Original subtitles

Narrator: The Ngorongoro crater

is an environment both beautiful and unusual.

It contains an array of habitats

and a yearlong supply of water.

This ensures that it is always teeming with life -

even at the height of the dry season.

But this blessing can quickly become a curse.

Its closed-off nature

has caused behavior unseen anywhere outside of its walls.

This is Ngorongoro crater,

the cursed haven.

40 million years ago, "The Rifting" began.

When the Earth's crust along Africa's eastern plain

started to thin,

a massive fault line formed.

As the continent split apart,

the land on either side collapsed.

And lava thrust up from within the earth,

Leaving a massive depression of highlands and volcanoes -

The Great Rift Valley.

2.5 million years ago

one of these volcanoes erupted.

The Ngorongoro volcano was about the same size as Kilimanjaro.

Trapped lava from within the base had nowhere to move,

and the entire mountain imploded,

forming what is known as a caldera.

For years it remained desolate and uninhabited.

But as the fires settled and the slopes cooled

vegetation started to colonize the steep banks,

thriving off the rich soils and moisture.

Herbivores followed the flora over the rim,

and down into the crater.

Soon after, the carnivores followed.

With no incentive to leave,

the animals have stayed here ever since.

The result is an oasis of wildlife

known as the Ngorongoro crater.

Covering an area of 125 square miles,

the Ngorongoro crater in Tanzania

is the largest intact caldera on earth.

Today 25,000 large animals make their home here.

Among these is the greatest concentration

of carnivores on the planet;

Some of the world's oldest elephants,

Largest grazers -

And most charismatic birds.

And their desire to stay

is closely related to the unusual layout of the land.

The Ngorongoro crater has a range of habitats

within one consolidated arena.

From plains

to freshwater swamps,

soda lakes,

forests

and wetlands.

During Tanzania's dry season

the crater's savanna becomes frail and desolate.

Each resident must embark

on a migration within the crater walls

to reach its water source.

The wetlands in the center of Ngorongoro

provide generously all year round.

Tempted to stay inside

because of its permanent supply of water,

the inhabitants rarely step outside of the sheer walls.

This has caused behavior not seen

in any other animals on the planet.

Imprisoned by their natural instincts

they stay within this amphitheater

even when it is to their detriment.

Leaving the question as to whether it is a paradise

or a prison.

Lions are the famed hunters of the African savanna.

They are highly effective pack predators,

able to take on large prey

due to their size and strength.

But the Lions in the crater are different.

The dominant prides,

unwilling to share in the bounty of Ngorongoro,

have chased away all migrating Lions that attempted to enter.

Because of this,

the Crater has caused what is referred to as

a genetic bottleneck, limiting the gene pool.

All of the crater Lions

are descended from a single isolated population.

Generations of interbreeding

have left these lions more prone to disease.

Because of the consolidated nature of the crater,

their natural survival instincts

have become their biggest detriment.

Years of holding onto the spoils of Ngorongoro

has taken its toll.

And this has caused another inversion

in the usual hierarchies of the animal world.

This is the only place on the planet

where Lions are not the kings of the savanna.

In Ngorongoro Lions scavenge up to 80 percent of their food

from the dominant hyena clans.

The crater is home to 400 Spotted hyenas.

And here they are unmatched for their size,

power, and hunting efficiency.

The crater hyenas do not suffer from interbreeding

as the Lions do.

Males are chased from their birth group

by the dominant females;

this forces them to reproduce elsewhere.

The hyenas roam the dry plains of the crater

as the unexpected rulers of an unorthodox domain.

Even in the depths of the dry season,

the Ngorongoro crater boasts an abundance of residents.

And their desire to stay

is closely related to the history of the land.

During the formation of the Great Rift Valley,

a surge of landscapes emerged.

As the ground broke apart,

a range of new environments and species were born.

The crater is a product of this tectonic flux

and it has inherited some interesting characteristics

because of this.

As clouds scrape the top of the montane forest on the rim,

moisture is continuously flushed through the system.

As a result, it creates its own climate

separate from the surrounding areas.

Even in the dry season when everything else begins to wither

the crater forests still flourish.

This dense greenery is a result

of the unique topography of the rim.

It is a forest haven, unhindered by the changing seasons.

Every year outside of the caldera walls,

tens of thousands of animals migrate across the Serengeti

to escape Tanzania's dry season.

But the crater animals stay where they are.

They circulate around the crater floor

every day on internal migrations

in search of grazing and water.

Though the cloud forests on the rim

maintain moisture all year round,

during periods of drought

little of this trickles down to the savanna on the crater floor.

And the majority of the animals that live here

are confined to endure this scarce habitat.

Wildebeest are restricted to eat

on the Ngorongoro crater's savanna biome.

Their broad muzzle and loose lips

are adaptations suited to rapid, bulk feeding.

They feast on grass that responds well to grazing,

trampling and manure.

They cannot graze the grasses on the rim,

which are too delicate to deal with the wildebeest's

boisterous eating habits.

This keeps the wildebeest on the dry plateau below.

When rains are minimal,

these shallow-rooted grasses quickly stop growing.

The confined nature of the crater

means that the plains become crowded wastelands

with little moisture.

But wildebeest need to drink daily.

So they are limited to pastures

no further than 9 miles away from water.

Every day they must embark on a migration to the wetlands.

But they are not the only ones caught in this unforgiving loop.

Ngorongoro is also home to 4,000 Grant's zebra.

The two groups of animals constantly feed

as they move across the crater floor every day to the wetlands

in the search for water.

Where the wildebeest prefer the shoots of new grass

closer to the ground,

zebra enjoy the coarser, taller stalks.

Zebra are known to be pioneer grazers,

moving over a patch of earth first

and cropping it down to a size that other species

including wildebeest, prefer.

Moving in bigger mixed herds

reduces an individual's chance of being attacked

by creating an added distraction from predators.

This makes traveling in large numbers beneficial,

especially in the crater.

For the scavengers the dry season is a time of opportunity.

Every life taken within the crater is a chance to feed.

Golden jackals stalk the grasslands,

eating whatever they can, when they can.

More adapted to an arid lifestyle

than any other species of jackal,

they owe their success to their ability to live on anything

from fruit and berries to rodents and carrion.

They will eat whatever food can be acquired

with the least amount of effort.

This is paramount in Ngorongoro

where they have much competition from some formidable foes.

In Ngorongoro, hyenas have dominion over all.

Hyena clans exist in strict hierarchies.

Social rank is fundamental to the success

of their highly coordinated hunting excursions.

And strength is the principle that underlies the whole system.

Females are ranked according to how many fights they have won.

In their world the most feared is at the top.

Their ferocity makes them formidable hunters.

The best fighters have priority at carcasses.

And they are highly territorial.

They roam this unusual land as distinctive emperors,

unrivaled for both their strength and hunting efficiency.

For the scavengers the dry season is a time of plenty.

Tawny eagles are well-known pirates of the savanna,

often intimidating others off a kill

in order to enjoy it for themselves.

Their keen eyesight and rapid flight speed

ensure that they are quick on the uptake

when the crater claims an animal.

The flat, open nature of the crater floor

provides ideal conditions

for another scavenger's impeccable sense of sight.

Vultures soar on thermals to look for carrion.

But the layout of the caldera suits other birds too,

and not all of them favor taking to the skies

in the search of food.

Secretary birds thrive in the crater's barren grasslands

and this is because of the structure of their body.

Secretary birds prefer moving around

on their long powerful legs over flying.

They can move over 18 miles a day in the search for food.

Unlike most birds of prey,

their favored method of killing is not with their beaks

but their legs.

Using these powerful pistons to stamp smaller prey,

they are efficient predators.

And the desolate plains of Ngorongoro

are the ideal hunting ground.

The open layout of the floor

is also important for the crater's biggest bird.

Unable to fly, Ostriches rely on their speed

to evade predators like Lions and hyenas.

When they need to, they can sprint over 40 miles an hour.

But when there is no danger around they do something else.

This dance is an invitation to mate.

Ostrich mating precedes the rains.

This is so that their chicks will be born

in the abundance of the wet season.

And they are not the only crater birds joining in the ritual.

Crowned cranes eagerly await the rains.

These elegant birds

need permanent marshes to make their nests.

But once again, the dry grass is the reason

they have been drawn out from their wetland homes.

The crater floor is a prime hunting ground for them.

They are mixed feeders;

eating anything from insects and lizards to flowers and seeds.

These short dry grasslands

enable them to use their long limbs

to comb through the savanna in search of smaller prey.

Like everything else in the crater,

they need to make the migration every day

from the dry savanna feeding grounds

to the lush marshlands in search of water.

Raising young in these conditions is no easy feat.

Buffalo are the largest members of their family

and they require a lot of water to maintain their massive bulk.

But they too can only feed

on the dry grasses of the crater floor.

Calves weigh just under 100 pounds at birth

and are largely defenseless until they mature.

They are utterly dependent on their mother's knowledge

to survive the long periods of drought.

And they too must journey between the crater's savanna

and its marshes every day.

Water is the driving force

behind the continued occupancy of the Ngorongoro animals.

There are other areas nearby

that support life throughout the year,

but their waters are inaccessible to most.

The lakes of the Rift Valley

are a product of aggressive geological forces,

and some have retained inhospitable characteristics

because of this.

Before the Rifting, there were no lakes in Africa.

But as the earth was violently reshaped, water began to settle.

When the lakes of the Great Rift Valley formed,

much of the ground was covered in lava and ash.

As water filtered through the ground,

volcanic chemicals were carried into the lakes,

creating a hostile aquatic world.

Lake Natron lies at the foot of Mount Ol Donyo Legai,

60 miles to the north of Ngorongoro.

Its caustic waters are strong enough to corrode human limbs.

Only about 15 inches of rain reaches it per year,

much of which is 'phantom rain'.

The water evaporates

before it has even touched the surface of the lake.

As a result, the lake's waters do not come from the sky,

but rather from under the ground.

Little that comes into contact

with the volcanic waters survives.

But a single-celled organism,

visible only when magnified a thousand times,

thrives here.

Spirulina platenisis flourish in the carbonate-rich water,

under high temperatures and plenty of sunlight.

Providing a source of food

for one of the planet's oldest birds.

The flamingo's specially adapted bill

allows it to graze the upper inch of the corrosive water

and harvest the Spirulina .

The heavy arch of the bill allows great quantities

to be sucked over fine hairs inside their mandible,

filtering out the food.

These waters can sometimes exceed 120 degrees Fahrenheit.

A flamingo's hard, featherless leg is one of the few things

that can withstand the corrosive lake.

This allows them to wade to the mud flats right in the middle -

And these are no more welcoming than the surrounding waters.

Temperatures are high, winds are strong.

Almost no vegetation survives,

and movement across the thick muddy terrain

is impossible for most mammals.

The mud flats also create the harshest nursery on the planet.

Using Lake Natron's volcanic water as a moat

against all land based predators;

the flamingos have made the barren ground in the middle

the ideal breeding site.

This is the largest flamingo breeding ground in the world.

The land's unusual and inhospitable nature

has given them exclusive feeding and breeding rights.

But they are not the only creatures that have adapted

to withstand the volcanic waters.

The Alkaline tilapia.

These fish live on the edge of the hot spring inlets

where the water reaches 100 degrees Fahrenheit.

They have evolved to endure the high temperatures

and dense alkalinity.

The only places in the world that they occur

are the soda lakes of the Great Rift Valley.

The landscape is harsh and unyielding

yet over time life has adapted to survive.

Thriving off the volcanic hostility and unusual geography,

the animals that live here have learned to cope

with the severe landscape

and in return they are provided with a haven.

Because so few animals can survive here,

the inhabitants of the Rift Valley soda lakes

have their own sanctuary crafted from lava and ash.

The anomalous formation of the crater highlands

ensures that Ngorongoro has water all year around.

Outside of the caldera the nearby Empakai crater

remains full and luscious,

regardless of the surrounding changes in climate.

Water moves from this basin into Ngorongoro,

feeding its wetlands throughout the year.

And this enables animals to live here

no matter how little is provided by the rain.

Every day the inhabitants must make the walk

across the crater's savanna

to reach its enduring water supply.

This brings the entire population

of the crater together.

Though they all have different feeding requirements,

every animal needs to drink.

Throughout the day

they spread to different sides of the crater floor,

but when it is time to get to the water the entire range

of the park's wildlife

all funnel towards the marshes.

The Ngorongoro crater

is a sanctuary for Tanzania's last few remaining Black rhinos.

Even when the dry season is at its harshest

they are provided with water.

They are normally elusive,

hiding within the forests.

But they are drawn out to join the rest of the residents

in the search for nourishment.

The wetland is the life force of the Ngorongoro crater.

It ties together all of the park's residents.

It is the only reason

that they can endure the severity of the dry season.

The Ngorongoro waters support all stages of life

from the youngest animals to some of the planets oldest.

It is a haven for old elephant bulls

that wander inside the crater

for the safety and seclusion that it offers.

Elephants' tusks keep growing their entire lives.

By the time a bull is 60 years old

his tusks can reach a combined weight of 260 pounds.

As a result,

the Ngorongoro elephants are endowed with tusks of a size

seldom seen outside the crater walls.

For the waterfowl, the wetland is a constant home.

Great white pelicans are bound to the water throughout the day.

In the morning they will hunt for fish

and for the rest of the day

they will socially bathe and preen.

Their fishing techniques

see them dependent on the shallow warm waters.

They are joined by other birds on the hunt.

The Yellow-billed stork's odd shaped bill

is perfectly adapted to fishing in drying rivers.

As fish become trapped in shallower pools,

the storks use their feet to stir up the muddy water

before stabbing fish with their sharp beak.

They also have an intriguing way of cooling themselves

in the heat of the day -

While standing around preening

they will urinate on themselves to cool their legs.

As the urine crystallizes,

the whitish colors act as a screen to reflect the sun.

For them water is a constant source of food and nourishment.

And the crater's wetlands are a constant home

for another far larger resident.

For hippo to live comfortably they need a water source

that is deep enough for them to submerge completely -

And they also need to be close to grasslands.

These pools provide them with the ideal home.

This water haven is the beating heart of the park.

It supports and provides for all of its residents all year round,

and without its dependable sustenance,

life in the crater would not be able to endure.

The sheer 1,900 foot drop of the caldera walls

sever this landscape from the surrounding areas in many ways.

It has its own apex predators,

a separate climate

and a wealth of habitats unseen outside.

But what is on the face of it a wildlife oasis

may just be something closer to a natural prison.

Even at the height of drought,

most animals stay and endure the severity of the land.

It is a constant home for herbivores

no matter how frail

and overpopulated the grasslands become,

or how many predators roam the enclosed amphitheater.

Seduced by the temptations of a yearlong water supply,

abundant grazing and large numbers of prey;

the inhabitants were tempted over the crater walls

thousands of years ago

and many of their descendants have never left.

Shackled by the promises that it offers,

their instincts for survival keep them bound to Ngorongoro,

even when this is to their detriment.

The life that endures here does so according to its own rules.

Produced by the hostility of a volcanic environment,

the Ngorongoro crater

is both a generous habitat and a dangerous trap.

And each of its residents has to navigate this boundary

in the daily search for water.

The result is an animal kingdom like no other.