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A hundred years ago there were one and a half billion people on Earth.
Now,
over six billion crowd our fragile planet.
But even so,
there are still places barely touched by humanity.

This series will take to the last wildernesses,
and show you the planet and its wildlife as you have never seen them before.

Imagine our world without sun.
Male Emperor Penguins are facing the nearest that exists on planet Earth -
winter in Antarctica.
It's continuously dark and temperatures drop to minus seventy degrees centigrade.

The penguins stay when all other creatures have fled because each guards a treasure:
A single egg rested on the top of its feet and kept warm beneath the downy bulge of its stomach.

There is no food and no water for them,
and they will not see the sun again for four months.
Surely no greater ordeal is faced by any animal.

As the sun departs from the Antarctic it lightens the skies in the far north.

It's March and light returns to the high Arctic,
sweeping away four months of darkness.

A polar bear stirs.
She has been in her den the whole winter.
Her emergence marks the beginning of spring.
After months of confinement underground she slides down the slope.

Perhaps to clean her fur,
perhaps for sheer joy.
Her cubs gaze out of their bright new world for the very first time.
The female calls them,
but this steep slope is not the easiest place to take your first steps.

But they are hungry and eager to reach their mother,
who's delayed feeding them on this special day.

Now she lures them with the promise of milk,
the only food the cubs have known since they were born deaf and blind beneath the snow some two months ago.

Their mother has not eaten for five months,
and she has lost half her body weight.

Now she converts the last of her fat reserves into milk for her cubs.
The spring sun brings warmth but also a problem for the mother.
It starts to melt the sea ice.
That is where she hunts for the seal she needs to feed her cubs.

And she must get there before the ice breaks up.
For now, though,
it's still minus thirty degrees and the cubs must have the shelter of the den.

It's six days since the bears emerged and spring is advancing rapidly.

But even now blizzards can strike without warning.
Being so small,
the cubs are easily chilled,
and they will be more comfortable resting in the den.

But their mother must keep them out and active.
She's becoming weak from hunger,
and there's no food on these nursery slopes.

The sea ice still holds firm,
but it won't last much longer.
Day 10,
and the mother has led her cubs a mile from the den.
It's time to put them to the test.
They've grown enormously in confidence,
but they don't have their mother's sense of urgency.

At last it seems that they're ready for their journey,
and they're only just in time,
for a few miles from the coast the ice is already splitting.

Now the mother can start hunting for the seals they must have,
but she's leading her cubs into a dangerous new world.

Nearly half of all cubs die in their first year out on the ice.
Summer brings 24 hours of sunlight and the thawing shifting landscape.

Further south the winter snows have almost cleared from the Arctic tundra.
Northern Canada's wild frontier.
Here nature stages one of her greatest dramas -
Every year three million caribou migrate across the Arctic tundra.

The immensity of the herd can only be properly appreciated from the air.
Some herds travel over 2,000 miles a year in search of fresh pastures.
This is the longest overland migration made by any animal.
They're constantly on the move.
Newborn calves have to be up and running the day they are born.
But the vast herds do not travel alone.

Wolves.
Packs of them,
eight to ten strong,
shadow the migration.
And they are hungry.
It's the newly born calves that they are after.
Running directly at the herd is a ploy to generate panic.
The herd breaks up,
and now it's easier to target an individual.

In the chaos a calf is separated from its mother.
The calf is young,
but it can outrun the wolf if only it manages to keep its footing.
At this stage the odds are even -
either the caribou will make a mistake
or after a mile the wolf will give up.

Midsummer on the tundra and the sun does not set.
At these latitudes the sun's rays are glancing,
and not enough of their energy reaches the ground to enable trees to grow.
You'll need to travel 500 miles south from here before that is possible.

These stunted shrubs mark the tree line -
the beginning of this forest.
The needle-shaped leaves of the conifers are virtually inedible
so this forest supports very little animal life.

It's a silent place
where the snow is unmarked by footprints.
In the Arctic winter,
snow forms a continuous blanket across the land.

But as spring creeps up from the south
the forest is unveiled.

This vast forest circling the globe contains a third of all the trees on Earth,
and it produces so much oxygen that it changes the composition of the atmosphere.

As we travel south so the sun's influence grows stronger,
and at 50 degrees of latitude a radical transformation begins.

Summers here are long enough for broadleaf trees to replace cone trees.
Broadleaves are much easier to eat and digest,
so now animals can collect their share of the energy that has come from the sun.

It's summer,
and these forests are bustling with life.
But the good times will not last.
Broad leaves must be shed in winter for their damage by frost.

As they disappear,
so the land becomes barren with little for animals to eat.
The inhabitants must migrate,
hibernate,
or face months of near starvation.


5 Minutes

This leopard -
the rarest cat in the world.
Here,
in the forests of eastern Russia
the winter makes hunting very difficult.

Pray animals are scarce,
and there's no concealing vegetation.
The cub is a year old and still dependent on its mother.

Deer are frequent casualties of the harsh winter,
and these leopards are not above scavenging from a corpse.
African leopards could never survive here,
but the Russian cats have thick fur to shield them from the cold.
There are only forty of these leopards left in the wild,
and that number is falling.

Like so many creatures,
the cats have been pushed to the very edge of extinction by hunting,
and by the destruction of their habitat.

This leopard symbolizes the fragility of our natural heritage.
The future of an entire species hangs on survival of a tiny number of mothers like this one.

All animals, rare or common,
ultimately depend for their energy on the sun.

In Japan the arrival of the cherry blossom announces the beginning of spring.

The sun's energy brings color to the landscape.
The earth,
as it makes its annual journey around the sun,
spins on a tilted axis.

And it's this tilt that creates the seasons.
The advance of the seasons brings constant change.
As the sun's influence diminishes in the north,
so the forests of America begin to shut down
losing their leaves in preparation for the dark cold months ahead.

One season hands over to another.
Some organisms thrive on decay,
but most must make special preparations for winter and a life with little sun.

Whole populations of animals are now forced to travel great distances
in pursuit of food and warmth.

300,000 teal birds gather to escape from the Siberian winter by migrating south to Korea -
the world's entire population in a single flock.
But there are parts of the world that have no seasons.
In the tropics the sun's rays strike the earth head on
and their strength is more or less constant all year round.

That is why the jungle grows so vigorously,
and supports so much life.
This forest covers only 3 percent of the planet's surface,
but it contains more than 50 percent of all its plants and animals.

The canopy is particularly rich.
There are monkeys, birds
and millions of species of insects,
exactly how many we have no idea.

The character of the forest changes as we descend,
becoming ever darker and damper,
favoring different kinds of animals and plants.
Less than 2 percent of the sunlight reaches the floor,
but even here there is extraordinary variety.

In the great island of New Guinea,
there are 42 different species of birds of paradise,
each more bizarre than the last.

This forest is so rich that nourishing food can be gathered very quickly.
That leaves the male six-plumed bird of paradise with time to concentrate on other matters,
like tidying up his display area.

Everything must be spick and span.
All is ready.
Very impressive,
but no one is watching.
The superb bird of paradise calls to attract a female.
And he has more luck.

But what does he have to do to really impress her?
She retires to consider her verdict.
It's hard not to feel deflated,
when even your best isn't good enough.

The sun influences life in the oceans just as it does on land.
Its richest parts are those where waves and currents bring fertilizing nutrients
to surface waters that are bathed in sunlight.
The seas off the Cape in South Africa have this magic recipe,
and they are hugely productive.

Summer is the time of plenty and it's now that the seals start to breed.

The strike of a great white shark lasts a mere second.
Slowing it down forty times reveals the technique and immense strength
of this massive predator.
If surprise fails,
there will be a chase.
The shark is faster on a straight course,
but it can't turn as sharply as the seal,
its agility versus power.

Once the seals have finished breeding,
the giant sharks will move on.
It's now becoming clear that great whites migrate thousands of miles across the oceans
to harvest seasonal abundances in different seas.

The sun,
beating down on tropical waters,
powers the weather systems of the globe.
Moisture evaporates from the warming ocean,
and rises to create great storms.

The winds generated out at sea sweep inland across the continents.
As they travel across the desert,
they create the biggest of all sand storms,
blowing sand halfway round the world to fertilize the Amazon jungle.

Winds blowing across the Indian Ocean collect moisture
and sweep northwards towards the Himalayas.
As the air rises,
so it cools.
The water it carries condenses into clouds
and then falls as the life-giving rains of the monsoon.

So air currents powered by the sun carry wet air to the middle of continents.
Without water there can be no life,
but its distribution over the land is far from even.

Deserts cover one third of the land's surface,
and they're growing bigger every year.
This is a desert in Southern Africa.
It's the dry season,
and thousands of elephants have started to travel in desperate search for water.

All across Southern Africa animals are journeying for the same reason.
Buffalo join the great trek.
Nowhere else on Earth are so many animals on the move with the same urgent purpose.

They're all heading for swamps,
a vast inland delta.

At the moment it is dry,
but water is coming.
The travelers are hampered by dangerous dust storms.
Females and calves can easily get separated from the main herd.
For this pair sanctuary lies in the patch of woodland a few miles ahead.

They can't rest until they reach it.
The main has already got there safely.
Finally,
the stragglers emerge from the dust.
The exhausted calf is still blinded by sand.


10 Minutes

Its mother does everything possible to help it.
The storm is now subsiding,
but not all the elephants have been so lucky.

One youngster has got lost.
Thirsty and exhausted,
it follows the tracks of its mother,
but sadly in the wrong direction.

At the peak of the dry season
water arrives in the swamps.
It fell as rain a thousand miles away in the highlands
and has taken nearly five months to reach here.

The water drives out insects from the parched ground,
which are snapped up by plovers.
Catfish,
traveling with the flood,
collect any drowning creatures the birds have missed.

It's a seasonal feast for animals of all kinds.
Birds are the first to arrive in any numbers -
wattled cranes,
then black storks.
Behind the birds come buffalo.

After weeks of marching their trek is coming to an end.
As the water sweeps into the swamps,
a vast area of the desert is transformed into a fertile paradise.

Nowhere on our planet is the life giving power of water so clearly demonstrated.
The swamp becomes criss-crossed with trails as animals move into its heart.

The new arrivals open up paths like arteries
along which water flows,
extending the reach of the flood.

This is an Africa rarely seen -
a lush water world.

Some creatures are completely at home here.
These are antelope with hooves that splay widely,
enabling them to move its speed through the water.
For others the change is far less welcome.

Baboons are somewhat apprehensive bathers.
The water brings a season of plenty for all animals.
Hunting dogs.
These are now among the rarest of Africa's mammals,
but then nonetheless the continent's most efficient predators.

Their secret is teamwork.
Impala are their favorite prey.
They start to hunt,
and the pack splits up.

An aerial viewpoint gives a new insight into their strategy.
As the dogs approach their prey,
they peel off to take up separate positions around their target.

They seem to form a cordon around the impala.
Moving in total silence,
they take up their positions.
Those ears can detect the slightest rustle.
The hunt is on.

Three dogs close in on one impala.
Missed.
The lead dog drives the impala towards the hidden flankers.
Anticipating their line,
the leader cuts the corner,
and joins a flanker for the final assault.

It's all or nothing.
One on one.
The dog has stamina,
the impala has speed.
Leaping into the lake is an act of desperation -
impala can barely swim.

The dogs know their prey must come out or drown -
now it's a waiting game.
The rest of the pack are calling.
They've made a kill in the forest,
and this is an invitation to join in the meal.

The impala is in luck.
A pack this size kills once a day and everything is shared.
And this impala is reprieved.

The elephants are nearing the end of their long journey.
After weeks of marching they're desperately tired.
The matriarch can smell water,
and encourages the herd to make one last effort.

The youngsters are exhausted
but their mothers have made this journey before
and they know that they're close to water.
After many hundreds of miles they've arrived.

The lives of these elephants are dominated by the annual rhythm of wet and dry,
a seasonal cycle created by the sun.
At the southern end of the earth,
after four months of total darkness,
the sun once more rises over Antarctica.

Now at last the Emperor penguins abandon their huddle.
The males are still carrying the precious eggs that they've cherished throughout the Antarctic winter.

With the returning sun the eggs hatch.
Other birds have not even arrived.
But the Emperors,
by enduring the long black winter,
have given their chicks a head start.

These youngsters are now ready and eager to make the most of the brief Antarctic summer.

Only 3 percent of the water on our planet is fresh.
Yet these precious waters are rich with surprise.

All life on land is ultimately dependent upon fresh water.

In these mysterious mountain regions -
isolated mountain plateaus rising high above the jungle.

This was the inspiration for Arthur Conan Doyle's 'Lost World,'
an imagined prehistoric land.

Here,
strange towers of sandstone have been sculptured over time,
by battering wind and torrential rain.

Moisture rising as water vapour from the surface of the sea
is blown inland by wind.

On reaching mountains,
the moisture is forced upwards,
and as it cools,
it condenses into cloud and finally rain -
the source of all fresh water.

There is a tropical downpour here almost every day of the year.
Fresh water's journey starts here,
high in the mountains.
Growing from humble streams to mighty rivers,
it will travel hundreds of miles to the sea.

Angel Falls,
the highest waterfall in the world.
Its waters drop unbroken for almost a thousand metres.

Such is the height of these falls,
that long before the water reaches the base in the Devil's Canyon

it's blown away as a fine mist.
In their upper reaches,
mountain streams are full of energy.
Streams join to form rivers,
building in power,
creating rapids.

The water here is cold.
Low in nutrients,
but high in oxygen.
The few creatures that live in the torrent have to hang on for dear life.
Invertebrates dominate these upper reaches.

This invertebrate,
its body flattened to reduce drag,
has bushy gills to extract oxygen from the current.

Black fly larvae anchor themselves with the ring of hooks,
but if these become unstuck,
they're still held by a silicon safety line.

There are advantages to life in the fast stream -
bamboo shrimps can just sit and sift out passing particles with their fan-like forearms.

Usually,
these mountain streams only provide enough food for small animals to survive.
But with the spring melt here in Japan,
monsters stir in their dens.
Giant salamanders,
world's largest amphibian,
almost six feet long.
They're the only large predator in these icy waters.


15 Minutes

They begin their hunt at night.
These salamanders have an exceptionally slow metabolism.
Living up to 80 years they grow into giants.
The fish they hunt are scarce and salamanders have poor eyesight.
But sensory nodes on their head and body detect the slightest changes in water pressure.

Free from competition,
these giants can dine alone.
Pickings are usually thin for the salamanders,
but every year some of the world's high rivers are crowded by millions of visitors.

The salmon have arrived.
This is the world's largest fresh water fish migration.
Across the northern hemisphere,
salmon,
returning from the ocean to their spawning grounds,
battle their way for hundreds of miles upstream.

Up here,
there are fewer predators to eat their eggs and fry.
A grizzly bear.
From famine to feast -
he's spoilt for choice.
This Canadian bear is very special -
he's learnt to dive for his dinner.
But catching salmon in deep water is not that easy and the cubs have lots to learn.

The annual arrival of spawning salmon
brings huge quantities of food into these high rivers
that normally struggle to support much life.

Although relatively lifeless,
the power of the upland rivers to shape the landscape
is greater than any other stage in a river's life.

Driven by gravity,
they're the most erosive forces on the planet.

For the past 5 million years,
Arizona's Colorado river has eaten away at the desert's sandstone to create a gigantic canyon.

It's over a mile deep,
and at its widest,
it's 17 miles across.
The Grand Canyon.
This river has cut the world's longest canyon system -
a 1,000 mile scar clearly visible from space.

As rivers leave the mountains behind,
they gradually warm and begin to support more life.
Indian rivers are home to the world's most social otter -
smooth-coated otters form family groups up to 17 strong.

Group rubbing not only refreshes their coats,
but strengthens social bonds.
When it comes to fishing,
there is real strength in numbers.
Fishing practice begins when the cubs are four months old.

Only the adults have the speed and agility needed to make a catch.
Adults share their catches with their squabbling cubs.

Most otters are solitary,
but these rich warm waters can support large family groups,
and even bigger predators.

Mugger crocodiles,
eight feet long,
could easily take a single otter.
But,
confident in their gangs,
the otters will actively harass these great reptiles.
Team play wins the day.

The Mara river,
snaking across the plains of East Africa.
As the land flattens out,
rivers slow down and lose their destructive power.
Now they are carrying heavy loads of sediment that stains their waters brown.
Lines of antelope are on their march.
Each year nearly two million animals migrate across the plains,
in search of fresh green pastures.

For these thirsty herds
the rivers are not only a vital source of drinking water,
but also dangerous obstacles.

This is one of the largest concentrations of Nile crocodiles in Africa,
giants that grow over five metres long.
From memory,
the antelope are coming
and gather in anticipation.
The crocodile's jaws snap tight like a steel trap -
once they have a hold,
they never let go.

It took over an hour to drown this full-grown bull.
To surprise their prey,
crocodiles must strike with lightning speed.
Here,
only the narrowest line separates life from death.

Most rivers drain into the sea,
but some end their journey in vast lakes.
Worldwide lakes hold twenty times more fresh water than all the rivers.
The East African Rift Valley holds three of the world's largest.

The first,
smallest of the three,
is still bigger than Wales.
Its tropical waters teem
with more fish species
than any other lake.

There are 850 different of one species alone,
all of which evolved from just one single ancestor,
isolated here thousands of years ago.
These six foot wide craters are fish-made.

Carefully maintained by the males,
these bowls are courtship arenas.
These fish are caring parents.
Brooding young in the mouth is a very effective way of protecting them.

This lake can be a dangerous place.
After dark,
predatory dolphin fish emerge from their daytime lairs among the rocks.
Like packs of sharks,
they're on the prowl for sleeping fish.

In the darkness these electric fish hunt
by detecting distortions in the electric field they create around their bodies.
Any fish that trenches out will be snapped up.
The floor drops almost a mile into an abyss.

Here,
in this dead zone,
the larvae of lake fly midges
hide out away from predators.
In the rainy season,
they balloon up to the surface
and undergo a magical transformation.

At dawn the first adult midges
start to break out.
Soon,
millions upon millions of newly hatched lake flies are taking to the wing.

Early explorers told tales of lakes that smoked, as if on fire.

But these spiraling columns hundreds of feet high are mating flies.

Once the flies have mated,
they will all drop to the water surface,
release their eggs and die.

This may look like an inland sea,
but it's dwarfed by the world's largest lake in Eastern Siberia.

400 miles long and over a mile deep,
This lake contains one fifth of all the fresh water
found in our planet's lakes and rivers.

For five months of the year it's sealed by an ice sheet over three feet thick.
This is the oldest lake in the world and,
despite the harsh conditions,
life flourishes here in isolation.

80 percent of its species are found nowhere else on Earth,
including the world's only fresh water seal.

With this seal,
and its marine-like forests of sponges
This seems more like
an ocean than a lake.

There are shrimp-like creatures -
as large as mice.
They are the key scavengers in this lake.


20 Minutes

The water here is just too cold for the bacteria that normally decompose the dead.

Most rivers do not end in lakes
but continue their journey to the sea.
The planet's indisputable super-river is the Amazon.

It carries as much water as the next top-ten biggest rivers combined.

Rising in the mountains,
its main trunk flows eastwards across Brazil.
On its way the system drains a third of South America.
Eventually,
over 4,000 miles from its source,
it empties into the Atlantic Ocean.

The Amazon transports a billion tons of sediment a year,
clearly visible at the mixing of the waters where one massive tributary,
flows into the main river.

Its waters are wonderfully rich.
To date over 3,000 species of their fish have been described -
more than in the whole of the Atlantic Ocean.

The Amazon is so large and rich in fish
that it can support fresh water dolphins.

These dolphins are huge -
more than six feet long.

In these murky waters they rely on sonar to navigate and hunt.
They work together to drive fish into the shallows.

These dolphins are highly social,
and in the breeding season,
there is stiff competition for mates.

The males hold court in a unique way.

They pick up rocks in their jaws,
and flaunt them to their attending females.

Maybe each male is trying to show how strong he is,
and that he therefore is the best father a female could have for her young.

Successful displays lead to mating.
Even for giant rivers like the Amazon
the journey to the sea is not always smooth or uninterrupted.

The border of Brazil and Argentina is home to one of the widest waterfalls
in the world -
one and a half miles across.

In flood 30 million liters of water spill over every second.

All the world's great broad waterfalls
are only found in the lower courses of their rivers.

In their final stages,
rivers broaden and flow wearily across their flat flood plains.

Each wet season here,
in Brazil,
this river overflows its banks
and floods an area the size of England.

This is the world's largest wetland.

In these slow-flowing waters,
aquatic plants flourish,
like the Victoria giant water lily with leaves eight feet across.

These underwater forests are nursery grounds for fish.
Over 300 species breed here,
including fish
and other predators.

Ripening fig trees overhanging the water's edge
provide welcome food for hungry fish.

The commotion attracts the river tiger.
They patrol,
looking for a chance to strike.
And waiting in the wings,
ready to pick off any injured fish,
are the piranhas.

The feeding frenzy quickly develops.
Piranha can strip a fish to the bone in minutes.

Great numbers of fish sustain vast flocks of water birds.
The rose-eared spoonbill is just one of the 650 bird species found in the wetlands.

They nest alongside wood stocks in colonies thousands strong.
Reptiles linger below,
waiting for a meal to fall out of the sky.

When rivers finally reach the sea,
they slow down,
release their sediment and build deltas.

In Bangladesh two rivers join to form the world's biggest.
Every year almost 2 thousand million tons of sediment,
eroded from the Himalayas,
is delivered to the ocean.

At the delta's mouth -
the largest mangrove forest in the world.

These extraordinary forests spring up throughout the tropics
in these tidal zones where rivers meet the sea.

Crab-eating monkeys are mangrove specials.
In Indonesia these monkeys have adopted a unique lifestyle -
they fish out fallen food.
The troop also uses the waters to cool off during the heat of the day.
But the channels are also the playground
for restless young monkeys.

Some of the young have even taken to underwater swimming.
They can stay down for more than 30 seconds,
and appear to do this just for fun.
Yet these swimming skills acquired during play
will certainly be useful later in life in these flooded mangrove forests.

In cooler climates,
mud is colonized by salt marsh grasses
and form one of the most productive habitats on the planet.

Greater snow geese flock to the grasses along the Atlantic coast of the United States
to rest and refuel on their long migratory journeys.

This is the end of the river's journey.
Collectively they've worn down mountains
and carried them to the sea.

And all along the way,
their fresh water has brought life and abundance to planet Earth.

 

When you look down on the Earth's surface,
it's impossible not to be impressed by the sheer grandeur,
splendor and power of the natural world.

It's been ten years since we explored these wonders since the first series of Planet Earth.
And since then,
much has changed.

We can now show life on our planet in entirely new ways,
bring you closer to animals than ever before,
and reveal new wildlife dramas for the very first time.

But that is not all.
The planet has changed, too.
Never have our wildernesses been as fragile and as precious as they are today.

At this crucial time for the natural world,
we will journey to every corner of the globe
to explore the greatest treasures of our living planet,
and reveal the extreme lengths animals go to survive.

Finally,
we will explore our cities to see how life is adapting to the newest habitat on Earth.
This is Planet Earth II.

There are hundreds of thousands of islands,
each one a world in miniature.


25 Minutes

The struggles to survive on these remote lands reflect
the challenges faced by all life on Earth.

This tiny island,
home to the pygmy three-teed sloth.

This is a male,
and life here suits him well.
Mangroves provide all the leaves he can eat and there are no predators to worry him.

Island life may seem idyllic,
but it comes at a price.
There are only a few hundred pygmy sloths in existence,
and he needs a mate.

That's an enticing call...
...from a female somewhere out there.
And this,
for a sloth,
is a quick reaction.

The problem is there's deep water between them.
So what should any red-blooded sloth do?
Swim, of course.

Could this be her?
He does his best to put on a turn of speed.

But she's not the one.
She already has a baby and she won't mate again
until it leaves her in about six months' time.
Even life on a paradise island can have its limitations.
But at least she can't be far away.

The world's entire population of pygmy sloths is isolated on a speck of land no bigger than New York's Central Park.
The size of an island has a huge influence on the fate of those cast away there.

This island in Indonesia.
Home to dragons.
Ten feet long and massive,
these are the largest living lizards on the planet.

It's unusual to find large predators on islands.
Yet,
for four million years,
the Komodo dragon has dominated here.

It might seem there wouldn't be enough food to support such giants
on this relatively small island,
but reptiles,
being cold-blooded,
need only about a tenth of the food a mammal would.
A single meal will last a dragon a month.

They're so successful,
that their only serious competition comes from others of their own kind,
and there are some 2,000 of them here.

This giant, however,
isn't looking for food.
He's looking for a mate.
Female dragons come into season only once a year.

She is receptive.
So far, so good.
But he strayed into someone else's patch.
Another huge male thinks he is the king here.

Space being limited on islands,
dragon territories overlap,
and that creates continual conflict.

In dragon society,
size is everything.
But if rivals are closely matched,
the outcome can be uncertain.

Muscular tails strike with the power of sledgehammers.
And their serrated teeth
are as sharp as steak knives.

Each tries to topple his opponent.
Defeated.
Only the most powerful dragons win the right to mate.

The limited food and space on the small islands can often lead to intense competition.
But some islands are immense.
More like miniature continents.
And these provide opportunities for life to experiment and evolve.

This is one of the biggest islands and also one of the oldest,
having split away from Africa over 120 million years ago.
With time and isolation,
its animals have adapted to take advantage of every available niche.

The island now has thousands of different species,
most found nowhere else on Earth.

These are not monkeys, but lemurs.
From a single ancestor,
about a hundred,
different types have evolved.

The largest lemur seldom comes down from the branches.

The much smaller ring-tails wander in troops across the forest floor searching for fruit.
And tiny bamboo lemurs eat nothing except bamboo.

With few competitors,
lemurs have been free to roam
every environment on the island,
even the most extreme.

This baby lemur has a hard life ahead of it.
He's been born in the most arid and hostile corner of this vast landscape.

If he is to survive here,
he has much to learn.

The spiny forest is like a desert.
It rarely rains, so water and food is very hard to find.
Moving from tree to tree is a perilous business.
Here,
nearly all the plants are covered with ferocious spines.

His mother searches the treetops for the youngest leaves.
They provide the only food and water to sustain the family.

At three months old,
the youngster is starting to explore.

All too soon, he will have to fend for himself up here.

But it's altogether easier to stay on Mother's back.

If he can master the strange ways of this forest,
he will have a little corner to himself.

Island life encourages animals to do things differently,
and on some islands, that is essential.

There are islands still forming today built by volcanoes.
Some erupt explosively,
others pour out rivers of molten rock,
lava.

In the last 50 years,
ten new volcanic islands have been formed.

Newly created and often remote,
they're hard to reach.

Even those that do,
find these are tough places to survive.

This island in the Pacific Ocean is still
young and still volcanically active,
it's a desolate place.

The surrounding sea, however,
is particularly rich with life,
and the frontier between these two very different worlds
is the home of one of the strangest reptiles,
sea-going iguanas.

They are vegetarians,
but since there's little food for them on the land,
marine iguanas graze on the sea floor.

A big male like this one can dive to ninety feet and hold his breath for half an hour.

There are more than 7,000 individuals on this island alone.
And by bringing nutrients from the sea to the land,
the iguanas help other animals to survive here,
too.

Crabs feed on dead skin on the iguanas' back and,
in turn,
provide a welcome service.

Smaller lizards prey on the flies that pester the colony.
But not all the relationships on this island are so harmonious.

Marine iguanas lay their eggs in sand.
In June, when the hatchlings emerge,
they're vulnerable.

They must join the adults at the edge of the sea.
But the journey will be a dangerous one.

Racer snakes.
The snakes missed their chance.
But more babies are hatching.
And now the snakes are on the alert.

This is the best feeding opportunity they will get all year.

On flat ground a baby iguana can outrun a racer snake.
But others are waiting in ambush.

30 Minutes