0:00:07 > 0:00:09Yellowstone.
0:00:13 > 0:00:15Volcanic wonderland.
0:00:18 > 0:00:22Two million acres of wild space...
0:00:22 > 0:00:25right in the heart of North America.
0:00:33 > 0:00:34The heat of the summer
0:00:34 > 0:00:38has unveiled the full extent of the Yellowstone wilderness,
0:00:38 > 0:00:42and for a few precious months, it has blossomed.
0:00:49 > 0:00:52But now, Yellowstone is changing.
0:00:55 > 0:01:00In just a few weeks, the snow and ice of winter will be back.
0:01:05 > 0:01:08As the animals of Yellowstone now turn to face
0:01:08 > 0:01:12perhaps the biggest challenges of their year.
0:01:15 > 0:01:19The true value of the world's first national park
0:01:19 > 0:01:23is about to become clearer than ever.
0:01:51 > 0:01:53It's late August.
0:01:53 > 0:01:58On Yellowstone's peaks, there is already a dusting of fresh snow.
0:02:01 > 0:02:04Now a new sound marks the new season.
0:02:04 > 0:02:06ELK BELLOWS
0:02:11 > 0:02:13Fuelled by testosterone,
0:02:13 > 0:02:17the bugle call of this male elk is a boast of his strength.
0:02:24 > 0:02:26All over Yellowstone,
0:02:26 > 0:02:29male elk are challenging each other for dominance.
0:02:29 > 0:02:31ELKS BELLOW
0:02:31 > 0:02:33The sound of Yellowstone's autumn.
0:02:33 > 0:02:36BELLOWING CONTINUES
0:02:52 > 0:02:55They are trying to win the admiration of females
0:02:55 > 0:02:58and gather them into a harem.
0:02:58 > 0:03:03Only then do they stand a chance of mating with them before winter.
0:03:03 > 0:03:05But the females are not yet in season,
0:03:05 > 0:03:09so they are not really that interested.
0:03:09 > 0:03:13And for now, they have a more practical concern.
0:03:18 > 0:03:20Winter will soon be here.
0:03:21 > 0:03:24They are eager to head down to lower ground
0:03:24 > 0:03:26before the snow comes in earnest.
0:03:28 > 0:03:31Some will move down into nearby valleys...
0:03:32 > 0:03:35..whilst others will journey much further -
0:03:35 > 0:03:40even beyond the boundaries of Yellowstone itself.
0:03:50 > 0:03:53Yellowstone is deep in the Rocky Mountains of North America.
0:03:57 > 0:04:02An isolated high plateau, defended by rugged peaks.
0:04:08 > 0:04:11In the middle is the national park.
0:04:17 > 0:04:19The park and the surrounding mountains
0:04:19 > 0:04:21form one of the most important
0:04:21 > 0:04:24and spectacular wilderness areas on Earth.
0:04:28 > 0:04:30In just two months,
0:04:30 > 0:04:33this great plateau will become a deep freeze once more.
0:04:36 > 0:04:41Before then, the animals of Yellowstone have to get ready...
0:04:43 > 0:04:44..or get out.
0:04:48 > 0:04:53But for now, below the snow-dusted peaks,
0:04:53 > 0:04:56summer still lingers in the heart of Yellowstone.
0:05:04 > 0:05:06The sun has revitalised this place
0:05:06 > 0:05:11and now there are more living things here than at any time of the year.
0:05:16 > 0:05:19The summer has brought visitors too...
0:05:21 > 0:05:25..who are enjoying Yellowstone at its most vibrant.
0:05:35 > 0:05:38As the sun now starts to get lower in the sky,
0:05:38 > 0:05:43the rich colours make this one of the best times to see the geysers.
0:05:57 > 0:06:01On the grasslands, the good times are already over.
0:06:02 > 0:06:06These bison are making the most of the grazing
0:06:06 > 0:06:08but it is now dry and parched.
0:06:08 > 0:06:12From now on, they will have to rely heavily on stored fat
0:06:12 > 0:06:14to keep them going
0:06:14 > 0:06:18as these meadows become covered in more than four feet of snow.
0:06:26 > 0:06:29Others are already thinking of leaving.
0:06:36 > 0:06:41Pronghorn evolved to outrun a now-extinct North American cheetah
0:06:41 > 0:06:45and so are the fastest antelope on Earth.
0:06:57 > 0:07:01But unlike bison, their lightweight bodies can't store enough energy
0:07:01 > 0:07:05to keep them here through the winter, so now they must head out.
0:07:13 > 0:07:16Their journey will be the longest of all.
0:07:23 > 0:07:25But as many are preparing to get out,
0:07:25 > 0:07:27some have no choice but to stay.
0:07:31 > 0:07:36In the remote north-east of the Yellowstone wilderness are the Beartooth Mountains.
0:07:39 > 0:07:42Here, surviving above 8,000 feet,
0:07:42 > 0:07:46a tree now welcomes the change of season.
0:07:48 > 0:07:50The whitebark pine.
0:07:56 > 0:08:00All summer, these trees have been soaking up the energy of the sun,
0:08:00 > 0:08:02preparing for this moment.
0:08:06 > 0:08:11Now they offer the animals a bumper crop of pine cones.
0:08:17 > 0:08:22The whitebark pine is gambling on the fact that animals now need
0:08:22 > 0:08:25all the food they can get before winter
0:08:25 > 0:08:28and is hoping it can entice them to spread its seeds
0:08:28 > 0:08:31far and wide across Yellowstone.
0:08:38 > 0:08:44So, inside the cones, it has put tasty, nutritious pine nuts.
0:08:48 > 0:08:50A pine squirrel.
0:09:18 > 0:09:21It snacks on a few of the nuts to keep going.
0:09:31 > 0:09:35And then buries them, one by one, in a sheltered hollow beside the tree.
0:09:39 > 0:09:42If it hides them well and packs them carefully,
0:09:42 > 0:09:44they should last through the winter.
0:09:44 > 0:09:48But this is not much good for the tree.
0:09:48 > 0:09:51Its seeds have gone nowhere.
0:09:58 > 0:10:01A grizzly bear mother and cubs.
0:10:04 > 0:10:09It's unusual for a grizzly to have so many cubs.
0:10:09 > 0:10:13This mother has found two orphans and adopted them.
0:10:19 > 0:10:21Now she has four cubs to fatten up
0:10:21 > 0:10:25before they go into the den to hibernate this winter.
0:10:36 > 0:10:40She's after pine nuts too. They are 50% fat.
0:10:45 > 0:10:51In a good year, a grizzly can put on five pounds a day eating nuts alone.
0:11:12 > 0:11:15If squirrels have done the hard work,
0:11:15 > 0:11:18it doesn't matter that grizzlies can't climb trees.
0:11:38 > 0:11:42The squirrel will just have to start again.
0:11:44 > 0:11:48Luckily, this year, the trees are being particularly generous.
0:11:56 > 0:11:59A Clark's nutcracker.
0:11:59 > 0:12:03This is what the tree has been waiting for.
0:12:07 > 0:12:09With its perfectly-shaped beak,
0:12:09 > 0:12:12it prises the nuts from the cones
0:12:12 > 0:12:16and tucks them, one by one, into a special pouch under its tongue...
0:12:18 > 0:12:21..up to 150 at a time -
0:12:21 > 0:12:25a fifth of its entire body weight.
0:12:44 > 0:12:47Then it flies as much as 15 miles away
0:12:47 > 0:12:52and drills the nuts into the ground in sets of ten...
0:13:00 > 0:13:04..placing a stone on top of the stash to mark the site.
0:13:15 > 0:13:20It goes back for more...
0:13:20 > 0:13:21and more.
0:13:26 > 0:13:32Over the autumn, a single bird can bury 30,000 nuts
0:13:32 > 0:13:34across an area of 100 square miles.
0:13:39 > 0:13:42When the winter comes, it will remember the location
0:13:42 > 0:13:44of a staggering 70% of these seeds,
0:13:44 > 0:13:47even when hidden beneath the snow.
0:13:52 > 0:13:56But as it remembers its way into surviving the winter,
0:13:56 > 0:14:00it becomes the whitebark's greatest ally.
0:14:02 > 0:14:06Although its feat of memory is extraordinary,
0:14:06 > 0:14:09for every 1,000 seeds it buries,
0:14:09 > 0:14:11it still forgets 300.
0:14:14 > 0:14:16From all those missed seeds,
0:14:16 > 0:14:19carried far and wide across Yellowstone,
0:14:19 > 0:14:23new whitebark pines will germinate next spring.
0:14:48 > 0:14:52It's now September and the elk have made their way down to graze
0:14:52 > 0:14:55where the grass on the river banks is still green
0:14:55 > 0:15:00and they can browse the nutritious shoots of young willow trees.
0:15:17 > 0:15:20The males are now upping their game.
0:15:21 > 0:15:26This bull urinates on himself to increase his masculine appeal.
0:15:28 > 0:15:31And by thrashing his antlers to decorate them,
0:15:31 > 0:15:34he hopes to make himself look more impressive.
0:15:43 > 0:15:46ELK BELLOWS
0:15:47 > 0:15:50The females are paying a little more attention now.
0:15:54 > 0:15:58The bull has succeeded in gathering a fair-sized harem.
0:16:02 > 0:16:06But the females are still not quite ready to mate.
0:16:06 > 0:16:10They are now focused on feeding as much as they can
0:16:10 > 0:16:12before moving lower still.
0:16:18 > 0:16:21But the elk are being watched.
0:16:21 > 0:16:23WOLVES HOWL
0:16:27 > 0:16:32Over the summer, wolves have been less mobile because of their young pups.
0:16:32 > 0:16:34But their strength is building again.
0:16:50 > 0:16:54The elk get twitchy and head for the cover of trees.
0:17:03 > 0:17:05They may be a little safer here.
0:17:08 > 0:17:13But the food in the forest is far less nutritious than on the river banks.
0:17:18 > 0:17:22If they want to eat well and avoid wolves this winter,
0:17:22 > 0:17:24they'll need to keep on moving.
0:17:35 > 0:17:37As the elk move gradually downwards,
0:17:37 > 0:17:41they follow the rivers out of Yellowstone's central plateau.
0:17:47 > 0:17:50The rivers, in turn, follow the path of glaciers
0:17:50 > 0:17:54that flowed from this great bowl in the last ice age
0:17:54 > 0:17:58and carved their way right through the surrounding mountains.
0:18:05 > 0:18:09Today, these valleys are escape routes for animals
0:18:09 > 0:18:12from the returning ice of winter.
0:18:20 > 0:18:24Lower down, the valleys broaden,
0:18:24 > 0:18:26the rivers slow,
0:18:26 > 0:18:31and a richer variety of trees grows in the alluvial soils.
0:18:36 > 0:18:40The perfect home for Yellowstone's most industrious creature.
0:18:56 > 0:19:00A beaver can fell a cottonwood tree in just a few hours...
0:19:01 > 0:19:03..hundreds in a year.
0:19:08 > 0:19:12The beaver doesn't chew through the whole trunk -
0:19:12 > 0:19:14just enough to make the tree unstable.
0:19:14 > 0:19:16It then retreats...
0:19:16 > 0:19:19and lets the wind do the rest.
0:19:44 > 0:19:48It cuts branches into more manageable lengths
0:19:48 > 0:19:53and swims them down a network of purpose-built canals towards a dam.
0:19:57 > 0:20:01The pond gives this beaver protection from predators
0:20:01 > 0:20:05and the canals allow it to forage far into the forest,
0:20:05 > 0:20:09carrying many times its own weight with ease.
0:20:16 > 0:20:20Autumn is the busiest time of year for beavers.
0:20:20 > 0:20:23It won't be so easy to make repairs when the pond is frozen over.
0:20:36 > 0:20:39The sound of running water is their stimulus
0:20:39 > 0:20:42to shore up gaps with timber and plug leaks with mud.
0:20:50 > 0:20:53But the dam not only serves the beavers.
0:21:02 > 0:21:06Moose come here from the forests around to feed on weeds
0:21:06 > 0:21:09that thrive in the beavers' shallow pond.
0:21:10 > 0:21:13The weed is rich in vital sodium
0:21:13 > 0:21:16that the forest can't easily provide.
0:21:20 > 0:21:23But now that winter is approaching,
0:21:23 > 0:21:27another essential role for the dam is revealed.
0:21:37 > 0:21:41These smaller branches are not for fixing the dam...
0:21:42 > 0:21:44..they're for eating.
0:21:54 > 0:21:58The beaver secures them to the mud in the lake bottom.
0:22:03 > 0:22:07In just a few weeks, this lake will be frozen
0:22:07 > 0:22:12and the beavers won't be able to cut and move trees
0:22:12 > 0:22:15but they will be able to swim right under the ice
0:22:15 > 0:22:17to feed from this underwater larder.
0:22:26 > 0:22:28Moose also eat twigs and branches
0:22:28 > 0:22:32and often try to take advantage of the beavers' hard labour.
0:22:39 > 0:22:44This young male is getting a little too close to the beavers' larder.
0:22:58 > 0:23:00Autumn is not a time for sharing.
0:23:22 > 0:23:23It's mid September.
0:23:27 > 0:23:29As the sun drops further in the sky,
0:23:29 > 0:23:35the aspens, cottonwoods and maples start shutting down for the winter.
0:23:36 > 0:23:41They now digest the green pigments in their leaves,
0:23:41 > 0:23:46to claw back what nutrients they can into the trunk and roots.
0:23:46 > 0:23:50What's left behind make the colours of Autumn.
0:24:34 > 0:24:38Groves of aspen all turn at the same time.
0:24:43 > 0:24:46Each grove descended from one tree,
0:24:46 > 0:24:49interconnected by roots,
0:24:49 > 0:24:51colour co-ordinated.
0:25:05 > 0:25:08As cold air sinks further down from the mountains,
0:25:08 > 0:25:12it brings Autumn mists to Yellowstone's valleys.
0:25:24 > 0:25:26It was in the Autumn of 1870
0:25:26 > 0:25:30that the first official exploration party to Yellowstone
0:25:30 > 0:25:35began to plan for the creation of the world's first national park...
0:25:37 > 0:25:39..the beauty of Yellowstone's autumn
0:25:39 > 0:25:43inspiring a complete change in the way we value the wild.
0:25:49 > 0:25:52ELK BELLOW
0:26:14 > 0:26:19For the last six weeks of strutting and herding,
0:26:19 > 0:26:21male elk have eaten almost nothing.
0:26:21 > 0:26:23They are exhausted.
0:26:27 > 0:26:29MALE ELK BELLOWS
0:26:33 > 0:26:35This bull has done well.
0:26:35 > 0:26:38He has successfully held on to his harem
0:26:38 > 0:26:42and now the females are finally coming into season.
0:26:46 > 0:26:49But they are being distracted by another male.
0:26:54 > 0:26:58If a bull elk can't dominate all rivals,
0:26:58 > 0:27:00he can't have access to the females
0:27:00 > 0:27:03and all his effort will have been in vain.
0:27:04 > 0:27:08Now he must gather the last of his strength.
0:27:09 > 0:27:12The rival wants to take him on.
0:27:26 > 0:27:30The aim is to get an antler point into his neck.
0:27:34 > 0:27:36But they are evenly matched.
0:27:36 > 0:27:39Neither can penetrate the other's guard.
0:27:42 > 0:27:44Now it's all about power.
0:27:46 > 0:27:50A well-aimed thrust or a broken neck will kill.
0:28:16 > 0:28:21This challenger is lucky to get off with a parting stab in the rump.
0:28:38 > 0:28:41The victor returns to his females.
0:28:41 > 0:28:43His young will be born next spring.
0:28:52 > 0:28:55But the prospects are not so good for a defeated bull.
0:28:55 > 0:28:56After all his effort,
0:28:56 > 0:29:01he will now have to wait until next autumn to try his luck again.
0:29:02 > 0:29:04That's if he even makes it.
0:29:07 > 0:29:09Bull elk, exhausted by the rut,
0:29:09 > 0:29:13struggle to survive the Yellowstone winter.
0:29:26 > 0:29:30It's now October and the winter is catching up with the elk once more.
0:29:33 > 0:29:38An early flurry of snow is a sign that it's time to make a decision.
0:29:39 > 0:29:44To stay is to face the certainty of snow and wolves.
0:29:44 > 0:29:46To go offers the chance of an easier life
0:29:46 > 0:29:50but the uncertainty of the world beyond Yellowstone.
0:29:50 > 0:29:52ELK BELLOW
0:30:09 > 0:30:13Every Autumn, thousands of elk do leave Yellowstone
0:30:13 > 0:30:16and as they go they cross an invisible line
0:30:16 > 0:30:20out of the protection of the national park.
0:30:21 > 0:30:24Here, they confront new danger.
0:30:32 > 0:30:36Dressed in orange to avoid each other,
0:30:36 > 0:30:41but a colour that elk can't see, hunters come to the forests
0:30:41 > 0:30:46just around Yellowstone in October to shoot elk.
0:31:12 > 0:31:13GUN FIRES
0:31:16 > 0:31:20Elk, of course, have no understanding of park boundaries
0:31:20 > 0:31:22or of Yellowstone.
0:31:24 > 0:31:27To them, this is simply an instinctive migration
0:31:27 > 0:31:31to find more hospitable land and so they just keep going.
0:31:39 > 0:31:41Beyond the ring of hunting lands,
0:31:41 > 0:31:44the natural mosaic of forest and grass
0:31:44 > 0:31:47is replaced by an alien geometry.
0:31:51 > 0:31:53Circles of irrigated grass.
0:31:56 > 0:31:58Squares of maize.
0:31:59 > 0:32:02Golf courses.
0:32:02 > 0:32:05The signature patterns of mankind.
0:32:09 > 0:32:12It's unlikely they'll be welcome here.
0:32:21 > 0:32:24By now, the pronghorn have pushed further
0:32:24 > 0:32:27than any of Yellowstone's animals.
0:32:27 > 0:32:31Out of forests, through farmland and down into the wide prairies
0:32:31 > 0:32:34at the foot of the Rocky Mountains themselves.
0:32:44 > 0:32:47Their search for winter grazing takes them over a hundred miles
0:32:47 > 0:32:50to the south of Yellowstone -
0:32:50 > 0:32:53the longest migration of any American mammal.
0:32:58 > 0:33:02They have made this journey every year since the last ice age.
0:33:04 > 0:33:06But nowadays they have a problem.
0:33:12 > 0:33:13HORN BLARES
0:33:13 > 0:33:17Their traditional winter refuges lie right above
0:33:17 > 0:33:21some of the richest natural gas deposits in America.
0:33:28 > 0:33:31The wells are no direct threat to pronghorn.
0:33:31 > 0:33:32HORN BLARES
0:33:36 > 0:33:37But pronghorn are timid.
0:33:41 > 0:33:43At the slightest noise they run
0:33:43 > 0:33:48and when they run, they run at 60 miles per hour.
0:33:51 > 0:33:55They evolved to avoid cheetahs, not juggernauts.
0:33:58 > 0:34:00Trucks, fences,
0:34:00 > 0:34:03and the disturbance from the wells have put pronghorn at risk.
0:34:07 > 0:34:10There are 1.2 million acres here
0:34:10 > 0:34:15but 75% of it has now been earmarked for gas and oil.
0:34:25 > 0:34:28Back in the farmland, the elk have found food.
0:34:31 > 0:34:34But this grass is not meant for them.
0:34:36 > 0:34:39CATTLE MOO
0:34:46 > 0:34:48Ranchers will tolerate elk,
0:34:48 > 0:34:53as long as they don't compete too much with their cattle.
0:34:59 > 0:35:00But as the elk move in,
0:35:00 > 0:35:05their old enemy follows them out of Yellowstone -
0:35:05 > 0:35:08an animal that's more difficult for ranchers to accept.
0:35:14 > 0:35:18In their minds, fear of the wolf runs deep.
0:35:24 > 0:35:27Even Yellowstone lost its wolves.
0:35:27 > 0:35:30They were wiped out over 80 years ago.
0:35:33 > 0:35:38After years of prejudice, they were reintroduced in 1995...
0:35:39 > 0:35:42..brought back by the authorities
0:35:42 > 0:35:45to restore Yellowstone's natural balance.
0:35:49 > 0:35:51But the wolves have done so well
0:35:51 > 0:35:55that now they are moving out of the park looking for new territories...
0:35:56 > 0:35:57..and prey.
0:36:00 > 0:36:05Out here, it's clearer to see why wolves have a bad reputation.
0:36:20 > 0:36:24If ranchers' cattle are at risk, by law, wolves can be shot.
0:36:34 > 0:36:40As wolves come back, ranchers are being forced to return to the old ways...
0:36:43 > 0:36:47..to get back into the saddle and protect their herds.
0:36:52 > 0:36:55GADGET BEEPS
0:37:00 > 0:37:03But opinion is changing.
0:37:03 > 0:37:06Working with scientists, who have radio-collared Yellowstone wolves,
0:37:06 > 0:37:09ranchers can now keep track of them
0:37:09 > 0:37:12and when they know they are near, shoot not to kill
0:37:12 > 0:37:13but to scare them away.
0:37:18 > 0:37:20GUNFIRE ECHOES
0:37:34 > 0:37:37The return of the wolf will always be controversial.
0:37:40 > 0:37:42But evidence is now emerging
0:37:42 > 0:37:46that wolves are far more important than anyone imagined...
0:37:48 > 0:37:52..especially back in the heart of Yellowstone.
0:37:57 > 0:38:00It's nearly the end of October.
0:38:00 > 0:38:03The cold autumn nights have brought a thin crust of ice
0:38:03 > 0:38:06to a beaver's pond.
0:38:07 > 0:38:11Unlike in the river valleys below, up here,
0:38:11 > 0:38:13there are not many tall cottonwood trees,
0:38:13 > 0:38:16so this beaver has built his dam from the shoots of young willows
0:38:16 > 0:38:20sprouting all along the side of his pond.
0:38:35 > 0:38:37But he is something of a novelty.
0:38:39 > 0:38:43Even by the time Yellowstone was made a national park,
0:38:43 > 0:38:48beavers had been virtually hunted to extinction by fur trappers.
0:38:54 > 0:38:58They only began to reappear here in 1995 -
0:38:58 > 0:39:00the year the wolves came back.
0:39:06 > 0:39:09Now wolves are chasing elk again,
0:39:09 > 0:39:12elk have less time to eat willows,
0:39:12 > 0:39:15so willows are sprouting everywhere.
0:39:17 > 0:39:21Today, as winter approaches, all over Yellowstone,
0:39:21 > 0:39:24beavers are using those willows
0:39:24 > 0:39:28to put the finishing touches to a dam-building renaissance.
0:39:41 > 0:39:45And for every dam, there is a new habitat for new life
0:39:45 > 0:39:49and a richer, more diverse, Yellowstone.
0:39:58 > 0:40:01SWANS HOOT
0:40:07 > 0:40:12But just as Yellowstone reveals the complexity of life,
0:40:12 > 0:40:14it also exposes its fragility.
0:40:19 > 0:40:21On its lofty ridges,
0:40:21 > 0:40:25there are signs that all is not well with the whitebark pine.
0:40:29 > 0:40:33From above, it looks like autumn colours in an evergreen world.
0:40:39 > 0:40:43But these trees are dying.
0:40:52 > 0:40:56Small eruptions of resin dot the trunk of the tree -
0:40:56 > 0:41:00evidence of an invasion.
0:41:08 > 0:41:12Tiny beetles are chewing through the tree's outer defences.
0:41:20 > 0:41:26Once inside, they lay eggs that turn into larvae that eat the tree.
0:41:34 > 0:41:37Each tree that is lost threatens all the animals
0:41:37 > 0:41:40that rely on its autumn bounty.
0:41:45 > 0:41:50The only thing that can stop the beetles is extreme cold.
0:41:51 > 0:41:54But recently, the climate here
0:41:54 > 0:41:56has been getting warmer and warmer.
0:41:59 > 0:42:02No national park can protect against that.
0:42:08 > 0:42:11This is a tree that needs a cold winter.
0:42:23 > 0:42:27It's November and the elk have found their feeding grounds just in time -
0:42:27 > 0:42:31the snows of winter at their heels.
0:42:37 > 0:42:41Here they join other herds who come to this place every year,
0:42:41 > 0:42:45where the snow will be less deep and life a little easier.
0:42:54 > 0:42:59But today, they graze on an island of grass surrounded by development.
0:43:04 > 0:43:09As they run from winter, their fate outside the national park
0:43:09 > 0:43:14is decided not by the cold but by people.
0:43:19 > 0:43:21These elk are lucky.
0:43:21 > 0:43:25This refuge has been kept aside to give them some degree of sanctuary.
0:43:32 > 0:43:34So although the park isn't big enough
0:43:34 > 0:43:37to protect all its animals all the time,
0:43:37 > 0:43:41its influence can spread beyond its boundaries
0:43:41 > 0:43:45and if even ranchers can come to tolerate wolves,
0:43:45 > 0:43:46then anything is possible.
0:44:04 > 0:44:06In the mountains of Yellowstone,
0:44:06 > 0:44:10where the elk's bugle signalled the beginning of autumn
0:44:10 > 0:44:14just two months ago, all seems deserted.
0:44:20 > 0:44:25But now, the final act of the season is about to take place.
0:44:25 > 0:44:30From out of apparently nowhere come the bighorn sheep.
0:44:32 > 0:44:34The toughest of all Yellowstone's animals,
0:44:34 > 0:44:38they can stay here all winter on slopes and crags
0:44:38 > 0:44:40that the biting wind keeps clear of snow.
0:44:40 > 0:44:43WIND HOWLS
0:44:49 > 0:44:53Now, they are coming together to rut.
0:44:53 > 0:44:58Like elk, the males battle for females,
0:44:58 > 0:45:02but where elk do their best to avoid fights,
0:45:02 > 0:45:04bighorn relish them.
0:45:13 > 0:45:15A quick test of horn size
0:45:15 > 0:45:19and of other important bits of anatomy,
0:45:19 > 0:45:21and the males get straight to the point
0:45:21 > 0:45:24of sorting out who is toughest.
0:46:00 > 0:46:05As the sound of their battles echoes across the Yellowstone wilderness,
0:46:05 > 0:46:07it marks the end of autumn.
0:46:14 > 0:46:17Now, the great change is coming again.
0:46:19 > 0:46:21Winter is here.
0:46:52 > 0:46:55As the snow returns to Yellowstone,
0:46:55 > 0:46:58it seems like the clock is turning back.
0:47:02 > 0:47:06All traces of the human world are covered up.
0:47:11 > 0:47:14A reminder that when the heart of this great wilderness
0:47:14 > 0:47:17was made a national park nearly 140 years ago,
0:47:17 > 0:47:20it was one of the most remote places on earth.
0:47:22 > 0:47:26But as the human world has crept up on Yellowstone,
0:47:26 > 0:47:30the true value of this remarkable space has become ever clearer.
0:47:38 > 0:47:42Though in many ways, Yellowstone is not big enough, its influence
0:47:42 > 0:47:44reaches far beyond its boundaries,
0:47:44 > 0:47:46not just to the land around,
0:47:46 > 0:47:50but wherever there is a wilderness preserved for its own sake.
0:47:58 > 0:48:01Here, in the heart of America,
0:48:01 > 0:48:04the first national park was born.
0:48:08 > 0:48:10An idea that has led the way
0:48:10 > 0:48:16in re-defining our relationship with the wild all over the world.
0:48:19 > 0:48:23Some say America's best idea.
0:48:41 > 0:48:45Bringing Yellowstone's unique natural beauty to the screen
0:48:45 > 0:48:47would have been impossible
0:48:47 > 0:48:51without the tireless help of the local experts that know it
0:48:51 > 0:48:55like the back of their hand. Each has their own story to tell.
0:49:10 > 0:49:12Howdy, my name's Mike Kasic.
0:49:12 > 0:49:15I'm the sound recordist for the Yellowstone programme.
0:49:20 > 0:49:22I live in Livingston, Montana,
0:49:22 > 0:49:25just north of the Yellowstone National Park
0:49:25 > 0:49:27right by the Yellowstone River.
0:49:27 > 0:49:32Being a sound recordist isn't the only thing that I do.
0:49:32 > 0:49:33My friends say that I'm half fish.
0:49:33 > 0:49:35Yeah, he's half fish.
0:49:44 > 0:49:48I like to spend my days swimming the Yellowstone River.
0:49:55 > 0:49:57I just let the current take me.
0:50:07 > 0:50:12And sometimes when I want to stop, I catch an eddy just like the fish.
0:50:17 > 0:50:19This is the Yellowstone River.
0:50:21 > 0:50:24This is the same river that flows out the heart of Yellowstone,
0:50:24 > 0:50:28past geysers, and bison to just outside my door.
0:50:38 > 0:50:39This is heavy traffic.
0:50:43 > 0:50:45Sometimes I have to share the water.
0:50:52 > 0:50:53Brr!
0:51:02 > 0:51:05This is the heart of the wild.
0:51:06 > 0:51:11A life blood that courses through wilderness and ends in the prairie.
0:51:15 > 0:51:17Not a single dam holds back its waters -
0:51:17 > 0:51:21it's the longest free-flowing river around.
0:51:21 > 0:51:25It's what many rivers long to be, unstoppable.
0:51:27 > 0:51:29This is the West as it was meant to be.
0:51:54 > 0:51:56One of the reasons I love to do this
0:51:56 > 0:52:01is because beneath the waves swims a creature that I've grown fond of.
0:52:01 > 0:52:04The Yellowstone cutthroat trout.
0:52:05 > 0:52:08They just have an aura about them.
0:52:08 > 0:52:12With big red slits under their jaws, they are simply unmistakeable.
0:52:15 > 0:52:19The Yellowstone cutthroat trout is the soul of this river.
0:52:19 > 0:52:22It's been here for thousands of years.
0:52:24 > 0:52:27They're a wild animal,
0:52:27 > 0:52:33they're in an underwater wilderness that is spectacular and amazing
0:52:33 > 0:52:36and I think it's the best part of Yellowstone.
0:52:55 > 0:52:57I know it's a little quirky,
0:52:57 > 0:52:59but looking for fish is what I like to do.
0:53:03 > 0:53:06When I'm in the river I see the world from a fish's point of view.
0:53:06 > 0:53:11When they look up, what they're looking for is food.
0:53:20 > 0:53:24This is the Mother's Day Caddis Fly hatch.
0:53:24 > 0:53:25Trout food.
0:53:27 > 0:53:31This is another of the Yellowstone's amazing events.
0:53:31 > 0:53:34I'm swimming along and there's not a fly to be seen
0:53:34 > 0:53:40and suddenly there's millions, and a few hours later it's back to nothing.
0:53:43 > 0:53:47Caddis flies are not the only food in this river.
0:53:47 > 0:53:51Many animals need a cutthroat trout to survive -
0:53:51 > 0:53:55ospreys, grizzly bears, otters, the list goes on.
0:53:59 > 0:54:02But the more I see this world like the cutthroat sees it,
0:54:02 > 0:54:05the more I see that things are not quite right.
0:54:06 > 0:54:08Long ago the US Fish Commission
0:54:08 > 0:54:12wanted more fish in Yellowstone for sport fishing,
0:54:12 > 0:54:17so they stocked 310 million fish from Scotland and the Great Lakes
0:54:17 > 0:54:20and one of the fish they chose was a lake trout.
0:54:20 > 0:54:24The trouble with lake trout is they like to eat cutthroat.
0:54:24 > 0:54:28In fact, 80 to 90% of their diet is cutthroat trout.
0:54:28 > 0:54:34I'm not sure how cutthroats like these stand a chance.
0:54:34 > 0:54:37The cutthroat are up against a lot of things besides lake trout -
0:54:37 > 0:54:41warming river temperatures, pollution, industrial development.
0:54:41 > 0:54:44And if they can survive all these things,
0:54:44 > 0:54:48will they then survive being gobbled up by lake trout?
0:54:48 > 0:54:53This is Yellowstone Lake - it's nearly 2,200 metres.
0:54:58 > 0:55:02Right here's Carrington Island which is...
0:55:02 > 0:55:08the primary spawning grounds for the lake trout
0:55:08 > 0:55:11and it's the kind of site of the big battle that the biologists
0:55:11 > 0:55:14and the National Park Service has going against these fish.
0:55:20 > 0:55:24So this is the National Park Service boat, the drift gill net boat,
0:55:24 > 0:55:31and they are out here gilling, fishing for lake trout.
0:55:54 > 0:55:57By the end of the season,
0:55:57 > 0:56:02they will have taken about 350,000 lake trout out of Yellowstone Lake.
0:56:05 > 0:56:07It's hard to see so many fish dying,
0:56:07 > 0:56:09but watching a species disappear would be even harder.
0:56:13 > 0:56:17They caught this fish before she had time to spawn this year.
0:56:20 > 0:56:22They're getting many more fish every year,
0:56:22 > 0:56:27so they're making progress, but they haven't won the war by any means.
0:56:37 > 0:56:39But now the cutthroat trout
0:56:39 > 0:56:43are spawning, one of the natural world's most fantastic spectacles.
0:56:43 > 0:56:48These fish swim up this creek every year to spawn and it's here
0:56:48 > 0:56:53in their native gravel that more fish will begin the cycle again.
0:56:53 > 0:56:55With that there's hope,
0:56:55 > 0:56:59hope that against all odds these fish will survive.
0:57:05 > 0:57:06In 1,000 years,
0:57:06 > 0:57:10I hope the cutthroat trout will swim these waters.
0:57:13 > 0:57:16The river is more than just its water.
0:57:16 > 0:57:22The Yellowstone is a river flowing fast and free like no other,
0:57:22 > 0:57:24a wilderness underwater.
0:57:28 > 0:57:31I need this kind of wilderness,
0:57:31 > 0:57:33I need it for my heart to beat right.
0:57:33 > 0:57:35Take it away,
0:57:35 > 0:57:40and I think we all lose the ability to understand the world.
0:57:47 > 0:57:50The secret to swimming in the river
0:57:50 > 0:57:55is to let go, let the river take you wherever that may be.
0:57:55 > 0:57:58I think that is a lesson we could all learn from.
0:58:14 > 0:58:17I guess for now I just feel lucky that I've had the chance to swim
0:58:17 > 0:58:21in a wild river with the Yellowstone cutthroat trout.
0:58:46 > 0:58:49Subtitles by Red Bee Media Ltd
0:58:49 > 0:58:52E-mail subtitling@bbc.co.uk
0:58:59 > 0:59:01Spring is arriving - in a whirlwind of pink.
0:59:01 > 0:59:04We're in Japan to celebrate the sakura.