"They are born to move." "To move...or die." "Forging ahead, against terrifying odds." "Navigating the first of millions of miles." "Spanning continents on fledgling wings." "Clattering ever onward." "Right now our planet is on the march... on the wing... on the run." "And these are the tales of its creatures... born into the most moving stories on Earth... the stories of the great migrations." "Life on Earth is hard." "Perhaps nowhere harder than here...and now." "Every year, a timeless drama plays out on the Mara River." "The elders have been through this many times." "They must remember what awaits them." "Their young know only the pervasive smell of fear... and the instinct to stay close." "But they must press on." "What on Earth could drive this headlong rush to slaughter?" "Only Earth herself, with her insistent clocks." "This story begins in the Great Rift Valley-- where the continent is tearing itself apart... and being reborn." "The plains in the shadow of the rift-- the Serengeti-- are threaded with the paths of the millions on the move... in a constant burning search for fresh grass." "Every year, more than a million wildebeest and 200,000 zebras must chase the seasonal rains, in a 300-mile loop around Tanzania and Kenya." "But here in the Serengeti, they pause... for an avalanche of young... the most migration-ready newborns on Earth." "The wildebeest have a scant three weeks to deliver half a million calves... who have only minutes to get up on their feet." "Because the predators-- and the scavengers-- have the migration clock etched in their genes as well." "For them, this is a weak and moveable feast." "For the newborns, it's get going... or get eaten." "Apprentice killers wait for their first taste of the chase." "But they're about to learn... that hell hath no fury like a zebra protecting her foal." "Older cheetahs know the value of patience." "Soon the herd will move on." "Hungry eyes turn to one of the last-born wildebeest, just learning to kick up its heels." "[calf bleating]" "Serengeti vultures have timed their breeding cycles so their young can share this bounty." "[vultures squawking]" "Five out of six wildebeest calves won't make it through their first year." "Only the fit--and the lucky-- will inherit the relay race of their lives." "It is a race that is increasingly endangered," "like many of the world's great migrations." "Climate change disrupts weather patterns... and exploding human populations encroach on their ancient paths." "But today they take up their relentless legacy." "To move...chasing the rains." "[thunder]" "Rain." "Wherever it falls, life waits for it, yearns for it-- and above all, moves according to its whims." "Water from the skies is a reminder to all land-dwelling species that their origins were in the seas." "And nowhere is this more remarkably played out than on a tiny island in the Indian Ocean called Christmas Island." "Deep in the forests-- far from the shores where any sensible crustacean should be-- red crabs the size of dinner plates hear the call of the monsoon." "It's time to return to the seas of their birth." "With the humidity soaring, their moisture-dependent lungs can now function beyond the damp confines of the forest." "The males go first." "Like generals at the head of a red tank division, they begin their clicking, yearly march to breed." "Millions of generations have engineered these crabs for life on land-- but their young must hatch in the ocean." "It's a brutal, month-long migration-- up to five miles-- an ultra-marathon for a crab." "The cruel sun makes its appearance, threatening them with dehydration." "And they face a gauntlet of roads crisscrossing the island." "They stop only to nourish themselves wherever-- and however--they can." "For those who have made it this far, a more horrible fate awaits." "Yellow crazy ants." "Aliens accidentally introduced by cargo ships." "Now super-colonies of billions terrorize the migrating crabs." "The ants attack...spraying acid into their mouths and eyes." "Blinding them..." "leaving them helpless." "In the 1 990s, the crazy ants slashed the crab population by a third, from 80 million to 50 million." "Beyond the ants lies a dizzying descent." "40 feet straight down to the beach." "Now the males face the waters of their birth." "They dip into the ocean to restore their bodies with salts and moisture." "But these land crabs are air-breathers... and the Indian Ocean plays no favorites with her prodigal sons." "Ravenous triggerfish seize the luckless." "An unceremonious end to an epic quest." "For the surviving males, the odyssey has just begun." "The females will arrive within days-- urged on by celestial forces, demanding they reach the males and the sea in time." "Like the crabs, creatures around the globe are moving to the music of the spheres." "They register the sun, the moon, the earth's magnetic field... and move at their bidding." "Even the navigational feats of the most delicate of creatures beggar the imagination... and confound our understanding." "And in tiny slices of endangered Mexican forest-- hundreds of millions of the world's most astounding navigators are stirring." "These monarch butterflies have waited patiently through the winter, barely moving, for the sun to tell them it's time." "They stream to water to slake a winter-long thirst." "Water that will bring spring's sexual awakening." "Males pluck females from the trees like reluctant flowers." "And they mate." "Then, the brilliant masses take to the wing, heading to a place they've never been." "Their only map-- imprinted on their genes." "A mysterious interplay of sun on eyes and antennae-- an uncanny sense of magnetic north guides the way." "It will take five months for three generations to get the species as far north as Canada... and a fourth super-generation to get them back to Mexico." "Such a multi-generational migration is incredibly rare." "It takes the leading generation three weeks to fly 500 miles into the southern U.S." "These intrepid elders sense that death is approaching fast." "There is urgency now to pass on the migratory baton." "The female, having carried her eggs from Mexico, now searches for the monarch's life-giving grail:" "The milkweed sprouting all around." "Her offspring will be laid on it, hatch on it, nurse on its toxic milk, and become toxic themselves... a defense they will flaunt with their singular beauty." "She is dying-- but with luck, her children, grandchildren and great-grandchildren will carry on the journey as far north as Canada... and then an astounding 2,000 miles back to Mexico." "For the delicate monarch, it may as well be a trip to the moon." "And yet somehow they do it, their tiny bodies attuned to a seasonal sundial and resonating to the invisible signature of the earth's core-- its magnetic field." "Around the planet, animals large and small are responding to these forces, as palpable to them as they are indecipherable to us." "And far out to sea, the largest brains on Earth fix on these mysterious cues." "The male sperm whale-- a creature of superlatives." "It is the largest toothed predator alive today-- weighing up to 50 tons." "It dives deeper and faster than any other whale." "And it undertakes some of the greatest journeys." "In a lifetime, this whale may log a million nautical miles." "The males often circle the Arctic to feast." "But for the species to survive, their paths must intersect with the females' own astounding journeys-- coursing warmer waters." "Many will meet in the Azores... nine tiny islands where clashing currents create an explosion of life." "A mother ushers her newborn calf into coastal waters... guided by sun, sea currents and perhaps even magnetic sensors in her brain." "She also navigates by sonar, bouncing her clicks and creaks off the sea floor." "[clicking]" "Some of the loudest sounds made by any creature on Earth." "Females travel in family groups, sometimes leading their young on yearly wanderings of up to 20,000 miles." "Each day, they gather to reaffirm their bonds." "They seem to crave physical contact." "Finally, the mothers disperse-- to feed in shifts." "They leave their calves for up to 40 minutes of every hour." "They may dive up to two miles for a daily catch of 300 pounds of octopus and squid." "[whale clicking]" "This calf, too young to dive, tracks his mother closely from above," "listening intently for her signature clicks." "[clicking]" "Chunks of octopus rise to the surface from the matriarchs hunting below," "like breadcrumbs leading back to safety." "From the depths, mother finally returns." "All of his young life, the calf has been on the move." "Now his mother and aunts seem to be waiting for something big." "Unknown to the calf, he's about to be welcomed into a world of giants-- a world rarely seen and little understood." "Migrations are journeys of attrition" "Darwinian in the extreme." "A quarter of a million wildebeest will die in their yearly odyssey." "In the sun burnt Serengeti, hunger keeps the wildebeests thundering northward, following the rain." "A collective intelligence keeps the herd on track." "Neighbor leading neighbor along ancestral paths." "Testosterone drives young males to flaunt their strength, fleetness and stamina." "The plain is awash in hormones... and young male ostriches gyrate in outlandish displays." "[crickets chirping]" "But most of the march is a blistering slog... with patient scavengers and predators knowing some will falter." "[wildebeest snorting]" "One of the last born, his young body exhausted beyond measure, simply cannot carry on." "His mother, caught between the pull of maternity and the need to survive, waits, urges... and gives up." "It's a grim end to a short life." "But many of the surviving calves will face a more terrifying death." "In the Mara River, another migration is culminating." "Crocodiles have memorized when and where the wildebeest will try to cross." "They have gathered in massive numbers-- waiting, watching... and hungering for what's to come." "While the wildebeest migration has converged on a small crossroad of terror versus hunger... the monarch butterfly migration has spread to fill a continent." "The second and third generations of monarchs have been moving progressively north." "They have fanned out across North America-- and the migration has reached its tipping point." "It's August-- time for the super-generation to be born-- and to take the species all the way back to Mexico." "Tattered females alight, their brilliance dimmed by the arduous flight." "One by one, the female lays her 200 eggs." "She deposits them on the leaves of milkweed, ensuring the hatchlings will have a ready supply of food to fuel the marathon ahead." "These new travelers will be different," "living ten times longer than their parents." "Only longevity and uncanny endurance can take them back to Mexico-- this time in a single generation." "It takes four days for the larva to emerge." "It gorges on its own egg case... before turning to tender milkweed." "It must grow fat, build up its reserves for the long migration ahead." "After two weeks of manic feasting, its body mass now 2,000 times what it was at birth, the caterpillar is ready." "Anchored by silk..." "it begins its miracle." "Over the next two weeks, the caterpillar literally dissolves into a bag of rich fluid." "Its cells sprout anew, giving rise to wings, legs, antennae." "And then..." "After a scant few hours, it's ready to fly." "This is a creature truly born to move." "Born to outstrip its parents' and grandparents' heroic efforts-- carrying aloft the genetic hopes of a species." "Incredibly, more than a billion super-monarchs are now taking off." "And for the first time in four generations... they are heading south... heading for their winter home." "[loon walls]" "On Christmas Island, a different kind of homecoming preparation has begun." "The males, though exhausted by their long pilgrimage, are readying snug burrows before the demanding females arrive in search of nursery-ready homes." "Having dipped in the ocean to renew themselves, the bright-red would-be mothers seek out the males." "Once entwined, the tangle may last half an hour." "When she's ready, the female disengages and descends into her den." "The male, duty done, begins the long trek back to the forest." "But for the female, the odyssey has just begun." "In darkness, she produces up to 1 00,000 glistening eggs-- and broods them for 12 or 13 days... waiting for the cue that drives her entire migration:" "The waning moon... and the resulting mild tides." "Eggs stowed in abdominal sacs, the females make a clattering dash to the sea." "Here, on the moonlit beaches of their own birth, they brace themselves at the water's edge and release their offspring... in an antic dance born of instinct and desperation." "Many will drown in their frenzy to launch their eggs seaward." "Most years, only a handful of their offspring survive." "But sometimes, if wind and sea and luck are with them... a tidal wave of tiny crablings will return to these shores." "There's no way to predict if this will be... the year of the crab." "Far out in the Atlantic Ocean, a cacophony of clicks announces the return of titans." "[whales clicking]" "Mother and calf listen intently." "Only she knows what these clicks mean." "The males have arrived... stupendous, battle-scarred bulls-- back from epic wanderings." "The oldest may be 70 years old and have traveled 60 times the circumference of the earth." "Most of the time, utterly alone." "Now gentle greetings take place." "The whales seem to revel in displays of affection." "Young males bounce sounds off each other, sizing up the competition... in more ways than one." "The curious calf joins in." "Soon there may be violence-- as males joust to win female affections." "But for now, everyone enjoys a touching reunion." "The calf, out of his depth among these goliaths, returns to the mentoring eye of his mother." "He may not leave her for another ten years, to join other young males in wandering bachelor groups." "And he may be 40 before he masters the global oceans on his own." "It's September in North America-- and over one billion monarchs have been winging their way south, racing to get to Mexico before the first frost." "By soaring on wind currents, they save enormous amounts of energy, and about half will survive the 2,000-mile journey." "Their flashy coloration signals their toxic nature." "But some predators can withstand the toxins..." "like the praying mantis." "After more than two months and up to 900 hours of flying, the survivors begin to flutter into their wintering grounds in late October." "Hundreds of millions of them now alight on this threatened patch of Mexican forest." "They cluster in the same grove, sometimes even the same tree, as the great-grandparents who started this strange odyssey." "Finally...they can rest." "For another five months, they will cling to this winter refuge... entering a sort of waking trance of energy conservation... until the longer days of spring awaken them again to mate... and pass along to the young their migratory imperative... to fill the skies with a sun-spangled yearning to move... to start the whole glorious, impossible journey...once again." "On the other side of the world, another spectacular generation of nomads is about to hatch." "Over the next three weeks, the red crab eggs will drift in the perilous nursery of the Indian Ocean... and morph into larvae." "Most years, the larvae never make it home, swept away by ocean currents... or devoured by fish." "But once or twice every decade, a confluence of mild weather and scarce predators gives birth to a moving miracle." "By the millions, they pour over the beaches of their birth" "like a living pink tide." "They shed their larval casing-- becoming air breathers." "And retrace their parents' tortuous course-- guided only by instincts encoded deep in their DNA." "From this moment on, they are migrants." "Compelled to move." "No matter what." "The merciless yellow crazy ants take a terrible toll." "But by sheer force of numbers-- and the inexorable will of their genes-- they prevail." "That is the fierce logic of migrations." "But what is logical for the many... can be madness for the few." "At the Mara River..." "the madness has begun." "The crocodiles, from long experience, know who to target... the young." "Calves strain to stay by their mothers' sides... to no avail." "[wildebeest bellowing]" "Powerful, sharp hooves descend on the reptiles again and again." "On the far banks, wrenching scenes of those who almost made it... watched helplessly by distraught mothers." "[calf bellowing]" "But there is desperation here for the crocs as well." "Eat well now, and they may survive leaner times for months, even a year." "It's easy to forget that death is as vital to the herd as life." "The young emerge from this brutal baptism stronger and wiser." "Battered but unbroken, they exude the will to live." "They will continue to chase the rains and face down the crocs for the rest of their lives." "Moving in masses... surviving as one." "Every year, new generations are born into lives of perpetual motion... maiden flights fine-tuned by sunlit antennae... young giants resonating to the earth's cues... red battalions of moon-dancing mothers and skittering pink spirits... compelled by the courage of numbers... and the guts of the one..." "But most of all by the earth herself, who whispers to all:" "Move... move... move... and live."