0:00:03 > 0:00:07We're about to follow the world's greatest migrations,
0:00:07 > 0:00:11and reveal their secrets in a way that's never been done before.
0:00:13 > 0:00:17All over the world, animals are on the move...
0:00:17 > 0:00:22embarking on vast journeys that they depend upon for survival -
0:00:22 > 0:00:27to find food, to give birth, or to escape danger.
0:00:29 > 0:00:31Travelling hundreds of miles
0:00:31 > 0:00:34through some of the world's most breathtaking wildernesses...
0:00:36 > 0:00:39..that can turn against them at any moment.
0:00:39 > 0:00:41That rapid's really picking up.
0:00:41 > 0:00:43They're just disappearing under the water.
0:00:43 > 0:00:46Ground-breaking technology allows our team
0:00:46 > 0:00:50to follow these migrations more closely than ever before,
0:00:50 > 0:00:53and understand them in unprecedented detail.
0:00:55 > 0:00:59We can track this ele's movement in real-time.
0:00:59 > 0:01:02Using the latest satellite tracking technology,
0:01:02 > 0:01:05we can monitor individual animals
0:01:05 > 0:01:08and witness first-hand their struggles for survival.
0:01:08 > 0:01:10We've got a drama down here.
0:01:10 > 0:01:14We've got it. We've got the wolf. We've got the wolf.
0:01:14 > 0:01:17This time, we'll follow thousands of zebra
0:01:17 > 0:01:21as they undergo their gruelling annual migration in search of food.
0:01:24 > 0:01:26They must reach their grazing grounds
0:01:26 > 0:01:29just as the rainy season begins.
0:01:29 > 0:01:33Arriving too early or too late could spell disaster.
0:01:35 > 0:01:39For the first time, satellite tracking allows us
0:01:39 > 0:01:43to stay with individual mothers, foals and dominant males
0:01:43 > 0:01:47as they brave drought, hunger and ferocious predators.
0:01:49 > 0:01:52Below me, this wilderness has kept hidden
0:01:52 > 0:01:55a journey that's never been followed before,
0:01:55 > 0:01:58and about which virtually nothing is known.
0:01:58 > 0:02:03It's the longest land migration in all of Africa.
0:02:03 > 0:02:07This is the untold story of the great zebra migration.
0:02:21 > 0:02:23Northern Botswana -
0:02:23 > 0:02:26a vast, parched wilderness
0:02:26 > 0:02:27the size of the United Kingdom.
0:02:29 > 0:02:32At the end of Botswana's brutal dry season,
0:02:32 > 0:02:35thousands of zebra gather on the Chobe floodplain
0:02:35 > 0:02:39as they prepare to travel 250km south
0:02:39 > 0:02:41to Nxai Pan National Park.
0:02:47 > 0:02:51The journey takes them through one of the most punishing landscapes
0:02:51 > 0:02:53in southern Africa.
0:02:55 > 0:02:57Travelling in family groups,
0:02:57 > 0:03:02many of the females are heavily pregnant or supporting young foals.
0:03:03 > 0:03:06Each year, their goal is the same -
0:03:06 > 0:03:08to reach Nxai Pan's fertile plains
0:03:08 > 0:03:13just as the rains produce the first flush of nutrient-rich vegetation.
0:03:13 > 0:03:17The timing of this journey is crucial.
0:03:17 > 0:03:20Leave too early and they risk arriving at Nxai Pan
0:03:20 > 0:03:22before the lush grass appears.
0:03:22 > 0:03:26Leave too late and they'll miss out on the best food on arrival.
0:03:32 > 0:03:35Our first camp is on the edge of the Chobe River,
0:03:35 > 0:03:37the starting line for the migration.
0:03:37 > 0:03:41Yeah, I've been looking at her data over the last...
0:03:41 > 0:03:44'I've joined a team of specialist biologists and cameramen'
0:03:44 > 0:03:47to attempt something that's never been done before.
0:03:50 > 0:03:53We plan to travel with the zebra on the ground,
0:03:53 > 0:03:55following their every move.
0:04:05 > 0:04:08Around 2,000 zebra are gathering
0:04:08 > 0:04:10across the vast Chobe River floodplain,
0:04:10 > 0:04:15dotted across the landscape in family groups of up to 20 animals.
0:04:15 > 0:04:18They won't be travelling en masse.
0:04:18 > 0:04:21Instead, each individual family will make its own decisions
0:04:21 > 0:04:23during the migration.
0:04:25 > 0:04:28'I'm joining the scientists who are collaring the zebra,
0:04:28 > 0:04:30'so that the team can track them.'
0:04:40 > 0:04:42OK, Mike, Larry's getting ready to dart.
0:04:44 > 0:04:45Great shot.
0:04:45 > 0:04:48I wouldn't even recognise which one he was focusing on.
0:04:48 > 0:04:50Next minute - boof, done.
0:04:50 > 0:04:51The dart contains a sedative
0:04:51 > 0:04:55that immobilises the zebra within five to ten minutes.
0:05:03 > 0:05:05Once the zebra goes down,
0:05:05 > 0:05:08the team have to act as quickly as possible.
0:05:08 > 0:05:09You tell me when it's OK to get out.
0:05:09 > 0:05:11- You can get out.- Yeah?
0:05:16 > 0:05:20'A towel is put over the animals eyes to help keep it calm.'
0:05:21 > 0:05:22Well done.
0:05:25 > 0:05:27Just check it. Is that all right?
0:05:27 > 0:05:30It's really thanks to this technology
0:05:30 > 0:05:34that we'll be able to stick with these zebra,
0:05:34 > 0:05:36getting readings every hour.
0:05:36 > 0:05:40And that means, for the first time, we'll be able to follow them.
0:05:40 > 0:05:43That's not only going to give us insights into where they go when,
0:05:43 > 0:05:47but also into their behaviour, their decision-making process.
0:05:47 > 0:05:53That's bound to reveal some unknowns into the lives of these zebra.
0:05:53 > 0:05:57'The collaring data will not only help us to keep up with them,
0:05:57 > 0:05:59'but we'll see for ourselves just how tough they need to be
0:05:59 > 0:06:02'to take on this migration.'
0:06:02 > 0:06:04It's only when you get really close to these animals
0:06:04 > 0:06:07that you realise just how sturdy they are, how hardy.
0:06:09 > 0:06:11You know, they need to be -
0:06:11 > 0:06:12they're about to embark on what is
0:06:12 > 0:06:16the longest land migration in Africa.
0:06:16 > 0:06:18'The hourly updates from the satellite collars
0:06:18 > 0:06:21'will allow us to follow a number of different families,
0:06:21 > 0:06:24'each with a collared animal in it.'
0:06:25 > 0:06:27Awesome. That was hugely satisfying.
0:06:31 > 0:06:32One of the zebra collared
0:06:32 > 0:06:37is a very special nine-year-old female called Janet.
0:06:37 > 0:06:41She was the first zebra in this population to be collared,
0:06:41 > 0:06:43way back in 2012.
0:06:45 > 0:06:49We first discovered this migration in 2012.
0:06:49 > 0:06:52Up until that point, people didn't know where the zebra move.
0:06:52 > 0:06:55So, in the dry season, you had zebra up here,
0:06:55 > 0:06:58and then, in the rainy season, they disappeared...
0:06:58 > 0:07:00Exactly. So, 2012 the first collars went up.
0:07:00 > 0:07:04- OK.- And, Janet, she was collared just up here on the floodplains.
0:07:04 > 0:07:05It was very exciting -
0:07:05 > 0:07:08we didn't know where she was going to go, or what she was going to do.
0:07:08 > 0:07:13She moved 250km all the way down to Nxai Pan,
0:07:13 > 0:07:14down here, in the south.
0:07:14 > 0:07:18This is the longest mammal migration in the whole of Africa,
0:07:18 > 0:07:19which is amazing.
0:07:19 > 0:07:23The average round trip distance is about 955km,
0:07:23 > 0:07:26which beats the wildebeest migration in East Africa.
0:07:27 > 0:07:29The first year she was collared,
0:07:29 > 0:07:35Janet's data completely changed our understanding of zebra migrations.
0:07:35 > 0:07:39It was assumed that the zebra travelled just 60km or so
0:07:39 > 0:07:43to the grassy plains of Saruti Marsh or Seloko.
0:07:43 > 0:07:44But Janet's collar revealed
0:07:44 > 0:07:46fascinating new information to scientists.
0:07:48 > 0:07:50She was travelling much further,
0:07:50 > 0:07:54all the way to Nxai Pan.
0:07:54 > 0:07:57That year, Janet became the official record holder
0:07:57 > 0:08:00for the longest land migration in Africa.
0:08:01 > 0:08:04But this huge journey takes the zebra
0:08:04 > 0:08:07through an area with virtually no food or water,
0:08:07 > 0:08:09and plenty of cover for predators.
0:08:13 > 0:08:15'So why do they leave Chobe at all?'
0:08:16 > 0:08:20Chobe can sustain wildlife all year round.
0:08:20 > 0:08:23The rains obviously hit Chobe as well, the grasses get better.
0:08:23 > 0:08:26Why would zebra leave Chobe in the first place?
0:08:26 > 0:08:29The zebra there have competition with other animals,
0:08:29 > 0:08:31so they need a new resource,
0:08:31 > 0:08:35and the vegetation that comes up in Nxai Pan is very nutritious,
0:08:35 > 0:08:39the soils are very fertile, and so the grasses are so much better.
0:08:39 > 0:08:44For the zebra, the potential rewards seem to outweigh the risks.
0:08:44 > 0:08:47But how exactly do they survive this immense journey?
0:08:48 > 0:08:52How do they navigate through a featureless landscape?
0:08:52 > 0:08:54How does it all even begin?
0:08:55 > 0:08:57We're down on the floodplains.
0:08:57 > 0:08:58We've been looking for Janet this morning.
0:08:58 > 0:09:00Cameraman Max Hug Williams' mission
0:09:00 > 0:09:04will be to follow the frontrunners all the way to Nxai Pan,
0:09:04 > 0:09:06250km to the south.
0:09:08 > 0:09:10Our other cameraman, Bob Poole,
0:09:10 > 0:09:14will hang back following the families that are last to leave.
0:09:24 > 0:09:28Making the journey are heavily pregnant females...
0:09:29 > 0:09:32..as well as mothers with young foals.
0:09:36 > 0:09:38For them, the 250km migration
0:09:38 > 0:09:41will be particularly dangerous.
0:09:45 > 0:09:48Filming the zebra as they gather on the plain
0:09:48 > 0:09:50gives Bob the chance to familiarise himself
0:09:50 > 0:09:53with the collared individuals.
0:09:53 > 0:09:55If you look at these zebra,
0:09:55 > 0:09:59each one of them has totally different patterns in their stripes.
0:09:59 > 0:10:03And she has got some pretty distinguishing markings on her.
0:10:03 > 0:10:08She's got a beautiful sort of W on her left shoulder,
0:10:08 > 0:10:10and so we've called her Winnie.
0:10:10 > 0:10:12She's got a foal -
0:10:12 > 0:10:15it hangs right next to its mother almost all the time,
0:10:15 > 0:10:17and they seem quite affectionate together.
0:10:24 > 0:10:28At six years old, Winnie may have already had three other foals
0:10:28 > 0:10:30and carried out six migrations.
0:10:32 > 0:10:36Although zebra foals can stand at less than an hour old,
0:10:36 > 0:10:41these babies won't have walked more than a few kilometres a day.
0:10:41 > 0:10:45You can see these little things can run.
0:10:45 > 0:10:47And I suppose all this behaviour is really important,
0:10:47 > 0:10:51because they're going to have to move all the way south.
0:10:56 > 0:11:00These zebra are about to move in a mass exodus
0:11:00 > 0:11:03towards the south of Botswana,
0:11:03 > 0:11:06and one of the biggest mysteries is just what triggers this.
0:11:06 > 0:11:10One theory is that the start of the rainy season
0:11:10 > 0:11:13sets off an irresistible urge to migrate.
0:11:14 > 0:11:18Luckily, the team don't have to wait long before the first downpour.
0:11:19 > 0:11:21THUNDER RUMBLES
0:11:40 > 0:11:43With the rains, everything changes.
0:11:47 > 0:11:50Very excited right now.
0:11:50 > 0:11:53I mean, we've been waiting for the rains, and here they are.
0:11:53 > 0:11:55Poola.
0:11:55 > 0:11:57"Poola" they call it here in Botswana.
0:11:57 > 0:12:00And that's the same word they use for money.
0:12:00 > 0:12:01In Africa, just add water,
0:12:01 > 0:12:03and everything works.
0:12:05 > 0:12:09And it's not just Bob who's reacting to the change in the weather.
0:12:12 > 0:12:16Our satellite data shows that in the last few hours,
0:12:16 > 0:12:18all the zebra have crossed the Chobe River
0:12:18 > 0:12:21and have started to move south.
0:12:25 > 0:12:27The migration has started.
0:12:30 > 0:12:33250km to go.
0:12:36 > 0:12:40There's absolutely nothing on these plains any more.
0:12:40 > 0:12:44There's just the last pocket of five or six,
0:12:44 > 0:12:47but, otherwise, this plain is absolutely empty.
0:12:47 > 0:12:49Now the migration is under way,
0:12:49 > 0:12:53we'll have to keep up with them every step of this journey.
0:12:55 > 0:12:59The open floodplain offered some safety from predators,
0:12:59 > 0:13:01but now they face thick forest...
0:13:03 > 0:13:07..and their first big challenge -
0:13:07 > 0:13:09a pack of African wild dogs,
0:13:09 > 0:13:12the continent's most relentless predators.
0:13:15 > 0:13:19Surrounded by trees, the zebra won't see them coming.
0:13:23 > 0:13:27Even without cover, wild dogs are a real threat.
0:13:27 > 0:13:30They may not be the biggest of Africa's predators,
0:13:30 > 0:13:33but their highly efficient method of hunting as a pack
0:13:33 > 0:13:36certainly makes them one of the most effective.
0:13:38 > 0:13:41During a hunt, each dog has a role.
0:13:45 > 0:13:47A leader drives the prey forward...
0:13:49 > 0:13:52..while others act as flankers,
0:13:52 > 0:13:55corralling the prey towards the rest of the pack.
0:13:56 > 0:14:00The ultimate endurance hunters,
0:14:00 > 0:14:05their ability to run up to 70kph and use sophisticated teamwork
0:14:05 > 0:14:09allows them to take down animals far larger than themselves.
0:14:12 > 0:14:14Meticulous coordination results in a kill
0:14:14 > 0:14:17more often than any other predator.
0:14:19 > 0:14:24In the forest, the wild dogs have already left Max far behind.
0:14:27 > 0:14:30You can see, actually, there's dog tracks everywhere.
0:14:30 > 0:14:33They split out. There's one here...
0:14:36 > 0:14:38Look at that. That's a leopard track.
0:14:38 > 0:14:41I mean, on the plains they can see what's around,
0:14:41 > 0:14:44and when one gets a sense of some danger, they all bolt.
0:14:44 > 0:14:48But in here, this is where leopards, wild dogs,
0:14:48 > 0:14:51have a chance of actually taking... Especially the foals.
0:14:51 > 0:14:53I mean, some of them were even struggling
0:14:53 > 0:14:54to cross the river this morning,
0:14:54 > 0:14:58and you think, "How are they going to make this epic journey of 250km?"
0:14:58 > 0:15:00I have absolutely no idea.
0:15:00 > 0:15:02With so many predators about,
0:15:02 > 0:15:04Max needs to catch up with the zebra
0:15:04 > 0:15:07to see if they've managed to stay safe.
0:15:07 > 0:15:10'Max, Max, Max. This is Rob, at base camp.'
0:15:10 > 0:15:12Just got some updated coordinates for you.
0:15:12 > 0:15:16So, 1791 has moved south...
0:15:16 > 0:15:20In the forest just south of the wild dog tracks,
0:15:20 > 0:15:23the satellite data leads Max to his first collared zebra,
0:15:23 > 0:15:27who still has 230km to go.
0:15:27 > 0:15:29She looks heavily pregnant.
0:15:29 > 0:15:30You can see.
0:15:33 > 0:15:36A zebra with so few stripes on her front legs...
0:15:36 > 0:15:39I mean, it looks like someone's got an eraser and rubbed them out.
0:15:39 > 0:15:42It's like she's got a pair of tights on or something.
0:15:42 > 0:15:45She's very relaxed, though. That's great.
0:15:45 > 0:15:46What are we going to call her, then?
0:15:46 > 0:15:48Because we've got Winnie -
0:15:48 > 0:15:51she's really easy to identify with the W.
0:15:51 > 0:15:54And we've got to come up with something with...
0:15:54 > 0:15:56She's definitely got a pair of socks on or something.
0:15:56 > 0:15:58- Socks.- Socks, OK.
0:15:58 > 0:16:00Socks it is.
0:16:02 > 0:16:04At only four years old,
0:16:04 > 0:16:07Socks is a young and inexperienced mother.
0:16:07 > 0:16:10This may even be her first pregnancy.
0:16:12 > 0:16:15She's in a small family of just seven animals.
0:16:15 > 0:16:20But these families, or harems, can be up to 20 animals strong,
0:16:20 > 0:16:23and are usually made up of unrelated females and their young,
0:16:23 > 0:16:26led by a single dominant male.
0:16:26 > 0:16:31The more experienced and powerful the stallion, the bigger the harem.
0:16:31 > 0:16:33Look at this male.
0:16:33 > 0:16:35He's got really obvious thick, black bands on his neck,
0:16:35 > 0:16:38and also on his right flank there's a marking
0:16:38 > 0:16:40which almost looks like a wishbone.
0:16:42 > 0:16:44We'll have to call him Wishbone.
0:16:46 > 0:16:48Wishbone's job is crucial.
0:16:48 > 0:16:51He must protect Socks and the others from predators,
0:16:51 > 0:16:55particularly now as they travel through this dense forest.
0:17:02 > 0:17:05Wishbone, Socks and the rest of the family
0:17:05 > 0:17:06are ahead of the other zebra...
0:17:08 > 0:17:10..closely followed by Max.
0:17:11 > 0:17:14Bringing up the rear is Bob.
0:17:14 > 0:17:16He now has the chance to see how Winnie
0:17:16 > 0:17:20and the other herds at the back deal with the dangers of the forest.
0:17:20 > 0:17:22This is pretty exciting.
0:17:22 > 0:17:24There's a lot of zebra now, packed together,
0:17:24 > 0:17:26and they all seem to be on the move south.
0:17:28 > 0:17:29Winnie's in the middle, there,
0:17:29 > 0:17:33and she's travelling along with her foal and the rest of her family.
0:17:33 > 0:17:36But, you know, for the first time, there's so many zebra.
0:17:42 > 0:17:47Amongst the large group at the rear are two other collared females -
0:17:47 > 0:17:50a pregnant mare called Spirit
0:17:50 > 0:17:52and a ten-year-old called Jewel.
0:17:57 > 0:18:01Travelling together for safety is a good idea.
0:18:02 > 0:18:04Just a few kilometres to the west,
0:18:04 > 0:18:08Max has found a young family who haven't been so wise...
0:18:11 > 0:18:14..as the wild dogs are well aware.
0:18:26 > 0:18:28Believe you me, when they get going,
0:18:28 > 0:18:29if they want to run something down,
0:18:29 > 0:18:32there's pretty much nothing that they can't take.
0:18:32 > 0:18:35But, luckily for the zebra, it looks like these guys have fed
0:18:35 > 0:18:38and they're just relaxing in the shade.
0:18:48 > 0:18:50When the dogs' hunger returns,
0:18:50 > 0:18:52the pregnant females or those with foals
0:18:52 > 0:18:55will be particularly vulnerable to attack.
0:18:57 > 0:19:00If Socks gave birth,
0:19:00 > 0:19:02she's not a million miles away from here.
0:19:02 > 0:19:05I mean, that would be an easy prey for them.
0:19:11 > 0:19:14Meanwhile, there's been some worrying news
0:19:14 > 0:19:16about another collared animal.
0:19:18 > 0:19:21The satellite data shows that one zebra
0:19:21 > 0:19:24didn't travel far from the Chobe floodplain,
0:19:24 > 0:19:27and it hasn't moved for the last two days.
0:19:31 > 0:19:32We've got a signal, Max.
0:19:32 > 0:19:34Is it strong? Are you getting something close by?
0:19:34 > 0:19:36Yeah, it's a strong signal.
0:19:36 > 0:19:37It's certainly around here somewhere.
0:19:37 > 0:19:39The team will have to home in
0:19:39 > 0:19:43using the VHF radio signal emitted by the collar.
0:19:43 > 0:19:46Numan Chuma, tracker and wildlife guide, leads us in.
0:19:49 > 0:19:50But if the zebra is dead,
0:19:50 > 0:19:53there may still be predators feeding on the carcass.
0:19:53 > 0:19:55If it is a lion on a kill,
0:19:55 > 0:19:58- I mean, we've got to be pretty careful here, haven't we?- Yeah.
0:19:58 > 0:20:01- You need to spot the animal before the animal sees you.- Sees you.
0:20:01 > 0:20:05As they get closer, clues emerge as to what might have happened.
0:20:05 > 0:20:08You know, I can see quite a few tracks - a hyena...
0:20:08 > 0:20:10Something dragging it this way.
0:20:10 > 0:20:11That way.
0:20:11 > 0:20:13- Oh.- I can see something.
0:20:13 > 0:20:14Here's the carcass, so...
0:20:16 > 0:20:18It looks like this zebra may have fallen prey
0:20:18 > 0:20:21to one of the forest's many predators.
0:20:21 > 0:20:22- Collar there.- Uh-huh.
0:20:26 > 0:20:28Look how many maggots there are already. It's only...
0:20:28 > 0:20:29- Yeah.- ..two days old.
0:20:29 > 0:20:32- Nothing lasts very long out here. - Mm-mmm.- So you can see this...
0:20:32 > 0:20:35- It looks like a puncture wound. - They're claw marks...
0:20:35 > 0:20:38It's difficult to know exactly how it died,
0:20:38 > 0:20:41but this zebra's collar is fitted with a camera.
0:20:41 > 0:20:43It still looks intact, doesn't it?
0:20:43 > 0:20:44It does, yeah.
0:20:44 > 0:20:46OK, let's take this off.
0:20:46 > 0:20:51Once the footage is downloaded, it may reveal exactly what happened.
0:20:51 > 0:20:54So, that's the last shot from the morning...
0:20:54 > 0:20:56So...
0:20:56 > 0:20:57- Oh, look.- Is that you?
0:20:57 > 0:20:58That's me, yeah.
0:20:58 > 0:21:02This is when the animal was collared, on 20th November.
0:21:02 > 0:21:05'The camera recorded in short bursts to extend its battery life.
0:21:10 > 0:21:13'For the first few days, the zebra behaved normally,
0:21:13 > 0:21:15'grazing and moving around the floodplain like Socks,
0:21:15 > 0:21:17'Janet and the others.
0:21:17 > 0:21:21'Then, four days later, it crossed the Chobe River again.'
0:21:21 > 0:21:24All right, so it's back on the Botswanan side.
0:21:24 > 0:21:27Looks like it's moving a bit faster there.
0:21:27 > 0:21:30Haven't seen many zebra around him, do you?
0:21:30 > 0:21:31Oh, you can see his shadow.
0:21:31 > 0:21:34- Yeah.- So he's swinging his tail...
0:21:34 > 0:21:36- And now...- Now he's lying down.
0:21:36 > 0:21:38Looks like he's on the ground.
0:21:38 > 0:21:39Zebra tend not to lie down,
0:21:39 > 0:21:42especially when they're by themselves.
0:21:42 > 0:21:43Yeah. That makes sense.
0:21:43 > 0:21:46- It's not particularly safe to lie down like that.- Well, yeah.
0:21:50 > 0:21:54The zebra stayed here for around 36 hours,
0:21:54 > 0:21:58moving about a little, but never leaving this location.
0:21:58 > 0:22:00Something was clearly wrong.
0:22:04 > 0:22:07BUZZING
0:22:07 > 0:22:08Yeah, lots of flies.
0:22:08 > 0:22:12- Yeah.- And he's doing something with his mouth, but he's not grazing.
0:22:12 > 0:22:15We can't see if there's any blood or any sort of...
0:22:15 > 0:22:16foam coming from the mouth,
0:22:16 > 0:22:19so we're not sure what's happening there.
0:22:20 > 0:22:23With no clear evidence of predation,
0:22:23 > 0:22:25our team thinks he may have been bitten
0:22:25 > 0:22:28by one of Botswana's poisonous snakes.
0:22:33 > 0:22:34He's down again, look.
0:22:34 > 0:22:36We don't know how long he stayed down for.
0:22:36 > 0:22:38Between the... Yeah. How long, during the day...
0:22:38 > 0:22:41'Before long, vultures begin to gather.'
0:22:43 > 0:22:46And just a few hours later, the zebra is dead.
0:22:48 > 0:22:49Oh...
0:22:50 > 0:22:52- That's it.- That's it. Game over.
0:22:56 > 0:23:00Despite not being able to determine the exact cause of death,
0:23:00 > 0:23:03the collar data shows just how dangerous it can be out here.
0:23:11 > 0:23:13Our latest satellite data shows
0:23:13 > 0:23:17that many of the zebra are making steady progress south.
0:23:18 > 0:23:22But Socks, the four-year-old female that Max spotted in the forest,
0:23:22 > 0:23:25is pushing ahead of Winnie, Janet and the others,
0:23:25 > 0:23:27with her family in tow.
0:23:27 > 0:23:29I guess she's just a lot slinkier than we are.
0:23:29 > 0:23:33Helping Max get as close to them as possible is Duncan Rowles,
0:23:33 > 0:23:36an experienced tracker and safari guide.
0:23:37 > 0:23:40Max, Max, Max. This is Rob, at base camp.
0:23:40 > 0:23:43Max has Socks' latest satellite position
0:23:43 > 0:23:47and is trying desperately to catch up with her and her family.
0:23:49 > 0:23:52And you can just see how far Socks has come.
0:23:52 > 0:23:5430km just yesterday.
0:23:54 > 0:23:58Now she's still in this really thick bush here.
0:23:58 > 0:24:02The only way for us to have a chance of even getting a glimpse of her
0:24:02 > 0:24:08is carry on...on this, which is as good as a road as you'll ever get,
0:24:08 > 0:24:10travel all the way round,
0:24:10 > 0:24:14and then hope that she pops out somewhere near here.
0:24:17 > 0:24:21It's not clear why Socks' family has broken away from the others,
0:24:21 > 0:24:23but since she's heavily pregnant,
0:24:23 > 0:24:26she might be trying to reach Nxai Pan before giving birth.
0:24:29 > 0:24:33Her incredible pace means that the hourly satellite data
0:24:33 > 0:24:36is not accurate enough to locate her precisely.
0:24:40 > 0:24:43So the team have to resort to another system.
0:24:45 > 0:24:48These collars allow scientists to track animal movements
0:24:48 > 0:24:49in two different ways.
0:24:49 > 0:24:52The first part uses a network of satellites
0:24:52 > 0:24:53to calculate its location,
0:24:53 > 0:24:56in the same way as your phones and your cars
0:24:56 > 0:24:57use their navigation systems.
0:24:57 > 0:25:00But for real-time, on-the-ground tracking,
0:25:00 > 0:25:03the collar also emits a VHF signal
0:25:03 > 0:25:06that can be picked up with radio telemetry equipment,
0:25:06 > 0:25:09and every single animal will have its own unique frequency.
0:25:13 > 0:25:17With Socks fast disappearing into this vast landscape,
0:25:17 > 0:25:21it's the VHF radio signal that will give Max his best chance
0:25:21 > 0:25:24of catching up with her to see if she's OK.
0:25:29 > 0:25:34But in forest this thick, he might get close and still not see her.
0:25:34 > 0:25:36She's very close.
0:25:36 > 0:25:37We know that.
0:25:37 > 0:25:39The best chance is to just get the telemetry up
0:25:39 > 0:25:41and just see where that ping's coming from.
0:25:44 > 0:25:45She's super close now.
0:25:45 > 0:25:47She's... She's just in these bushes.
0:25:47 > 0:25:49A really strong signal from here.
0:25:52 > 0:25:56- That is zebra tracks.- Oh, man...
0:25:56 > 0:25:59And that's completely fresh. That's a split second.
0:25:59 > 0:26:03She must have just crossed before we came round that corner.
0:26:03 > 0:26:06Having so narrowly missed Socks and her family,
0:26:06 > 0:26:09Max now has very little chance of spotting them
0:26:09 > 0:26:12as they head into the ever-thickening forest.
0:26:12 > 0:26:14And how are we supposed to follow that?
0:26:14 > 0:26:16I can't even see you from here.
0:26:17 > 0:26:22Socks has covered an amazing 50km in the last day and a half,
0:26:22 > 0:26:25but still has 200km to go.
0:26:28 > 0:26:30'This migration is so new to science
0:26:30 > 0:26:34'that every bit of data we gather helps scientists to understand
0:26:34 > 0:26:37'the nature of this extraordinary journey.'
0:26:37 > 0:26:39We need more data to really build up that picture.
0:26:41 > 0:26:43Then the satellite data shows something
0:26:43 > 0:26:45that stops us in our tracks.
0:26:45 > 0:26:47Within hours of each other,
0:26:47 > 0:26:50almost all the other zebra have made a U-turn
0:26:50 > 0:26:53and are heading right back to their starting point
0:26:53 > 0:26:55on the Chobe floodplain.
0:27:01 > 0:27:03- Do you have a signal? - Yes, I've got a signal.
0:27:03 > 0:27:05Let me just turn it up for you.
0:27:05 > 0:27:08Bob tries to intercept the zebra families as they return north,
0:27:08 > 0:27:12hoping to see them cross the only tarmac road in Chobe.
0:27:12 > 0:27:15The radio telemetry shows that Winnie's family
0:27:15 > 0:27:17are just about to cross.
0:27:19 > 0:27:22Where's Winnie? Where's Winnie? Where's Winnie?
0:27:22 > 0:27:25Shoot. There she is.
0:27:25 > 0:27:28Winnie and her herd are an experienced family,
0:27:28 > 0:27:32so what could possibly have made them turn back?
0:27:32 > 0:27:34Has some other cue in the environment
0:27:34 > 0:27:36told them they've left too soon?
0:27:36 > 0:27:40Or could the number of predators in the forest have driven them back?
0:27:42 > 0:27:46It seems like confusing times for these zebra.
0:27:46 > 0:27:49It's almost like they can't make up their mind.
0:27:49 > 0:27:51Are they going to go on this migration or not?
0:27:53 > 0:27:55They might not be comfortable yet
0:27:55 > 0:27:59with the amount of rain that's fallen to make the commitment.
0:27:59 > 0:28:01So they have to be very confident
0:28:01 > 0:28:03that there's enough water down there.
0:28:05 > 0:28:07Zebra need to drink pretty much every day,
0:28:07 > 0:28:11and normally stay within 10 to 15km of water.
0:28:11 > 0:28:15Perhaps a lack of water further south has influenced their return.
0:28:15 > 0:28:19So there's a lot of fascinating behaviour going on. Not only...
0:28:19 > 0:28:20'Revealing as it is,
0:28:20 > 0:28:23'the satellite data can only tell us so much.'
0:28:23 > 0:28:25These are complex animals, aren't they?
0:28:25 > 0:28:28They certainly are, and it's not a straightforward migration.
0:28:28 > 0:28:30No. It's not. It's not like wildebeest just,
0:28:30 > 0:28:31"Right, go, all together!"
0:28:31 > 0:28:34- Exactly.- They make very different decisions.
0:28:34 > 0:28:36Exactly. Now, that's what we've observed so far -
0:28:36 > 0:28:39different family groups will make different decisions
0:28:39 > 0:28:40and some groups will leave earlier,
0:28:40 > 0:28:43some groups will hang back and then move later.
0:28:43 > 0:28:45Combining the satellite data that's coming in
0:28:45 > 0:28:47with the information we're getting from the teams on the ground,
0:28:47 > 0:28:50that's going to build a much, much bigger and better picture.
0:28:53 > 0:28:55Whatever the reason,
0:28:55 > 0:28:57the majority of families have decided to head back
0:28:57 > 0:29:01to the food and water of the Chobe floodplain.
0:29:12 > 0:29:17With an entire 250km still to go,
0:29:17 > 0:29:20Bob finds that Janet, Winnie, Spirit and Jewel
0:29:20 > 0:29:24are showing no signs of restarting any time soon.
0:29:26 > 0:29:28So Bob will wait with them until they're ready
0:29:28 > 0:29:30to start the journey again.
0:29:32 > 0:29:35So there's Winnie, coming down.
0:29:35 > 0:29:37God... That is great.
0:29:39 > 0:29:41Getting a nice drink.
0:29:42 > 0:29:47It must be hard for them to make the decision to move south,
0:29:47 > 0:29:48like Socks has now.
0:29:48 > 0:29:52Why in the world would you want to leave this amazing paradise?
0:29:52 > 0:29:56But this paradise won't last forever.
0:29:56 > 0:30:00If too many zebra stay here, the food will run out.
0:30:01 > 0:30:05And they'll miss out on the more nutritious vegetation at Nxai Pan.
0:30:10 > 0:30:12If our female zebra want to give their foals
0:30:12 > 0:30:14the best possible start in life,
0:30:14 > 0:30:17they'll have to leave here very soon.
0:30:19 > 0:30:21Socks and her family, however,
0:30:21 > 0:30:25are well on their way to having Nxai Pan all to themselves.
0:30:25 > 0:30:28She's actually moved quite far south now.
0:30:28 > 0:30:31'24.9818.'
0:30:31 > 0:30:34Socks is motoring 8k an hour.
0:30:34 > 0:30:37That's unbelievable. There's no way we can keep up with that.
0:30:37 > 0:30:41It's taken us an hour to do 1.5km!
0:30:48 > 0:30:51Not only is Socks' family now well ahead of the others,
0:30:51 > 0:30:55they travel in a direct line to Nxai Pan.
0:31:03 > 0:31:05In the flat wilderness of Botswana,
0:31:05 > 0:31:08the zebra somehow navigate perfectly,
0:31:08 > 0:31:10with no hills or landmarks for reference.
0:31:11 > 0:31:16Scientists still don't fully understand exactly how they do this.
0:31:17 > 0:31:20Until very recently, it was assumed these routes were learned
0:31:20 > 0:31:24and then passed down from generation to generation.
0:31:26 > 0:31:28But I'm travelling to meet a scientist
0:31:28 > 0:31:32who made a ground-breaking discovery that turned this theory on its head.
0:31:33 > 0:31:38In the 1950s and '60s, thousands of miles of fences were erected
0:31:38 > 0:31:41in an attempt to stop diseases being transmitted
0:31:41 > 0:31:43from wildlife to domestic livestock.
0:31:43 > 0:31:45But these fences stopped many animals
0:31:45 > 0:31:49from carrying out their annual movements.
0:31:49 > 0:31:52A few years ago, when some of these fences were removed,
0:31:52 > 0:31:56an ancient migration was seen to start up once more,
0:31:56 > 0:31:58following its exact same route.
0:32:01 > 0:32:04Dr Hattie Bartlam-Brooks of the Royal Veterinary College
0:32:04 > 0:32:06made this discovery.
0:32:06 > 0:32:08So if the fence was up for 36 years
0:32:08 > 0:32:11and zebra live to about 15 years in the wild,
0:32:11 > 0:32:14so there was no zebra that knew about this route
0:32:14 > 0:32:16that was alive when this fence went down.
0:32:16 > 0:32:18I think that's the most exciting part about the story.
0:32:18 > 0:32:21Everyone presumes that terrestrial migrations are taught.
0:32:21 > 0:32:22But in this case, it can't.
0:32:22 > 0:32:25The mothers couldn't have taught the foals.
0:32:25 > 0:32:28So I think there's a genetic urge to make the move.
0:32:28 > 0:32:32Something in the zebra's genetic code drives them to migrate,
0:32:32 > 0:32:35but what's even more fascinating about Hattie's discovery
0:32:35 > 0:32:39is that it seems their genes also tells them where to go -
0:32:39 > 0:32:43something that zebra scientists didn't think possible.
0:32:43 > 0:32:45I think it just shows how complex they are.
0:32:45 > 0:32:47We take it for granted that it's just a zebra,
0:32:47 > 0:32:50it walks around, it eats grass, when it gets hungry,
0:32:50 > 0:32:52it walks to some more grass, but it's not like that.
0:32:52 > 0:32:55There's a huge complex interplay of things going on.
0:32:55 > 0:32:56They're not just a stripy donkey.
0:33:01 > 0:33:03For the zebras still in Chobe,
0:33:03 > 0:33:06something else is telling them to stay put.
0:33:06 > 0:33:09- Hopefully we can get you out there. - Great.- OK, good luck.
0:33:09 > 0:33:12But they have moved off the floodplain
0:33:12 > 0:33:14to an area just south of the main road.
0:33:18 > 0:33:21Bob is catching up with them to try to understand what's going on.
0:33:23 > 0:33:27He finds them 240km from Nxai Pan,
0:33:27 > 0:33:30in an area recently razed to the ground by a forest fire.
0:33:36 > 0:33:37Sam, look at this, eh?
0:33:37 > 0:33:41All the ash on the ground is giving it nutrients.
0:33:41 > 0:33:43The result is amazing, isn't it?
0:33:43 > 0:33:47Suddenly, you get this beautiful green grass coming up,
0:33:47 > 0:33:50and that's what they're eating right now, and they're loving it.
0:33:50 > 0:33:53Ash is an excellent source of trace elements
0:33:53 > 0:33:56that new vegetation thrives in.
0:33:56 > 0:33:59Seeing exactly what the zebra are doing on the ground
0:33:59 > 0:34:02allows a deeper insight into the movement data.
0:34:02 > 0:34:05So we know that our zebra haven't moved south yet,
0:34:05 > 0:34:09and that there's a burnt area here now.
0:34:09 > 0:34:12How does it affect the migration, the timing of it?
0:34:12 > 0:34:13This could delay it,
0:34:13 > 0:34:16especially if there's not enough water or vegetation further south.
0:34:16 > 0:34:18They're going to stay in this area
0:34:18 > 0:34:21and take full advantage of this new growth of grass.
0:34:21 > 0:34:24So this is doing the zebra quite a big favour,
0:34:24 > 0:34:27giving them an extra source of food, as they need to wait, anyway.
0:34:27 > 0:34:29Next rains, you're ready to move down.
0:34:32 > 0:34:37Janet, Winnie, Spirit and Jewel are staying put for a very good reason.
0:34:41 > 0:34:45150km south, Socks and her family
0:34:45 > 0:34:48have stopped for the first time in six days.
0:34:51 > 0:34:54Socks is past the halfway point of the migration
0:34:54 > 0:35:00and now she's stopped in an area for over 24 hours,
0:35:00 > 0:35:04so does this mean that even though she left really early,
0:35:04 > 0:35:08possibly to have her foal in the Nxai Pan area,
0:35:08 > 0:35:11that she gave birth to the foal over the past 24 hours?
0:35:11 > 0:35:13It would be very, very good
0:35:13 > 0:35:16if Max could catch up with her and see for himself.
0:35:16 > 0:35:20The problem is, it's still extremely tough terrain to get through.
0:35:33 > 0:35:35Oh, she's so close.
0:35:35 > 0:35:38She's literally straight in front of us,
0:35:38 > 0:35:40and that's as strong a signal as you get.
0:35:40 > 0:35:45I'm just worried that this is a really bad place on the journey
0:35:45 > 0:35:50to have a youngster, because she'll be feeling weak,
0:35:50 > 0:35:53there's very little water, next to no food,
0:35:53 > 0:35:56and she's still got a third of this journey to make.
0:35:59 > 0:36:02As if that wasn't enough, it still hasn't rained.
0:36:11 > 0:36:13Scattered across this hostile wilderness
0:36:13 > 0:36:17are depressions on the landscape called pans.
0:36:17 > 0:36:19As long as there is rain,
0:36:19 > 0:36:22the water in these pans offers a lifeline for wildlife.
0:36:23 > 0:36:27Using data from the last 24 hours, Max searches the landscape.
0:36:30 > 0:36:34He finds a pan, but it's certainly not the oasis Socks needs.
0:36:34 > 0:36:37There's nothing to drink here.
0:36:37 > 0:36:40You can see they've been trying, because these are zebra tracks here.
0:36:40 > 0:36:43- Oh, they're zebs, yeah.- And they've actually been into the mud,
0:36:43 > 0:36:46obviously just trying to suck whatever they can off the top.
0:36:46 > 0:36:48That's definitely got to be Socks.
0:36:48 > 0:36:52She's come here, and trying to get water from this mud wallow,
0:36:52 > 0:36:54I mean, she must be desperate.
0:36:54 > 0:36:57This elephant's come into drink, there's nothing even for him.
0:36:57 > 0:36:58He's not even trying.
0:37:02 > 0:37:04Again.
0:37:04 > 0:37:05With the light fading,
0:37:05 > 0:37:08there's little chance of finding Socks today.
0:37:11 > 0:37:15It's too dangerous for Max and Duncan to drive at night,
0:37:15 > 0:37:19but Socks could keep pushing south and leave them behind again.
0:37:23 > 0:37:26But there's nothing Max and Duncan can do till morning.
0:37:37 > 0:37:40Back at base camp, it's time to take stock
0:37:40 > 0:37:42of what we've discovered so far.
0:37:42 > 0:37:46As of today, here's what we know about our collared zebra.
0:37:46 > 0:37:49The majority of them are back in the floodplain.
0:37:49 > 0:37:52They've been moving between the burnt area and the floodplain.
0:37:52 > 0:37:54We've had a few showers,
0:37:54 > 0:37:57but it indicates that it's not quite the trigger,
0:37:57 > 0:37:59the environmental cue,
0:37:59 > 0:38:02that these zebras need to actually embark on the migration.
0:38:02 > 0:38:07So why has Socks dashed towards Nxai Pan?
0:38:07 > 0:38:10Is it that she simply misread the cues?
0:38:12 > 0:38:15It's becoming clear that their decision-making process
0:38:15 > 0:38:18is much more complex than we first thought.
0:38:20 > 0:38:24The following morning, Max might finally be in for a lucky break.
0:38:26 > 0:38:31Firebreaks are swathes cut in the forest to stop fires spreading.
0:38:31 > 0:38:33It looks like Socks' path
0:38:33 > 0:38:35might take her directly across one.
0:38:38 > 0:38:40Our best chance of catching her in the open
0:38:40 > 0:38:42and seeing what condition she's in
0:38:42 > 0:38:45is to try and intercept her as she crosses.
0:38:47 > 0:38:49With the data coming in every hour,
0:38:49 > 0:38:52they need to get into position before she arrives.
0:38:52 > 0:38:54We don't know what kind of state she's in
0:38:54 > 0:38:56or even if she's had her foal.
0:38:56 > 0:38:59- Ready.- This is five minutes old.
0:38:59 > 0:39:0019.2425.
0:39:08 > 0:39:12You know, it's vital that we actually set eyes on her,
0:39:12 > 0:39:14because we're starting to really worry.
0:39:16 > 0:39:18- SOFT WHISTLE - Right here.
0:39:18 > 0:39:20She's crossing. It's her, it's her.
0:39:24 > 0:39:26There's only three of them, which is strange.
0:39:26 > 0:39:29I didn't see Wishbone, the stallion.
0:39:30 > 0:39:34It's only the briefest of glimpses, and of only three of them,
0:39:34 > 0:39:38but 90km from her destination, Socks is alive and well.
0:39:38 > 0:39:40We'll have to look at this footage again.
0:39:43 > 0:39:46The footage suggests that she hasn't had her foal yet,
0:39:46 > 0:39:50which is good news, and information we'd never have gleaned
0:39:50 > 0:39:52from the satellite data alone.
0:39:52 > 0:39:56But the absence of Wishbone, the stallion, is a real concern.
0:39:56 > 0:39:59He should be protecting the herd from predators
0:39:59 > 0:40:01during this last push to Nxai Pan.
0:40:09 > 0:40:12Then, out of the blue, Socks' satellite collar
0:40:12 > 0:40:15stops sending location updates.
0:40:15 > 0:40:18Without this essential data, we have no way of finding Socks
0:40:18 > 0:40:21in this vast wilderness.
0:40:21 > 0:40:25Her last known position is 40km from Nxai Pan.
0:40:30 > 0:40:33Max's only option now is to continue south
0:40:33 > 0:40:37and hope that he can spot her emerging onto the open pan.
0:40:43 > 0:40:46Back in Chobe, Winnie, Janet, Spirit and Jewel
0:40:46 > 0:40:49have at last started to move south.
0:40:55 > 0:40:58This time, they don't stop at the burnt area,
0:40:58 > 0:41:02they keep going, and now they have 180km to go.
0:41:07 > 0:41:11At last, the main migration has started in earnest.
0:41:13 > 0:41:16It's time for the rest of the team to break camp
0:41:16 > 0:41:18and head south to Nxai Pan.
0:41:43 > 0:41:47Around 10,000 years ago, Nxai Pan was an enormous lake.
0:41:47 > 0:41:50Now dried up, its soil is packed
0:41:50 > 0:41:53with potassium, calcium and magnesium.
0:41:54 > 0:41:56During the rainy season,
0:41:56 > 0:41:59these minerals produce lush and highly nutritious grass.
0:42:01 > 0:42:04But when Max arrives, things are not as he'd hoped.
0:42:07 > 0:42:11We've arrived expecting to see a flush of green grass,
0:42:11 > 0:42:13which is why the zebra come this way,
0:42:13 > 0:42:15but the rains have not hit here yet.
0:42:27 > 0:42:30Even if the zebra make it through the forest,
0:42:30 > 0:42:32there'll be nothing for them to eat at the end of it.
0:42:34 > 0:42:36And that's not their only threat.
0:42:41 > 0:42:44A pride of 14 hungry lions are lying in wait
0:42:44 > 0:42:47for the exhausted zebra as they arrive.
0:42:52 > 0:42:56Lions are the largest predators in Africa.
0:42:56 > 0:42:58They have explosive speed and power.
0:42:59 > 0:43:01Unlike African wild dogs,
0:43:01 > 0:43:04a single lion can take down a fully grown zebra.
0:43:12 > 0:43:16When there are lots of zebra around, the lions will kill frequently,
0:43:16 > 0:43:18feeding on the most nutritious parts
0:43:18 > 0:43:20and leaving the leftovers for scavengers.
0:43:22 > 0:43:26But the harsh dry season has taken its toll on the Nxai Pan lions.
0:43:29 > 0:43:31These lions will have had a tough time.
0:43:31 > 0:43:33You can see they're quite skinny.
0:43:33 > 0:43:35But they've got through the dry season
0:43:35 > 0:43:38and they know that all the grazing animals are coming,
0:43:38 > 0:43:41and their number one food choice will be zebra,
0:43:41 > 0:43:45and all of our collared animals in a week or so are going to be here.
0:43:48 > 0:43:53Not only will the zebra find hungry lions waiting for them,
0:43:53 > 0:43:56they may also find themselves facing a complete lack of food
0:43:56 > 0:43:59if they arrive here before the rains.
0:44:06 > 0:44:11The changing of the seasons in Botswana could not be more dramatic.
0:44:11 > 0:44:13At the end of the dry season,
0:44:13 > 0:44:17temperatures soar as high as an unbearable 45 degrees C.
0:44:17 > 0:44:22The land is scorched and cracked until, on the horizon,
0:44:22 > 0:44:26a lightning bolt announces the beginning of the rains,
0:44:26 > 0:44:27and everything changes.
0:44:30 > 0:44:35As the heat soars, moisture builds in the atmosphere
0:44:35 > 0:44:39and enormous clouds appear, looming across the skies.
0:44:39 > 0:44:41THUNDER RUMBLES
0:44:47 > 0:44:51For a while, the showers are localised,
0:44:51 > 0:44:53but then the heavens open.
0:44:53 > 0:44:55THUNDER CRASHES
0:45:13 > 0:45:18Here, as much as 12cm of rain can fall in a single downpour.
0:45:24 > 0:45:27This is what the zebra have been waiting for.
0:45:27 > 0:45:31Several weeks late but, finally, the rains have come,
0:45:31 > 0:45:34and soon, this dry, parched saltpan
0:45:34 > 0:45:37is going to transform into a lush, green field,
0:45:37 > 0:45:43full of protein and mineral-rich grass that the zebra rely on,
0:45:43 > 0:45:45especially now that they're foaling.
0:45:49 > 0:45:51The satellite data shows
0:45:51 > 0:45:55that all our collared zebra are now just north of Nxai Pan,
0:45:55 > 0:45:58having averaged 30km a day for over a week.
0:46:00 > 0:46:03Somehow, they knew that all of this was about to happen.
0:46:03 > 0:46:06They have timed this to perfection.
0:46:11 > 0:46:13Now the rains have truly arrived,
0:46:13 > 0:46:17the nutritious grasses of Nxai Pan will start growing.
0:46:18 > 0:46:20But the lions will be waiting.
0:46:26 > 0:46:30We've established our new base camp at the northern end of Nxai Pan,
0:46:30 > 0:46:34to catch the zebra as they come out of the forests and onto the plains.
0:46:37 > 0:46:39The morning after the rains,
0:46:39 > 0:46:42the satellite data reveals some great news.
0:46:42 > 0:46:43- Janet!- It's Janet.- In the open.
0:46:43 > 0:46:45She's been giving us the run-around,
0:46:45 > 0:46:47but now we're going to finally clock eyes on her,
0:46:47 > 0:46:49see what condition she's in.
0:46:49 > 0:46:52- She can't be very far. - It's just about 3k from camp.
0:46:54 > 0:46:58We know she's here, but the data point is now an hour old.
0:46:59 > 0:47:04In this flat and open pan, radio telemetry should work well.
0:47:09 > 0:47:11- Strongest signal's from this... - This group here.
0:47:18 > 0:47:21- Have a look. See, I think the second one's got a collar.- OK.
0:47:24 > 0:47:27- That's her. - Fantastic.- Amazing.
0:47:27 > 0:47:30Look, she's coming right through the middle of these springbok.
0:47:30 > 0:47:34And this zebra, she was the first one documented
0:47:34 > 0:47:36making this huge migration down here,
0:47:36 > 0:47:39and we're meeting up with her again, she's done it again.
0:47:39 > 0:47:42Amazing.
0:47:42 > 0:47:45In Chobe, Janet was part of a family of 15.
0:47:46 > 0:47:49But now there are only five of them.
0:47:50 > 0:47:54Hopefully, the rest of her herd are also here somewhere
0:47:54 > 0:47:57and haven't succumbed to exhaustion or predation.
0:48:03 > 0:48:05Thankfully, the data shows
0:48:05 > 0:48:08that all the other families are also pouring into the park.
0:48:08 > 0:48:10Max, Max, it's Liz. Do you copy?
0:48:10 > 0:48:12'Hey, Liz, how are you doing?'
0:48:12 > 0:48:14'Well, 14km away from camp
0:48:14 > 0:48:16'is Spirit.'
0:48:17 > 0:48:22But when Max catches up with Spirit, he finds that all is not well.
0:48:25 > 0:48:27That's Spirit.
0:48:28 > 0:48:30Spirit was pregnant.
0:48:32 > 0:48:35We can't be sure what happened to her foal,
0:48:35 > 0:48:38but it looks like her family have had a recent run-in with the lions.
0:48:44 > 0:48:47Fresh wounds on three of the zebra in this group.
0:48:47 > 0:48:51I mean, it's the unmistakable marks left by a lion.
0:48:52 > 0:48:54There's a small foal,
0:48:54 > 0:48:58and you can see his whole hind has been ripped open.
0:48:58 > 0:49:00That must have happened last night.
0:49:00 > 0:49:03The lions were around, we heard them roaring.
0:49:03 > 0:49:07It's bumper season for them now that the zebra are here.
0:49:13 > 0:49:15We need to find out if Socks is still alive.
0:49:18 > 0:49:21Even though her collar's GPS has failed,
0:49:21 > 0:49:23it may still have a VHF signal.
0:49:25 > 0:49:28On the ground, the range is just a few kilometres,
0:49:28 > 0:49:31but from the air, it's closer to 40.
0:49:32 > 0:49:34It's only when you get up here
0:49:34 > 0:49:36that you really realise the vast expanse of this place.
0:49:36 > 0:49:38I mean, where could she be
0:49:38 > 0:49:40and how far do we have to look in every direction?
0:49:40 > 0:49:45She could be anywhere in an area up to 15,000 square kilometres.
0:49:45 > 0:49:49That is absolutely huge, so it's needle in a haystack stuff.
0:49:49 > 0:49:52We absolutely had no hope on the ground. What are our chances?
0:49:52 > 0:49:54If the telemetry transmitter is still working,
0:49:54 > 0:49:57we've got a very good chance of finding her.
0:49:59 > 0:50:01So, Liz, we've got a little bit of altitude now,
0:50:01 > 0:50:03and I'm going to put this receiver on.
0:50:03 > 0:50:06You'll hear some static start to come through.
0:50:06 > 0:50:08This is set on Socks' frequency.
0:50:08 > 0:50:11We'll just listen through a lot of noise initially,
0:50:11 > 0:50:13cos all you can hear is static,
0:50:13 > 0:50:16and then you're just listening for a tiny, tiny little beep.
0:50:16 > 0:50:18Beep. And when we hear that,
0:50:18 > 0:50:21we start honing in and trying to zone in on where she is.
0:50:21 > 0:50:25- OK.- You keep your ears peeled. - I am going to do my best for you.
0:50:25 > 0:50:28STATIC
0:50:28 > 0:50:32But finding a signal in an area this size seems next to impossible,
0:50:32 > 0:50:34even from the air.
0:50:40 > 0:50:42Max is standing by, ready to go in on the ground,
0:50:42 > 0:50:44should we find anything.
0:50:44 > 0:50:47STATIC
0:50:48 > 0:50:50FAINT BEEP
0:50:53 > 0:50:55You hear that?
0:50:55 > 0:50:58There was the faintest, tiniest little beep through this static.
0:50:58 > 0:51:01- I'm just hearing the static. - Yeah, yeah, so listen really...
0:51:01 > 0:51:03- Can you hear a beep? - Yeah, yeah, but it's tiny.
0:51:03 > 0:51:05- It really is very subtle. - FAINT BEEP
0:51:07 > 0:51:10BEEPING
0:51:10 > 0:51:12It's Socks!
0:51:12 > 0:51:13BOTH LAUGH
0:51:13 > 0:51:15Oh, my gosh, that's brilliant!
0:51:15 > 0:51:21That is definitely the unmistakable beep of a VHF collar.
0:51:21 > 0:51:23Socks is here, she's in Nxai Pan.
0:51:25 > 0:51:29Now that we've picked up a signal, we have to fly in a search pattern
0:51:29 > 0:51:31until we pinpoint its exact location.
0:51:38 > 0:51:40BEEPING
0:51:42 > 0:51:46- It's her, it's her. It's this group of zebra there. It has to be.- Yeah.
0:51:49 > 0:51:52'Max, Max, it's Liz. I've got some fantastic news for you.'
0:51:52 > 0:51:54We've just located Socks.
0:51:54 > 0:51:57That's amazing news.
0:51:57 > 0:51:58She's in a group of ten zebra.
0:51:58 > 0:52:02Now, we couldn't get a visual on Socks herself, but...
0:52:02 > 0:52:04'If we're to see how Socks and her family are doing,
0:52:04 > 0:52:07'Max will have to catch up with them on the ground.'
0:52:07 > 0:52:11We'll head that way and let you know how we get on.
0:52:11 > 0:52:14Oh, I'm so happy about this. Good luck with it all.
0:52:19 > 0:52:22Last time we saw Socks, she was travelling
0:52:22 > 0:52:24without the protection of Wishbone, the stallion.
0:52:24 > 0:52:28We need to know how she's doing, and if she's had her foal.
0:52:29 > 0:52:30We're not far off now.
0:52:30 > 0:52:34We're almost parallel with them, so if you start scanning a bit.
0:52:34 > 0:52:36It looks like there's some animals just...
0:52:37 > 0:52:39Oh, look. Amazing, amazing.
0:52:39 > 0:52:42Look. That's Socks.
0:52:42 > 0:52:46She's got her unmistakable white socks on.
0:52:46 > 0:52:49She's with the stallion.
0:52:49 > 0:52:51It looks like they're all there.
0:52:53 > 0:52:57Then Max spots something moving in the long grass.
0:52:57 > 0:52:58It's her foal.
0:53:04 > 0:53:05He's absolutely tiny.
0:53:05 > 0:53:08She must have dropped this foal in the last couple of days.
0:53:11 > 0:53:12How cool is that?!
0:53:21 > 0:53:25When you look at Socks now and see what fantastic condition she's in...
0:53:25 > 0:53:28She made this journey really early on,
0:53:28 > 0:53:30but that's given her time to recuperate
0:53:30 > 0:53:33and now she's given birth in the best possible place.
0:53:33 > 0:53:35She's found this little Garden of Eden here
0:53:35 > 0:53:38where there's more grass than we've seen anywhere else,
0:53:38 > 0:53:42so she's given this little fella the best possible start in life.
0:53:43 > 0:53:47The funny thing is, her foal has stripes on its legs.
0:53:47 > 0:53:49He's taken after Dad.
0:53:56 > 0:54:00As more and more zebra families pour into Nxai Pan
0:54:00 > 0:54:04at the end of a gruelling migration, the plains come to life.
0:54:23 > 0:54:25The first green shoots are pushing up,
0:54:25 > 0:54:31and the time to rest, give birth and feed on the bounty has arrived.
0:54:36 > 0:54:41This little foal is only hours old
0:54:41 > 0:54:44and it's still so unsure on its feet.
0:54:48 > 0:54:52I mean, it is just the most beautiful scene,
0:54:52 > 0:54:55and the stallion is just standing by,
0:54:55 > 0:55:00being extremely protective of his mare and his new foal.
0:55:05 > 0:55:07And we know so little about these interactions,
0:55:07 > 0:55:10there's still so much to understand,
0:55:10 > 0:55:12but just seeing this scene today
0:55:12 > 0:55:15really does paint a wonderful picture.
0:55:18 > 0:55:21And as much as I couldn't help but question
0:55:21 > 0:55:25why on earth an animal would decide to make
0:55:25 > 0:55:28such a ridiculously long and arduous journey...
0:55:30 > 0:55:33..watching this now, it all makes sense.
0:55:34 > 0:55:38It's worth the journey, it's worth the trial and tribulations,
0:55:38 > 0:55:40because as a mother,
0:55:40 > 0:55:45you have every instinct telling you, we need to make it down here,
0:55:45 > 0:55:48this is going to make our family stronger,
0:55:48 > 0:55:49our foals will be stronger.
0:55:49 > 0:55:53Ultimately, that's what survival is all about.
0:56:03 > 0:56:07During our time in Botswana, we've had a privileged insight
0:56:07 > 0:56:12into Africa's longest and most recently discovered land migration.
0:56:17 > 0:56:19We've discovered the importance
0:56:19 > 0:56:22of each family making the right decision at the right time.
0:56:24 > 0:56:27And we've revealed that part of their ability to navigate
0:56:27 > 0:56:29is written in their genes.
0:56:31 > 0:56:36The discovery of this zebra migration is so important.
0:56:36 > 0:56:38It represents what ground-breaking science
0:56:38 > 0:56:41can reveal about the natural world
0:56:41 > 0:56:44in a way that simply wasn't possible before.
0:56:44 > 0:56:48What surprised me the most is just how complex these animals are.
0:56:48 > 0:56:54A strong biological instinct, a drive to explore and to navigate,
0:56:54 > 0:56:57a constant adjustment to a changing environment.
0:56:57 > 0:56:59They're all at play here.
0:57:01 > 0:57:06As difficult as this migration is, these zebra achieve it perfectly.
0:57:08 > 0:57:10There is still so much to understand,
0:57:10 > 0:57:13but ultimately, this research will help scientists
0:57:13 > 0:57:16to preserve this precious migratory route,
0:57:16 > 0:57:19but it will also provide invaluable insights
0:57:19 > 0:57:24that could help to save species and their habitats across the world.