Vast open plains.

 Immense spaces.

 Eerie silence.

 But any feeling of emptiness is an illusion.

 The plains of our planet support the greatest gatherings of wildlife on Earth.

 At the heart of all that happens here is a single living thing.

 Grass.

 This miraculous plant covers a quarter of all the lands of the Earth.

----

 Grasslands exist wherever

  there is a little rainbut not enough to sustain a forest.

 Some are huge.

 The Central Asian Steppe alone

 extends one third of the way around our planet.

 It's summerand eagles effortlessly cruise the thermals,

 scanning the ground beneath for signs of prey.

 In the distant reaches of outer Mongolia,

 one of the planet's great migrations is underway.

  Few people ever see this extraordinary annual event.

 Mongolian gazelle.

Two million are thought to live herebut no one really knows.

 For much of the timethey're scattered through this vast landscape,

 but once a year they come together to have their young.

 Nearly all will give birth within the next   days.

ut in the opencommunal calving is the safest way to have young.

 With so many pairs of eyes keeping watch,

 it's almost impossible for predators to sneak up.

There are no bushesno trees. There's only one thing to hide behind.

 Grass.

 And it's not very effective.

 Predators also have a hard time raising their young on open grassland.

Without treeseagles have to nest directly on the ground.

 All the inhabitants of the Great Plains are exposed to the elements.

(THUNDER RUMBLING)

 Fire sparks panic in the herd.

 Gazelles are born to run

 and even young calves easily outpace the flames

 if they can avoid being trampled.

 With nothing to stand in its way

 the blaze consumes anything that can't flee.

Huge quantities of grassvaluable foodhave been lost.

 And with itthe old and the weak.

  The gazelles move on to new pastures and leave the desolation behind them.

 From the ashes rises the phoenix.

 Grassthe incredible survivor.

 Because it grows from a protected part at the base of its stems,

 grass is almost indestructible.

 Able to repair and reproduce itself rapidly

 it covers more of the Earth's land than any other plant

 and feeds more wildlife than any other.

 Red-billed quelea.

 ne and a half billion swarm across the savannahs of Africa.

 These are the most numerous birds on Earth.

 Some flocks are so vast

 that they can take five hours to pass overhead.

 nly grass can feed plagues of these proportions.

 The ravenous hordes devour the seeds.

 And the leaves and stems are cropped by great herds of antelope.

 The East African savannahs alone sustain nearly two million wildebeest.

 They trim the grass down to its rootsleaving little in their wake

 but within days the plant will recover

 and continue to sustain the biggest herds on Earth.

 Grass is not confined to the tropics.

 It manages to grow even in the bitter conditions of the Arctic.

Beyond the limits of the last treethe planet is barren and ice-locked.

 A frozen no-man's land at the end of the Earth.

  But for a short time each yearthe longdark winter releases its grip.

 Temperatures rise

 and grass that has lain dormant and frozen throughout the winter

 sprouts once more.

 Green returns to the Arctic.

The receding ice reveals an immense flat plain the size of Australia.

 This is the Arctic tundra.

It's a desolatesilent wilderness.

 But it's about to change.

 Snow geese.

 They winter along the Gulf of Mexico

 and in spring they fly the entire length of North America

 to reach the Arctic tundra.

 Five million birds make this journey every year.

 Their marathon migration is almost miles long

 and has taken them three months.

Exhausted and starvingthey touch down inside the Arctic Circle,

 back at their traditional breeding grounds at last.

 Snow geese pair for life.

 As soon as couples arrivethey must stake a claim to a nesting patch.

Ideal sites are in short supply and quarrelsome neighbours are all around.

(SQUAWKING)

 Disputes can be vicious.

 Point taken!

 It's a long way to travelbut for a short periodthe tundra is the ideal place for a grazer.

 The grass grows vigorously during the shortintense summer

 and there are fewer predators than further south.

 Heregeese can nest on the ground in relative safety.

 Nonethelessthis female must incubate her eggs for three weeks

 and throughout this time she will be very vulnerable.

 An Arctic fox surveys the colony.

 She's been waiting for the geese all winter.

 Sneaking up unnoticed is impossible.

 Perhaps fortune will favour the bold.

(HNKING)

The colony is well-defended. There are no easy pickings here.

(HNKING)

 She's driven away from every nest

 but hunger compels her to continue.

(HNKING)

 There are more eggs here than she can possibly eat now.

 But the nesting season is short.

 So she stashes much of her plunder for later in the year

 when all the geese have gone.

 Further southother bigger predators prowl the tundra.

 Wolves.

 For themfinding food on the plains is an even greater challenge.

Not only is their prey seasonalit's also hard to find.

 They've been searching for days without a sign.

Somewhere in this immense landscape there is food for them.

 This is it.

 Caribou.

 Travelling  miles a day,

 they can cover nearly miles during the summer months.

 The wolves will starve if they don't find the caribou.

 But it's no easy task to locate prey that never stops travelling.

 Biting flies and the quest for new pasture drives the migration ever onwards.

 A wolf has finally picked up the trail.

 The caribou are close.

 At lasta chance.

 The hunt is on.

 The wolf panics the herdand the weak and young are singled out.

 A calf is separated from its mother.

At the goose colonyit's high summer and eggs are hatching.

 The young all emerge within a day or twoa marvel of timing.

 The colony is now home to a million goslings.

(HNKING)

 The fox is still gathering all she can get.

 Sometimes one mouth simply isn't enough.

 ne will have to do.

 Not all food is stored.

 Some is needed right now.

 She has seven hungry cubs to feed.

 As their appetites grow

 the mother must work tirelessly to raise her family.

 nly fathealthy cubs will survive the Arctic winter.

 The vast majority of the goslings are still flourishing.

 Their parents lead them down to the safety of the water

 as soon as they're strong enough to make the journey.

 For the foxesboom time has come to an end.

 But the mother has given her cubs the best possible start in life.

 The geese will continue grazing the tundra

 until the summer ends and they're forced to head south for the winter.

 At these latitudesthe sun's rays are weak

 and grass can only grow here for a few months a year.

,But further southsummers are longer and the grasslands flourish.

 The prairies of North America.

  This rich pasture once supported the greatest herds ever seen on our planet.

 There were once  million bison,

 but no animal is immune to intensive hunting by man

 or the destruction of its habitat.

 And a century agothe bison were reduced to barely  ,.

Nowthanks to rigorous protectionthe species is recovering.

 The growing season is long

 and the grass here can support herds all year round.

 Male bison weigh in at one ton.

 In high summerthe bulls are fat from the rich grazing

. and in prime conditionbut only a few will mate.

 Exactly which few is about to be decided.

(BELLWING)

n temperate plains around the worldsummer is a time for growth and reproduction.

 Now the grass produces its flowers.

 New colours also come to the plains.

 The northern flowering is mirrored by the grasslands of the southern hemisphere,

 and nowhere is more impressive than on the veldt of South Africa.

 Not all temperate plains are so rich and colourful in the summer.

 This is midsummer on the Tibetan plateau,

 the highest great plain in the world.

 Despite the conditionsgrass survives

 and in sufficient quantities to support the highest of all grazing herds

 those of the wild yak.

 Even in summerlife is hard.

 Temperatures rarely rise above freezing and the air is thin.

It's also exceptionally dry for one very big reason,

 the Himalayas.

 The great mountain range acts as a barrier

 preventing clouds moving in from the south

 and this casts a giant rain shadow

 that leaves Tibet high and dry.

 Grass clings to life

 even as desiccating winds remove what little moisture remains in the soil.

 So long as grass can survive

 so can grazers.

 Wild ass.

 The males are fighting to win territories.

 Those that hold the best are more likely to attract a herd of females.

 It's a frisky business.

 That counts as a victory,

 but he can't assume the females will actually turn up.

 Female asses are mysterious creatures.

 They come and go as they please

 and much of their behaviour seems unfathomable to an outsider.

 They're the great nomads of the plateau

 and will often trek vast distances across these parched plains

 in search of oases.

 But when they do find paradise,

  they are liable to feed and drink for just a few hours

 and then head back to the dust for no apparent reason.

 Wild ass are the most conspicuous pioneers of this high frontier,

 but the most numerous grazer in Tibet lives underground.

 Pikaa relative of the rabbit. Ittoofeeds on grass.

 n the exposed plateau

 pikas never stray far from their burrows.

 But even sosquatters will move in given half a chance.

(lie) While ground peckers and snow finches can be a nuisance,

 they're worth tolerating because they provide a valuable early warning system.

  The bizarre Tibetan fox. The pika's nemesis.

When stalkingit keeps below the skyline

 perhaps helped by its curious body shape.

 But why the square head?

 In summer

 the Tibetan plateau heats up,

 drawing in warmwet air from the south.

 But the water never arrives.

 As the moist air approachesit's forced upwards by the Himalayas

 and condenses into huge rain clouds.

 These clouds drop all their water on the southern side of the mountains.

 The very peaks that keep Tibet dry

 are responsible for the monsoon rains falling farther south

 and the greening of India.

Heresoaked by rain and bathed in tropical sun,

 grass reaches its full potential.

 Elephant grass is the tallest in the world.

 Grass that towers over an elephant

 can conceal all sorts of surprises.

 The male Lesser Florican.

 It's hard work getting noticed when you go courting in high grass.

 The long-grass plains of tropical India

 are home to some of the largest grass-eating mammals on our planet.

 And some of the smallest.

 Pygmy hogs are no bigger than rabbits.

 They're the tiniest and rarest of all wild pigs.

 The female is busy collecting grass

 but not for eating.

 She's building a nest.

 Each piglet may be small enough to fit in the palm of a hand,

 but she does have .

 This is how grass can growgiven unlimited sunshine and water.

 But on most tropical plains across our planet

 the wet season is followed by a dry one.

 n the African savannahs,

 grazers are marching in search of grass and water.

  Without rainthese plains can become dust bowls.

 Grass can now lose its hold.

 Elephants are in immediate danger.

 They must drink almost daily.

 Driven on by thirst,

 they march hundreds of miles across the parched plains.

 Relying on memorythe matriarchs lead their families

 to those special water holes that saved them in previous years.

 This one still has water

 but they must share what remains

 with desperately thirsty animals of all kinds.

 These are tense times.

 The elephants dominate the water hole

 but as night falls the balance of power will shift.

(TRUMPETING)

 Thirsty herds continue to arrive throughout the night.

 It's a cooler time to travel.

 In the darknessthe tables turn.

 The elephant's night vision is little better than our own.

 But lions have much more sensitive eyes.

  The cats are hungry and the elephants seem to sense it.

 Lions don't usually hunt elephants,

 but desperate times require desperate measures.

 This herd contains calveseasier targets.

 But how to reach them?

(GRWLING)

 The adults encircle their young.

 It's an impenetrable wall of grey.

 A few exhausted stragglers are still arriving.

 ne of them is alone.

(TRUMPETING)

 But it's too big for the lions to tackle.

 This one looks a little smaller.

 A solitary lion stands no chance,

 but the whole pride is here.

There are  of them and they are specialist elephant hunters.

 This elephant will feed the whole pride for at least a week.

 Elephants know these drinking holes are dangerous,

 but they have no choice.

 The dramas that play out here are a savage reminder

 of how important water is for all life on these plains.

 As the dry season finally draws to a close

 Africa's baked savannahs undergo a radical change.

 Rain sweeps across the continent

 and grassthe great survivorrises again.

 And the herds return.

 For months they've been scattered over huge areas

 clinging to existence around tiny water holes.

 Nowthe good times are back.

 A few African savannahs are very special.

  Hererainwater from far and wide flows across the flat plains.

 Grass is submergedbut still it grows.

 Floodedburntbaked and frozen,

 grass can withstand it all.

 After six months of drought

 grass replaces dust over great areas.

  Fresh new shoots draw animals from great distances.

  Many undertake epic migrations to catch the boom time.

 Some resourceful animals live here all the year round.

 Baboons are permanent residents

 but they have to change their behaviour

 if they are to gather what they need on the newly flooded plains.

 There's plenty to eat

 but getting to it can be a little uncomfortable.

 New water poses problems for the youngsters,

 but they know where to find a dry seat.

 Ajuicy snail is ample recompense for sodden paws.

 Having survived the drybarren times,

. animals can now reap the rewards.

 n this seasonal planet

 the great plains are lands of feast and famine.

 At their peakthey support the greatest gatherings of wildlife found anywhere on Earth.