centimetres thick,
which helps protect their brains.
But the impact is so loud...
..it can be heard a mile away.
CRUNCHING
The dominant male tries to turn his challenger around.
If he can strike at his flank, it will all be over.
With the competition seen off, the male returns to his females.
If he can keep other bulls away,
it will be his calves born on these pastures next spring.
With winter just around the corner,
this is a critical time for young animals, too.
They've grown up through summer's good times and now they must start
learning to fend for themselves.
For some, it's a steep learning curve.
This grey seal pup on the coast of Norfolk is only two weeks old,
but his mother is already teaching him to swim.
In another week, she'll be off
starting another family and the pup will
have to face winter completely on his own.
In North America, grizzly bear cubs
stay with their mother for two years,
but it's never too early to start tackling your first fish.
These young stoats in a British meadow
have only one summer to grow up.
By autumn, they have to have learnt the art of hunting for themselves.
The stalk...
..the chase...
..the ambush - deadly skills all learnt through play.
These young animals rush towards independence
as the world changes around them.
But for some,
the shifting of the seasons brings unexpected advantages.
In the northern hemisphere, as the days shorten,
the trees are almost bare.
With less life and the temperature dropping,
the leaves can no longer produce food.
So the trees get rid of them.
Nearer the equator, autumn is the beginning of the dry season.
The leaves are falling, but it's not because of lack of light.
There's not enough water.
Zimbabwe in southern Africa.
The trees are getting ready for seven months with no rain.
Trees lose moisture through their leaves
so it's better to drop them now.
And that's a great opportunity for two young cheetah cubs just on
the brink of adulthood.
These sisters are 18 months old and they are ready to leave home.
But first, they must learn how to hunt,
and autumn is the perfect time to practise.
With fewer leaves on the trees, their prey has nowhere to hide.
They pick out a target.
GRUNTING
A male impala is tricky prey,
but they've spent weeks fighting during the autumn rut.
They're exhausted
and visible.
The cheetah sisters have their chance.
They'd usually hunt in the open.
When they're hunting among trees,
it'll be more about agility and speed.
If they can start their chase close to the impala,
they'll have a better chance of running him down.
But they'll need to work together.
The sisters creep as close as they dare.
The trap is set.
But she loses her stride and the impala gains ground.
That's when her sister makes her move.
This is a dangerous moment.
As long as the impala is still on his feet,
he could inflict some serious injuries.
But the young cheetahs deliver the killing bite.
With this first success, they've entered adulthood.
By next autumn, they'll be experts.
For some animals, the race to independence
takes place in one of the most hostile places on Earth.
This is autumn in Antarctica.
The snow is already falling
and temperatures are plunging to minus 20 degrees centigrade.
A colony of Adelie penguins
is rushing to get their chicks to adulthood.
They only have a few weeks before winter is back in full force.
The chicks are only three weeks old.
Their downy coats aren't waterproof,
so they huddle together to keep warm,
while their parents are out at sea.
They may be gone for days...
..and the chicks can hardly wait for them to come back
with something to eat.
The adults work round the clock to keep their ravenous chicks fed.
When they return, it's an excited dash for food.
SQUAWKING AND CHITTERING
There are two chicks in these families,
but there's probably only enough food for one.
Most Adelie couples only manage to raise a single chick in a season.
In a place like this...
..there's just not enough for everyone.
Meanwhile, chick number one is getting bigger by the day.
He'll pack away 30kg of food while he's growing up.
A month on, and the chicks are losing the last of their baby down.
Now they have their feathers, it's time for their next rite of passage.
The adults go first.
They make it look effortless.
But the chicks don't seem so sure.
Apparently, penguins aren't born with a love of water.
Even when they're in, they're having problems staying submerged.
They're going to have to practise their buoyancy control.
They might seem awkward, but they're just about ready.
Now they'll drift off with their parents,
out into the Southern Ocean,
where they'll spend the next five months
fishing and avoiding the worst of the Antarctic winter.
As autumn moves on, changing ocean currents
can bring a wealth of food to some parts of the world.
And off the coast of South Africa,
there is a perfect opportunity for one animal
to make a spectacular leap into adulthood.
Bird Island, the world's largest colony of Cape gannets.
The parents have been feeding their young for three months.
Now it's time the chicks learned to fend for themselves.
But first, they must learn how to fly.
They flap their wings to build up muscle strength.
Gradually, they lift themselves off the rocks.
Some are up and away first time.
Others end up floundering in the breaking waves.
But they all have to make the leap.
The fledglings leave the nest
with enough fat reserves to last only ten days.
So now, they need to learn how to fish.
Fast.
Luckily for them, as winter approaches,
the seas are about to fill with food.
Billions of sardines are moving in,
following seasonal currents of cold water,
running along the South African coast.
The young gannets have mastered their wings
and they've joined the hunt.
They're following a super pod of dolphins,
who are also chasing the sardines.
The dolphins drive the shoal to the surface
and round them up into a ball.
And the gannets make their move.
They climb to 30 metres above the surface
and plunge into the feast.
They hit the surface at 60mph.
So they must enter the water with their bodies perfectly streamlined.
Get it wrong and it's like hitting concrete.
For the young gannets, it's a skill they have to master first time.
These birds have had a steep learning curve.
Chasing the seasonal bounty
has given them a dramatic start to adulthood.
Life has one chance to take advantage of autumn's opportunities.
It's a race against the clock
to prepare for the challenges of winter.
Battles for partners are over.
Migrants have escaped the cold.
And young animals have learnt what they need to know
to begin their adult lives.
Autumn's survivors are ready.
The world is changing.
There's a chill in the air and the last leaves are caught up in frost.
For a chipmunk,
winter won't be such a hardship.
With a full store of nuts...
..he can rest easy
until spring.
In Yellowstone, the waterways are starting to freeze over.
CRACKING
But the beavers are still active.
Their underwater lodge is well insulated, and inside
there's a young family depending on the hard-earned larder of branches.
On Alaska's frozen tundra, the musk ox are toughening it out.
For the pregnant females, it will be a game of endurance,
as they wait until spring, when their calves will be born.
As winter takes over, autumn's glory is finished for another year.