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We're about to follow the world's greatest migrations,
and reveal their secrets in a way that's never been done before.
All over the world, animals are on the move...
embarking on vast journeys that they depend upon for survival -
to find food, to give birth, or to escape danger.
Travelling hundreds of miles
through some of the world's most breathtaking wildernesses...
..that can turn against them at any moment.
That rapid's really picking up.
They're just disappearing under the water.
Ground-breaking technology allows our team
to follow these migrations more closely than ever before,
and understand them in unprecedented detail.
We can track this ele's movement in real-time.
Using the latest satellite tracking technology,
we can monitor individual animals
and witness first-hand their struggles for survival.
We've got a drama down here.
We've got it. We've got the wolf. We've got the wolf.
This time, we'll follow thousands of zebra
as they undergo their gruelling annual migration in search of food.
They must reach their grazing grounds
just as the rainy season begins.
Arriving too early or too late could spell disaster.
For the first time, satellite tracking allows us
to stay with individual mothers, foals and dominant males
as they brave drought, hunger and ferocious predators.
Below me, this wilderness has kept hidden
a journey that's never been followed before,
and about which virtually nothing is known.
It's the longest land migration in all of Africa.
This is the untold story of the great zebra migration.
Northern Botswana -
a vast, parched wilderness
the size of the United Kingdom.
At the end of Botswana's brutal dry season,
thousands of zebra gather on the Chobe floodplain
as they prepare to travel 250km south
to Nxai Pan National Park.
The journey takes them through one of the most punishing landscapes
in southern Africa.
Travelling in family groups,
many of the females are heavily pregnant or supporting young foals.
Each year, their goal is the same -
to reach Nxai Pan's fertile plains
just as the rains produce the first flush of nutrient-rich vegetation.
The timing of this journey is crucial.
Leave too early and they risk arriving at Nxai Pan
before the lush grass appears.
Leave too late and they'll miss out on the best food on arrival.
Our first camp is on the edge of the Chobe River,
the starting line for the migration.
Yeah, I've been looking at her data over the last...
'I've joined a team of specialist biologists and cameramen'
to attempt something that's never been done before.
We plan to travel with the zebra on the ground,
following their every move.
Around 2,000 zebra are gathering
across the vast Chobe River floodplain,
dotted across the landscape in family groups of up to 20 animals.
They won't be travelling en masse.
Instead, each individual family will make its own decisions
during the migration.
'I'm joining the scientists who are collaring the zebra,
'so that the team can track them.'
OK, Mike, Larry's getting ready to dart.
I wouldn't even recognise which one he was focusing on.
Next minute - boof, done.
The dart contains a sedative
that immobilises the zebra within five to ten minutes.
Once the zebra goes down,
the team have to act as quickly as possible.
You tell me when it's OK to get out.
-You can get out.
'A towel is put over the animals eyes to help keep it calm.'
Just check it. Is that all right?
It's really thanks to this technology
that we'll be able to stick with these zebra,
getting readings every hour.
And that means, for the first time, we'll be able to follow them.
That's not only going to give us insights into where they go when,
but also into their behaviour, their decision-making process.
That's bound to reveal some unknowns into the lives of these zebra.
'The collaring data will not only help us to keep up with them,
'but we'll see for ourselves just how tough they need to be
'to take on this migration.'
It's only when you get really close to these animals
that you realise just how sturdy they are, how hardy.
You know, they need to be -
they're about to embark on what is
the longest land migration in Africa.
'The hourly updates from the satellite collars
'will allow us to follow a number of different families,
'each with a collared animal in it.'
Awesome. That was hugely satisfying.
One of the zebra collared
is a very special nine-year-old female called Janet.
She was the first zebra in this population to be collared,
way back in 2012.
We first discovered this migration in 2012.
Up until that point, people didn't know where the zebra move.
So, in the dry season, you had zebra up here,
and then, in the rainy season, they disappeared...
Exactly. So, 2012 the first collars went up.
-And, Janet, she was collared just up here on the floodplains.
It was very exciting -
we didn't know where she was going to go, or what she was going to do.
She moved 250km all the way down to Nxai Pan,
down here, in the south.
This is the longest mammal migration in the whole of Africa,
which is amazing.
The average round trip distance is about 955km,
which beats the wildebeest migration in East Africa.
The first year she was collared,
Janet's data completely changed our understanding of zebra migrations.
It was assumed that the zebra travelled just 60km or so
to the grassy plains of Saruti Marsh or Seloko.
But Janet's collar revealed
fascinating new information to scientists.
She was travelling much further,
all the way to Nxai Pan.
That year, Janet became the official record holder
for the longest land migration in Africa.
But this huge journey takes the zebra
through an area with virtually no food or water,
and plenty of cover for predators.
'So why do they leave Chobe at all?'
Chobe can sustain wildlife all year round.
The rains obviously hit Chobe as well, the grasses get better.
Why would zebra leave Chobe in the first place?
The zebra there have competition with other animals,
so they need a new resource,
and the vegetation that comes up in Nxai Pan is very nutritious,
the soils are very fertile, and so the grasses are so much better.
For the zebra, the potential rewards seem to outweigh the risks.
But how exactly do they survive this immense journey?
How do they navigate through a featureless landscape?
How does it all even begin?
We're down on the floodplains.
We've been looking for Janet this morning.
Cameraman Max Hug Williams' mission
will be to follow the frontrunners all the way to Nxai Pan,
250km to the south.
Our other cameraman, Bob Poole,
will hang back following the families that are last to leave.
Making the journey are heavily pregnant females...
..as well as mothers with young foals.
For them, the 250km migration
will be particularly dangerous.
Filming the zebra as they gather on the plain
gives Bob the chance to familiarise himself
with the collared individuals.
If you look at these zebra,
each one of them has totally different patterns in their stripes.
And she has got some pretty distinguishing markings on her.
She's got a beautiful sort of W on her left shoulder,
and so we've called her Winnie.
She's got a foal -
it hangs right next to its mother almost all the time,
and they seem quite affectionate together.
At six years old, Winnie may have already had three other foals
and carried out six migrations.
Although zebra foals can stand at less than an hour old,
these babies won't have walked more than a few kilometres a day.
You can see these little things can run.
And I suppose all this behaviour is really important,
because they're going to have to move all the way south.
These zebra are about to move in a mass exodus
towards the south of Botswana,
and one of the biggest mysteries is just what triggers this.
One theory is that the start of the rainy season
sets off an irresistible urge to migrate.
Luckily, the team don't have to wait long before the first downpour.
With the rains, everything changes.
Very excited right now.
I mean, we've been waiting for the rains, and here they are.
"Poola" they call it here in Botswana.
And that's the same word they use for money.
In Africa, just add water,
and everything works.
And it's not just Bob who's reacting to the change in the weather.
Our satellite data shows that in the last few hours,
all the zebra have crossed the Chobe River
and have started to move south.
The migration has started.
250km to go.
There's absolutely nothing on these plains any more.
There's just the last pocket of five or six,
but, otherwise, this plain is absolutely empty.
Now the migration is under way,
we'll have to keep up with them every step of this journey.
The open floodplain offered some safety from predators,
but now they face thick forest...
..and their first big challenge -
a pack of African wild dogs,
the continent's most relentless predators.
Surrounded by trees, the zebra won't see them coming.
Even without cover, wild dogs are a real threat.
They may not be the biggest of Africa's predators,
but their highly efficient method of hunting as a pack
certainly makes them one of the most effective.
During a hunt, each dog has a role.
A leader drives the prey forward...
..while others act as flankers,
corralling the prey towards the rest of the pack.
The ultimate endurance hunters,
their ability to run up to 70kph and use sophisticated teamwork
allows them to take down animals far larger than themselves.
Meticulous coordination results in a kill
more often than any other predator.
In the forest, the wild dogs have already left Max far behind.
You can see, actually, there's dog tracks everywhere.
They split out. There's one here...
Look at that. That's a leopard track.
I mean, on the plains they can see what's around,
and when one gets a sense of some danger, they all bolt.
But in here, this is where leopards, wild dogs,
have a chance of actually taking... Especially the foals.
I mean, some of them were even struggling
to cross the river this morning,
and you think, "How are they going to make this epic journey of 250km?"
I have absolutely no idea.
With so many predators about,
Max needs to catch up with the zebra
to see if they've managed to stay safe.
'Max, Max, Max. This is Rob, at base camp.'
Just got some updated coordinates for you.
So, 1791 has moved south...
In the forest just south of the wild dog tracks,
the satellite data leads Max to his first collared zebra,
who still has 230km to go.
She looks heavily pregnant.
You can see.
A zebra with so few stripes on her front legs...
I mean, it looks like someone's got an eraser and rubbed them out.
It's like she's got a pair of tights on or something.
She's very relaxed, though. That's great.
What are we going to call her, then?
Because we've got Winnie -
she's really easy to identify with the W.
And we've got to come up with something with...
She's definitely got a pair of socks on or something.
Socks it is.
At only four years old,
Socks is a young and inexperienced mother.
This may even be her first pregnancy.
She's in a small family of just seven animals.
But these families, or harems, can be up to 20 animals strong,
and are usually made up of unrelated females and their young,
led by a single dominant male.
The more experienced and powerful the stallion, the bigger the harem.
Look at this male.
He's got really obvious thick, black bands on his neck,
and also on his right flank there's a marking
which almost looks like a wishbone.
We'll have to call him Wishbone.
Wishbone's job is crucial.
He must protect Socks and the others from predators,
particularly now as they travel through this dense forest.
Wishbone, Socks and the rest of the family
are ahead of the other zebra...
..closely followed by Max.
Bringing up the rear is Bob.
He now has the chance to see how Winnie
and the other herds at the back deal with the dangers of the forest.
This is pretty exciting.
There's a lot of zebra now, packed together,
and they all seem to be on the move south.
Winnie's in the middle, there,
and she's travelling along with her foal and the rest of her family.
But, you know, for the first time, there's so many zebra.
Amongst the large group at the rear are two other collared females -
a pregnant mare called Spirit
and a ten-year-old called Jewel.
Travelling together for safety is a good idea.
Just a few kilometres to the west,
Max has found a young family who haven't been so wise...
..as the wild dogs are well aware.
Believe you me, when they get going,
if they want to run something down,
there's pretty much nothing that they can't take.
But, luckily for the zebra, it looks like these guys have fed
and they're just relaxing in the shade.
When the dogs' hunger returns,
the pregnant females or those with foals
will be particularly vulnerable to attack.
If Socks gave birth,
she's not a million miles away from here.
I mean, that would be an easy prey for them.
Meanwhile, there's been some worrying news
about another collared animal.
The satellite data shows that one zebra
didn't travel far from the Chobe floodplain,
and it hasn't moved for the last two days.
We've got a signal, Max.
Is it strong? Are you getting something close by?
Yeah, it's a strong signal.
It's certainly around here somewhere.
The team will have to home in
using the VHF radio signal emitted by the collar.
Numan Chuma, tracker and wildlife guide, leads us in.
But if the zebra is dead,
there may still be predators feeding on the carcass.
If it is a lion on a kill,
-I mean, we've got to be pretty careful here, haven't we?
-You need to spot the animal before the animal sees you.
As they get closer, clues emerge as to what might have happened.
You know, I can see quite a few tracks - a hyena...
Something dragging it this way.
-I can see something.
Here's the carcass, so...
It looks like this zebra may have fallen prey
to one of the forest's many predators.
Look how many maggots there are already. It's only...
-..two days old.
-Nothing lasts very long out here.
-So you can see this...
-It looks like a puncture wound.
-They're claw marks...
It's difficult to know exactly how it died,
but this zebra's collar is fitted with a camera.
It still looks intact, doesn't it?
It does, yeah.
OK, let's take this off.
Once the footage is downloaded, it may reveal exactly what happened.
So, that's the last shot from the morning...
-Is that you?
That's me, yeah.
This is when the animal was collared, on 20th November.
'The camera recorded in short bursts to extend its battery life.
'For the first few days, the zebra behaved normally,
'grazing and moving around the floodplain like Socks,
'Janet and the others.
'Then, four days later, it crossed the Chobe River again.'
All right, so it's back on the Botswanan side.
Looks like it's moving a bit faster there.
Haven't seen many zebra around him, do you?
Oh, you can see his shadow.
-So he's swinging his tail...
-Now he's lying down.
Looks like he's on the ground.
Zebra tend not to lie down,
especially when they're by themselves.
Yeah. That makes sense.
-It's not particularly safe to lie down like that.
The zebra stayed here for around 36 hours,
moving about a little, but never leaving this location.
Something was clearly wrong.
Yeah, lots of flies.
-And he's doing something with his mouth, but he's not grazing.
We can't see if there's any blood or any sort of...
foam coming from the mouth,
so we're not sure what's happening there.
With no clear evidence of predation,
our team thinks he may have been bitten
by one of Botswana's poisonous snakes.
He's down again, look.
We don't know how long he stayed down for.
Between the... Yeah. How long, during the day...
'Before long, vultures begin to gather.'
And just a few hours later, the zebra is dead.
-That's it. Game over.
Despite not being able to determine the exact cause of death,
the collar data shows just how dangerous it can be out here.
Our latest satellite data shows
that many of the zebra are making steady progress south.
But Socks, the four-year-old female that Max spotted in the forest,
is pushing ahead of Winnie, Janet and the others,
with her family in tow.
I guess she's just a lot slinkier than we are.
Helping Max get as close to them as possible is Duncan Rowles,
an experienced tracker and safari guide.
Max, Max, Max. This is Rob, at base camp.
Max has Socks' latest satellite position
and is trying desperately to catch up with her and her family.
And you can just see how far Socks has come.
30km just yesterday.
Now she's still in this really thick bush here.
The only way for us to have a chance of even getting a glimpse of her
is carry on...on this, which is as good as a road as you'll ever get,
travel all the way round,
and then hope that she pops out somewhere near here.
It's not clear why Socks' family has broken away from the others,
but since she's heavily pregnant,
she might be trying to reach Nxai Pan before giving birth.
Her incredible pace means that the hourly satellite data
is not accurate enough to locate her precisely.
So the team have to resort to another system.
These collars allow scientists to track animal movements
in two different ways.
The first part uses a network of satellites
to calculate its location,
in the same way as your phones and your cars
use their navigation systems.
But for real-time, on-the-ground tracking,
the collar also emits a VHF signal
that can be picked up with radio telemetry equipment,
and every single animal will have its own unique frequency.
With Socks fast disappearing into this vast landscape,
it's the VHF radio signal that will give Max his best chance
of catching up with her to see if she's OK.
But in forest this thick, he might get close and still not see her.
She's very close.
We know that.
The best chance is to just get the telemetry up
and just see where that ping's coming from.
She's super close now.
She's... She's just in these bushes.
A really strong signal from here.
-That is zebra tracks.
And that's completely fresh. That's a split second.
She must have just crossed before we came round that corner.
Having so narrowly missed Socks and her family,
Max now has very little chance of spotting them
as they head into the ever-thickening forest.
And how are we supposed to follow that?
I can't even see you from here.
Socks has covered an amazing 50km in the last day and a half,
but still has 200km to go.
'This migration is so new to science
'that every bit of data we gather helps scientists to understand
'the nature of this extraordinary journey.'
We need more data to really build up that picture.
Then the satellite data shows something
that stops us in our tracks.
Within hours of each other,
almost all the other zebra have made a U-turn
and are heading right back to their starting point
on the Chobe floodplain.
-Do you have a signal?
-Yes, I've got a signal.
Let me just turn it up for you.
Bob tries to intercept the zebra families as they return north,
hoping to see them cross the only tarmac road in Chobe.
The radio telemetry shows that Winnie's family
are just about to cross.
Where's Winnie? Where's Winnie? Where's Winnie?
Shoot. There she is.
Winnie and her herd are an experienced family,
so what could possibly have made them turn back?
Has some other cue in the environment
told them they've left too soon?
Or could the number of predators in the forest have driven them back?
It seems like confusing times for these zebra.
It's almost like they can't make up their mind.
Are they going to go on this migration or not?
They might not be comfortable yet
with the amount of rain that's fallen to make the commitment.
So they have to be very confident
that there's enough water down there.
Zebra need to drink pretty much every day,
and normally stay within 10 to 15km of water.
Perhaps a lack of water further south has influenced their return.
So there's a lot of fascinating behaviour going on. Not only...
'Revealing as it is,
'the satellite data can only tell us so much.'
These are complex animals, aren't they?
They certainly are, and it's not a straightforward migration.
No. It's not. It's not like wildebeest just,
"Right, go, all together!"
-They make very different decisions.
Exactly. Now, that's what we've observed so far -
different family groups will make different decisions
and some groups will leave earlier,
some groups will hang back and then move later.
Combining the satellite data that's coming in
with the information we're getting from the teams on the ground,
that's going to build a much, much bigger and better picture.
Whatever the reason,
the majority of families have decided to head back
to the food and water of the Chobe floodplain.
With an entire 250km still to go,
Bob finds that Janet, Winnie, Spirit and Jewel
are showing no signs of restarting any time soon.
So Bob will wait with them until they're ready
to start the journey again.
So there's Winnie, coming down.
God... That is great.
Getting a nice drink.
It must be hard for them to make the decision to move south,
like Socks has now.
Why in the world would you want to leave this amazing paradise?
But this paradise won't last forever.
If too many zebra stay here, the food will run out.
And they'll miss out on the more nutritious vegetation at Nxai Pan.
If our female zebra want to give their foals
the best possible start in life,
they'll have to leave here very soon.
Socks and her family, however,
are well on their way to having Nxai Pan all to themselves.
She's actually moved quite far south now.
Socks is motoring 8k an hour.
That's unbelievable. There's no way we can keep up with that.
It's taken us an hour to do 1.5km!
Not only is Socks' family now well ahead of the others,
they travel in a direct line to Nxai Pan.
In the flat wilderness of Botswana,
the zebra somehow navigate perfectly,
with no hills or landmarks for reference.
Scientists still don't fully understand exactly how they do this.
Until very recently, it was assumed these routes were learned
and then passed down from generation to generation.
But I'm travelling to meet a scientist
who made a ground-breaking discovery that turned this theory on its head.
In the 1950s and '60s, thousands of miles of fences were erected
in an attempt to stop diseases being transmitted
from wildlife to domestic livestock.
But these fences stopped many animals
from carrying out their annual movements.
A few years ago, when some of these fences were removed,
an ancient migration was seen to start up once more,
following its exact same route.
Dr Hattie Bartlam-Brooks of the Royal Veterinary College
made this discovery.
So if the fence was up for 36 years
and zebra live to about 15 years in the wild,
so there was no zebra that knew about this route
that was alive when this fence went down.
I think that's the most exciting part about the story.
Everyone presumes that terrestrial migrations are taught.
But in this case, it can't.
The mothers couldn't have taught the foals.
So I think there's a genetic urge to make the move.
Something in the zebra's genetic code drives them to migrate,
but what's even more fascinating about Hattie's discovery
is that it seems their genes also tells them where to go -
something that zebra scientists didn't think possible.
I think it just shows how complex they are.
We take it for granted that it's just a zebra,
it walks around, it eats grass, when it gets hungry,
it walks to some more grass, but it's not like that.
There's a huge complex interplay of things going on.
They're not just a stripy donkey.
For the zebras still in Chobe,
something else is telling them to stay put.
-Hopefully we can get you out there.
-OK, good luck.
But they have moved off the floodplain
to an area just south of the main road.
Bob is catching up with them to try to understand what's going on.
He finds them 240km from Nxai Pan,
in an area recently razed to the ground by a forest fire.
Sam, look at this, eh?
All the ash on the ground is giving it nutrients.
The result is amazing, isn't it?
Suddenly, you get this beautiful green grass coming up,
and that's what they're eating right now, and they're loving it.
Ash is an excellent source of trace elements
that new vegetation thrives in.
Seeing exactly what the zebra are doing on the ground
allows a deeper insight into the movement data.
So we know that our zebra haven't moved south yet,
and that there's a burnt area here now.
How does it affect the migration, the timing of it?
This could delay it,
especially if there's not enough water or vegetation further south.
They're going to stay in this area
and take full advantage of this new growth of grass.
So this is doing the zebra quite a big favour,
giving them an extra source of food, as they need to wait, anyway.
Next rains, you're ready to move down.
Janet, Winnie, Spirit and Jewel are staying put for a very good reason.
150km south, Socks and her family
have stopped for the first time in six days.
Socks is past the halfway point of the migration
and now she's stopped in an area for over 24 hours,
so does this mean that even though she left really early,
possibly to have her foal in the Nxai Pan area,
that she gave birth to the foal over the past 24 hours?
It would be very, very good
if Max could catch up with her and see for himself.
The problem is, it's still extremely tough terrain to get through.
Oh, she's so close.
She's literally straight in front of us,
and that's as strong a signal as you get.
I'm just worried that this is a really bad place on the journey
to have a youngster, because she'll be feeling weak,
there's very little water, next to no food,
and she's still got a third of this journey to make.
As if that wasn't enough, it still hasn't rained.
Scattered across this hostile wilderness
are depressions on the landscape called pans.
As long as there is rain,
the water in these pans offers a lifeline for wildlife.
Using data from the last 24 hours, Max searches the landscape.
He finds a pan, but it's certainly not the oasis Socks needs.
There's nothing to drink here.
You can see they've been trying, because these are zebra tracks here.
-Oh, they're zebs, yeah.
-And they've actually been into the mud,
obviously just trying to suck whatever they can off the top.
That's definitely got to be Socks.
She's come here, and trying to get water from this mud wallow,
I mean, she must be desperate.
This elephant's come into drink, there's nothing even for him.
He's not even trying.
With the light fading,
there's little chance of finding Socks today.
It's too dangerous for Max and Duncan to drive at night,
but Socks could keep pushing south and leave them behind again.
But there's nothing Max and Duncan can do till morning.
Back at base camp, it's time to take stock
of what we've discovered so far.
As of today, here's what we know about our collared zebra.
The majority of them are back in the floodplain.
They've been moving between the burnt area and the floodplain.
We've had a few showers,
but it indicates that it's not quite the trigger,
the environmental cue,
that these zebras need to actually embark on the migration.
So why has Socks dashed towards Nxai Pan?
Is it that she simply misread the cues?
It's becoming clear that their decision-making process
is much more complex than we first thought.
The following morning, Max might finally be in for a lucky break.
Firebreaks are swathes cut in the forest to stop fires spreading.
It looks like Socks' path
might take her directly across one.
Our best chance of catching her in the open
and seeing what condition she's in
is to try and intercept her as she crosses.
With the data coming in every hour,
they need to get into position before she arrives.
We don't know what kind of state she's in
or even if she's had her foal.
-This is five minutes old.
You know, it's vital that we actually set eyes on her,
because we're starting to really worry.
She's crossing. It's her, it's her.
There's only three of them, which is strange.
I didn't see Wishbone, the stallion.
It's only the briefest of glimpses, and of only three of them,
but 90km from her destination, Socks is alive and well.
We'll have to look at this footage again.
The footage suggests that she hasn't had her foal yet,
which is good news, and information we'd never have gleaned
from the satellite data alone.
But the absence of Wishbone, the stallion, is a real concern.
He should be protecting the herd from predators
during this last push to Nxai Pan.
Then, out of the blue, Socks' satellite collar
stops sending location updates.
Without this essential data, we have no way of finding Socks
in this vast wilderness.
Her last known position is 40km from Nxai Pan.
Max's only option now is to continue south
and hope that he can spot her emerging onto the open pan.
Back in Chobe, Winnie, Janet, Spirit and Jewel
have at last started to move south.
This time, they don't stop at the burnt area,
they keep going, and now they have 180km to go.
At last, the main migration has started in earnest.
It's time for the rest of the team to break camp
and head south to Nxai Pan.
Around 10,000 years ago, Nxai Pan was an enormous lake.
Now dried up, its soil is packed
with potassium, calcium and magnesium.
During the rainy season,
these minerals produce lush and highly nutritious grass.
But when Max arrives, things are not as he'd hoped.
We've arrived expecting to see a flush of green grass,
which is why the zebra come this way,
but the rains have not hit here yet.
Even if the zebra make it through the forest,
there'll be nothing for them to eat at the end of it.
And that's not their only threat.
A pride of 14 hungry lions are lying in wait
for the exhausted zebra as they arrive.
Lions are the largest predators in Africa.
They have explosive speed and power.
Unlike African wild dogs,
a single lion can take down a fully grown zebra.
When there are lots of zebra around, the lions will kill frequently,
feeding on the most nutritious parts
and leaving the leftovers for scavengers.
But the harsh dry season has taken its toll on the Nxai Pan lions.
These lions will have had a tough time.
You can see they're quite skinny.
But they've got through the dry season
and they know that all the grazing animals are coming,
and their number one food choice will be zebra,
and all of our collared animals in a week or so are going to be here.
Not only will the zebra find hungry lions waiting for them,
they may also find themselves facing a complete lack of food
if they arrive here before the rains.
The changing of the seasons in Botswana could not be more dramatic.
At the end of the dry season,
temperatures soar as high as an unbearable 45 degrees C.
The land is scorched and cracked until, on the horizon,
a lightning bolt announces the beginning of the rains,
and everything changes.
As the heat soars, moisture builds in the atmosphere
and enormous clouds appear, looming across the skies.
For a while, the showers are localised,
but then the heavens open.
Here, as much as 12cm of rain can fall in a single downpour.
This is what the zebra have been waiting for.
Several weeks late but, finally, the rains have come,
and soon, this dry, parched saltpan
is going to transform into a lush, green field,
full of protein and mineral-rich grass that the zebra rely on,
especially now that they're foaling.
The satellite data shows
that all our collared zebra are now just north of Nxai Pan,
having averaged 30km a day for over a week.
Somehow, they knew that all of this was about to happen.
They have timed this to perfection.
Now the rains have truly arrived,
the nutritious grasses of Nxai Pan will start growing.
But the lions will be waiting.
We've established our new base camp at the northern end of Nxai Pan,
to catch the zebra as they come out of the forests and onto the plains.
The morning after the rains,
the satellite data reveals some great news.
-In the open.
She's been giving us the run-around,
but now we're going to finally clock eyes on her,
see what condition she's in.
-She can't be very far.
-It's just about 3k from camp.
We know she's here, but the data point is now an hour old.
In this flat and open pan, radio telemetry should work well.
-Strongest signal's from this...
-This group here.
-Have a look. See, I think the second one's got a collar.
Look, she's coming right through the middle of these springbok.
And this zebra, she was the first one documented
making this huge migration down here,
and we're meeting up with her again, she's done it again.
In Chobe, Janet was part of a family of 15.
But now there are only five of them.
Hopefully, the rest of her herd are also here somewhere
and haven't succumbed to exhaustion or predation.
Thankfully, the data shows
that all the other families are also pouring into the park.
Max, Max, it's Liz. Do you copy?
'Hey, Liz, how are you doing?'
'Well, 14km away from camp
But when Max catches up with Spirit, he finds that all is not well.
Spirit was pregnant.
We can't be sure what happened to her foal,
but it looks like her family have had a recent run-in with the lions.
Fresh wounds on three of the zebra in this group.
I mean, it's the unmistakable marks left by a lion.
There's a small foal,
and you can see his whole hind has been ripped open.
That must have happened last night.
The lions were around, we heard them roaring.
It's bumper season for them now that the zebra are here.
We need to find out if Socks is still alive.
Even though her collar's GPS has failed,
it may still have a VHF signal.
On the ground, the range is just a few kilometres,
but from the air, it's closer to 40.
It's only when you get up here
that you really realise the vast expanse of this place.
I mean, where could she be
and how far do we have to look in every direction?
She could be anywhere in an area up to 15,000 square kilometres.
That is absolutely huge, so it's needle in a haystack stuff.
We absolutely had no hope on the ground. What are our chances?
If the telemetry transmitter is still working,
we've got a very good chance of finding her.
So, Liz, we've got a little bit of altitude now,
and I'm going to put this receiver on.
You'll hear some static start to come through.
This is set on Socks' frequency.
We'll just listen through a lot of noise initially,
cos all you can hear is static,
and then you're just listening for a tiny, tiny little beep.
Beep. And when we hear that,
we start honing in and trying to zone in on where she is.
-You keep your ears peeled.
-I am going to do my best for you.
But finding a signal in an area this size seems next to impossible,
even from the air.
Max is standing by, ready to go in on the ground,
should we find anything.
You hear that?
There was the faintest, tiniest little beep through this static.
-I'm just hearing the static.
-Yeah, yeah, so listen really...
-Can you hear a beep?
-Yeah, yeah, but it's tiny.
-It really is very subtle.
Oh, my gosh, that's brilliant!
That is definitely the unmistakable beep of a VHF collar.
Socks is here, she's in Nxai Pan.
Now that we've picked up a signal, we have to fly in a search pattern
until we pinpoint its exact location.
-It's her, it's her. It's this group of zebra there. It has to be.
'Max, Max, it's Liz. I've got some fantastic news for you.'
We've just located Socks.
That's amazing news.
She's in a group of ten zebra.
Now, we couldn't get a visual on Socks herself, but...
'If we're to see how Socks and her family are doing,
'Max will have to catch up with them on the ground.'
We'll head that way and let you know how we get on.
Oh, I'm so happy about this. Good luck with it all.
Last time we saw Socks, she was travelling
without the protection of Wishbone, the stallion.
We need to know how she's doing, and if she's had her foal.
We're not far off now.
We're almost parallel with them, so if you start scanning a bit.
It looks like there's some animals just...
Oh, look. Amazing, amazing.
Look. That's Socks.
She's got her unmistakable white socks on.
She's with the stallion.
It looks like they're all there.
Then Max spots something moving in the long grass.
It's her foal.
He's absolutely tiny.
She must have dropped this foal in the last couple of days.
How cool is that?!
When you look at Socks now and see what fantastic condition she's in...
She made this journey really early on,
but that's given her time to recuperate
and now she's given birth in the best possible place.
She's found this little Garden of Eden here
where there's more grass than we've seen anywhere else,
so she's given this little fella the best possible start in life.
The funny thing is, her foal has stripes on its legs.
He's taken after Dad.
As more and more zebra families pour into Nxai Pan
at the end of a gruelling migration, the plains come to life.
The first green shoots are pushing up,
and the time to rest, give birth and feed on the bounty has arrived.
This little foal is only hours old
and it's still so unsure on its feet.
I mean, it is just the most beautiful scene,
and the stallion is just standing by,
being extremely protective of his mare and his new foal.
And we know so little about these interactions,
there's still so much to understand,
but just seeing this scene today
really does paint a wonderful picture.
And as much as I couldn't help but question
why on earth an animal would decide to make
such a ridiculously long and arduous journey...
..watching this now, it all makes sense.
It's worth the journey, it's worth the trial and tribulations,
because as a mother,
you have every instinct telling you, we need to make it down here,
this is going to make our family stronger,
our foals will be stronger.
Ultimately, that's what survival is all about.
During our time in Botswana, we've had a privileged insight
into Africa's longest and most recently discovered land migration.
We've discovered the importance
of each family making the right decision at the right time.
And we've revealed that part of their ability to navigate
is written in their genes.
The discovery of this zebra migration is so important.
It represents what ground-breaking science
can reveal about the natural world
in a way that simply wasn't possible before.
What surprised me the most is just how complex these animals are.
A strong biological instinct, a drive to explore and to navigate,
a constant adjustment to a changing environment.
They're all at play here.
As difficult as this migration is, these zebra achieve it perfectly.
There is still so much to understand,
but ultimately, this research will help scientists
to preserve this precious migratory route,
but it will also provide invaluable insights
that could help to save species and their habitats across the world.