0:00:05 > 0:00:09Every year, spectacular seasons transform our planet.
0:00:11 > 0:00:14They're the driving force of all life on Earth...
0:00:17 > 0:00:21..bringing opportunities and huge challenges.
0:00:23 > 0:00:25Spring bursts with new life...
0:00:28 > 0:00:30..but it's a race to grab fleeting chances.
0:00:33 > 0:00:36Summer brings glorious abundance,
0:00:36 > 0:00:39but the heat can push animals to their limits.
0:00:41 > 0:00:44Autumn is nature's great gold rush...
0:00:47 > 0:00:50..but competition is fierce.
0:00:53 > 0:00:55Winter creates a frozen wonderland...
0:00:58 > 0:01:01..but only the most resourceful will survive.
0:01:09 > 0:01:11In every corner of the planet,
0:01:11 > 0:01:15animals rise to overcome the seemingly impossible...
0:01:19 > 0:01:21..to thrive against the odds...
0:01:22 > 0:01:27..as the seasons create the greatest shows on Earth.
0:01:43 > 0:01:48Autumn - the season when nature puts on its most flamboyant displays.
0:01:50 > 0:01:54It's as generous with its bounty as it is with its beauty.
0:01:58 > 0:02:02But the good times won't last. The clock is ticking.
0:02:04 > 0:02:08For many animals, it's their last chance to get ready before the cold
0:02:08 > 0:02:09closes in.
0:02:11 > 0:02:15And the first challenge is to fatten up and fill the larder.
0:02:27 > 0:02:29The great Northwoods of North America...
0:02:31 > 0:02:34..26 million acres of forest.
0:02:36 > 0:02:40In autumn, as the days get shorter and the light fades...
0:02:42 > 0:02:45..the trees go through a stunning transformation.
0:02:47 > 0:02:49They draw all the goodness out of their leaves...
0:02:51 > 0:02:53..and then they let them go.
0:02:57 > 0:03:01In a Canadian forest, along with the falling leaves,
0:03:01 > 0:03:04the trees are releasing a seasonal feast...
0:03:05 > 0:03:06..acorns.
0:03:11 > 0:03:14For a chipmunk, it's manna from heaven.
0:03:19 > 0:03:22He's stockpiling acorns for winter,
0:03:22 > 0:03:26and the quickest way to carry them is cramming as many into his mouth
0:03:26 > 0:03:27as possible.
0:03:28 > 0:03:31He can get six in, at a push.
0:03:40 > 0:03:41There's no time to waste.
0:03:41 > 0:03:45Within a couple of weeks, the forest could be under half a metre of snow.
0:03:47 > 0:03:50He needs to gather at least 100 acorns
0:03:50 > 0:03:53to see him through the lean months ahead.
0:04:00 > 0:04:04A chipmunk keeps his store of nuts hidden away in his winter burrow,
0:04:04 > 0:04:08a metre underground, and for good reason.
0:04:08 > 0:04:10There are thieves around.
0:04:15 > 0:04:17As soon as the coast is clear,
0:04:17 > 0:04:20a light-fingered neighbour takes his chance.
0:04:29 > 0:04:33With winter coming, pinching someone else's supplies
0:04:33 > 0:04:35is a serious business.
0:04:36 > 0:04:39The precious pile is starting to look very thin...
0:04:41 > 0:04:44..and that could mean starvation for the rightful owner.
0:04:50 > 0:04:53The honest chipmunk is still slogging away, gathering acorns...
0:04:55 > 0:04:59..but, when he returns, he's in for a shock -
0:04:59 > 0:05:01there's almost nothing left of the store.
0:05:06 > 0:05:08Retribution is swift.
0:05:11 > 0:05:15CHATTERING AND SQUEAKING
0:05:36 > 0:05:40With the thief sent packing, it's straight back to work.
0:05:41 > 0:05:44When winter comes, every nut will count.
0:05:47 > 0:05:49Autumn's abundance will be a lifeline.
0:05:56 > 0:05:58Chipmunks aren't the only ones getting ready.
0:06:00 > 0:06:04In Yellowstone in North America, the trees are turning gold.
0:06:19 > 0:06:23This moose has spent the summer fattening up on greenery.
0:06:23 > 0:06:26She'll stand up to her knees in water for hours at a time,
0:06:26 > 0:06:28feasting on pond weed.
0:06:30 > 0:06:35When there's good food underwater, a long nose comes in useful,
0:06:35 > 0:06:39and she can close her huge nostrils to keep the water out.
0:06:41 > 0:06:44But the good times are coming to an end.
0:06:45 > 0:06:49Once winter takes hold, the lake will freeze
0:06:49 > 0:06:52and she'll be reduced to eating bare twigs from trees.
0:06:53 > 0:06:57So she's packing away more than 10kg of greens a day...
0:06:58 > 0:06:59..while she still can.
0:07:03 > 0:07:06But there's another animal in this neck of the woods with a more
0:07:06 > 0:07:08radical approach to gathering food.
0:07:08 > 0:07:14TREE CRACKS
0:07:23 > 0:07:29A beaver - the only animal capable of chopping down an entire tree.
0:07:31 > 0:07:36He'll fell a cottonwood in a couple of hours, using only his teeth.
0:07:37 > 0:07:40He chews away just enough to make it unstable...
0:07:42 > 0:07:44..and lets the wind do the rest.
0:07:44 > 0:07:47TREE CRACKS
0:07:54 > 0:07:56And then the real hard work starts.
0:08:01 > 0:08:03He chops the branches into manageable chunks to eat later...
0:08:05 > 0:08:08..and the best way to get them back home is by water.
0:08:11 > 0:08:14So he and his partner have built a network of waterways
0:08:14 > 0:08:16especially for the job.
0:08:18 > 0:08:21While he's busy bringing in the supplies,
0:08:21 > 0:08:23she's doing some maintenance to the dam.
0:08:29 > 0:08:33In a couple of weeks, their canal system will freeze up,
0:08:33 > 0:08:36so they're gathering food now, while they still can.
0:08:44 > 0:08:48They'll survive all winter eating nothing but these branches.
0:08:54 > 0:08:58He drags them one at a time to his underwater larder.
0:08:58 > 0:09:00He might bring in several hundred of them...
0:09:01 > 0:09:03..so even when the pond has frozen over,
0:09:03 > 0:09:05there will still be plenty of food.
0:09:19 > 0:09:22All this industry has caught the attention of a young moose.
0:09:26 > 0:09:29A beaver's pond could be the perfect place to find something to eat.
0:09:32 > 0:09:34But he can forget that idea.
0:09:44 > 0:09:47This is no time for sharing.
0:09:55 > 0:09:58Autumn might be the season of glorious colour,
0:09:58 > 0:10:00but it can be a wild time, too.
0:10:02 > 0:10:05THUNDER RUMBLES
0:10:09 > 0:10:11As the temperature starts to fall,
0:10:11 > 0:10:15changes in air pressure cause massive storms.
0:10:15 > 0:10:20THUNDER RUMBLES
0:10:26 > 0:10:28In the river in southern Alaska,
0:10:28 > 0:10:32the storms are about to bring in one of autumn's biggest feasts,
0:10:32 > 0:10:36and on the river bank, a hungry crowd is gathering...
0:10:42 > 0:10:43..grizzly bears.
0:10:44 > 0:10:46If they're going to survive the coming winter,
0:10:46 > 0:10:50they need to build up their weight by more than half in just a few weeks.
0:10:58 > 0:11:01It's the wettest time of the year
0:11:01 > 0:11:03but all this rain is good news for the bears.
0:11:11 > 0:11:12It's flooding the rivers...
0:11:14 > 0:11:18..opening the way for millions of fish to start heading their way.
0:11:23 > 0:11:25Pacific salmon.
0:11:25 > 0:11:29They've travelled thousands of miles of sea and now they're swimming
0:11:29 > 0:11:30inland to spawn.
0:11:32 > 0:11:35They're returning to the very rivers where they were born.
0:11:47 > 0:11:50And the bears are lining up to meet them.
0:11:55 > 0:11:56They're gathering at a waterfall.
0:11:58 > 0:12:01They know that the salmon must pass through this bottleneck in the river.
0:12:03 > 0:12:06It will be the best fishing for miles around.
0:12:07 > 0:12:09BEARS GRUNT
0:12:13 > 0:12:17The biggest males start to fight over the prime spots.
0:12:17 > 0:12:18BEARS ROAR
0:12:40 > 0:12:43The salmon are starting to collect in a whirlpool at the bottom of
0:12:43 > 0:12:44the falls.
0:12:48 > 0:12:53With one almighty push, the first fish starts its ascent.
0:12:58 > 0:13:02It uses its whole body to leap more than two metres in the air...
0:13:03 > 0:13:06..and if it's lucky, past the waiting bears.
0:13:20 > 0:13:23But eventually, the migration hits its peak.
0:13:33 > 0:13:36There are so many salmon, the bears can hardly miss.
0:13:41 > 0:13:45A big male bear can catch as many as 30 fish a day.
0:14:04 > 0:14:06But it's not always as easy as it looks.
0:14:07 > 0:14:09This is a tough neighbourhood.
0:14:14 > 0:14:18A female with three young cubs nervously approaches the river.
0:14:18 > 0:14:23She's desperate to fish, but these big males could attack her family...
0:14:23 > 0:14:25BEARS ROAR
0:14:25 > 0:14:26..so it's dangerous.
0:14:28 > 0:14:29BEARS ROAR
0:14:38 > 0:14:42BEARS ROAR
0:14:48 > 0:14:53After a long summer nursing three cubs, she's skin and bone.
0:14:53 > 0:14:57Unless she can eat soon, she'll struggle to get them through winter.
0:15:03 > 0:15:05The big males carry on bingeing...
0:15:07 > 0:15:12..but one by one, they haul themselves out of the river for an afternoon nap.
0:15:25 > 0:15:29They're so full, they can hardly move.
0:15:38 > 0:15:40It's the young mother's big chance.
0:15:44 > 0:15:48She climbs to the top of the falls, but she'll have to be quick.
0:16:01 > 0:16:02SHE GROWLS
0:16:06 > 0:16:07SHE GROWLS
0:16:13 > 0:16:14SHE GROWLS
0:16:17 > 0:16:18Finally!
0:16:25 > 0:16:29The salmon run is vital to every bear on the river.
0:16:30 > 0:16:34They'll sleep for six months, all through the bitter Alaskan winter...
0:16:35 > 0:16:39..so the fat they lay down now will help guarantee
0:16:39 > 0:16:40their survival.
0:16:44 > 0:16:46If this young mother can keep fishing...
0:16:48 > 0:16:52..she'll give her family the best chance of making it through till spring.
0:17:01 > 0:17:04But not everywhere offers such rich autumn pickings.
0:17:11 > 0:17:16For animals across the planet, sometimes, the only option is to leave home
0:17:16 > 0:17:19and look for better times elsewhere.
0:17:28 > 0:17:31In North America every autumn,
0:17:31 > 0:17:33hundreds of pronghorn trek across Yellowstone...
0:17:34 > 0:17:36..to escape the advancing snow.
0:17:41 > 0:17:45They leave their summer pastures and race to the safety of the lowlands,
0:17:45 > 0:17:47where they can graze all winter.
0:17:54 > 0:17:58In the Arctic, birds that came here in spring are starting to make
0:17:58 > 0:17:59an exit.
0:18:01 > 0:18:07The seas have provided a bounty all summer, but as autumn creeps in,
0:18:07 > 0:18:08food is getting harder to find.
0:18:10 > 0:18:13The bonanza is over.
0:18:15 > 0:18:18Hundreds of thousands of birds are heading south.
0:18:18 > 0:18:23SQUAWKING
0:18:23 > 0:18:26Snow geese spend the short summer in the Canadian Arctic,
0:18:26 > 0:18:28raising their families,
0:18:28 > 0:18:32but in autumn, they travel 3,000 miles south
0:18:32 > 0:18:34to the warmth of the Gulf of Mexico.
0:18:38 > 0:18:41The birds fly together in enormous flocks.
0:18:41 > 0:18:44There may be more than five million of them,
0:18:44 > 0:18:46all making this vast round trip.
0:18:51 > 0:18:54But for some animals, these journeys are fraught with danger.
0:18:57 > 0:18:59On the Norwegian island of Svalbard,
0:18:59 > 0:19:04100,000 Brunnich's guillemots have been here since spring,
0:19:04 > 0:19:05nesting on the safety of the sea cliffs.
0:19:10 > 0:19:12Now their food's running out
0:19:12 > 0:19:14and it's time for these young families to go.
0:19:18 > 0:19:20But these parents face the worst possible mission.
0:19:25 > 0:19:29SQUAWKING
0:19:29 > 0:19:32Each pair have one precious chick
0:19:32 > 0:19:34and they've spent all summer looking after it.
0:19:34 > 0:19:39Now they must persuade it to jump off the cliff, down to the sea.
0:19:40 > 0:19:43It's a drop of 150 metres.
0:19:49 > 0:19:52The chicks are only three weeks old...
0:19:53 > 0:19:55..and they can't fly properly.
0:19:56 > 0:19:59It's a terrifying leap of faith.
0:20:08 > 0:20:09And there's worse.
0:20:09 > 0:20:13There's a family of hungry Arctic foxes waiting on the beach.
0:20:18 > 0:20:22The chicks must make it all the way to the sea without touching land.
0:20:27 > 0:20:30The first dad encourages his chick over the edge.
0:20:39 > 0:20:40Not far enough.
0:20:45 > 0:20:47He makes a desperate dash for the sea.
0:20:52 > 0:20:53FOX GROWLS
0:20:54 > 0:20:55CHICK SQUEAKS
0:20:59 > 0:21:01The next family step up to take their turn.
0:21:05 > 0:21:09Anxious to save his offspring from the same fate,
0:21:09 > 0:21:10his dad goes with him.
0:21:14 > 0:21:15But they both fall short.
0:21:22 > 0:21:24So close and yet so far.
0:21:26 > 0:21:27FOX BARKS
0:21:33 > 0:21:36A third family has witnessed the grim fate of the neighbours,
0:21:36 > 0:21:38but there's no other way down.
0:21:50 > 0:21:53SPLASHING
0:21:53 > 0:21:57It may not be the most graceful landing, but they're all down safe.
0:22:05 > 0:22:07When parents fly with their chicks,
0:22:07 > 0:22:10they have a much better chance of survival.
0:22:13 > 0:22:15THEY CHIRP
0:22:18 > 0:22:20But this is only the start of their journey.
0:22:20 > 0:22:23Now they have to travel south to the coast of Greenland,
0:22:23 > 0:22:25where they will spend the winter.
0:22:31 > 0:22:34And because they're not strong enough to fly,
0:22:34 > 0:22:35the chicks are going to have to swim there...
0:22:37 > 0:22:39..and it's 600 miles.
0:22:42 > 0:22:44But Mum and Dad will be with them all the way.
0:22:51 > 0:22:56Even when you can fly, these autumn journeys are an enormous challenge.
0:22:59 > 0:23:01In the skies above Central Asia,
0:23:01 > 0:23:04it's the start of one of the toughest migrations on the planet.
0:23:08 > 0:23:10THEY SQUAWK
0:23:14 > 0:23:16Demoiselle cranes.
0:23:16 > 0:23:21They've spent the summer in Mongolia and Kazakhstan, but now winter is
0:23:21 > 0:23:26breathing down their necks, so they're flying south to India.
0:23:28 > 0:23:32But first, they must cross the world's highest mountain range,
0:23:32 > 0:23:33the Himalayas.
0:23:38 > 0:23:42In places, these peaks tower five miles high.
0:23:52 > 0:23:54The cranes can't go round them
0:23:54 > 0:23:58because this mountain range spans five countries.
0:23:58 > 0:24:00They have to find a way through.
0:24:08 > 0:24:09And to make things worse,
0:24:09 > 0:24:13autumn brings treacherous storms to this part of the world.
0:24:24 > 0:24:29The cranes gain height, trying to break through the clouds,
0:24:29 > 0:24:31but strong headwinds force them back.
0:24:40 > 0:24:41They're beaten, for now...
0:24:42 > 0:24:44..so they set up camp for the night.
0:24:45 > 0:24:49SQUAWKING
0:24:49 > 0:24:51But they dare not linger.
0:24:51 > 0:24:53There'll be more storms on the way.
0:24:53 > 0:24:56SQUAWKING
0:24:57 > 0:25:00At dawn, there's a window of clear weather.
0:25:03 > 0:25:05SQUAWKING
0:25:05 > 0:25:07It's now or never.
0:25:20 > 0:25:24But to get any further, the cranes must cross Sniper Alley.
0:25:25 > 0:25:29The golden eagles that live here have been expecting them.
0:25:45 > 0:25:48The eagles know the cranes will be coming this way in autumn.
0:25:49 > 0:25:52Normally, they'd be too fast to catch...
0:25:55 > 0:25:58..but, right now, they're flying tired...
0:25:59 > 0:26:02..and the eagles work in pairs.
0:26:08 > 0:26:11One eagle picks out a young bird and sets up an ambush.
0:26:15 > 0:26:16BIRD SQUAWKS
0:26:24 > 0:26:27He drives it into the talons of his partner.
0:26:35 > 0:26:38The exhausted crane never stood a chance.
0:26:43 > 0:26:46One man down, the rest of the flock pushes on.
0:26:52 > 0:26:55They use rising columns of air to help them gain height.
0:26:58 > 0:27:01They may reach altitudes of 26,000 feet.
0:27:10 > 0:27:14And finally, they're across this vast mountain barrier and heading
0:27:14 > 0:27:16south towards India.
0:27:17 > 0:27:22Many of them won't make it, but this monumental journey is the only way
0:27:22 > 0:27:24to stay ahead of a brutal winter.
0:27:28 > 0:27:33They'll fly a distance of more than 1,000 miles and, in spring,
0:27:33 > 0:27:34they'll fly all the way back.
0:27:48 > 0:27:51For another animal, autumn starts a migration
0:27:51 > 0:27:53of a totally different kind...
0:27:54 > 0:27:56..and it happens under the sea.
0:28:00 > 0:28:03The oceans cool more slowly than the land,
0:28:03 > 0:28:05but as the temperature starts to change,
0:28:05 > 0:28:07it triggers an unusual autumn spectacle.
0:28:11 > 0:28:14In the Southern Ocean of South Australia,
0:28:14 > 0:28:16there's a big crowd starting to gather.
0:28:19 > 0:28:23Giant spider crabs are marching in unison across the sea floor.
0:28:28 > 0:28:30They spend most of the year offshore...
0:28:31 > 0:28:36..but, in the autumn, these big orange crabs head to the shallows.
0:28:39 > 0:28:41They're getting ready to moult.
0:28:53 > 0:28:57They've outgrown their shells and they need to grow a new one.
0:28:57 > 0:29:02It can take them up to an hour to crack open their old armour plating
0:29:02 > 0:29:03and wriggle out.
0:29:08 > 0:29:10But it takes a couple of weeks for their new shells to develop...
0:29:13 > 0:29:15..and waiting naked on the sea floor...
0:29:17 > 0:29:18..is dangerous.
0:29:23 > 0:29:25A stingray.
0:29:25 > 0:29:27The crabs scatter in a panic.
0:29:29 > 0:29:34There may be 250,000 to choose from, but the ray is particular.
0:29:39 > 0:29:43The softer the crabs, the easier they are to swallow.
0:29:57 > 0:30:00But the ray barely makes a dent in the population.
0:30:04 > 0:30:06There's safety in numbers.
0:30:10 > 0:30:13And with so many crabs gathered together,
0:30:13 > 0:30:16some take the opportunity to look for a partner.
0:30:33 > 0:30:35With the party over,
0:30:35 > 0:30:39the crabs step over the discarded remains of their old wardrobe
0:30:39 > 0:30:41and head back to the deep.
0:30:48 > 0:30:51For lots of animals, autumn is the season for finding a mate.
0:30:53 > 0:30:54But it's an intense time of year.
0:30:55 > 0:30:58And with winter round the corner,
0:30:58 > 0:31:01the search for a partner is full of challenges.
0:31:03 > 0:31:05Only the toughest will succeed.
0:31:14 > 0:31:19Male wild ass, fuelled with testosterone,
0:31:19 > 0:31:23tear up the Tibetan plains as they compete for mares.
0:31:25 > 0:31:27Timing is critical.
0:31:27 > 0:31:30They need to mate now so their foals will be born next summer,
0:31:30 > 0:31:31when there is plenty to eat.
0:31:35 > 0:31:39Off the coast of Britain, grey seal bull fights are a bloody affair.
0:31:44 > 0:31:47Only the biggest and bravest will get to breed...
0:31:48 > 0:31:51..and he'll mate with every female on the beach.
0:31:59 > 0:32:04In North America, male elk live quiet lives until autumn,
0:32:04 > 0:32:07when they come together for the rut.
0:32:11 > 0:32:14They grow a new set of antlers every year,
0:32:14 > 0:32:16weighing almost 20kg.
0:32:19 > 0:32:22The bigger the antlers, the stronger the bull.
0:32:27 > 0:32:28ELK GRUNTS
0:32:32 > 0:32:37But for one animal, the battle to breed is not only about brute force,
0:32:37 > 0:32:39it's also about technique.
0:32:46 > 0:32:49Patagonia, South America.
0:32:52 > 0:32:53Autumn is approaching
0:32:53 > 0:32:56and a male Darwin's beetle is looking for a partner.
0:32:57 > 0:33:01His success will be down to the size of his jaws...
0:33:02 > 0:33:03..and how he uses them.
0:33:13 > 0:33:15He heads off to the forest to start his search.
0:33:19 > 0:33:22The females will be in the trees,
0:33:22 > 0:33:24probably feeding somewhere on the trunk.
0:33:24 > 0:33:26They should be easy enough to find.
0:33:32 > 0:33:35But when the trees are more than 25 metres tall,
0:33:35 > 0:33:37it's a long way to climb.
0:33:47 > 0:33:48There she is.
0:33:54 > 0:33:56Unfortunately for him,
0:33:56 > 0:33:59all the other males in the neighbourhood are also after her.
0:34:01 > 0:34:04He has no choice but to fight them off.
0:34:08 > 0:34:11But it's not just about strength.
0:34:11 > 0:34:13It's about...
0:34:13 > 0:34:14grappling.
0:34:21 > 0:34:25He reaches over the rival's head and hooks his enormous jaws under
0:34:25 > 0:34:26his wing covers.
0:34:37 > 0:34:39He gets a grip,
0:34:39 > 0:34:41lifts...
0:34:42 > 0:34:43..and chucks.
0:34:51 > 0:34:53He climbs onwards.
0:34:53 > 0:34:56There are other males standing in his way,
0:34:56 > 0:34:58but nothing will stop him now.
0:35:11 > 0:35:13They meet at last.
0:35:20 > 0:35:22She doesn't appear to be totally smitten.
0:35:36 > 0:35:39But she finally allows him to wrap his great big jaws around her...
0:35:41 > 0:35:42..and they get intimate.
0:35:57 > 0:35:59But then,
0:35:59 > 0:36:01he throws HER out of the tree.
0:36:06 > 0:36:09Beetle armour is tough and, luckily,
0:36:09 > 0:36:13she's just where she needs to be to lay her eggs on the forest floor,
0:36:13 > 0:36:14among the roots.
0:36:24 > 0:36:26For many animals, these fights to breed
0:36:26 > 0:36:29are triggered by the shortening days.
0:36:29 > 0:36:33It's a race to get ahead of your rivals before time runs out.
0:36:35 > 0:36:39In Alaska, the tundra is turning red
0:36:39 > 0:36:43and the stage is set for an almighty showdown.
0:36:47 > 0:36:49A musk ox.
0:36:50 > 0:36:52He's spent the last few weeks
0:36:52 > 0:36:55fighting to keep control of a harem of females.
0:36:58 > 0:37:02Over the few weeks that they are in season, he'll mate with all of them.
0:37:04 > 0:37:07But he needs to be on his guard
0:37:07 > 0:37:08because he has competition.
0:37:12 > 0:37:14Another bull is trying to muscle in.
0:37:21 > 0:37:24The dominant bull is going to have to fight him off.
0:37:24 > 0:37:26The interloper turns his back
0:37:26 > 0:37:29and the king charges.
0:37:55 > 0:37:58These bulls have a layer of horn across their heads
0:37:58 > 0:37:59ten centimetres thick,
0:37:59 > 0:38:01which helps protect their brains.
0:38:04 > 0:38:06But the impact is so loud...
0:38:08 > 0:38:09..it can be heard a mile away.
0:38:11 > 0:38:12CRUNCHING
0:38:27 > 0:38:30The dominant male tries to turn his challenger around.
0:38:30 > 0:38:33If he can strike at his flank, it will all be over.
0:38:45 > 0:38:49With the competition seen off, the male returns to his females.
0:38:50 > 0:38:52If he can keep other bulls away,
0:38:52 > 0:38:55it will be his calves born on these pastures next spring.
0:39:05 > 0:39:08With winter just around the corner,
0:39:08 > 0:39:11this is a critical time for young animals, too.
0:39:12 > 0:39:17They've grown up through summer's good times and now they must start
0:39:17 > 0:39:19learning to fend for themselves.
0:39:27 > 0:39:29For some, it's a steep learning curve.
0:39:30 > 0:39:35This grey seal pup on the coast of Norfolk is only two weeks old,
0:39:35 > 0:39:38but his mother is already teaching him to swim.
0:39:39 > 0:39:41In another week, she'll be off
0:39:41 > 0:39:44starting another family and the pup will
0:39:44 > 0:39:46have to face winter completely on his own.
0:39:52 > 0:39:54In North America, grizzly bear cubs
0:39:54 > 0:39:58stay with their mother for two years,
0:39:58 > 0:40:01but it's never too early to start tackling your first fish.
0:40:15 > 0:40:18These young stoats in a British meadow
0:40:18 > 0:40:20have only one summer to grow up.
0:40:20 > 0:40:24By autumn, they have to have learnt the art of hunting for themselves.
0:40:29 > 0:40:31The stalk...
0:40:32 > 0:40:33..the chase...
0:40:35 > 0:40:41..the ambush - deadly skills all learnt through play.
0:40:46 > 0:40:48These young animals rush towards independence
0:40:48 > 0:40:51as the world changes around them.
0:40:51 > 0:40:52But for some,
0:40:52 > 0:40:56the shifting of the seasons brings unexpected advantages.
0:40:58 > 0:41:01In the northern hemisphere, as the days shorten,
0:41:01 > 0:41:02the trees are almost bare.
0:41:04 > 0:41:06With less life and the temperature dropping,
0:41:06 > 0:41:08the leaves can no longer produce food.
0:41:10 > 0:41:11So the trees get rid of them.
0:41:21 > 0:41:25Nearer the equator, autumn is the beginning of the dry season.
0:41:25 > 0:41:29The leaves are falling, but it's not because of lack of light.
0:41:30 > 0:41:32There's not enough water.
0:41:40 > 0:41:42Zimbabwe in southern Africa.
0:41:43 > 0:41:46The trees are getting ready for seven months with no rain.
0:41:49 > 0:41:51Trees lose moisture through their leaves
0:41:51 > 0:41:53so it's better to drop them now.
0:42:03 > 0:42:07And that's a great opportunity for two young cheetah cubs just on
0:42:07 > 0:42:09the brink of adulthood.
0:42:15 > 0:42:19These sisters are 18 months old and they are ready to leave home.
0:42:19 > 0:42:23But first, they must learn how to hunt,
0:42:23 > 0:42:26and autumn is the perfect time to practise.
0:42:27 > 0:42:31With fewer leaves on the trees, their prey has nowhere to hide.
0:42:38 > 0:42:39They pick out a target.
0:42:42 > 0:42:43GRUNTING
0:42:46 > 0:42:50A male impala is tricky prey,
0:42:50 > 0:42:53but they've spent weeks fighting during the autumn rut.
0:42:54 > 0:42:56They're exhausted
0:42:56 > 0:42:57and visible.
0:43:07 > 0:43:09The cheetah sisters have their chance.
0:43:14 > 0:43:16They'd usually hunt in the open.
0:43:18 > 0:43:20When they're hunting among trees,
0:43:20 > 0:43:23it'll be more about agility and speed.
0:43:27 > 0:43:31If they can start their chase close to the impala,
0:43:31 > 0:43:33they'll have a better chance of running him down.
0:43:51 > 0:43:53But they'll need to work together.
0:44:04 > 0:44:07The sisters creep as close as they dare.
0:44:23 > 0:44:25The trap is set.
0:44:36 > 0:44:40But she loses her stride and the impala gains ground.
0:44:58 > 0:45:00That's when her sister makes her move.
0:45:09 > 0:45:11This is a dangerous moment.
0:45:12 > 0:45:15As long as the impala is still on his feet,
0:45:15 > 0:45:17he could inflict some serious injuries.
0:45:20 > 0:45:22But the young cheetahs deliver the killing bite.
0:45:33 > 0:45:36With this first success, they've entered adulthood.
0:45:39 > 0:45:41By next autumn, they'll be experts.
0:45:46 > 0:45:49For some animals, the race to independence
0:45:49 > 0:45:53takes place in one of the most hostile places on Earth.
0:45:55 > 0:45:58This is autumn in Antarctica.
0:46:02 > 0:46:04The snow is already falling
0:46:04 > 0:46:07and temperatures are plunging to minus 20 degrees centigrade.
0:46:13 > 0:46:14A colony of Adelie penguins
0:46:14 > 0:46:17is rushing to get their chicks to adulthood.
0:46:17 > 0:46:22They only have a few weeks before winter is back in full force.
0:46:27 > 0:46:30The chicks are only three weeks old.
0:46:30 > 0:46:33Their downy coats aren't waterproof,
0:46:33 > 0:46:35so they huddle together to keep warm,
0:46:35 > 0:46:37while their parents are out at sea.
0:46:41 > 0:46:43They may be gone for days...
0:46:44 > 0:46:46..and the chicks can hardly wait for them to come back
0:46:46 > 0:46:48with something to eat.
0:46:58 > 0:47:01The adults work round the clock to keep their ravenous chicks fed.
0:47:04 > 0:47:08When they return, it's an excited dash for food.
0:47:08 > 0:47:10SQUAWKING AND CHITTERING
0:47:17 > 0:47:19There are two chicks in these families,
0:47:19 > 0:47:22but there's probably only enough food for one.
0:47:38 > 0:47:42Most Adelie couples only manage to raise a single chick in a season.
0:47:45 > 0:47:46In a place like this...
0:47:47 > 0:47:49..there's just not enough for everyone.
0:47:55 > 0:47:59Meanwhile, chick number one is getting bigger by the day.
0:47:59 > 0:48:02He'll pack away 30kg of food while he's growing up.
0:48:10 > 0:48:15A month on, and the chicks are losing the last of their baby down.
0:48:15 > 0:48:19Now they have their feathers, it's time for their next rite of passage.
0:48:24 > 0:48:25The adults go first.
0:48:33 > 0:48:35They make it look effortless.
0:48:40 > 0:48:42But the chicks don't seem so sure.
0:48:48 > 0:48:50Apparently, penguins aren't born with a love of water.
0:48:56 > 0:48:59Even when they're in, they're having problems staying submerged.
0:49:02 > 0:49:05They're going to have to practise their buoyancy control.
0:49:17 > 0:49:20They might seem awkward, but they're just about ready.
0:49:22 > 0:49:25Now they'll drift off with their parents,
0:49:25 > 0:49:27out into the Southern Ocean,
0:49:27 > 0:49:29where they'll spend the next five months
0:49:29 > 0:49:32fishing and avoiding the worst of the Antarctic winter.
0:49:48 > 0:49:51As autumn moves on, changing ocean currents
0:49:51 > 0:49:55can bring a wealth of food to some parts of the world.
0:49:56 > 0:49:58And off the coast of South Africa,
0:49:58 > 0:50:01there is a perfect opportunity for one animal
0:50:01 > 0:50:04to make a spectacular leap into adulthood.
0:50:08 > 0:50:13Bird Island, the world's largest colony of Cape gannets.
0:50:17 > 0:50:19The parents have been feeding their young for three months.
0:50:21 > 0:50:23Now it's time the chicks learned to fend for themselves.
0:50:28 > 0:50:30But first, they must learn how to fly.
0:50:49 > 0:50:51They flap their wings to build up muscle strength.
0:50:53 > 0:50:56Gradually, they lift themselves off the rocks.
0:51:05 > 0:51:07Some are up and away first time.
0:51:17 > 0:51:19Others end up floundering in the breaking waves.
0:51:29 > 0:51:31But they all have to make the leap.
0:51:36 > 0:51:38The fledglings leave the nest
0:51:38 > 0:51:40with enough fat reserves to last only ten days.
0:51:40 > 0:51:44So now, they need to learn how to fish.
0:51:44 > 0:51:45Fast.
0:51:48 > 0:51:51Luckily for them, as winter approaches,
0:51:51 > 0:51:53the seas are about to fill with food.
0:51:55 > 0:51:59Billions of sardines are moving in,
0:51:59 > 0:52:01following seasonal currents of cold water,
0:52:01 > 0:52:04running along the South African coast.
0:52:14 > 0:52:17The young gannets have mastered their wings
0:52:17 > 0:52:18and they've joined the hunt.
0:52:21 > 0:52:23They're following a super pod of dolphins,
0:52:23 > 0:52:25who are also chasing the sardines.
0:52:40 > 0:52:42The dolphins drive the shoal to the surface
0:52:42 > 0:52:44and round them up into a ball.
0:52:58 > 0:53:00And the gannets make their move.
0:53:09 > 0:53:12They climb to 30 metres above the surface
0:53:12 > 0:53:14and plunge into the feast.
0:53:32 > 0:53:35They hit the surface at 60mph.
0:53:37 > 0:53:41So they must enter the water with their bodies perfectly streamlined.
0:53:52 > 0:53:55Get it wrong and it's like hitting concrete.
0:53:56 > 0:53:59For the young gannets, it's a skill they have to master first time.
0:54:23 > 0:54:25These birds have had a steep learning curve.
0:54:26 > 0:54:28Chasing the seasonal bounty
0:54:28 > 0:54:31has given them a dramatic start to adulthood.
0:54:38 > 0:54:42Life has one chance to take advantage of autumn's opportunities.
0:54:47 > 0:54:49It's a race against the clock
0:54:49 > 0:54:52to prepare for the challenges of winter.
0:54:54 > 0:54:57Battles for partners are over.
0:55:01 > 0:55:03Migrants have escaped the cold.
0:55:07 > 0:55:10And young animals have learnt what they need to know
0:55:10 > 0:55:12to begin their adult lives.
0:55:13 > 0:55:16Autumn's survivors are ready.
0:55:21 > 0:55:23The world is changing.
0:55:23 > 0:55:28There's a chill in the air and the last leaves are caught up in frost.
0:55:38 > 0:55:40For a chipmunk,
0:55:40 > 0:55:41winter won't be such a hardship.
0:55:48 > 0:55:49With a full store of nuts...
0:55:51 > 0:55:53..he can rest easy
0:55:53 > 0:55:54until spring.
0:56:06 > 0:56:09In Yellowstone, the waterways are starting to freeze over.
0:56:14 > 0:56:16CRACKING
0:56:16 > 0:56:18But the beavers are still active.
0:56:23 > 0:56:28Their underwater lodge is well insulated, and inside
0:56:28 > 0:56:31there's a young family depending on the hard-earned larder of branches.
0:56:54 > 0:56:58On Alaska's frozen tundra, the musk ox are toughening it out.
0:57:03 > 0:57:06For the pregnant females, it will be a game of endurance,
0:57:06 > 0:57:09as they wait until spring, when their calves will be born.
0:57:12 > 0:57:17As winter takes over, autumn's glory is finished for another year.
0:57:51 > 0:57:53Hit it! Over on CBeebies,
0:57:53 > 0:57:55our mission is discovering more about the world.
0:57:55 > 0:57:56ALL: Wow!
0:57:56 > 0:57:58We've got a rocket ship, we've got a unicorn,