DAVID ATTENBOROUGH: The power of the sun drives the seasons,
transforming our planet.
Vast movements of ocean and air currents
bring dramatic change throughout the year.
And in a few special places, these seasonal changes
create some of the greatest wildlife spectacles on Earth.
One of the most awe-inspiring events
takes place in the vast open plains of East Africa.
Once a year, three million animals
gather in a small corner of the Serengeti.
This is the greatest concentration of grazing animals on the planet.
But the herds only stay for a few months
before continuing on their epic journey.
And when the Great Migration moves on,
the predators they leave behind become suddenly vulnerable.
How can they survive until the Great Migration returns?
The eastern edge of the Serengeti is dominated by a volcano,
known to the Maasai people as Ol Doinyo Lengai,
the Mountain of God.
It's one of many volcanoes, that have shaped the landscape here
for millions of years, that lie along Africa's Great Rift.
To the west lie the grasslands of the Serengeti
and a particularly fertile area known as the short-grass plains.
For a few months each year,
hundreds of thousands of grazers cram into this corner of the Serengeti.
And of course, wherever you find grazers,
you find predators.
More meat-eaters hunt and scavenge on the short-grass plains
than anywhere else in Africa.
For lions in particular, this is, for the moment, a savannah paradise.
With so much food on offer, it's a good time to raise young cubs.
But lions are territorial.
Each pride only controls a small area of grassland.
They can only hunt the animals that come into their territory.
So, to give these cubs a good start,
they'll have to make the most of this bonanza
while it's here.
When the great herds move on, the lions can't go with them,
and prides like this one face a stern test.
What happens next
is a side of lion life that is rarely seen.
It's May.
The rains that watered the short-grass plains have moved north
and the vast herds follow, seeking out fresh green pastures.
Wildebeest are so in tune with the seasons
that they can hear thunderstorms 30 miles away,
and they home in on the scent of wet soil
that carries the promise of fresh grass.
Unlike lions, wildebeest are free to travel
wherever the quest for food leads them.
This young calf is at the start of an incredible seven-month journey.
Without rain, the grasslands behind them wither and die.
Within weeks the short-grass plains start to turn brown.
Within a few months, they're unrecognisable.
90% of grazing animals have moved on.
Not a single wildebeest remains.
It's now August. With so few animals here,
the short-grass plains are no longer a great place to be a lion.
For the lion pride living at the southern edge of these plains,
in a place known as Ndutu,
the test now is to survive until the herds return again.
The Ndutu pride has four lionesses and seven cubs,
and already they're struggling to find enough food and water.
The youngest are weak and underweight.
Surrounded by other lion prides with their own territories,
the Ndutu pride must make the most of what they can find here.
But there isn't enough food for them all.
This male cub is not only hungry, he's sick.
On this morning the pride is heading for a woodland
where there is more cover and more animals to hunt.
It's a long journey for the exhausted cubs.
For the weakest male it's a real struggle to keep up.
He's trying, but slowly he gets left behind.
This is a brutal world. The lionesses simply cannot wait.
If they don't keep hunting and eat soon,
they, too, will become weak,
and then there'll be no hope for any of them.
Warthogs are a valuable catch at this time of year.
The lives of the cubs depend on a successful outcome.
While one lioness slowly creeps forward...
another approaches from cover.
(WARTHOG GRUNTS)
It's been a while since their last kill,
and all the hungry pride pile in.
All, that is, except one.
A mile away, a young life is fading away.
The kill has come too late for him.
At less than a year old,
these cubs are still totally dependent on the lionesses.
To survive, they must keep up.
Only three months into the dry season,
the Ndutu pride is down to six cubs.
Sadly, this young male will not survive.
It's late August, and the rains are still moving north,
taking the grass and the wildebeest
even further away from the Ndutu lions.
With no territory to enclose them,
the wildebeest can travel wherever they like.
But a calf, just like a lion cub, still has to stick close to mum.
The biggest danger is getting lost in the vastness of the herd
as it treks up to 30 miles a day.
Back at Ndutu, the dry season is biting harder.
There's little grass here, but that's not a problem for some.
Giraffe find most of the nutrients and moisture they need in acacia leaves.
And, like impala, they can cope well in the dry season.
Serengeti mice positively thrive in the drier months
thanks to the abundance of seeds.
So some of the smaller predators, like wild cats,
still find plenty of food.
(MEOWS)
This kitten is unlikely to go hungry.
Perhaps surprisingly, it's the creature often called the king of the beasts
that is suffering the most.
It's early September, and on this afternoon
there are only two male cubs with the Ndutu lionesses.
And they're little more than skin and bone.
What's happened to the rest?
Sadly, it seems others have been left behind.
One young female cub is just two miles away.
She's limping and the black patches on her face
reveal that she's losing her fur.
(WEAK ROAR)
But she hasn't given up. She calls for her pride.
(DISTANT ROAR)
She's hears a faint call, and hurries towards it.
And is reunited with one of her brothers.
Nearby there is prey. But these cubs are unable to hunt.
They are still too young.
If they're going to survive, they must rejoin the pride.
While she still has strength, she continues to try and make contact.
Far away, the lionesses also call constantly.
(GRUNTS)
And listen for their lost youngsters.
Even a sick cub joins in the search for his sisters and brothers.
But there are no replies.
After an hour of calling, the lionesses can wait no longer,
they must move on.
The pride will have to move to another part of their territory
if they are to find food.
None of them have eaten for days
and now the chances of being reunited with the lost cubs
seems remote indeed.
It's September, one of the driest months in Ndutu.
The wildebeest herds are over a hundred miles away,
having followed new pastures to the northern edge of the Serengeti.
But they have a huge challenge of their own to face.
They must cross the Mara River.
Over several days, the herds crowd together at the water's edge.
The adults seem to sense a hidden danger.
But the numbers keep piling up on the river's edge
and ultimately they face the danger together.
The crocodiles are spoilt for choice...
but they can only take one victim at a time.
There is safety in numbers here
and most of the wildebeest make it across to the grasslands beyond.
Back in the south, the Ndutu plains are tinder-dry.
Seed and insect-eaters can scratch a living,
and the smaller cats like serval, that hunt them,
can still find plenty to eat.
And a cheetah mother is managing to keep her cubs fit and healthy
on the small antelope that remain.
It's now October, the peak of the dry season,
and the Ndutu pride are resting in the heat of the day.
In a bizarre twist of fate, one of the two male cubs has died,
but amazingly, the lost female, with the black face patches,
has found her way back.
She's still weak, and clearly hasn't eaten for days.
Meanwhile, it's getting hotter.
Just when it seems life couldn't get any worse, it does.
Flames race across the Ndutu pride territory,
burning the last of the grass and any remaining bush cover.
At first glance there's little left here.
Yet animals like impala quickly return to investigate.
The impalas' world has changed beyond recognition.
There's nowhere left to hide.
The Ndutu pride has also lost the cover they use for hunting.
The young female may have survived her first fire,
but her chances of a meal have fallen even lower.
For the cheetah family, the fire is not such bad news,
as their prey can actually become easier to find.
The steenbok relies on blending into its surroundings and sitting still
to avoid being spotted.
But in this emptiness, its camouflage is useless.
It's a sitting target.
And apparently unaware of the approaching danger.
Larger prey, like Grant's gazelle,
are constantly on the lookout for danger,
and easily see the Ndutu pride in the distance.
The task for the hunters now seems virtually impossible.
But they do have one advantage.
There are four lionesses
and they've been hunting together for years.
It'll be hard to get close to the warthogs.
But if they can split up and attack on two sides,
they may stand a chance.
This is how a young lioness learns.
As ever, teamwork is critical.
In a well-practiced routine,
a lioness moves round to block the warthog's escape.
As one is flushed into the open,
the flanking lioness rushes in for the kill.
(WARTHOG SQUEALS)
Warthogs are a favourite food.
It's a welcome feast enjoyed by all.
At the toughest of times, the lionesses have provided for the cubs.
But it's an unpredictable year, in more ways than one.
For the first time in 40 years
the sleeping Mountain of God, Ol Doinyo Lengai, awakens.
(RUMBLING)
Vast clouds of volcanic ash drift towards the short-grass plains
and the home of the Ndutu pride lions.
Ravaged by fire, scorched by the sun,
the plains now become shrouded in a layer of ash.
It's November, and the rains that would bring
the return of the grass and the herds are now overdue.
The Ndutu lionesses rest in the intense heat,
and the cubs' batteries are now running very low.
But the winds are changing,
a sign that the season is turning.
The wildebeest seem to know what's about to happen.
They begin heading south.
One and a half million wildebeest
start their journey back to the short-grass plains.
The Great Migration of the wildebeest is one of the longest treks
of any land animal on our planet.
As they follow the rains around the Serengeti,
many will travel over a thousand miles.
But there's no guarantee
that these wildebeest will return to the territory of the Ndutu pride.
They will feed only where the best grasses grow.
All that's needed now is rain.
(THUNDERING)
For the Ndutu pride, rain brings hope.
But how long will it take for the grass to grow
and the herds to return?
Within a matter of days,
fresh grass transforms the arid plains into the lush pastures
that will lure the herds to return.
It's December, and the migrating herds start to arrive
at the northern boundary of the short-grass plains,
just 30 miles from the Ndutu lions.
After seven months away the herd is returning.
Stretching back some 25 miles,
it will take weeks for all the wildebeest to arrive.
And nothing will stop them now.
(ROARING)
The Mountain of God chooses this moment to throw up a column of ash
1 5,000 metres into the air.
But the link between this ash and these herds
is more than a mere coincidence.
For this ash is rich in minerals,
and over several million years
as volcanoes in the Great Rift have erupted,
layer upon layer of ash has fertilised the ground,
creating this uniquely fertile grassland.
It's this that draws animals from all over the Serengeti.
The ash also discourages the growth of trees.
So on these plains, that might otherwise be covered in woodland,
little grows except grass.
It's possibly the best grazing land in all of Africa.
And probably the only place
where one and a half million wildebeest could feed together.
In the northern half,
the short-grass plains have once again become a savannah paradise.
The conditions are so good
that the wildebeest also use these plains for another important purpose.
The females are carrying the next generation
and they've come here to calve.
(GRUNTING)
It only takes seconds.
Some calves are on their feet in just two minutes.
Others take a little longer.
Then they're good to go.
Phosphorus and calcium in the volcanic ash
pass through the grass, into the mother's milk
and into the growing calves.
Nowhere else on their epic journey
could young wildebeest get such a good start in life.
In just two to three weeks,
over half a million wildebeest calves are born here.
And of course, this provides an irresistible opportunity
for all of Africa's top predators.
This is boom time for meat-eaters.
The Ndutu lions, to the south, have yet to enjoy this feast,
but this cheetah family now has an endless supply of fresh meat.
There is certainly enough to feed the six cubs.
She'll make a kill every day to keep her cubs properly fed.
And it's not just wildebeest the predators have come to eat.
Many of Africa's antelope are here, too.
Eland, Africa's largest.
And they're joined by more than half a million
Thomson and Grant's gazelles.
And 200,000 zebra.
Just north of the Ndutu lion territory,
these lions are now lucky enough to enjoy a time of plenty.
A favourite lion ploy is to wait by waterholes
knowing that the herd will ultimately have to drink.
As the herds move further south,
they at last enter the homeland of the Ndutu pride.
The question is, have the weak cubs managed to survive
to witness the great return?
The Ndutu pride is still together. They are healthy and strong.
Somehow they have managed to make it through the long dry season
and the endless wait for the returning herds.
The young male now has the beginnings of a mane.
And though still limping,
the female has grown new fur over her black patches.
Now at last, with endless food around them,
the lion cubs have the time and the energy to play.
And they can relax in a way that only lions know how.
By March, the great event on the Ndutu plains is in full swing,
and where there are kills, there are scavengers.
(BIRDS SQUAWKING)
Vultures fly in from all over the Serengeti.
On her own a mother cheetah has little chance
of keeping this mob off her kill.
She may be agile, but she lacks the necessary brute force.
Even now it's not easy raising cheetah cubs.
Over half her kills will be stolen by thieves.
Spotted hyenas are notorious scavengers and they arrive in force.
(HYENAS LAUGHING)
Hyenas now become the most numerous carnivores on the Ndutu plains.
They'll even take on a lion pride.
As the Ndutu lions finish off a wildebeest,
the hyena clans gather around, trying to intimidate them.
The young male cub faces up to them.
He's finally coming of age.
He's learning how to protect a pride.
But this time, with their bellies full,
the pride decide the bones aren't worth the hassle.
Well-fed at last,
the two young cubs are beginning to look more like adults.
But it will be another six months before they can hunt on their own.
It's April, and there's a flurry of excitement
as the wildebeest turn their attention to courting.
Or at least the males do.
The young bulls limber up for the rut,
when they will have to fight for the right to mate with a female.
High spirits are infectious.
In three months the young calves become boisterous and bounce with good health.
These plains have been a nursery.
But change is in the air.
The season is turning again.
The arrival of seed-eating quelea
is a sign that the grass on the Ndutu plains is changing.
Once the grass flowers and sets seed,
it loses the succulent green leaves that the wildebeest prefer.
Time for them to move on again,
to follow the distant storms that are now rumbling to the north.
Despite the arduous journey that lies ahead,
a wildebeest calf in the Serengeti
still has a better chance of surviving its first year
than a lion cub.
The Great Migration is leaving Ndutu,
and once again the pride will have to face life without the herds.
A brother and sister have survived an eventful year
that has brought sickness and drought, fires and volcanic eruptions.
Theirs is just one of countless stories
that unfold every year on the short-grass plains,
the grasslands at the centre of this great event.
All in the shadow of the Mountain of God.