0:00:06 > 0:00:0830 million years ago,
0:00:08 > 0:00:11tropical Africa was covered in dense jungle.
0:00:12 > 0:00:14But not any more.
0:00:16 > 0:00:18Here in East Africa,
0:00:18 > 0:00:21the forest has all but vanished,
0:00:21 > 0:00:23a changed landscape that is the stage
0:00:23 > 0:00:26for the most epic wildlife story on the continent.
0:00:28 > 0:00:30And it begins in the forest.
0:00:39 > 0:00:42Chimpanzees are perfectly adapted for life in the trees.
0:00:50 > 0:00:53They gather almost all their food from the canopy.
0:01:12 > 0:01:16But these chimps live in the Kyambura Gorge of Uganda,
0:01:16 > 0:01:19and will sometimes embark on an unusual journey.
0:01:29 > 0:01:32Their home, in this narrow strip of forest,
0:01:32 > 0:01:34is surrounded by vast, open savannas...
0:01:42 > 0:01:46..mile after mile of rich, grass-covered plains.
0:01:55 > 0:02:00Living on the border between forest and savanna means the chimps
0:02:00 > 0:02:05sometimes venture into this new and exciting habitat in search of food.
0:02:12 > 0:02:14But they don't feel comfortable in the open grasslands,
0:02:14 > 0:02:20so only forage for a few hours at a time before returning to the forest.
0:02:26 > 0:02:29However, for countless other species, this new habitat,
0:02:29 > 0:02:34the East African plains, has become fundamental to their survival.
0:02:34 > 0:02:39So how did this part of Africa change so dramatically?
0:02:41 > 0:02:4530 million years ago, when the jungle still shrouded the continent,
0:02:45 > 0:02:50a vast plume of molten lava pushed up beneath the plateau of East Africa.
0:02:54 > 0:02:57The Earth's crust cracked under the strain,
0:02:57 > 0:03:00creating Africa's Great Rift.
0:03:10 > 0:03:13Great volcanoes sprang up along the rift,
0:03:13 > 0:03:14and triggered a chain of events
0:03:14 > 0:03:17that changed the face of the landscape for ever.
0:03:20 > 0:03:22RUMBLING
0:03:27 > 0:03:32Ol Doinyo Lengai is still an active volcano.
0:03:32 > 0:03:35Its Masai name means "Mountain of the Gods".
0:03:36 > 0:03:41Its latest eruption covered the plains below in a blanket of thick ash.
0:04:10 > 0:04:13Ash has a profound effect on the surrounding vegetation.
0:04:13 > 0:04:16It dries harder than concrete.
0:04:16 > 0:04:20It's so solid that tree roots struggle to grow through it.
0:04:38 > 0:04:40Huge swathes of East Africa's Great Rift
0:04:40 > 0:04:43are covered in tree-resistant volcanic ash...
0:04:45 > 0:04:50..stretching on the east side from Tanzania into northern Kenya,
0:04:50 > 0:04:54and along the arm of the shorter Western Rift up the valley floor of Uganda.
0:05:17 > 0:05:22The rising rift valley not only created towering volcanoes,
0:05:22 > 0:05:25it forced up great chains of mountains like these,
0:05:25 > 0:05:28the mighty Ruwenzori.
0:05:29 > 0:05:32They stand three miles high,
0:05:32 > 0:05:34and like all the great highlands of the Rift,
0:05:34 > 0:05:38they have a huge effect on the local weather
0:05:38 > 0:05:41and, in turn, the surrounding vegetation.
0:05:59 > 0:06:03Mist and cloud rolls in from the drenched jungles of the Congo Basin
0:06:03 > 0:06:06that lie directly west of the Ruwenzori.
0:06:06 > 0:06:10Warm, moist air rises up the mountains.
0:06:10 > 0:06:15As it does, it cools, so most of the moisture falls on the slopes,
0:06:15 > 0:06:18and little rain reaches the plains to the east.
0:06:19 > 0:06:25It's the Rift's unique combination of restricted rain and volcanic ash
0:06:25 > 0:06:27that keeps the forests at bay.
0:06:29 > 0:06:33But the space left behind is now a battleground.
0:06:34 > 0:06:39Two determined colonisers fight to stake their claim on the plains.
0:06:41 > 0:06:45One competitor is rather small and unassuming -
0:06:45 > 0:06:47grass...
0:06:51 > 0:06:53RUSTLING
0:06:54 > 0:06:59..its challenger the only tree that still holds out for its place in the savannas...
0:07:00 > 0:07:04..the thorn tree of Africa - the acacia.
0:07:05 > 0:07:08It's able to cope because its shallow roots
0:07:08 > 0:07:13can extract any moisture from the soil above the hard ash pan...
0:07:15 > 0:07:18..and its tiny leaves reduce water lost by evaporation.
0:07:22 > 0:07:25It's so successful, it can grow six metres tall.
0:07:29 > 0:07:31But it has a predator to match.
0:07:37 > 0:07:40The acacia's small leaves are nutritious enough
0:07:40 > 0:07:42to support the world's tallest antelope...
0:07:44 > 0:07:47..lofty enough to exploit a niche that no others can reach.
0:07:57 > 0:08:01But the acacia crown is not only attacked from the top down,
0:08:01 > 0:08:04but also from the bottom up.
0:08:08 > 0:08:11The gerenuk has a skeleton that's adapted
0:08:11 > 0:08:15to enable it to spend all day standing on its hind legs.
0:08:22 > 0:08:25But height isn't the only key to unlock the acacia's defences.
0:08:27 > 0:08:30The dik-dik is one of Africa's shortest antelopes.
0:08:33 > 0:08:36It can't reach the high crown, and at ground level,
0:08:36 > 0:08:38the acacia thorns are at their fiercest.
0:08:42 > 0:08:46But the dik-dik's tiny head fits perfectly between the spikes,
0:08:46 > 0:08:50and so the acacia is attacked from every angle.
0:08:52 > 0:08:56The acacia can just about cope with the impact of nibblers like these,
0:08:56 > 0:09:00but there's one heavyweight that does more than just snack.
0:09:00 > 0:09:03LOW-PITCHED RUMBLING
0:09:12 > 0:09:15Seedling acacias are simply annihilated
0:09:15 > 0:09:18by the world's heaviest vegetarian.
0:09:18 > 0:09:20But adult trees aren't safe, either.
0:09:22 > 0:09:26The elephant's trunk is sensitive enough to select individual leaves...
0:09:27 > 0:09:30..but strong enough to rip off entire branches.
0:09:39 > 0:09:44The combination of tusk and trunk makes short work of heavy wood...
0:09:49 > 0:09:53..and a three-tonne body makes an effective bulldozer.
0:10:05 > 0:10:08A single African elephant can flatten a tree a day.
0:10:14 > 0:10:19And in the savannas of the Rift, the herds number over 150,000...
0:10:20 > 0:10:24..capable of wiping out entire acacia woodlands.
0:10:26 > 0:10:31Landscape gardening on this scale plays an important role
0:10:31 > 0:10:34in helping the acacia's competitor, grass.
0:10:39 > 0:10:44Grass makes up over 50% of an elephant's diet, so it's in their own interests
0:10:44 > 0:10:49to clear the trees and maintain space for grass to grow.
0:10:56 > 0:11:00Grass, unlike other plants, grows from its roots instead of the tip.
0:11:02 > 0:11:05This gives it astonishing powers of regeneration.
0:11:05 > 0:11:09It also means it can be almost constantly cropped -
0:11:09 > 0:11:12a never-ending supply of food.
0:11:20 > 0:11:24This indestructible plant has taken over the Rift Valley plains.
0:11:24 > 0:11:27It supports the greatest numbers and diversity
0:11:27 > 0:11:29of large grazers in the world.
0:11:32 > 0:11:35SNORTING
0:11:37 > 0:11:38But there is a downside.
0:11:38 > 0:11:44Grass is hard to process, so grazers have to consume vast amounts.
0:11:44 > 0:11:49That means big guts, and big guts need a big body.
0:11:52 > 0:11:57A diet of grass also means eating for up to 16 hours per day,
0:11:57 > 0:12:01and that leaves little time for the other important tasks.
0:12:04 > 0:12:05These are Uganda kob,
0:12:05 > 0:12:09the most abundant antelope in the Western Rift Valley.
0:12:09 > 0:12:14Somehow they find time to indulge in a surprisingly complex mating ritual.
0:12:17 > 0:12:22The kob have a dedicated mating ground, known as a lek.
0:12:22 > 0:12:25It's where males gather to flaunt themselves,
0:12:25 > 0:12:27and the females turn up to pick a mate.
0:12:51 > 0:12:54The males want to hold the best spot.
0:12:54 > 0:12:56To win it, they have to fight.
0:13:21 > 0:13:23It's all to impress the ladies,
0:13:23 > 0:13:26who are very picky when it comes to choosing the right mate.
0:14:16 > 0:14:19The females are after the buck with the best blood -
0:14:19 > 0:14:22the strongest male, holding the most coveted position
0:14:22 > 0:14:25right in the middle of the lek.
0:14:27 > 0:14:30The female chooses her mate, and then allows him
0:14:30 > 0:14:34to test her scent for hormones to confirm she's ready to mate.
0:14:37 > 0:14:41A female comes into season every 20 days or so,
0:14:41 > 0:14:43but is only receptive for a couple of hours,
0:14:43 > 0:14:46so there's not much time for flirting.
0:14:59 > 0:15:02Job done. The exchange of genes is complete.
0:15:02 > 0:15:04WHISTLING CALL
0:15:05 > 0:15:06CALLS AGAIN
0:15:08 > 0:15:12Now the female can relax under the protection of her champion.
0:15:14 > 0:15:16There is a selfish reason behind her choice.
0:15:16 > 0:15:20The middle of the lek is actually the safest spot,
0:15:20 > 0:15:23as a concentration of distracted antelope
0:15:23 > 0:15:26attracts the inevitable antelope eaters.
0:15:33 > 0:15:36Adult lions hunt best working as a pride,
0:15:36 > 0:15:39but this single mother is alone,
0:15:39 > 0:15:44so providing for her family of three teenage cubs is all down to her.
0:15:45 > 0:15:48PLAYFUL GROWLING
0:15:49 > 0:15:50WHISTLES
0:15:50 > 0:15:54Kob are fast, with excellent eyesight,
0:15:54 > 0:15:58and so during the day, catching one is extremely tricky.
0:16:01 > 0:16:05But as night falls, the advantage swings to the hunter.
0:16:11 > 0:16:13LION ROARS
0:16:15 > 0:16:16ROAR REPEATED
0:16:29 > 0:16:32For the mother lioness, hunting is a serious business...
0:16:34 > 0:16:37..best done without her three boisterous cubs.
0:16:46 > 0:16:51The mother wears a radio collar so scientists can track her movements,
0:16:51 > 0:16:53but it doesn't hinder her hunting.
0:16:58 > 0:17:00In the pitch black of the moonless night,
0:17:00 > 0:17:04both the kob and lioness are reduced to near blindness.
0:17:06 > 0:17:10They can smell each other, but the lioness can't pinpoint a target
0:17:10 > 0:17:12unless it makes a sound.
0:17:13 > 0:17:19So as long as the kob hold their nerve and don't break cover, they'll be safe.
0:17:27 > 0:17:31Meanwhile, the hungry and impatient cubs wander into trouble.
0:17:36 > 0:17:38SNORTING
0:17:49 > 0:17:51BUFFALO SNORTS
0:17:56 > 0:17:58COUGHING ROAR
0:17:58 > 0:18:02HUFFING AND SNORTING
0:18:21 > 0:18:26The three cubs might look dangerous, but they are only ten months old
0:18:26 > 0:18:28and they won't learn to hunt properly until they're two.
0:18:30 > 0:18:33They're no match for these buffalo,
0:18:33 > 0:18:37but the opportunity for stalking practice is too good to miss.
0:18:56 > 0:18:58Meanwhile, their mother is on to something.
0:19:25 > 0:19:27She digs down almost a metre.
0:19:36 > 0:19:40SHE GROWLS
0:19:41 > 0:19:45After a huge effort, she only pulls out a tiny meal -
0:19:45 > 0:19:47barely a mouthful.
0:19:53 > 0:19:57But satisfying hunger is not on this mother's agenda tonight.
0:20:01 > 0:20:06These warthog piglets are a perfect size for the cubs to practise killing.
0:20:14 > 0:20:17LION GROWLS AND PIGLET SQUEAKS
0:20:18 > 0:20:20PIGLET SQUEALS
0:20:36 > 0:20:37SQUEALING
0:20:37 > 0:20:41She pulls out six and saves them all for her young.
0:20:44 > 0:20:47The sooner the cubs learn to hunt,
0:20:47 > 0:20:49the sooner they'll be able to help their mother.
0:20:58 > 0:21:01Ambushing prey at night is very effective,
0:21:01 > 0:21:04but it's not the only way for a cat to catch a meal.
0:21:25 > 0:21:29The cheetah is the fastest runner on the planet,
0:21:29 > 0:21:32but here, speed is no good without stealth.
0:21:35 > 0:21:39He must use camouflage to creep up on his target.
0:21:55 > 0:21:59With only the grass as cover, he can't get close enough for a sprint.
0:21:59 > 0:22:03and as the hartebeest is one of Africa's fastest antelopes,
0:22:03 > 0:22:06from this distance he has no chance in a straight race.
0:22:24 > 0:22:26But it might still be worth a go.
0:23:04 > 0:23:08Unfortunately for him, they are all fit and well.
0:23:16 > 0:23:21A full sprint is heavy work for a cheetah under the hot sun.
0:23:21 > 0:23:24He'll need time to recover before he can try again.
0:23:36 > 0:23:38Antelope like this topi use the long grass
0:23:38 > 0:23:41to hide their babies from predators.
0:23:42 > 0:23:45If they stay still they won't be found.
0:23:56 > 0:23:58But what if you want to be seen?
0:23:58 > 0:24:02Then long grass can be rather a nuisance.
0:24:24 > 0:24:29This male widow bird has prepared a dance floor to seduce a female.
0:24:30 > 0:24:33But first, he needs to get her attention.
0:24:35 > 0:24:39The modestly clad females are currently on the fence.
0:24:42 > 0:24:45When one flies in for a closer look...
0:24:46 > 0:24:47..a male gives it all he's got.
0:25:35 > 0:25:38The Rift's grasslands bake beneath the African sun.
0:25:44 > 0:25:47The long grass can become very dry,
0:25:47 > 0:25:52and that makes it vulnerable to one of nature's most powerful forces...
0:25:55 > 0:25:57CRACKLING
0:26:02 > 0:26:04..fire.
0:26:17 > 0:26:24Thousands of tonnes of dry grass is enough to fuel a blazing inferno.
0:26:41 > 0:26:44But the flames can provide a feast.
0:26:44 > 0:26:46BIRDS CHIRP
0:26:46 > 0:26:50Migrating sand martins brave the smoke to take advantage
0:26:50 > 0:26:53of the tiny insects that flee the flames...
0:26:55 > 0:26:56..a welcome windfall
0:26:56 > 0:27:00to a bird on a 1,000-mile journey from Africa to Europe.
0:27:35 > 0:27:37This looks like devastation.
0:27:37 > 0:27:42The grass has been burnt away, and so have the seedling trees.
0:27:42 > 0:27:47But because grasses store energy underground in their roots,
0:27:47 > 0:27:51within days, new sprouts push through the fertile ash.
0:27:55 > 0:27:59Grass may be tough enough to survive even the hottest fire...
0:28:01 > 0:28:05..but there is one force of nature here that grass cannot defend against.
0:28:05 > 0:28:08It's an extraordinary creature,
0:28:08 > 0:28:11and it only comes out at night.
0:28:17 > 0:28:21A hippopotamus has a mouth half a metre wide,
0:28:21 > 0:28:25built for devouring grass - 40 kilograms in one sitting.
0:28:27 > 0:28:29A fussy eater, it only likes short grass,
0:28:29 > 0:28:32which it tears up with great lips.
0:28:46 > 0:28:50Hippopotamus roam for miles between dusk and dawn
0:28:50 > 0:28:52in search of good grazing.
0:28:53 > 0:28:56But there's a limit to their range, and they must turn around
0:28:56 > 0:29:00and head back to water before the sun rises.
0:29:04 > 0:29:06RHYTHMIC GRUNTING
0:29:20 > 0:29:24RHYTHMIC GRUNTING
0:29:41 > 0:29:44The still, shallow waters bear their great weight.
0:29:46 > 0:29:51Now they relax, snooze, and socialise in comfort.
0:30:13 > 0:30:16Mzima Springs lie in the Eastern Rift,
0:30:16 > 0:30:21a source of water filtered through ancient Rift Valley lava that never dries up.
0:30:27 > 0:30:31This is a haven for a small population of hippo,
0:30:31 > 0:30:35who graze the savanna in a ten-mile radius around the spring.
0:30:35 > 0:30:39But now the surrounding area is in the deathly grip of drought.
0:30:41 > 0:30:44With no rain, the grass has stopped growing.
0:30:46 > 0:30:51Like all hippos, the Mzima herd are bound to their pool,
0:30:51 > 0:30:54so can't escape to search for pastures new.
0:31:12 > 0:31:16Before long, the hippos will eat everything within range,
0:31:16 > 0:31:19and that will create a disaster.
0:31:20 > 0:31:25They brave the sun in a desperate search for food, but to no avail.
0:31:30 > 0:31:34Weakened, they sicken and die...
0:31:47 > 0:31:50..but not before they have reduced this savanna to a dust bowl.
0:31:56 > 0:31:58The topsoil has blown away,
0:31:58 > 0:32:01and even the roots of the grasses are destroyed.
0:32:03 > 0:32:08It will take this part of the Great Rift Valley many years to recover.
0:32:24 > 0:32:29The rain shadow of the Rift Valley makes the grasslands extremely dry...
0:32:31 > 0:32:36..but just enough rain makes it across the mountains to keep the grass alive.
0:32:38 > 0:32:41THUNDER CRASHES AND ROLLS
0:33:27 > 0:33:29THUNDER RUMBLES
0:33:35 > 0:33:38Not everyone enjoys the rain.
0:34:28 > 0:34:33But for the Uganda kob, it's a joy not to feel plagued by hunger or thirst.
0:35:09 > 0:35:14When the rain clouds make it across the mountains of the Western Rift,
0:35:14 > 0:35:16they bring the grasslands exploding to life.
0:35:16 > 0:35:19GRUNTING
0:35:19 > 0:35:22THUNDER RUMBLES
0:35:36 > 0:35:41The prevailing winds that bring the rain move in a north-south cycle
0:35:41 > 0:35:43up and down the continent.
0:35:44 > 0:35:48The resulting wet seasons bring intense downpours,
0:35:48 > 0:35:50but not to everywhere at once.
0:36:00 > 0:36:03These isolated rains mean that some animals
0:36:03 > 0:36:07have to run for thousands of miles in search of freshly grown grass.
0:36:11 > 0:36:13LOWING
0:36:37 > 0:36:40Every year, almost two million wildebeest
0:36:40 > 0:36:42follow the thunder clouds like storm chasers,
0:36:42 > 0:36:46trekking from the Serengeti to the Masai Mara.
0:36:52 > 0:36:56And in their wake comes Thomson's gazelle.
0:36:56 > 0:37:00Tommies are one of the smaller antelope found in the Rift savannas.
0:37:00 > 0:37:04Their size makes them very vulnerable to predators.
0:37:20 > 0:37:24These cheetahs have been waiting for the tommies for months.
0:37:24 > 0:37:27Now's their chance to eat as much as they can.
0:37:34 > 0:37:36FLIES BUZZ
0:37:38 > 0:37:41Each cat has a different style of hunt,
0:37:41 > 0:37:43but stealth is always key
0:37:43 > 0:37:46if they are to stand a chance against the fleet-footed tommy.
0:38:26 > 0:38:29The cheetah is faster,
0:38:29 > 0:38:32but the tommy can turn quicker and has more stamina.
0:38:46 > 0:38:49Each chase lasts only 300 metres at most,
0:38:49 > 0:38:53but those few seconds decide the fate of the tommy.
0:38:57 > 0:38:59TOMMY BLEATS
0:38:59 > 0:39:01THEY SNORT
0:39:09 > 0:39:13In a fair chase, the cheetah has a 50/50 chance of catching a meal -
0:39:13 > 0:39:17the highest success rate of all the African big cats.
0:40:06 > 0:40:09An unlucky stumble is enough to seal a tommy's fate.
0:40:09 > 0:40:11BLEATS
0:40:19 > 0:40:21FLIES BUZZ
0:40:37 > 0:40:42For savanna herbivores, living here has a price.
0:40:43 > 0:40:46But the richness of these grasslands make it worth the risk,
0:40:46 > 0:40:51and the rewards are so tempting that even a primate has made them home.
0:40:53 > 0:40:56Primates are normally forest dwellers.
0:40:56 > 0:40:59To flourish on the open plains has been a hard step to take.
0:41:04 > 0:41:06The olive baboon is one of very few monkeys
0:41:06 > 0:41:09to make a success of savanna life.
0:41:13 > 0:41:17For a small animal on the plains, there's safety in numbers.
0:41:31 > 0:41:34Living in a large troop requires organisation.
0:41:36 > 0:41:38To avoid constant squabbling,
0:41:38 > 0:41:41the baboons have developed a sophisticated social order.
0:41:44 > 0:41:48Regular grooming is not just for reasons of hygiene.
0:41:48 > 0:41:52The constant contact is important for social bonding.
0:41:52 > 0:41:55It's a good way to make friends.
0:42:01 > 0:42:03Males are tough enough to look after themselves,
0:42:03 > 0:42:05and come and go as they choose.
0:42:07 > 0:42:10But mothers and babies must stick together.
0:42:16 > 0:42:20The little ones are very important for establishing rank and order.
0:42:27 > 0:42:29BABY SQUEALS
0:42:32 > 0:42:37This baby is being used to keep its mother in her place.
0:42:37 > 0:42:41The mother must sit and watch it being treated roughly
0:42:41 > 0:42:43by the more dominant female
0:42:43 > 0:42:45if she wants to stay within the safety of the troop.
0:42:45 > 0:42:50Her low rank means she has no choice but to tolerate her oppressor.
0:43:11 > 0:43:15Whilst the inequalities of baboon society might seem harsh,
0:43:15 > 0:43:19this system of complex relationships and communication
0:43:19 > 0:43:22is essential for their survival in the savanna.
0:43:22 > 0:43:24UNDERDOG SQUEALS
0:43:47 > 0:43:49When darkness falls,
0:43:49 > 0:43:51the baboons' sharp senses fail them
0:43:51 > 0:43:54and they must return to the trees to sleep,
0:43:54 > 0:43:56safe from night prowlers.
0:44:16 > 0:44:18Baboon behaviour can give an insight
0:44:18 > 0:44:22into what it takes for any primate to survive on the savanna.
0:44:25 > 0:44:30Our own primate ancestors may have coped on the open plains in a similar way.
0:44:33 > 0:44:36But there's another primate in the Rift Valley
0:44:36 > 0:44:39that can tell us more about our ancient history.
0:44:55 > 0:45:00In Uganda's Kibale Forest, chimps are bedding down for the night.
0:45:04 > 0:45:09They bend branches into a nest for a restful night's sleep,
0:45:09 > 0:45:11just as our common ancestors might have done
0:45:11 > 0:45:13over eight million years ago.
0:45:28 > 0:45:32Our ancient relatives living in the primeval jungles of Africa
0:45:32 > 0:45:37shared the well-developed brains and nimble hands of modern chimpanzees.
0:45:52 > 0:45:56But at the same time that the Great Rift Valley formed
0:45:56 > 0:45:59and the forests were pushed back, our ancestors moved out
0:45:59 > 0:46:04into the savannas, leaving their chimpanzee relatives behind.
0:46:12 > 0:46:16Chimpanzees are still poorly adapted for savanna life.
0:46:20 > 0:46:23Their bodies are too squat to see over the long grass,
0:46:23 > 0:46:26and their limbs aren't built for speed
0:46:26 > 0:46:29like an antelope that can outrun predators.
0:46:44 > 0:46:49But like humans today, our ancestors walked tall on two legs
0:46:49 > 0:46:54and had hands free to carry weapons for hunting and defence.
0:46:58 > 0:47:01More meat in our diet meant our brains expanded
0:47:01 > 0:47:06and our societies grew ever more complex and powerful.
0:47:08 > 0:47:12In time, we became masters of the savanna.
0:47:14 > 0:47:18We owe our extraordinary success as a species to this place -
0:47:18 > 0:47:20the cradle of humanity...
0:47:22 > 0:47:24..in Africa's Great Rift Valley.
0:47:43 > 0:47:47Filming sleeping chimps in the forests of Kibale National Park
0:47:47 > 0:47:50presented some serious challenges for the crew.
0:47:52 > 0:47:56They had to climb huge tropical trees in the pitch dark.
0:47:58 > 0:48:00But first they had to find the chimps,
0:48:00 > 0:48:04and that meant trekking for miles through the jungle
0:48:04 > 0:48:06with some serious baggage.
0:48:15 > 0:48:18Once they found them, they had to wait until dark,
0:48:18 > 0:48:20when the chimps had picked their nesting spots.
0:48:25 > 0:48:29Their mission was to climb into the canopy and film the chimps sleeping -
0:48:29 > 0:48:30from above.
0:48:30 > 0:48:33But this meant climbing in the dark,
0:48:33 > 0:48:35which would put the crew to the test.
0:48:37 > 0:48:42Chimps nest anywhere between 4 and 40 metres off the ground,
0:48:42 > 0:48:45and never in the same place twice.
0:48:45 > 0:48:48The first task is to find a tree suitable for climbing
0:48:48 > 0:48:50without disturbing the chimps.
0:48:52 > 0:48:53When darkness falls,
0:48:53 > 0:48:58the team use image-intensifying scopes to look into the canopy.
0:48:58 > 0:49:02The final say goes to tree-climbing expert Tim Fogg.
0:49:02 > 0:49:04- WHISPERS:- It's not good at all.
0:49:04 > 0:49:09There are no trees which give us a view of the nests tonight.
0:49:09 > 0:49:14It's just really frustrating, because they're...they're all here -
0:49:14 > 0:49:17there's about six or seven nests right above us
0:49:17 > 0:49:19and a bit off to that side,
0:49:19 > 0:49:21but there's no big trees overlooking them,
0:49:21 > 0:49:25so we're stuck... stuck on climbing tonight.
0:49:25 > 0:49:28I think we'll probably just do ground shots of them.
0:49:28 > 0:49:31I can't see anything I can get up that's any use at all.
0:49:31 > 0:49:35Grounded for the night, they set up the kit on the forest floor.
0:49:37 > 0:49:42Cameraman Martin Dohrn has developed a brand-new night-vision camera
0:49:42 > 0:49:46that can see without any artificial light at all.
0:49:46 > 0:49:49It's called a starlight camera
0:49:49 > 0:49:52and it uses an image intensifier that means it can capture
0:49:52 > 0:49:56unique animal behaviour not usually visible to the human eye.
0:49:58 > 0:50:04- WHISPERS:- Amazingly, we have now got a shot of a sleeping chimpanzee.
0:50:04 > 0:50:06It's not a great shot,
0:50:06 > 0:50:08it's not a remarkable shot,
0:50:08 > 0:50:11but it is probably the first time ever
0:50:11 > 0:50:16that a chimpanzee has been filmed asleep in its tree nest.
0:50:18 > 0:50:23This is actually kind of like Big Brother, only more interesting.
0:50:25 > 0:50:29But the team aren't satisfied with filming from the ground.
0:50:31 > 0:50:33Encouraged by their terrestrial success,
0:50:33 > 0:50:36the next night sees the crew stalk the chimps
0:50:36 > 0:50:38to a much better location for climbing.
0:50:41 > 0:50:44There is a big tree right in the back there.
0:50:44 > 0:50:47It's just whether we'd get a view through.
0:50:47 > 0:50:50The big tree behind that. There's a much higher tree behind that.
0:50:50 > 0:50:51Yeah, I think so.
0:50:51 > 0:50:55Tim aims his catapult at a branch high in the canopy.
0:50:58 > 0:51:00OK. I think I got that.
0:51:02 > 0:51:04Chimps are super-sensitive in the night,
0:51:04 > 0:51:08and no-one knows how they'll react to a film crew swinging above them.
0:51:09 > 0:51:12CHIMPS SHRIEK
0:51:16 > 0:51:20Getting the ropes up is just the start of the climbing process.
0:51:21 > 0:51:24We've got to load-test the ropes now,
0:51:24 > 0:51:27and what I'm dreading is that when we pull...
0:51:27 > 0:51:29We're going to hang two of us on the ropes
0:51:29 > 0:51:31to see if the branches will hold it,
0:51:31 > 0:51:33and if it breaks,
0:51:33 > 0:51:37I don't know, well, it's going to cause mayhem with the chimps.
0:51:37 > 0:51:39It's... But we have to try.
0:51:39 > 0:51:42Safety-wise, I can't go up there without seeing
0:51:42 > 0:51:45that the branches are strong enough to take me, so that's it.
0:51:52 > 0:51:54Satisfied the ropes are strong enough,
0:51:54 > 0:51:59Tim heads up the tree with no idea what he might find in the jungle canopy.
0:52:05 > 0:52:10OK, well, it didn't go to plan, really, because, er... I started climbing...
0:52:10 > 0:52:14The ropes went in really easily, amazingly, and then I started to climb,
0:52:14 > 0:52:21and as soon as I hit some foliage, I started getting the odd little itch.
0:52:21 > 0:52:25And by the time I got through the first bit of foliage, I was flailing.
0:52:25 > 0:52:29I was covered in tiny little ants that were just on a suicide mission.
0:52:29 > 0:52:32They were just eating me alive.
0:52:32 > 0:52:34And I tried to climb on,
0:52:34 > 0:52:38and I got a bit further up, and they were still going at me.
0:52:38 > 0:52:41They started getting in my sleeves
0:52:41 > 0:52:43and then all around my waist,
0:52:43 > 0:52:46and then they started getting all round my neck.
0:52:46 > 0:52:48They got in my helmet as well, so at one point
0:52:48 > 0:52:50I had to get my helmet off and try and shake them out.
0:52:50 > 0:52:52Nasty little things.
0:52:55 > 0:53:00Undeterred by creepy-crawlies, Tim and the team head back to the jungle
0:53:00 > 0:53:02hoping for a more successful climb.
0:53:02 > 0:53:05CHIMPS BARK
0:53:07 > 0:53:09- WHISPERS:- It's incredibly close.
0:53:09 > 0:53:16It's about...maybe six metres above and just behind me.
0:53:16 > 0:53:18The tree I'm going for is just over that way.
0:53:18 > 0:53:23That should give us a good shot down on him...in his nest.
0:53:23 > 0:53:26That's what we're aiming for.
0:53:26 > 0:53:29I've noticed that I'm right on a big pile of elephant-do.
0:53:33 > 0:53:36Just putting on some insect repellent.
0:53:36 > 0:53:38Then I'm going to tape my sleeves up
0:53:38 > 0:53:44because I want to try and keep the ants out if they're there this time.
0:53:49 > 0:53:54Geared up once again, Tim heads up to check the view.
0:53:58 > 0:54:01Martin prepares to record from the ground,
0:54:01 > 0:54:04and tree-climbing specialist cameraman Nick Turner
0:54:04 > 0:54:07can finally take to the trees.
0:54:11 > 0:54:14And right behind him, Martin sends up a precious cargo.
0:54:18 > 0:54:23The world's only HD starlight camera is in the bag,
0:54:23 > 0:54:27so let's not stand under it in case it falls.
0:54:34 > 0:54:38It's a real mess up here with gear, I mean, we know where everything is,
0:54:38 > 0:54:44but it's just everything has to be tied on so we don't drop anything.
0:54:44 > 0:54:47There's cables and tapes and ropes and karabiners all over the place.
0:54:47 > 0:54:51We're about 15 metres off the deck
0:54:51 > 0:54:57and the chimps are about 10 to 12 metres away from us, down slightly.
0:54:57 > 0:55:00The team are close to success.
0:55:00 > 0:55:02But before they can even take a shot...
0:55:02 > 0:55:04RATTLING
0:55:04 > 0:55:06What's going on?
0:55:06 > 0:55:08..the armed ranger has heard something.
0:55:12 > 0:55:16It seems we've got some elephants coming close to us
0:55:16 > 0:55:19and we're not sure what to do or what they're going to do.
0:55:19 > 0:55:23So we're leaving our lights on so the elephants can see us
0:55:23 > 0:55:25and don't get suddenly surprised.
0:55:25 > 0:55:29I'm pretty sure they'll just try and stay away from us...
0:55:29 > 0:55:31but you never know.
0:55:31 > 0:55:34Elephants have very poor eyesight in the dark.
0:55:34 > 0:55:39If they come across the crew, they might take fright and attack.
0:55:39 > 0:55:42We think that might be an elephant.
0:55:42 > 0:55:45- ON RADIO:- We should have a B-plan here.
0:55:45 > 0:55:50They're probably curious rather than dangerous, but...
0:55:50 > 0:55:53I'm not an expert in elephant behaviour.
0:55:53 > 0:55:57My plan is to run behind the tree and hide.
0:55:57 > 0:55:59Possibly even...
0:55:59 > 0:56:01try and climb up into it.
0:56:01 > 0:56:02Probably get up there.
0:56:04 > 0:56:08I'm afraid that's the best I can offer.
0:56:08 > 0:56:10You're probably quite safe up there.
0:56:10 > 0:56:12I don't think they'd be able to knock the tree down
0:56:12 > 0:56:15but what I'll make sure I do is I'll set the thing in
0:56:15 > 0:56:18to record before I go, so...
0:56:18 > 0:56:22I can't imagine the chimps will be too happy about having elephants
0:56:22 > 0:56:24running around like that.
0:56:25 > 0:56:29With nowhere to hide, the crew carries on
0:56:29 > 0:56:31and the guard comes back with news.
0:56:33 > 0:56:35There's a chimpanzee.
0:56:35 > 0:56:39- It's a chimpanzee. Are you sure? - Yes, of course.
0:56:41 > 0:56:44The chimps have been playing tricks on the crew.
0:56:44 > 0:56:47So once the fear of elephants is passed,
0:56:47 > 0:56:51they can get on and film the nesting chimps from high in the canopy.
0:57:04 > 0:57:08Martin's starlight camera gives us a grainy black-and-white image,
0:57:08 > 0:57:10but allows us to see into the night
0:57:10 > 0:57:14and watch wildlife at their most intimate moments.
0:57:31 > 0:57:33It showed for the very first time
0:57:33 > 0:57:36how these great apes snuggle down in the treetops
0:57:36 > 0:57:42and how it's possible to have a comfortable night's sleep in the jungle.
0:58:06 > 0:58:09Subtitles by Red Bee Media Ltd
0:58:09 > 0:58:12E-mail subtitling@bbc.co.uk