This is the great wildebeest migration as you've never seen it before.
The story of Africa's greatest travellers
is captured by state-of-the-art spycams.
Only cameras concealed in the most unlikely places
could capture such intimate images.
Here, they spy on the moment the wildebeest cross Kenya's Mara River.
Their greatest challenge on the astonishing 2,000 mile journey they make each year.
The hidden cameras immerse us in the action,
experiencing the drama as the wildebeest see it.
They show what it's like to be on the hit list of every African predator.
Wildebeest undertake the largest migration of land mammals on the planet.
Their epic march creates a spectacle that's beyond compare.
Over one and a quarter million wildebeest
participate in the migration,
but each individual has its own incredible story of survival.
The adult females carry new life inside them.
These yet-to-be-born calves will be the focus of this story.
We will see how they overcome the greatest dangers,
whether from predators... or from their journey.
Hundreds of individuals were filmed to recreate the calf's story
as it makes the most challenging trek that any mammal ever undertakes.
After crossing the Mara River,
the herds follow the seasonal rains
and head south to the lush plains
of Tanzania's Serengeti.
Here, volcanic soils create pasture rich in both minerals and nutrients.
And it's here that wildebeest make their longest stop
on a journey that takes a year to go full circle.
Their appearance has been eagerly anticipated.
For lush pasture is not the only reason for this annual get-together.
Africa's top predators are assembling for a very special event.
Each February, these plains experience the world's largest baby boom.
In just three short weeks, over half a million calves will be born.
It's with this moment of birth that our story begins.
Delivery is quick, every minute counts.
Mother and calf must form a lasting bond
based on smell, taste and sight.
It's this relationship that will sustain them on the long journey that lies ahead.
This is his most vulnerable time.
Hyenas - they may commute the distance of two marathons to get here,
but for such easy pickings, the rewards are worth it.
Vulnerable newborns are just what they're looking for.
Other antelopes hide their young away,
but wildebeest calves must be ready to follow their mother from birth.
He has just minutes to find his feet.
Hyenas prefer the easy option,
and prey doesn't come much easier than this.
To survive, the calf must master in minutes what a human baby takes a year to learn.
Hyenas separate as they move through the herds.
In this way, they cover more ground.
They hunt with both sight and sense of smell.
The calf learns to use his legs faster than any other mammal.
He's up and walking in under four minutes.
It's not a moment too soon.
He faces his first deadly challenge.
He's already proving his strength,
few calves can outrun a hyena on their first day.
And he's taken the first steps on a journey that will last a lifetime.
Danger past, he suckles for the first time.
This begins the unbreakable bond between mother and offspring.
One that will last the whole journey until they return here next year.
Tortoise-cam is just one of 20 different cameras
used to film the calf's story.
Between them, they will record over 500 hours of behaviour.
Tortoise-cam's harmless appearance
lets him infiltrate the herd.
Protected by a hard shell, he's never afraid to stick his neck out.
Helped by other undercover agents,
he will spy on the calf every step of the way.
Dawn brings no respite from danger.
Having young together helps spread the risk posed by predators.
The mothers form nursery herds, where newborns are hidden among the older calves.
A territorial male attaches himself to these nursing mothers
and drives out any males older than a year.
Ousting the males creates small secure nursing herds
within the super herd.
The calf may sometimes get caught in the chase,
but having a male around adds to his security.
Lions are an ever-present danger and when the calves are born,
nomadic lions swell the enemy's ranks.
As the male tries to keep control, the herd easily becomes distracted.
To increase their chances, pride lions often hunt as a team.
One lioness stalks directly forward.
Her aim is to close the gap as quickly as possible without being seen.
Another attempts a flanking manoeuvre.
They will try to stalk to within 30 metres before risking an attack.
Lions find it hard to outrun their prey,
so every inch nearer tips the odds in their favour.
One lioness finds a target...
the calf.
But the herd panics across her path,
and she spots a new victim.
Both calf and mother escape.
But in the chaos, the calf is separated from his mother.
He desperately needs to find her if he is to survive.
But the mother is just one among thousands.
He checks every wildebeest he meets, but the females reject any calf that's not their own.
Without the herd, he is hopelessly vulnerable,
and the lions are not far away.
The lions may be distracted now, but they have many mouths to feed.
The birth of their cubs coincides with this bumper harvest.
The calf's smell is unfamiliar.
He will never be adopted by another mother,
even if she has lost her own calf.
The herd drifts away.
His call is unique, if his mother hears his cries, she will react instantly.
Vultures keep an eye on everything that happens in the migration.
They react quickly to any new opportunity.
Lions don't give up their kill easily, but with bellies full,
it's easier to take a more relaxed view of scroungers.
But for some, it's simply a matter of principle.
The vultures are used to this game.
They make their living stealing food from lions.
Time is on the vultures' side.
He may be frustrated, but he's just wasting his energy.
As the day heats up, the desire to defend the carcass cools down.
This is a battle that vultures invariably win.
Lost calves are so desperate for company,
they will attempt to befriend any likely animal.
Even zebra are better than nothing.
But there is no warm welcome here for a lonely stranger.
Hyenas have now picked up the scent of the carcass.
But a lone calf makes a more tempting alternative.
Instinctively, he heads for the centre of the nearest herd.
It may not be his herd, or even his own kind,
but this was a fortunate move.
Zebras often tackle a threat head-on and a raging stallion,
at full throttle, is a force to be reckoned with.
By comparison, the carcass is easy meat,
even if it means battling it out with the vultures.
Between them, they will quickly polish off the lot.
It's midday, and the lost calf is feeling the heat.
Even his reluctant companions leave him.
Starved of his mother's milk, he's close to exhaustion.
No calf below six months old will survive on its own.
But there is still hope on the horizon.
The herd returns.
Whilst there is fresh grass to eat, herds don't move far.
He searches again, but even to a calf,
all adult wildebeest look the same.
Sound is a more reliable guide,
he can recognise his mother's call among a thousand others.
A glimmer of recognition,**
but smell is the final confirmation as the pair are reunited.
Remarkably, 95% of lost calves become reunited with their mothers.
Suckling reinforces the strong bond between them.
Once more, the herd provides security and protection,
especially against an old enemy.
Now, a lost eland calf has become a target.
The wildebeest calf was lucky that he didn't suffer the same fate.
Dung-cam, a camera modelled on a pile of elephant dung,
is soon capturing some rarely seen behaviour.
Hyenas have devised a method of extending the shelf life
of their surplus food.
The eland calf is destined for the same underwater larder,
as are the remnants of the wildebeest carcass.
Water not only hides the food,
but conceals the smell from other scavengers.
Skull-cam is in dangerous company.
Hyenas spend the hottest part of the day cooling off,
but this is also the time
when thirsty calves urgently need a drink.
They have no choice but to face off the enemy.
Dung-cam takes up battle stations,
but a gorged and lazy hyena has other things on his mind.
Wildebeest have learnt to live alongside their troublesome neighbours,
making the most of the hyenas' off-duty moments.
But a calf is never truly out of danger.
Hyenas can turn nasty at any moment.
But then something remarkable happens,
the wildebeest go on the offensive.
The mother, defending her calf, sends the hyena packing.
The hyena has deadly enemies of its own.
This is the worst mistake of its life.
Hyenas will steal food from lions and kill their cubs.
This looks like revenge.
A lioness vents her anger too, but all she gets is a bloody nose.
The war between lions and hyenas over food never ends.
Even for a whole pride, a hyena is a tough adversary.
It's late April, and the lush green plains have been eaten away
and become a barren wasteland.
Dust devils whip the dust into a swirling column.
A new and puzzling sight for a three-month-old calf.
As the choking clouds make life difficult,
the herd treks southwards
seeking greener pasture and fresh water.
Our spy-cams travel with them.
Meet dragonfly-cam.
Small and quiet, it can fly close to the herd without causing alarm.
It tracks the wildebeest south as they follow the seasonal rains.
For higher views, stealth-cam takes over.
It can zoom into a detail of the herd.
Ahead lies Lake Ndutu, in the far south of the Serengeti.
By now, the calf is used to being on the move.
but as the herd approaches the lake,
he is about to encounter a new challenge.
Lake Ndutu is a soda lake loaded with corrosive minerals.
Although the calf must be thirsty,
he has no alternative but to cross it as quickly as possible.
The calf needs to hurry.
Too long in the water, and the soda can burn.
The calf's first experience of deep water is traumatic,
and he still has a way to go.
A mile across, the lake is a true test of the calf's stamina.
Fortunately, there are no crocodiles to worry about,
and he's taken to swimming as easily as he took up walking.
Powerful strokes drive him forward.
Guided by his mother, the calf makes it to the shallows.
This ordeal by water is just a taste of things to come.
Having crossed the lake, the herd veers westwards
into new fresh pasture, where the seasonal rains have recently fallen.
Grass-cam is there to greet them.
But it's natural grass that revitalises the herd.
Replenished by these lush meadows,
there's even time for a game of chase.
It's not only calves that are expert at this game.
Cheetahs are the fastest running mammals on earth,
and one in every two of their hunts are successful.
For the calves, playing is a form of training, it hones their escaping skills.
But for all their speed, cheetahs still need the element of surprise.
A cheetah cannot sustain top speed for more than 15 seconds without overheating.
Spotting the predator before he ran gave the calf a vital head start.
In a few weeks, following the yearly cycle of the rains,
the calf's herd moves northwestwards.
They finally reach the acacia woodlands of the western Serengeti.
It's taken the calf four months to get here.
Here, the calf will find welcome shade
and good grazing between the trees.
But here lurks Africa's most elusive predator.
Leopards are the stealth hunters of the trek.
Masters of surprise, ambush is their modus operandi.
But for a six-month-old cub, a stone curlew is more his size.
The bird's distraction display is a tactic to lure the leopard away from its nest.
Today, the cub only manages to ruffle a few feathers.
It will be at least a year before he becomes a serious threat.
It's June, and midsummer madness
seems to have gone to the bulls' heads.
This tree-rubbing is a way to vent their aggression.
The thrashing of young saplings by a quarter of a million bulls
helps stop the spread of the woodlands.
The destruction inadvertently preserves their precious grasslands.
As well as needing good pasture, the wildebeest must make a daily trip to water.
Simply waiting for a meal to arrive
is the lazy lion's approach to hunting.
It's just a matter of remembering to wake up on time.
The calf has every reason to be wary, for this is when most ambushes occur.
The need for daily water helps drive the great trek.
The entire population drinks three Olympic-sized swimming pools of it each day.
No longer dependent solely on mother's milk,
the calf guzzles his fair share.
Head down, he is at his most vulnerable.
They sense danger. The lioness must make her move.
She isolates the calf, but he's more sure-footed now...
..and dust creates the perfect smokescreen.
Only one in five hunts are ever successful.
The trek moves on northwards through the woodlands.
The herd will soon arrive at one of the most dangerous spots
in the whole of Africa.
The calm waters of the Grumeti River are deceptive.
To capture the upcoming drama,
the river has been staked out with a variety of spy-cams.
A new camera makes an appearance.
Hippo-cam is designed to blend in with the local residents.
Hippos can be aggressive, but something far more sinister lurks here.
These are the biggest crocodiles in Africa.
Even Africa's biggest mammal gives them a wide berth.
Some are over 20 feet long and weigh more than a tonne.
They may not have eaten for a whole year.
But food is about to arrive.
It's rush hour, and for a baboon,
the traffic to the river can become quite a hazard.
It's best to look both ways!
The crocodile's long hungry wait is now over.
Wildebeest are always nervous facing new situations and in this case,
who can blame them?
For the calf, it's a totally new experience,
but the confidence of others boosts his own confidence.
If undisturbed, wildebeest can drink eight litres in a single session.
As his confidence builds, he is oblivious to what lurks beneath the surface.
The herd is bewildered. Some have never seen a crocodile before.
Even as the full horror unfurls,
there is great confusion about just what is going on.
And that was just the first attack.
300 hungry crocodiles live in the Grumeti River.
Wildebeest react differently to crocodiles than other predators.
Even the adults seem unsure of just how much danger they're in.
The calf's desire to quench his thirst
overcomes any fear he may have.
The crocodiles manoeuvre around them with surprising ease.
They are intelligent hunters,
plotting their attack with precision.
A strike can happen at any time.
Despite the carnage, the mother and calf survive.
They stampede back onto the plains.
For the baboons, it's more like a spectator sport.
They might as well settle down, a single croc
can take some time to overpower its victim.
But crocodiles are co-operative feeders, they work together.
The death roll breaks the prey into bite-sized chunks,
but aggression can spill over.
The calf has survived his first day at the Grumeti,
but as the river is the only water for 30 miles,
tomorrow, he must run the gauntlet again.
Meanwhile, our tortoise-cam has found a friend.
For tortoise-cam, it's soon back to business.
And these bulls are not to be messed with.
It's the rutting season.
Three weeks of mayhem in which the males fight over the females.
Not the time to be stuck in the danger zone.
It's a test of real strength and stamina.
The winner returns to the females.
At this time, a collective madness appears to infect the males.
The clashes can be quite violent.
Each bull tries to round up as many cows as possible.
The calf gets caught up in the confusion,
as his mother is corralled by the bull.
It's a chaotic and confusing time for the calf.
During the rut, bulls barely eat or sleep,
they're so charged up with testosterone.
They have to stay on guard for cattle rustlers.
It's total pandemonium as these rival males
try to steal the females.
They run through other males' territories
scattering the herd in an attempt to abduct their cows.
Troublemakers are challenged to a duel.
For the calf, it must be a relief when things finally calm down.
But for a male guarding females, there's no respite.
Challengers are always on the prowl.
The calf can only snatch a moment's rest.
He soon becomes caught up in more cattle-rustling.
The bull springs into action.
He sees off his rival and claims his prize.
Matings are more successful in this species than any other mammal.
95% succeed.
After all that activity, the herds head back to the river.
But dragonfly-cam is experiencing technical difficulties.
Its transmitter has mysteriously lost contact.
Dragonfly-cam refuses to die.
It gamely tries to continue its mission.
Even grounded, it keeps on filming.
The rut has proved thirsty work.
This time, the herds are more cautious.
Sensing danger, the calf holds back.
But crocodiles still seem more of a curiosity than a danger,
and other animals don't seem too concerned.
Guinea fowl seem remarkably happy to tempt fate.
A yellow-billed stork plays a game of dare.
All the signals are reassuring.
A baboon with young appears relaxed,
even with a crocodile just a stone's throw away.
Wildebeest are highly tuned to the signals given off by other animals.
Apparently, there's nothing to worry about.
But a glossy starling still gives them the jitters.
The calf takes his cue from the confidence of others.
He can still stare death in the face and not even know it.
A crocodile's low profile is its secret weapon.
It isn't seen as a threat.
Nose to nose,
but the calf is still oblivious to the clear and present danger.
The teeth miss by inches.
He may have escaped the jaws of death,
but his mother is not so lucky.
Without her, the calf is doomed.
But the croc can't keep his grip.
The bond between mother and calf has carried them through the first leg of their epic journey,
but will it be enough to overcome the ordeals that lie ahead of them?
In the next programme, the calf reaches Kenya's Masai Mara,
where he faces the greatest challenges of his epic trek.
Subtitles by Red Bee Media Ltd - 2007
E-mail subtitling@bbc.co.uk