0:00:02 > 0:00:06Our planet is the greatest living puzzle in the universe.
0:00:06 > 0:00:09A collection of worlds within worlds.
0:00:09 > 0:00:13Each one a self-contained ecosystem, bursting with life.
0:00:17 > 0:00:19But how do they work?
0:00:20 > 0:00:23The intricate web of relationships
0:00:23 > 0:00:26and the influence of natural forces
0:00:26 > 0:00:32makes each microworld complex and unique.
0:00:33 > 0:00:37So to discover their secrets, we need to explore them one by one -
0:00:39 > 0:00:42untangle their interlocking pieces
0:00:42 > 0:00:47and ultimately reveal the vital piece,
0:00:47 > 0:00:49the key to life itself,
0:00:49 > 0:00:54hidden deep within each of nature's microworlds.
0:01:05 > 0:01:09The Okavango Delta, Southern Africa.
0:01:13 > 0:01:16A vast wetland supporting a huge diversity of life,
0:01:18 > 0:01:22with over 1,000 species of plants
0:01:22 > 0:01:25and more than 400 types of bird.
0:01:27 > 0:01:29It's a magnet for wildlife,
0:01:29 > 0:01:31home to one of the biggest congregations
0:01:31 > 0:01:34of large animals in Africa.
0:01:36 > 0:01:39Fed by the Okavango river,
0:01:39 > 0:01:43this incredible, lush microworld is actually an oasis.
0:01:47 > 0:01:51A vast wetland in the very heart of the Kalahari desert.
0:01:56 > 0:01:59And what an oasis.
0:02:03 > 0:02:06At 22,000 square kilometres,
0:02:06 > 0:02:11the Okavango is the world's largest inland delta.
0:02:15 > 0:02:19A normal delta is formed where the river flows out to sea,
0:02:19 > 0:02:26but here the river flows into the middle of the African continent,
0:02:26 > 0:02:31creating an immense wetland, that can be seen from space.
0:02:34 > 0:02:38Inland deltas are extremely unusual,
0:02:38 > 0:02:42so just how does the Okavango function?
0:02:45 > 0:02:48To understand this and how it can support all this life,
0:02:48 > 0:02:53we have to take a look at it through the year.
0:02:53 > 0:02:56Because for at least three months of the year,
0:02:56 > 0:03:00this vast wetland transforms back into the desert that surrounds it,
0:03:04 > 0:03:08making life here formidably harsh.
0:03:16 > 0:03:19There is water in the desert even now,
0:03:19 > 0:03:23but it's confined to a few rapidly shrinking pools.
0:03:26 > 0:03:28So the animals of the delta,
0:03:28 > 0:03:33seemingly trapped in this vast dry arena, have to travel long distances
0:03:33 > 0:03:37to get to these remaining waterholes.
0:03:38 > 0:03:43These become packed with the unlikeliest of drinking partners.
0:03:45 > 0:03:49Elephants and lions.
0:04:01 > 0:04:03The lions are wary.
0:04:03 > 0:04:07An adult elephant could easily kill one of them.
0:04:08 > 0:04:11But the elephants are also wary -
0:04:11 > 0:04:14lions have been known to kill young elephants,
0:04:14 > 0:04:16and they have a baby with them.
0:04:19 > 0:04:25But this tense stand-off is just about getting a drink,
0:04:27 > 0:04:31no matter how disgusting the water is.
0:04:31 > 0:04:34The elephants have an advantage.
0:04:34 > 0:04:37They have a trick to get at the better water.
0:04:40 > 0:04:45They use their trunks to siphon off the cleanest water at the surface.
0:04:48 > 0:04:53Regardless of the dangers, elephants have to drink every four days.
0:05:10 > 0:05:14At the height of the dry season, the water is barely drinkable,
0:05:14 > 0:05:18but remarkably, it still supports some life.
0:05:20 > 0:05:23Trapped in these fetid, oxygen-starved pools,
0:05:23 > 0:05:25catfish are survivors.
0:05:25 > 0:05:28Able to gulp air from the atmosphere,
0:05:28 > 0:05:30they can live in wet mud,
0:05:32 > 0:05:36but this adaptation doesn't protect them from predators.
0:05:37 > 0:05:44African fish eagles and Marabou storks are quick to take advantage.
0:05:44 > 0:05:48The catfish are attacked from all sides.
0:05:53 > 0:05:56But they are not the only ones struggling to survive out here.
0:06:03 > 0:06:07It's January and all the animals far out in the desert
0:06:07 > 0:06:13are searching for water, but our microworld is on the cusp of change,
0:06:18 > 0:06:23because 1,000 kilometres away to the north, it's raining.
0:06:25 > 0:06:28The mountains of Angola were formed millions of years ago
0:06:28 > 0:06:31by the tectonic forces of the Earth's crust.
0:06:34 > 0:06:38In January and February, clouds condense on their high slopes
0:06:38 > 0:06:42and form rain, lots of it.
0:06:50 > 0:06:54This huge deluge pours out of the highlands,
0:06:54 > 0:06:57and slowly starts making its way towards our microworld.
0:07:05 > 0:07:09The first place to see the benefits is the Okavango river.
0:07:12 > 0:07:16Fresh water pours in and the water levels rise.
0:07:19 > 0:07:23Species like the hippo, that need to be able to completely submerge
0:07:23 > 0:07:26in water to survive, have retreated to these deep pools
0:07:26 > 0:07:29during the worst of the dry season.
0:07:33 > 0:07:36Soon they will be moving out into the seasonal swamps
0:07:36 > 0:07:38when the delta floods.
0:07:39 > 0:07:42But not quite yet,
0:07:42 > 0:07:46it takes three months for the rain that has poured off the highlands
0:07:46 > 0:07:49to finally reach the delta, 1,000 kilometres away.
0:07:55 > 0:07:57What this means for the wildlife in our microworld
0:07:57 > 0:08:00is that they just have to carry on as best they can,
0:08:00 > 0:08:04unaware that help is on its way.
0:08:06 > 0:08:10And conditions are creating conflicts.
0:08:16 > 0:08:17Bull elephants get aggressive
0:08:17 > 0:08:20when they are forced to share the same resources.
0:08:41 > 0:08:44Buffalo will have to wait their turn,
0:08:44 > 0:08:47or risk becoming the target of the elephants' frustrations.
0:09:01 > 0:09:02By early March,
0:09:02 > 0:09:06the Angolan rain has filled the Okavango river to overflow
0:09:06 > 0:09:10and water has started pouring into the delta.
0:09:15 > 0:09:18It moves painfully slowly over the sandy ground,
0:09:18 > 0:09:22gradually filling up the bone-dry channels.
0:09:41 > 0:09:44But it will be at least another three months
0:09:44 > 0:09:47before the delta is completely transformed.
0:09:47 > 0:09:52And during this time there's one species that will benefit
0:09:52 > 0:09:54from the last of the dry conditions.
0:09:56 > 0:09:58Lions.
0:09:58 > 0:10:02The long dry grass affords them cover,
0:10:02 > 0:10:05the firm sandy soil gives them purchase.
0:10:09 > 0:10:12These are the lions' good times.
0:10:15 > 0:10:18But the lions need to be careful who they pick on -
0:10:18 > 0:10:21a kick from a buffalo could cause serious injury.
0:10:27 > 0:10:32The weak and the old are an easier target for the lions.
0:10:45 > 0:10:49It might seem that this place offers the lions all they could need,
0:10:49 > 0:10:53but the tables will turn with the swing of the season.
0:10:57 > 0:11:01As the water creeps slowly into the delta,
0:11:01 > 0:11:07salvation has finally arrived for the last hardy catfish.
0:11:11 > 0:11:15The lifeblood of the delta reaches them at last.
0:11:23 > 0:11:26Since falling in the Angolan highlands,
0:11:26 > 0:11:28it has taken nearly three months
0:11:28 > 0:11:32for the water to travel 1,000 kilometres towards our microworld,
0:11:32 > 0:11:36and each year 10 trillion litres of water flows into the delta.
0:11:39 > 0:11:41Of course, this sheer volume of water
0:11:41 > 0:11:44plays its part in the size of the delta,
0:11:44 > 0:11:48but there's another factor that allows it to function
0:11:48 > 0:11:50on such a huge scale.
0:11:52 > 0:11:55The delta is almost completely flat.
0:11:57 > 0:12:02On average, it only slopes by a metre every 3.5 kilometres.
0:12:04 > 0:12:08Enough to create flow, but also create spread.
0:12:11 > 0:12:15So with the ground at roughly the same level, the water fans out,
0:12:15 > 0:12:19spreading across the entire Okavango basin.
0:12:19 > 0:12:25And life follows the waters as it overflows into the desert.
0:12:25 > 0:12:28Fish that have spent the dryer times in the main river
0:12:28 > 0:12:31can expand their territories and spawn.
0:12:32 > 0:12:36And the catfish can move with the water to find new areas to colonise.
0:12:42 > 0:12:45The herbivores that have risked starvation and thirst
0:12:45 > 0:12:49can now drink and feed again.
0:12:51 > 0:12:55And for the elephants, the wait is over.
0:12:57 > 0:13:00Now they relish the chance to play and swim
0:13:00 > 0:13:03in the deep, newly filled pools.
0:13:24 > 0:13:28However, the rain pouring off the Angolan highlands
0:13:28 > 0:13:31and the shallow gradient are not the only contributing factors
0:13:31 > 0:13:34to the massive scale of the Okavango delta.
0:13:34 > 0:13:39There is one other pivotal piece to this puzzle.
0:13:41 > 0:13:45Tectonic activity, that helped lift the Angolan highlands,
0:13:45 > 0:13:47the source of the flood,
0:13:47 > 0:13:51has also had a much more direct impact on the delta itself.
0:13:54 > 0:13:58The Okavango sits in a geological depression.
0:13:58 > 0:14:00The land that the delta sits on
0:14:00 > 0:14:04has dropped between two faults in the Earth's crust,
0:14:04 > 0:14:08creating the depression that the Okavango river pours into.
0:14:10 > 0:14:12The fault at the other end of the Okavango
0:14:12 > 0:14:16creates a natural dam across the southern end of the delta.
0:14:18 > 0:14:21It is this that backs the water up,
0:14:21 > 0:14:23greatly increasing the habitat in size
0:14:23 > 0:14:26and creating the Okavango delta.
0:14:32 > 0:14:36It's an oasis in the middle of the desert,
0:14:36 > 0:14:42capable of supporting a vast and surprising array of life,
0:14:42 > 0:14:46including species that you wouldn't expect to see
0:14:46 > 0:14:49in the middle of a desert.
0:14:49 > 0:14:50Like pelicans!
0:15:00 > 0:15:03Countless water birds fly for thousands of kilometres
0:15:03 > 0:15:06to take advantage of the seasonal swamps.
0:15:09 > 0:15:13They know that the flood will provide them with a bounty
0:15:13 > 0:15:17and they take advantage of these good times to breed,
0:15:17 > 0:15:20filling the trees with nests and young.
0:15:24 > 0:15:28It seems that nearly every space available fills up with birds.
0:15:36 > 0:15:40The seasonal flood has a huge effect on our microworld,
0:15:40 > 0:15:42but it doesn't last.
0:15:44 > 0:15:48So just where does 10 trillion litres of water disappear to?
0:15:52 > 0:15:56Incredibly, virtually all the water is lost to the atmosphere
0:15:56 > 0:16:00through the plants and evaporation.
0:16:02 > 0:16:05But this microworld has evolved over millennia,
0:16:05 > 0:16:08long enough to allow life to adapt.
0:16:12 > 0:16:14The wet times more than compensate for the dry,
0:16:14 > 0:16:18because grasses can survive long periods of drought
0:16:18 > 0:16:21and spring back into life as soon as they get wet.
0:16:31 > 0:16:35The grasses cover the plains in an incredible green flush.
0:16:41 > 0:16:45Their secret is that they grow from the base.
0:16:46 > 0:16:50Even though they face an onslaught from the grazers,
0:16:50 > 0:16:52this feature allows them to keep on growing
0:16:52 > 0:16:56and provide huge amounts of food.
0:16:56 > 0:17:00Enough to feed a collection of large mammals on a massive scale.
0:17:05 > 0:17:08Now hippos that have been stuck in their deep water pools
0:17:08 > 0:17:11through the dry season can find new territories,
0:17:11 > 0:17:14the females congregating in groups.
0:17:17 > 0:17:22Which leads to battles between males competing for mating rites.
0:17:27 > 0:17:30Hippos can weigh over 3,000 kilos
0:17:30 > 0:17:34and have forward-pointing tusks in their mouths,
0:17:34 > 0:17:37so fights can be brutal, even deadly.
0:17:59 > 0:18:02But these fights aren't just about females.
0:18:06 > 0:18:09They are also about territory.
0:18:09 > 0:18:14Although hippos rely on water, they feed on land.
0:18:18 > 0:18:23An adult hippo eats around 40 kilos of grass a day,
0:18:23 > 0:18:26maintaining hippo lawns that they feed on.
0:18:27 > 0:18:30They're creatures of habit,
0:18:30 > 0:18:34visiting the same feeding grounds along the same paths day after day.
0:18:38 > 0:18:41But all this water doesn't benefit everyone.
0:18:49 > 0:18:53The lions find it hard to hunt in the water of the swamps
0:18:53 > 0:18:56as they can't creep up easily on their prey.
0:18:59 > 0:19:02Red lechwe are swamp specialists.
0:19:02 > 0:19:06They move out of the permanent swamps every year with the floods.
0:19:06 > 0:19:11With long splayed hooves, they can run through the wetland easily.
0:19:11 > 0:19:15The lions need to try and hunt on dry land,
0:19:15 > 0:19:19where they can use the long grass for cover.
0:19:31 > 0:19:36Now the water has turned the tide in favour of the buffalo
0:19:36 > 0:19:39and they have young to look after.
0:19:43 > 0:19:44At the first sniff of danger
0:19:44 > 0:19:48the herd heads for the safety of deep water.
0:19:52 > 0:19:55They can move a lot more easily in the water than the lions
0:19:55 > 0:19:57and leave them in their wake.
0:20:07 > 0:20:11The vast expanses of water hinder some residents in our microworld
0:20:11 > 0:20:16and benefit others, but at least there's plenty of food.
0:20:23 > 0:20:26And even if you don't like getting wet, like these baboons,
0:20:26 > 0:20:30the feast here is a bit too appealing to miss.
0:20:44 > 0:20:47The physical processes that have created the Okavango
0:20:47 > 0:20:51are remarkable, but they are not the whole story.
0:20:51 > 0:20:55Similar inland deltas tend to end in lifeless salty lakes,
0:20:55 > 0:20:59devoid of the kind of richness seen here.
0:21:02 > 0:21:07So what is it that makes the Okavango delta so different?
0:21:07 > 0:21:09When trying to find an answer to that,
0:21:09 > 0:21:12scientists noticed something remarkable -
0:21:12 > 0:21:16this microworld is constantly changing.
0:21:22 > 0:21:26Each year it floods in a slightly different way from the last.
0:21:28 > 0:21:34And over time, some water courses dry up, leaving areas to dry out,
0:21:34 > 0:21:36while new areas flood.
0:21:38 > 0:21:43Eventually, these dry areas revert to grassland and end up providing
0:21:43 > 0:21:46more food and habitat for the animals that live here.
0:21:50 > 0:21:51But that is not all -
0:21:51 > 0:21:55the scientists discovered that this cycle of grassland and swamp
0:21:55 > 0:21:59has a crucial effect on the delta as a whole.
0:22:01 > 0:22:05It stops any area from becoming stagnant,
0:22:05 > 0:22:08constantly keeping the channels on the move
0:22:08 > 0:22:10and keeping the water flowing and clean.
0:22:13 > 0:22:17Without this process, the delta would become a saline lake,
0:22:17 > 0:22:20unable to support such a huge diversity of wildlife.
0:22:23 > 0:22:29Now here is the really crazy thing about this unique microworld.
0:22:29 > 0:22:34The process of change is being driven by just two key players.
0:22:34 > 0:22:38The first is the plants.
0:22:38 > 0:22:41By the way they grow,
0:22:41 > 0:22:44the plants actually manage the environment that they live in.
0:22:47 > 0:22:50The plants that line the channels stabilise the banks,
0:22:50 > 0:22:53stopping the sand from getting washed away.
0:22:53 > 0:22:58But in areas where the flow of water is slower, the plants build up,
0:22:58 > 0:23:02their roots mat together, making it harder for the water to flow.
0:23:04 > 0:23:08Water will always seek the path of least resistance
0:23:08 > 0:23:11so it flows away in a different direction.
0:23:13 > 0:23:17So the plants help spread the water out across the delta.
0:23:17 > 0:23:21They not only maintain the banks, but they also close off
0:23:21 > 0:23:25slow-flowing waterways before they become stagnant.
0:23:28 > 0:23:32And the sheer density of plants acts like a sponge,
0:23:32 > 0:23:36slowing the flow of water and helping divert it outwards
0:23:36 > 0:23:38across the delta,
0:23:38 > 0:23:42thus perpetuating the constant change within our microworld,
0:23:42 > 0:23:46and stopping it becoming a salty pan.
0:23:49 > 0:23:51The plants are not the only ones
0:23:51 > 0:23:55that affect the water's distribution.
0:23:55 > 0:23:58When the land is so flat, it is not always obvious
0:23:58 > 0:24:00what the path of least resistance might be.
0:24:00 > 0:24:04All around, the ground is virtually exactly the same level.
0:24:06 > 0:24:10Other than areas that have already been eroded, that is,
0:24:10 > 0:24:14and this leads us to the incredible twist in this tale.
0:24:16 > 0:24:17Hippos.
0:24:30 > 0:24:33These massive lawnmowers are the other key factor
0:24:33 > 0:24:36in the management of this microworld.
0:24:37 > 0:24:41So key that the indigenous people of the Okavango
0:24:41 > 0:24:45ascribe the origin of a major waterway to the hippos alone.
0:24:48 > 0:24:52When moving about between their deep water wallows
0:24:52 > 0:24:56and their feeding grounds, hippos act like four-legged trail blazers,
0:24:56 > 0:25:01creating holes in the vegetation along the edge of waterways.
0:25:01 > 0:25:05These paths allow water to flow to other parts of the swamps,
0:25:05 > 0:25:09and therefore distribute it to new areas of the delta.
0:25:11 > 0:25:13In doing so, they contribute
0:25:13 > 0:25:18to the ever-changing flow of water in this microworld.
0:25:25 > 0:25:31They also bulldoze clear thoroughfares in deeper water too.
0:25:33 > 0:25:36Their constant use means that the vegetation doesn't get a chance
0:25:36 > 0:25:39to grow inwards and block the channel.
0:25:44 > 0:25:47These underwater highways play an important role
0:25:47 > 0:25:50for the other creatures too, allowing them to get around
0:25:50 > 0:25:54using clear, plant-free underwater paths.
0:25:58 > 0:26:00But they don't stop there.
0:26:00 > 0:26:03Probably the most important bit of hippo-engineering
0:26:03 > 0:26:07happens when the waters reach their highest.
0:26:09 > 0:26:14Their paths to feeding grounds become well-trodden walkways.
0:26:16 > 0:26:21In years of lots of rain, these paths offer ready-made canals,
0:26:21 > 0:26:24to transport the deluge to parts of the Okavango
0:26:24 > 0:26:26that were previously dry,
0:26:28 > 0:26:31diverting water away from other areas,
0:26:31 > 0:26:34allowing them to become grassland again.
0:26:38 > 0:26:43So the hippos are the architects of change in our microworld,
0:26:43 > 0:26:46building new canals and maintaining the old ones,
0:26:46 > 0:26:50perpetually shaping and reshaping the entire Okavango,
0:26:50 > 0:26:54preventing it from becoming a stagnant, lifeless salt lake.
0:26:56 > 0:26:58So the world's biggest inland delta
0:26:58 > 0:27:02provides us with a unique look at how intricate and complex
0:27:02 > 0:27:06the interlocking pieces there are that make up a microworld,
0:27:06 > 0:27:10but unlike many others, not one piece holds the key.
0:27:10 > 0:27:13Everything plays its role.
0:27:14 > 0:27:18The water that pours into the desert each year.
0:27:19 > 0:27:22The shallow pan, created by tectonic processes,
0:27:22 > 0:27:25that also lifted the rain generators,
0:27:25 > 0:27:27the Angolan highlands to the north.
0:27:30 > 0:27:34The constant cycle of change that stops the water stagnating
0:27:34 > 0:27:36and generates new habitats.
0:27:41 > 0:27:45And the real surprise is that two key living inhabitants
0:27:45 > 0:27:50of our microworld also play a key role in orchestrating this change.
0:27:53 > 0:27:56By manipulating the way the water flows,
0:27:56 > 0:28:00the plants and the hippos keep the wetlands alive and flourishing,
0:28:03 > 0:28:07and in doing so, they enable this microworld to support
0:28:07 > 0:28:10one of Africa's greatest congregations of wildlife,
0:28:13 > 0:28:17creating the world's greatest inland delta,
0:28:17 > 0:28:20a glittering oasis in the middle of a desert
0:28:20 > 0:28:23that truly is a world within a world.
0:28:26 > 0:28:28The Okavango.
0:28:44 > 0:28:47Subtitles by Red Bee Media Ltd