"Our planet is a place of constant change." "Each year, the seasons shift and life is transformed." "But there are places where the changes are so epic in scale they can be seen from space." "In this series, we reveal three of the most miraculous transformations." "The islands of Svalbard - within a few weeks, frozen wastelands burst into life." "The African Okavango - a desert transforms into a magical waterworld." "And the mysterious forests of New England - erupting in a blaze of seasonal colour." "Life finds the most ingenious and surprising ways to thrive... ..in the world's fastest-changing landscapes." "New England - home to the most colourful forest in America." "Stretching across six states..." "..from Maine in the north to Connecticut in the south." "Every year, millions of people flock here to witness one of the planet's greatest spectacles, known here as the fall..." "..when billions of trees explode into a riot of red, orange and gold." "There's nowhere else on Earth quite like it." "But despite this beauty, there's a battle raging." "One that holds the secret to this magical forest's most flamboyant display." "The story of the fall begins while winter still has a grip on the forest." "17 billion trees, rich with maples and oaks, wait in suspended animation." "Amongst them, many of New England's animals are hibernating from the cold." "But America's tallest mammal remains at large." "Moose survive by chewing on twigs." "Their calves will be born in just two months... ..and their survival will depend on the same chain of events that will fuel the forest's climax of colour." "As the weather warms, water courses through every tree..." "..and it picks up sugar stored in the wood." "This liquid energy is the life force of the entire forest." "It's so rich with sugar that maple syrup is made from it." "The spring sunshine warms the land... ..and the sugar surges faster..." "..fuelling the growth of nutrient-rich buds." "These tiny packages contain everything needed to build a leaf." "But from this point on, each tree faces a battle." "All across New England, twigs are coming to life." "These creatures spend the winter disguised as twigs." "Looper caterpillars." "They awake with the warmth and immediately begin to seek out the freshest buds, on a hunt for sugar." "Nearby, hundreds of baby tent caterpillars hatch from their winter eggs." "Each smaller than a grain of rice." "They join the feast." "Swarming along the branches, a torrent of bud destruction." "This is just the first wave in a battle that will escalate through the year." "The buds race to open before they can be attacked." "Gradually, the first flush of green spreads across the forest." "But it will be a few weeks before the leaves are fully expanded..." "..and they will need a constant supply of sugary sap from under the bark." "In some trees, that sap is also at risk." "The warming spring weather attracts an animal with a serious sugar addiction." "TAPPING" "All the way from Mexico, he's one of the first to come back after the trees wake." "The yellow-bellied sapsucker." "His beak hammers six times a second..." "..wounding the tree deeply... ..and chiselling into the vessels carrying the precious sugar." "His feathery tongue quickly laps up the weeping liquid." "On this tree last year, he dug hundreds of holes, but now, all the wells are dry." "It's not enough to deter a determined sapsucker." "He can dig as many as 1,000 holes in a season." "And on another tree, he's excavating a nest." "If he finishes it and keeps his wells running sweetly, he could attract the attention of a female." "But there's another bird that could scupper his plans." "A ruby-throated hummingbird." "He's followed the sapsucker all the way from Mexico." "His wings beat 80 times a second, putting him on a calorific knife edge." "The weeping sap is the best source of sugar currently available, and feeding at 15 sips a second, he can quickly drain a well dry." "He's too fast for the sapsucker to chase off..." "..so the sapsucker opens more and more wells." "Eventually, despite the interruption, he finishes off his nest, creating a deep hollow in the tree." "Now, everything is prepared." "Despite relentless attack from birds and insects, the warming weather keeps the trees pumping sap, and, as the day length increases, the leaves continue to inflate." "As the leaves grow, they start to shade the forest floor." "In anticipation, the plants down below wake from their stupor." "The flowers must attract a pollinator before all the light is stolen." "Now, hummingbirds can feed on their favourite source of sugar." "Nectar." "In turn helping to pollinate the flowers." "A looper caterpillar feeds amongst the flowers, too." "He's no longer hiding amongst the twigs." "This master of disguise has a different trick up his sleeve." "Swaying back and forth, he mimics a flower moving in the breeze." "He sticks petals to his back so that he can feed unnoticed by predators." "And there's a whole army of flower arrangers sporting the latest spring fashion!" "As the sun strengthens, the building sap finally forces the leaves to fully unfurl." "As many as 200,000 leaves on every tree." "Together, they grow enough foliage to blanket an area six times the size of New England." "As the leaves expand, they produce one of nature's most powerful chemicals." "Chlorophyll." "This green pigment catches the sun's energy to power a reaction crucial to all life." "Photosynthesis - creating sugar from sunshine." "This sugar is essential for the tree to grow, but it's now in easy reach of New England's hungriest animals." "A moose." "Named by the Native Americans as moosu, "he who strips off", they are leaf-eating machines..." "..and can strip a branch clean in seconds..." "..but the trees can defend themselves." "In response, they flood their leaves with a repulsive chemical called tannin." "So moose must constantly roam to seek out fresh ones." "But this female doesn't want to travel far." "She has twins and they're just two weeks old." "Until now, they've remained hidden in the shade of the forest." "With the leaves now loaded with unpleasant tannins, she needs to find an alternative food source." "She leads the twins away from the cover of the trees for the very first time." "Out here, it's a big, new world." "The mother must stay close." "Another cow and her calf are already enjoying the coolness of the lake." "Moose have the longest legs in North America, which allows her to reach something that other animals can't get to." "It's what makes this lake irresistible." "Water plants." "Just what this mother needs to enrich her milk..." "..because they're packed with nutrients washed out of the leaf litter." "The twins will increase in weight tenfold over the next few months." "It's not just the females who need the nutrients." "Big bulls are here to feed for a different reason." "To grow their antlers, one of the fastest-growing animal organs." "They keep a safe distance." "Neither wants to damage his prized possessions." "Because their racks are not just for fighting." "Male moose concentrate on looking good... and attracting females." "With females watching on, it's a chance to show off." "A good try, but at this time of the year, this female's attention is still fully on her calves." "It won't be until the fall that she will be back on the market for a mate." "Late spring, the busiest time for the forest's most notorious tree-eater." "Signs of his appetites surround almost every lake." "The beaver, New England's most industrious animal." "His lodge is his castle, built of sticks and hardened by mud." "But his masterpiece is his dam." "Over 50 metres long and built of thousands of logs and branches." "For 20 years it has held back the water to create a moat - a defence against predators." "But this security comes at a price." "The dam needs constant maintenance." "A leak." "He's going to need supplies." "To avoid being spotted by predators, beavers work under the cover of darkness." "There iron-infused teeth make powerful tools with which they can fell a tree ten inches wide in just a couple of hours." "SNAPPING" "Fixing a leak can take all night and into the morning." "He stirs up mud, using this mortar to seal the cracks." "But fix one leak..." "and another is sure to spread." "A beaver's work is never done." "All this work isn't just for his own security." "MEWING" "In spring, a beaver's lodge is busy with the activity of baby beavers and their sounds as they call for milk." "MEWING AND PURRING" "This is a crucial time to practise using their teeth before they too are unleashed onto the forest." "PURRING" "The beavers of New England fell millions of trees every year." "But surprisingly, it's this that makes them heroes of the forest." "By removing softer trees, they create large open spaces where red maple saplings can take root." "And they leave bigger hardwoods standing, like maples and oaks, with space to spread their branches." "With more leaves to create sugar, trees can grow ten times faster, and their colours in the fall will be much brighter." "Beavers have helped to create a forest rich with maples and oaks." "But 400 years ago, something happened that was to rapidly speed up what the beavers had started." "Clues to this event can be seen threading through the forest." "Stone walls." "240,000 miles of them." "Enough to reach the moon." "In 1620, British settlers landed on these shores." "Attracted by tales of green and pleasant lands... ..they had hoped to create a prosperous life." "What they encountered was an ancient dark forest, creaking with giant trees." "And haunting sounds they had never heard before." "BIRDS SQUAWK" "The trees towered above them, far higher than any they had seen in Britain." "The biggest of them all was the white pine, said to have reached as high as 200 feet." "By royal decree, the King of England claimed every one with a diameter greater than 24 inches." "They were shipped across the Atlantic for use as the masts of the Royal Navy." "The rest were left for settlers." "They felled trees to build homes, churches and mills." "Many animals, like mountain lions and wolves, were wiped out as the wilderness was tamed." "By 1850, almost all of New England's forest had been chopped down, and much of this was turned to farmland, surrounded by stone walls." "But then everything changed as richer farmland and gold was discovered in the west..." "..and many of the settlers chased their fortunes elsewhere." "Towns like Livermore disappeared as quickly as they had been formed." "Slowly, the trees of New England grew around the ruins and reclaimed the land." "This new forest was very different." "By chopping down the old-growth trees, people had given fast-growing maples and oaks a chance to claim the land." "They grew back in greater numbers than ever before, and today they dominate this forest." "From now on, there would be nowhere else more colourful in the fall." "Today those stone walls are highways for one of New England's busiest animals." "The chipmunk." "There can be as many as 15 living in every acre... because New England is a chipmunk paradise." "The stone walls help them to get around the forest and keep an eye out for predators." "And the new forest provides all the acorns and maple seeds a chipmunk can eat." "Today the forest is treasured, and 80% of New England is covered in trees, ensuring the fall remains rich and colourful." "Because vast areas are uninhabited, in many places the sky is dark with little light pollution." "New England is further south than the UK." "But it's dark enough that on special nights the distant northern lights can be seen shining." "The growth of the new forest paved the way for wildlife to move back in, and animals that were once persecuted now thrive here." "DISTANT ANIMAL CALL" "It's the beginning of summer." "And with daytime temperatures now in the mid-20s, it's warm enough to draw out New England's most misunderstood animal." "RATTLING" "A timber rattlesnake." "A creature at home hiding amongst the trees." "It was once so feared, a bounty was placed on its head." "But the timber rattlesnake is making a comeback, with a few hundred now living in these forests." "Using his tongue, a large male seeks the scent of a potential meal." "He's detected a log heavy with the scent of rodents." "Coiled like a spring, he waits." "FAI NT RUSTLI NG" "FAI NT PATTERI NG" "Even one of the fastest hunters on the planet can sometimes be off target." "But he's patient." "15 hours later, he's still in position." "FAINT RUSTLING" "PATTERING" "MOUSE SQUEAKS" "He instantly withdraws his fangs, eager not to damage them." "It won't take long for the venom to kill." "He follows the mouse's scent to claim his prize." "This should satisfy his hunger for a few weeks." "It's the height of summer, and the trees' leaves are working at maximum capacity to turn sunlight into sugar." "This is when they face their greatest battle." "CHOMPING" "Billions of bugs are on the attack." "The trees do everything they can to resist the onslaught." "They increase the concentration of repulsive tannins in the surface of their leaves." "But even this isn't enough to stop one hungry insect." "Only a few millimetres long, this leaf miner is tunnelling under the skin, where he can avoid the bitter tannins and get to the juicy, sweet bits." "Under the safety of the leaf itself, he devours so much green chlorophyll that the leaf can no longer produce the sugar it needs to stay alive." "In just two days, he leaves a trail of destruction, and his appetite shows no signs of slowing." "Most insects are too big to squeeze inside a leaf, so they must be more selective in how they attack." "Many eat carefully between the veins, avoiding areas with higher concentrations of tannins..." "..leaving the leaf skeletonised in their wake." "The bigger caterpillars get, the more they can process the leaves' unpleasant chemicals." "And working en masse, caterpillars can devour a leaf in minutes." "But they themselves could easily fall prey to birds." "So disguise is the key to their success." "Some mimic dangerous New England animals to deter their predators." "Swallowtails have eye spots to look like snakes." "The hag moth caterpillar resembles a big spider." "And the fur of this one makes it tricky for a predator to get to the soft bits." "But the most cunning disguise of all is to mimic the parts of the leaf that they've already eaten." "Many New England caterpillars look like nothing more than leaf damage." "Filling in the gaps with their bodies makes them less visible to birds." "New England is swarming with undercover caterpillars." "But there's one predator that caterpillars can't hide from." "Because here the trees have an ally." "An army is being mobilised." "These are the Allegheny mound ants, and the trees are their hunting grounds." "Like lions in the leaf litter, they hunt in a pack..." "..efficiently trimming the hairs so they can get to the sugary juices..." "..draining the caterpillar dry." "But this isn't food for THEM to eat." "In the warm interiors of their mounds, the summer heat is incubating the next generation." "Caterpillar juice is the perfect nourishment for a growing soldier, supercharged with sugar that the caterpillars stole from the leaves." "Soon they will be ready to help the colony expand." "Every year ants dig miles of tunnels and excavate as much as 12 tonnes in every acre." "This aerates and breaks down the leaf litter, which fertilises the soil." "Trees with rich soil and ant protection produce more sugar, they're brighter, and they will hang on to their leaves for longer during the fall." "Despite the battles raging through the forest, billions of leaves continue to produce sugar." "This is transported down the trunk, where it's stored to replace the tree's reserves." "Each will gain as much as 100kg in weight before the end of the year." "FAI NT TAPPING" "BIRD CALLS" "The yellow-bellied sapsucker has attracted a female, and in their nest they have four young chicks just a few days old." "CHICKS CHEEP" "Their parents bring back food 20 times every hour." "BIRD CALLS" "It's exhausting, keeping up with the demand." "CHICK CHEEPS" "The summer sap is sweeter, and it attracts a swarm of insects." "This is why the father has been obsessively digging wells - because the sap leaking from them is now bait." "And not even the trees' allies, the ants, can resist a nibble of the free-flowing sugar." "CHICK CHEEPS" "For the chicks to grow, they need protein." "Sugar-coated bugs make up two-thirds of their summer diet." "Because of the constant supply of insects, the chicks increase in weight by 16 times in just four weeks." "CHICKS CHEEP" "And they're already learning the art of tapping for themselves." "CHICKS CHEEP" "In three months' time, they will depart the cooling forest for warmer climates in the south." "This will give the trees a chance to repair the damage before the summer ends." "This female rattlesnake has spent three months basking in the sun, but daytime temperatures are now dropping as low as 14 degrees Celsius." "Being cold-blooded, she is the first in the forest to feel a chill in the air as the days draw in." "She's getting too big for her skin, but yawning widely helps to loosen it." "And snags in the leaf litter help her to undress, peeling away the scaly layer." "This lethal hunter is now ready." "In a safe and secure place, specially adapted for filming, she waits." "Through the night, months of preparation comes to an end." "She's given birth to seven tiny rattlesnakes." "Only 20 centimetres long, and already their sharp fangs are fully loaded with potent venom." "Unlike most other snakes, timber rattlesnakes carry their babies inside their bodies to keep them warm." "And there's one more on the way." "The mother's work doesn't end there." "Her maternal bond is strong." "Having the fiercest mother in the forest, there's very little that could threaten these baby snakes." "One by one, they snuggle into the safety of her coils." "It won't be long until the cooling fall weather forces New England's rattlesnakes to lead their babies to underground dens, where they will hibernate as families until the spring." "The shortening days and cooling weather trigger a change in the behaviour of New England's biggest animal." "Male moose have been growing their antlers all year, and now they're dressed to impress." "And finally, the females are open to their advances." "FAINT BELLOW" "But some moose have more luck than others." "SPLASHING" "This younger male has been following a female for weeks in the hope of getting her attention." "It's tiring work, and to make matters worse, she's still caring for a calf." "But with antlers like this, how could she possibly resist?" "He decides to make a bolder move before a bigger bull shows up." "MOOSE SMACKS LI PS" "Lip-smacking makes his intentions clear." "Her scent is irresistible." "Not the response he was hoping for." "Urination gives him a sign that she's still not in the mood." "Even after weeks of trying to court her, persistence doesn't always pay off." "THUNDER RUMBLES" "Fortunately, every year, thanks to the nutrition from the forest, a moose grows a bigger rack." "THUNDER RUMBLES" "And next time, maybe his antlers will be big enough to impress the choosy female." "With the temperature now constantly below ten degrees, the leaves can no longer work efficiently." "And with less than 12 hours of sunshine a day, they have less time to create sugar for the trees." "There comes a point when they are no longer earning their keep, and the tree must start to close down for the winter." "At first, the effects are subtle." "Individual leaves start to turn yellow." "Like tiny factories closing down, the green pigment inside each cell is dismantled." "The tree salvages all that it can, carrying it down in the sap to be stored in the tree's trunk." "The cooling weather quickens the process, until the Midas touch of fall turns entire forests golden." "But this is only just the beginning of the most magical transformation of all." "The fall in New England." "While most trees are already preparing for the winter... ..some also take this opportunity to secure a future for their offspring." "They drop millions of winged maple seeds and acorns." "Many will soon be safely hidden beneath leaf fall to await the nourishing warmth of spring." "But they've been spotted." "Despite the cover, there's one animal who is able to sniff out a fresh nut amongst the leaf litter." "A chipmunk." "His small size means that he's unable to pile on enough body fat to survive hibernation through the winter." "And just when reserves are looking a little thin... ..a new air drop is delivered by the trees." "Perfect timing... ..if he can stockpile enough in his secret caches." "He can squeeze four acorns into his cheek pouches, allowing him to collect up to 160 a day." "It takes a lot of work to amass a big stash." "But there's always one who's less prepared to put in the hours." "A lazy chipmunk." "He's spotted his neighbour's acorn and where it's being hidden." "It's too tempting." "But it's not an easy steal." "SQUEAKING" "This is one chipmunk determined to protect his stash." "The chipmunk is a hero of the forest - because even after all that work, he will forget where he's buried some of his hard-earned treasure." "And protected underground, the seeds have a better chance of germinating." "Whether they are a tree's enemy or an ally, the animals of New England have conspired to make the fall a season of beauty." "And one thing is for sure - in the end, it's the entire forest that wins." "And as the trees make their final preparations for winter, the best is yet to come." "As the temperature drops towards freezing, the trees increase the speed at which they drain the leaves of their goodness." "A magical new chemical is conjured up from within the leaves of the maple and oak trees." "Red anthocyanin." "It keeps the sap flowing for longer as the temperature plummets, so the trees can hold on to their leaves and extract every last drop of sugar." "The reds and oranges join the golds, and together they set the forest ablaze." "From an ocean of green, every tree becomes an individual." "Red maples and oaks burn in shades of red." "Sugar maples glimmer in orange." "And for just a few weeks every year... ..New England is a wonderland of colour." "These colours can be seen from space, spreading across this corner of America like wildfire." "The spectacle is intense, but brief." "As the last of the nutrients and sugars are extracted by the trees, billions of leaves hang on tenterhooks." "All it takes...is a breeze." "It's the last chance for their most persistent enemy to feast." "CHOMPI NG" "Caterpillars..." "in a hungry race against time." "Leaf miners are still feeding as the leaf changes around them." "They eat all that they can before a quick getaway." "Some caterpillars chase the colour through the fall." "The spicebush swallowtail swaps the green costume of summer for a golden coat." "And, having had her fill, she sheds this new skin to form an overwintering pupa that," "like a leaf, fades to brown." "Many other caterpillars turn red and orange in the fall." "And as the leaves lose the last of their sugar, they climb to the edge of a leaf... and take a leap of faith." "Amongst the leaf litter they seek out a refuge from the winter." "In the spring, they will emerge as moths and unleash a new generation of caterpillars onto the forest." "It's the end of October, and the planet's most colourful forest fades as the last leaves fall." "They have given the trees all that they need to survive..." "..until the battles begin again next year." "Our planet is a place of constant change." "Each year, the seasons shift and life is transformed." "But there are places where the changes are so epic in scale they can be seen from space." "In this series, we reveal three of the most miraculous transformations." "The islands of Svalbard - within a few weeks, frozen wastelands burst into life." "The African Okavango - a desert transforms into a magical water-world." "And the mysterious forests of New England erupting in a blaze of seasonal colour." "Life finds the most ingenious and surprising ways to thrive in the world's fastest changing landscapes." "Svalbard - a frozen ice world," "lying far beyond the Northern tip of Norway." "A lonely group of islands, almost at the top of the world." "For four months, because of the tilt of the Earth," "Svalbard is cloaked in darkness, hidden from the life-giving light of the sun." "But every year, a miracle happens here." "As the sun returns," "Svalbard undergoes an extraordinary transformation." "From perpetual darkness to perpetual light." "From frozen ice world to land of vibrant life." "This is the story of how life survives one of the planet's most extreme changes." "WI ND HOWLS" "The Svalbard winter." "A night that lasts for months." "Without the sun's light, nothing can grow..." "..and ferocious winds are dragging temperatures to minus 40 and below." "How can anything survive here?" "One animal is in its element." "A polar bear has been sleeping peacefully through the storm." "Its unique coat reflects heat back into its body just" "like a survival blanket, so it is quite comfortable, even at minus 40." "And remarkably, for the polar bear, these are relatively good times." "The sea ice is at its maximum, connecting the islands of Svalbard to the whole of the Arctic..." "..so the bear can stride out over the frozen ocean, its prey right beneath its feet." "A ringed seal." "Just a metre beneath the bear, but protected by the ice." "Until it needs to breathe." "The seal scrapes out a network of breathing holes dotted about the ice." "It can hold its breath for 45 minutes, but then it must come up for air." "The trick for the polar bear is guessing where it will appear next." "But it only needs to catch one seal a week and it is very patient." "Bears can wait at a single hole for days." "Only a handful of animals are tough enough to survive the winter here." "The Svalbard reindeer is the world's most Northerly herbivore, and that's a challenge when the land is locked in ice." "They survive partly off their summer fat reserves," "losing up to half their body weight during winter." "But they do need to eat." "With their sharp hooves, they chisel through the crust of ice and then literally chew the rocks, scraping off the coating of frozen moss and lichen." "But after just seven or eight winters their teeth start to wear out..." "..and that's when many struggle to make it." "When winter claims one life, another is quick to profit." "An Arctic fox." "It scavenges its way through the winter, visiting frozen carcasses like this, and following polar bears to feed on their leftovers." "And this is the only bird to over-winter in Svalbard." "The ptarmigan, a relative of the grouse, but tougher." "Like the reindeer, they pack on extra fat in the autumn, but not for energy - for insulation." "So they are 50% heavier in the winter." "But now they're too fat to fly any distance." "On feathered feet, they scuttle across the tundra, seeking out the tiniest shoots of plants" "lying dormant in the frozen ground." "For everything but the polar bear, such conditions are hard to endure." "For the first explorers who came here from Europe 400 years ago, the Svalbard winter felt like an eternity." "They must have wondered whether the sun would ever return." "For many, it never did." "But there is light here." "When the moon rises, it can stay up for a week." "And every so often, the solar wind coming from the other side of the planet collides with the Earth's magnetic field, creating magical colours in the Arctic sky." "Aurora Borealis, the Northern Lights." "It's now mid" " February and after four long months, the sun finally returns." "At first, the sun is only up for an hour at a time so it brings little warmth, but it signals the beginning of Svalbard's miraculous transformation." "As the sun's light reaches out across the landscape, the true nature of this extraordinary wilderness is revealed." "Beautiful but brutal." "Vast glaciers flow from lonely peaks, pulverising mountains and bulldozing their remains to the frozen sea." "There are no forests or woodlands." "But surprisingly, the same titanic forces that make this place so inhospitable have also drawn people here." "Coal, brought right to the surface by the scouring of Svalbard's glaciers." "A source of great wealth for those who can survive here long enough to get it." "Svalbard belongs to Norway today, but in the past, many nations came to exploit its rich coal deposits, including Soviet Russia." "But one grand scheme after another succumbed to this frozen land." "This is Pyramiden." "Once home to over 1,000 people, now a ghost town." "Inside these buildings, Russian workers lived with their families." "But today it all lies abandoned." "The plan was to give the people of Pyramiden everything they needed to survive here through the long, dark winter." "Including the world's Northernmost piano." "But it couldn't last." "These mines were never profitable." "The cost of survival here at the frozen ends of the Earth was just too great." "Today, Arctic foxes roam the streets where people tried to tame the Svalbard winter." "Mid-March." "The days have been getting dramatically longer." "Only four weeks since the sun's return and there are already 12 hours of sunlight every day." "Though temperatures are still well below freezing, the sun's energy is now strong enough to trigger a chain of events, fundamental to life in Svalbard, under the sea ice." "These strange colours are caused by ice algae." "It lays dormant all winter, frozen into the fabric of the ice." "Just like a plant, it has the power to turn the sun's energy into food." "As the sunlight starts to penetrate the ice, it energises the algae's green cells." "The switch is flicked." "From the dark depths, tiny creatures are now drawn to the ice." "Copepods, just a couple of millimetres long." "They may look unimportant, but they hold a key to life here." "They've been waiting to gorge themselves on ice algae." "Very soon they are chomping away in their millions." "Now they take the sun's energy from the algae and concentrate it into a clear drop of fatty oil, which they store in a sack inside their bodies - bottled Arctic sunshine." "For now, all that energy is locked away beneath the sea ice." "But not for long." "The intensifying sun heats from above." "The warming water melts from below." "CRASHI NG" "It's April and the door to Svalbard's rich waters is opening." "It starts slowly at first, the silence of winter broken by the distant calls of seabirds." "But quickly their numbers build." "Guillemots," "little auks, elder ducks." "Around six million birds return to Svalbard every spring, travelling many thousands of kilometres from their winter homes in Europe, timing their arrival for just this moment." "Right away they start to refuel, diving into Arctic water to feast on the oil-rich copepods." "And beneath them, other life is stirring." "Vast shoals of fish now come for the copepods' bottled sunshine, and in turn become food for more birds." "The light from the strengthening sun has kick-started spring." "When the birds first reach their nesting cliffs, they find them covered in ice." "It's still bitterly cold here, but they need to stake their claim early." "Very soon there will be no more space available." "And they've got less than four months to raise their chicks before they'll have to be off again." "So immediately they get straight on with the business of breeding." "They don't have the luxury of time." "It's now the middle of April and Svalbard's transformation is moving into a whole new phase." "As the Earth travels further round the sun, spinning on its axis once every 24 hours," "Svalbard now moves into permanent day." "Welcome to the land of the midnight sun." "Now that the sun is shining all the time, it starts to have an impact on the land." "Under the snow, small plants are already absorbing the sun's light." "As they warm up, they start to melt themselves out of their icy prison." "The summer is short and it pays to get a head start." "One strange plant has taken this trick to an extreme." "This is the compass plant, one of the great survivors of the Svalbard tundra." "It can live for over 300 years." "Its success is down to a secret weapon - a central heating system." "The spongy dome catches the sun around the clock, absorbing its energy." "Though the air temperature is still hovering around freezing, the inside of the dome can rise to 30 degrees Celsius." "But it doesn't heat up evenly." "As the sun circles the horizon, its intensity varies." "The south side of the plant gets much more warmth than the north." "So when the flowers come, they erupt in synch with the sun, from south to north." "It was the early explorers who first noticed this and used the strange plant to help find their way, just like a compass." "As the snow melts further, it reveals a pile of old mining carts." "For plants that don't have their own central heating, the carts offer shelter from the biting wind." "A tiny walled garden where spring can really start to take hold." "And as the sun's warmth increases further, the whole tundra starts to bloom." "By the end of May, a greener Svalbard is emerging from the ice." "After such a long wait, for Svalbard's animals, the arrival of spring is miraculous." "The reindeer desperately need the grass that the melt is uncovering, but at first they seem a little unsure of this new, green world." "They still have their thick winter coats." "As temperatures rise, it's getting a little hot for them." "So whenever they can, they take a break from eating and settle down on the remaining islands of cool snow." "It's the latest arrivals who first really take advantage of the opportunities here." "Barnacle geese." "They've come all the way from Scotland, where they spent the winter." "As the tundra is revealed, it offers an untapped source of rich energy, worth coming over 2,000km for." "This little bird is a snow bunting." "He too has come far - all the way from Russia." "And this is the object of his affection." "Together, they have set up home in an abandoned miner's cabin." "In the middle of a whale vertebra, hanging on the wall, is a cosy nest, and in that, a ball of soft reindeer fluff, ready to nestle tiny eggs." "Now they are here, they are the Northern-most songbirds in the world." "And theirs is the song of Svalbard's spring." "As the Arctic fox trots out of winter, she sheds her coat quickly to avoid overheating." "She has a lot to do." "Foxes are nomadic in the winter, but now the race is on to establish her summer breeding territory." "She even rolls up a ball of her fur, adding a dash of urine to help signpost her patch." "And every so often she makes time to meet up with her mate." "They got together in the middle of the winter." "Very soon she'll be giving birth." "And then she will have just 90 days to raise her family." "It's now already June and off the coast of Svalbard the sea ice is breaking up fast." "The polar bear's world is changing." "Though a polar bear can smell a seal from over a kilometre away, in this constantly moving landscape, it's much harder to track it down." "It must take to the water to navigate through the drifting maze of ice." "Bears are excellent swimmers, but no match for a seal." "Life is getting harder." "As the ice cover falls below a critical 50%, the bear spends more energy catching seals than he gets from eating them." "While the breaking ice makes life more difficult for the bear, it allows Svalbard's heaviest resident to access the land." "Walruses." "At one and a half tonnes, they can be three times the weight of a polar bear." "After spending the winter at the edge of the sea ice, they now return to Svalbard's shores." "They haul out on their favourite beaches for the first time since last autumn." "Both males and females have tusks, some over a metre long." "The bigger the tusks, the more important you are." "They're also a good defence against polar bears, and useful props for a heavy head." "THEY GRUNT" "It's their handsome whiskers and extraordinary mouths that are their most important assets." "But they don't come into their own until they go out foraging." "And they're in no hurry." "Walrus siestas can last a week." "When they finally decide to go for a swim, there are some novel ways of getting all that way down to the water." "Once they're in, their strange features begin to make sense." "The giant body becomes weightless." "With just its nose on the seabed, it blasts away the mud with high-pressure jets of water forced through its nostrils, feeling around with its 500 highly sensitive whiskers for its favourite food - clams." "It just loves clams." "When it finds the clams, it sucks the flesh right out of them with its unique vacuum mouth." "A walrus can consume over 1,000 clams a day without eating a single shell." "But these extraordinary animals have only recently been making a comeback." "Not long ago, they were brought to the brink of extinction." "Just beyond their beach are strange lumps of what appears to be concrete." "In the middle of these rings were once great cauldrons in which the blubber from Svalbard's sea creatures was melted down into precious oil." "Year after year, as the oil spilled over, it congealed with the surrounding sand and set into stone." "Nearby is the evidence of the scale of this destruction." "The bones of thousands of beluga whales." "Long before it was known for its coal," "Svalbard was one of the places to hunt whales and walruses." "Their oil once lit the lamps and lubricated the machinery of industrial Europe." "For 300 years, the slaughter continued until there was almost nothing left to kill." "But it took its toll on humans too." "As the ground repeatedly freezes then thaws every year, anything buried is pushed to the surface." "A whaler's grave." "Though the promise of wealth and adventure drew many to these remote whaling stations," "life expectancy was so short, you even had to bring your own coffin." "July is the hottest month." "Even the great fjords that cut right into the mountains are free of sea ice and the summer heat kick-starts another chain of events that benefits life here." "For so long, the land and sea were united by ice." "Now open water laps against the faces of Svalbard's great glaciers." "Behind the face, the glacier stretches into the distant mountains." "Billions of tonnes of ice pushing down towards the coast." "As the sun starts to melt the ice on the glacier's surface, water funnels downwards and lubricates the junction between rock and ice under the immense weight of the glacier." "For some glaciers, the pressure gets too much." "They start to accelerate." "Svalbard's glaciers are unusual." "Many remain motionless for years and then suddenly take off." "These surging glaciers are some of the fastest on Earth, especially when summer melt-water lubricates them." "They can reach speeds of up to 25 metres per day." "At the face, the colossal weight of ice pushes from behind, while below, the warming sea erodes the base." "Something has to give." "CREAKING" "But this is not just a destructive force." "Where the glacier meets the sea, it enhances life." "In spite of the danger, kittiwakes and gulls are flocking in their thousands to the ice front." "Right in the impact zone, they start to feed." "Where the melt water flowing under the glacier reaches the sea, it billows upwards, right in front of the falling ice." "As this plume of freezing water rises, it stuns tiny plankton and brings them to the surface." "A microscopic feast, so rich it's worth risking your life for." "But you've got to keep your wits about you." "It's not only birds that come here." "Beluga whales." "Young calves that don't yet have the white colour of adults." "They swim in their family pods, feeding on fish that in turn eat the plankton at the foot of the ice cliff." "Though the years of whaling almost wiped them out, in 1961 they were finally given protection." "Today they are becoming a much more common sight, especially where the glaciers meet the sea." "By mid-summer, there is more life on Svalbard than at any other time of the year." "The bird cliffs are now at full capacity." "Every ledge is taken." "The chicks hatched three weeks ago and the race is now on to feed them fast enough." "In just three more weeks, they must be out of here." "Down below, the tundra too is alive with new life." "The reindeer have finally got their cool summer coats, and the males are sporting impressive new antlers." "The fox couple are busier than ever." "They've had six pups and the pressure is on to feed them." "They will need to be fully grown in less than a month." "Arctic fox cubs don't like to share food." "When the winter comes they will be completely on their own, so they need to learn to fend for themselves right from the start." "But for the parents, now is the crunch time." "As they work 24 hours a day, making many thousands of journeys to the den with food, they become exhausted, using up more energy than through the whole of the winter." "In the skies above, aerial traffic has reached fever pitch, as the birds frantically try to keep up with the demands of their offspring." "But as they shuttle back and forth, bringing food from the ocean to the cliffs, they do much more than feed their chicks." "Some of the ocean's rich nutrients passes straight through the birds." "As all that fertiliser is washed down from the bird cliffs, it has a profound effect on the land below." "The grass that now fattens up the reindeer for winter." "The soil that nourishes the plants." "The richness of Svalbard's land, ultimately, comes from the sea." "It's now late July and the last of Svalbard's summer visitors are only just settling in." "Arctic terns have come all the way from the other end of the Earth, from Antarctica, the longest migration of any animal - over 30,000km." "But in three weeks, they'll have to fly all the way back again and their chicks have only just hatched." "In only 21 days' time, this ball of fluff will need to fly 30,000km." "But it's well worth the parents travelling all this way." "Svalbard's super-rich waters contain all the energy required." "All they have to do is transport it from ocean to beak." "As the adults fish nonstop, sometimes they have to leave a chick on its own, and because terns nest on the ground, that can make it vulnerable." "The retreating sea ice has now forced Svalbard's largest predator onto the land and it's coming this way." "Now is the toughest time for polar bears." "It loses a kilo of body weight for every day it spends on the land." "The great ice bear turned scavenger - and he's starving." "Not a good moment to break your cover." "SQUEAKING" "But the chick's cries for help have been heard." "Terns may look dainty but they are highly aggressive, and totally fearless." "Repeated attacks draw blood from the bear's sensitive nose." "The Arctic's top predator, driven away by one of its smallest birds." "As August arrives," "Svalbard's transformation reaches its maximum extent." "It's only a fleeting transition." "By the end of the month, the sun will be setting again." "The winter is just around the corner." "But as Svalbard's yearly miracle prepares to come full circle, the summer sun helps trigger a final dramatic change." "In the far north east of Svalbard is a place where it always feels like winter." "A massive ice cap." "A frozen monster." "Like a giant fridge, it cools this whole area of Svalbard." "Only now in late summer does the sun start to have any effect here." "On the surface of the ice, melt water pools together and starts to flow." "Where the ice cap meets the sea is one of the world's greatest wonders." "The ice cliffs of Austfonna." "For nearly 200km, they rise uninterrupted from the ocean." "But recently, these cliffs have been changing." "Something we can see most clearly from space." "The very latest satellites can make precise measurements of ice thickness and speed of movement." "What they reveal is astonishing." "A massive tongue of ice, 50km long, is on the move, sliding downwards from the centre of the ice cap out into the ocean." "A wall of ice, advancing half a metre every hour." "4km a year." "It's thought that massive events like this are part of a natural surge cycle lasting several years, but no-one knows exactly what sets them off." "The latest research suggests that summer meltwater penetrating the ice cap may be a trigger." "Svalbard's ice world is incredibly delicately balanced." "Just tiny rises in global temperatures could have profound effects on the whole seasonal cycle of life here." "Today, as Svalbard heads for the winter once more, its future lies on a knife-edge of just a few degrees." "It's now the end of August and Svalbard is returning to the dark time." "Svalbard's summer visitors must now leave." "They've reaped the benefits of the rich summer, but if they stay here any longer they'll die." "As parents now force their young to take flight, some before they're really ready..." "..foxes get a last feast before the lean time." "Reindeer just keep on grazing." "What they eat now decides whether they will make it through." "Only one creature here welcomes the coming winter." "As the sun drops below the horizon for the last time and Svalbard moves back on to the dark side of the Earth, the big change comes once more." "Our planet is a place of constant change." "Each year, the seasons shift and life is transformed." "But there are places where the changes are so epic in scale, they can be seen from space." "In this series, we reveal three of the most miraculous transformations." "The islands of Svalbard." "Within a few weeks, frozen wastelands burst into life." "The African Okavango." "A desert transforms into a magical water world." "And the mysterious forests of New England erupting in a blaze of seasonal colour." "Life finds the most ingenious and surprising ways to thrive... ..in the world's most fast-changing landscapes." "The Kalahari basin." "2.5 million square kilometres of flat sand and scrub." "This desert stretches across southern Africa." "But at its heart lies a river." "A river that never reaches the sea." "And once a year, it floods." "Over five months, waters spread across a vast area of the Kalahari, transforming it into a wonderland." "The Okavango Delta." "This is the story of how nature creates a unique, flourishing wetland out of one of earth's great deserts." "Our story begins in the heart of the Delta." "The dry season is well advanced and water is becoming scarcer by the day." "At this time of year, predators rule." "Animals have another six months to wait before the flood turns this land back into a lush wetland." "Sable antelope." "After grazing on dry grass, they have to drink at a stagnant pool." "But they're nervous." "Predators watch their every move." "For a leopard, though, a sable's size and lethal scimitar horns pose too much of a risk." "There are plenty of easier targets." "A family of warthogs." "GRUNTING" "Where once there was a wide river, they use their tough snouts to truffle for bulbs." "But it's hard work in this dry, sun-baked ground." "And having your snout in the sand is decidedly risky." "GRUNTING" "SQUEAL!" "FRANTIC SQUEALING" "SQUEALING" "The leopard drags its kill to a hiding place, where it can dine in peace." "The warthog will keep it going for a week." "The dry season means good hunting for top predators." "For everyone else, food is scarce." "Chacma baboons survive through their knowledge... ..and eclectic taste." "BUZZING" "Elephant dung is a valuable source of seeds and insects." "CHATTERING" "But it looks like there's an appealing alternative." "A tree that fruits even in the dry season." "A fan palm." "The fruit is nutritious, if a bit tough and pithy." "But what's this?" "Elephants will eat virtually any vegetation." "And fruit is their favourite." "They can smell it from several kilometres away." "For the baboons, the feast is over." "TRUMPETING" "The fruit may be 20 metres up and out of reach, but the elephant's strategy is simple." "Brute force." "For a crafty baboon, though, it sometimes pays to hang around." "It's spotted one that the elephants missed." "Nearby, at a shrinking pool, something agitates the water." "Mouths gulp at the surface." "It's crowded with giant catfish up to a metre-and-a-half long." "There's no oxygen left in the water for their gills to use." "But these fish also have lung-like organs that breathe air." "Every day, under the Kalahari sun, more water evaporates." "African fish eagles gather expectantly for a banquet." "In desperation, some catfish attempt to make a run for it, using their fins to propel them." "Now exposed, they are easy targets for eagles and jackals." "SQUAWKI NG" "These catfish have run out of time." "Within two weeks, the pool has vanished." "When it floods, there will be plenty of water for everyone." "But now, at the end of the dry season, elephants must keep walking in search of water." "LOW ROAR" "Her calf needs 15 litres of milk a day, so she must find over 100 litres of water for both of them." "But elephants have a special technique to get at fresh water." "No other animal has such power." "Using their tusks, they pile-drive into the flood plain until they reach water beneath the surface." "TRUMPETING" "In doing so, elephants create a lifeline for others." "A hyena and jackal wait their turn." "Elephants with calves are not to be messed with." "So they dive in when they can." "But this jackal may have pushed its luck a little too far." "CHATTERI NG" "BI RDSONG" "For insect-eating birds, food is increasingly hard to find." "This mound makes a good lookout post." "But if only it knew what's inside." "It's a fortress for Macrotermes termites." "A colony a million strong." "A termite's mound is just the hub of an underground city." "Six kilometres of foraging tunnels." "Here, the Macrotermes process dead vegetation into food." "The mound is perfectly engineered to keep air at constant temperature and humidity." "Protecting the termites from drying out." "But these mounds will also prove essential for the survival of many other species when the floods come." "By the end of October, dryness and increasing temperatures turn the once-lush Okavango Delta into a tinderbox." "FLAMES ROAR" "But these birds seem to be attracted to the flames." "For the lilac-breasted roller and the fork-tailed drongo, it's a great opportunity." "Because the fire flushes out a bounty of insects." "Up to a quarter of the Okavango flood plain can burn in a single year." "For most of the plants and animals that live here, the end of the dry season can't come soon enough." "THUNDERCLAP" "RAIN PELTS" "November brings a little respite to the parched land." "THUNDERCLAP" "Warm, humid air moves in from the tropics." "Rain in the Kalahari." "Just enough to green the delta." "BIRDSONG" "CHATTERING" "The baboon troop has grown in number." "SQUEALING" "These youngsters were born just in time to enjoy what the rains bring." "More trees have come into fruit." "It makes for a delicious breakfast." "But there's a downside to such a wonderful scent." "TRUMPETING" "Sure enough, elephants aren't far away." "TRUMPETING" "GENTLE ROARING" "The troop scatters." "SQUEALING" "Maybe it's time to move on." "Mothers carry their newborns safely underneath, where they can keep suckling." "But the older ones must learn to ride on top." "CHATTERI NG" "On these open plains, the troop must stick together." "Some have already lost limbs to leopards." "All these animals will soon face a new world." "The Kalahari rains may have provided some temporary relief, but a much greater change is on its way." "In distant mountains beyond the Kalahari, the tropical air now brings much heavier downpours." "Rain, from highlands to the north, cascades ultimately into one river." "The Okavango River." "It creates a pulse of high water which takes two months to snake over a thousand kilometres to the top of the Okavango delta." "It will still be another month before the floodwaters reach the heart of the delta." "Here, the river always flows and is home to several thousand people, such as Sinabe." "His people are descendants of both Kalahari nomads and fishermen from central Africa." "As the river rises, water spills on to the surrounding land." "Creating shallows ideal for spear-fishing." "The rising pulse of water continues onwards." "South, towards the dry heart of the delta." "But to understand what happens next, we have to go back in time." "Two million years ago, great cracks ripped through the desert floor." "The land warped to create the shape of the Delta we know today." "The faults define the start and finish lines for the flood which is to come to the main delta." "The dry plains in the heart of the Delta will soon be transformed." "GRUNTING" "Life here is about to be turned upside down." "GRUNTING" "SQUEALING" "But for this family of warthogs, there's still a bit of time to get some truffling in." "The last rains softened the ground." "And now, getting at those tubers is much easier." "For the cunning baboons, it's an unmissable opportunity." "They muscle in to enjoy the fruits of the warthogs' hard work." "GRUNTING" "SQUAWKING" "The baboons may have no manners, but the warthogs don't really seem to mind." "Perhaps it's because the baboons provide extra security." "But this is one food source that will soon disappear." "Hidden in the reeds, it starts as the tiniest trickle." "The beginning of one of Africa's greatest floods." "As rising water spills into the main delta, it slows and spreads into countless, tiny rivulets." "RHYTHMIC DRUMBEAT" "Travelling at barely a kilometre a day, the flood will take another four months to cover the delta." "But straightaway, wherever water touches the land, it makes a remarkable impact." "Common sand frogs spend most of the year buried half a metre underground." "But now, water floods their burrows and forces them to the surface." "They inflate to scare off any predators." "He's off to find a female." "For tiny creatures whose homes are in the way, the trickle is more like a tsunami." "Ants are forced to evacuate their nest." "An easy snack for blacksmith lapwings." "Termites now face the flooding of their colony." "They beat a hasty retreat to the safety of their mound as their tunnels start to flood and collapse." "But in doing so, something miraculous happens." "The tunnels seal themselves up." "This blocks the flood's underground advance and forces the water back to the surface." "Back inside the mound, the termites are safe." "Incredibly, the flood provides just the opportunity they need." "Their fragile castle, made of sand, requires constant maintenance and rebuilding." "But the soil, now softened by floodwater, is easy to transport to damaged parts of the mound." "Gradually, thousands of termites reconstruct their fortress." "Repairing these mounds isn't just good for the termites." "These structures help to create something vital for all the delta's wildlife." "Its islands." "And it all starts like this." "Dung." "Readymade fertiliser laden with fruits and seeds." "Floodwater soaks up the dry side slopes of the mound to create the perfect bedding for new plants." "Gradually, season-by-season, termite mounds become home to more and more plants." "As they grow, they attract more animals, which in turn bring with them the seeds to grow even more plants." "Sycamore fig, fan palm, marula." "Until the termite mounds are barely recognisable under their lush green canopies." "As it floods, raised areas around termite mounds become islands." "They provide food, shelter and a refuge throughout the year for everything from elephants to baboons and birds." "In the delta, once featureless desert, there are now around 150,000 such islands." "For a lot of thirsty animals, the floods simply mean sweet drinking water." "Elephants no longer need to dig holes." "TRUMPETING" "CHATTERING" "GRUNTING" "Baboons, too, seem to delight in the precious liquid." "Curious youngsters, encountering the flood for the very first time, don't seem to know quite what to make of it." "The sand may look barren, but wherever the water touches it, something magical happens." "Within a couple of days, billions of freshwater plankton begin to awake and hatch." "Such tiny creatures are the delta's secret ingredients." "The foundation of its food chain." "Meanwhile, in a deeper channel, a mountain of foam has appeared." "It has been created by a pair of African pike." "Notoriously aggressive, but caring parents that watch over their offspring." "Hidden safely underneath the foam, hundreds of fish eggs are beginning to hatch." "The fry remain attached to the foam until they are well developed." "And now, the delta offers plenty for them to eat." "The tiny pike fry join small, hungry fish of 70 different species, swimming though the shallows in a nutritious soup of freshwater plankton." "BIRDSONG" "Before long, the skies fill with birds." "One of Africa's greatest wildlife spectacles." "Travelling nomads from far and wide." "The reason they're here?" "Wherever water covers the land, it fills up with little fish." "Each of the birds has its own special technique for catching them." "A saddle-billed stork jabs at its prey." "African spoonbills have the perfect equipment for filtering out the finest morsels." "Black egrets use their wings to form canopies over the water." "The shade lures nervous fish desperate for cover." "Others attack directly from above." "A pied kingfisher." "At 25 centimetres long, it's the world's largest hovering bird." "Hovering demands a lot of energy, so they have to catch a quarter of their weight in fish every day." "Keeping its head perfectly still, about ten metres above the water, it sees movement." "Then drops in a controlled dive." "If the fish sees it, the kingfisher can still abort and save energy." "If not, it commits and dives rapidly." "It's worth the effort." "Hovering allows them to hunt in the middle of the plains, where the pickings are especially rich." "The bird kills its prey with a blow to the head." "But before it can swallow, it must flip the fish, head first, or the spines will stick in its throat." "Within a few months, another type of organism vital to the delta breaks the surface." "Dozens of species of aquatic grasses, sedges and water lilies." "At dawn, day lilies open to attract pollinating bees and flies." "As dusk approaches, the day lilies begin to close, and give way to the night shift." "Night lilies open their brilliant petals... ..bright enough to attract insects in the moonlight." "Water lilies, flourishing in the middle of the Kalahari desert." "Perhaps the greatest miracle of the delta." "And only possible thanks to one thing." "Nature has found a unique way to keep the water of the Delta pure, very low in toxic salts." "Its secret lies with those extraordinary islands." "Trees on the islands act as pumps, sucking in water from the surrounding swamp." "As they do so, salts in the water are deposited in the sand of the islands." "By extracting salt from the water, it's as though the islands are kidneys, removing waste from the bloodstream." "This way, the islands keep the Delta's waters fresh and able to nurture abundant life." "As the morning sun heats the ground, rising vapours everywhere reveal that water has spread right across this plain." "It's a transformation that turns the tables between predator and prey." "Red lechwe appear in large numbers, looking for their favourite food... ..tender aquatic plants." "But a hyena hopes to take advantage of their distraction." "It just needs to get a little closer." "Time to run for it." "Lechwe have large splayed hooves that allow them to bound at speed through shallow water, giving them a big advantage over any predator." "It's an adaptation that helps to protect them during the time of flood." "Soon the aquatic vegetation sprouts everywhere and the water becomes impassable." "But crisscrossing the flooded plains, highways through the reeds appear." "And here's their creator - a hippopotamus." "He's a grazer and thinks nothing of bulldozing a way through." "As he does so, he excavates a channel." "And it's not only hippos that have to find a way through." "In the far north of the Delta," "Sinabe rows through dense beds of reeds." "To get through, he seeks the help of the spirit of the river." "Deep in the reeds, he discovers a hippo channel." "It's a highway for fish, so the perfect place to rig a net." "Sinabe's village is on the edge of the flood plain." "His family know that as long as the Delta provides, they will never go short of food." "He smokes the bream to preserve it for days when the catch isn't quite as good." "Meanwhile, his family weave baskets out of grass from the flood plains." "Later in the year, they will be used for catching fish." "By July, in the heart of the Delta, the once-dry savanna has become a lush water-world." "But this transformation has an odd effect on the baboons." "SQUEALING" "Each has developed its own funny walk." "SCREECHING AND GRUNTING" "SCREECHING" "All that is, except for the baby - who just gets a soaking." "SCREECHING" "It seems likely that baboons don't much enjoy being in the water - or they may be nervous of something in it." "Crocodiles are everywhere." "For the troop, a flooded Delta is a lawless place, but a threat worse even than a crocodile has appeared." "Lone male baboons." "The shrinking of territory on land forces the loners into contact with troops." "They may fight the troop's alpha male for control." "If the stranger wins, he may also kill the young and mate with the females." "An incumbent alpha male must keep a close eye on any rival." "HE BARKS" "To survive, it is crucial that he lay down his authority." "BARKING AND GRUNTING" "GRUNTING" "ROARING" "SCREECHING" "ROARING AND BARKING" "SCREECHING AND ROARING" "BARKING" "GRUNTING AND SQUEALING" "SCREECHING AND SQUEALING" "GRUNTING" "Insurgents must be sent packing." "As the Delta floods, everywhere, tension seems to be mounting." "Not least in the hippo community, where their watery territories are expanding dramatically." "Here, too, there is a young challenger." "The territory's resident bull snorts a warning." "HE SNORTS" "The adversaries declare their ownership of the pool by vigorously spreading dung with their tails." "SNORTING" "They yawn to display their weaponry - huge ivory tusks." "SNORTING" "First, a test of strength." "SNORTING" "The old bull makes a temporary retreat." "Females have a vested interest in the outcome." "They will only be prepared to accept a mate that can hold his own in a fight." "The resident bull retaliates brutally." "SNORTI NG" "SNORTI NG" "Hippos will often fight for hours and sometimes to the death." "Finally, a brutal headlock - the coup de grace that settles it for the older male - expelling the pretender from his territory." "Which means the resident bull passes the test to sire this year's crop of baby hippos." "GRUNTING" "The young male has been injured during the retreat, his flank exposed to his furious pursuer." "At least nature has arranged for him to be nursed - by these oxpeckers." "They eat anything that might cause an infection." "The pain is probably worth it and he should survive to fight another day." "By August, the floodwaters finally reach the Delta's southern fault line, its maximum extent." "The Okavango is now one of the largest inland deltas in the world." "The whole Delta is linked by water - shallow flood plains, pools, and deeper channels all fed by the Okavango River." "Billions of fish that fill the plains have grown rapidly." "And Sinabe's wives and daughters are ready for them with their baskets." "SINGING IN AFRICAN LANGUAGE" "SINGING CONTINUES" "SINGING STOPS" "Bulldog fish will make a fine stew." "In the main river, something strange is happening." "The waters appear to be boiling." "It's catfish, taking gulps of air at the surface." "And they are here in their millions." "Before the flood recedes, they return from their hunting grounds in the far reaches of the Delta to the safety of the deep channels." "Amongst the papyrus, they hunt smaller fish." "Flocks of egrets arrive to join in the feast." "No-one is safe in the mayhem." "African fish eagles swarm and dive-bomb the catfish." "Millions of fish that grew fat out in the flood plains bring life back to the river that brought them water." "When it's needed most, the flood creates a vast oasis in the desert - a wonderland." "Its 10,000 square kilometres of crystal waters attracting animals from all over the dry Kalahari desert." "HE ROARS" "HE ROARS" "But these waters will never reach the sea." "They will soon begin to evaporate or simply sink into the Kalahari sand, as the Okavango Delta gradually returns to dry savanna."