"Most of us live here... [siren] ...the concrete jungle." "Suburbia." "But if you get out of town just past our backyards, it's wilder than you think." "This is the story of life on the razor's edge." "From Alaska to Patagonia, a great mountain spine spans two continents." "You need true grit to survive up here." "Our journey begins here, in the mountains of North America." "And with a hunter stalking his prey." "He's been on the trail for weeks, covering up to 50 miles a day." "Unlike pack wolves with pups, this wolf needs to travel hundreds of miles to find food." "He's a lone and lonely hunter." "And this is what he's looking for." "Caribou on the march, heading to summer pastures on the tundra." "All across the far north, they're migrating." "It's the greatest movement of large mammals in the Americas." "Two million caribou." "And all he needs is one." "[grunting]" "He's found them." "Now, the real work begins." "With a maximum speed of 50 miles per hour, a caribou can outpace the wolf, who tops out at around 40." "But he's got stamina." "It's treacherous, rocky ground." "His strategy is to keep up with the herd and hope one of them makes a mistake." "[panting]" "He has to adapt and try a different tactic." "Ambush rather than chase." "Act more like a cat than a dog." "He waits too long and loses his chance." "It's back to "Plan A."" "He keeps up the chase for another 20 minutes." "Now's his best chance." "The caribou are pinned against a steep riverbank." "[panting]" "[whimpers]" "He's probably run 1 0 miles in the last half-hour, burned thousands of calories, and has absolutely nothing to show for it." "He has no choice but to get up and do it again." "Nothing comes easy in these mountains of ours." "[wind howling]" "You need backbone to live on this great spine." "It rises in the frozen north, in Alaska." "Here, it's as if the ice Age never ended." "ln places it's a half-mile thick." "Over 1 ,000 miles to the south, the most iconic North American mountain range of them all... the Rockies." "They're some of the highest mountains in all of North America." "And there's one animal here that's hard as the rock that gives it that name..." "Rocky Mountain bighorn sheep." "The arrival of fall is the cue for their annual battle, to decide who among them will get the females and father next spring's lambs." "This six-year-old is finally ready to compete." "His opponent is a bigger, stronger eight-year-old ram." "The challenger must provoke the fight." "With body kicks and tongue flicking, he taunts his opponent." "The older ram seems to walk away in submission." "But his posture is known as the low stretch." "It means, "You want a piece of me?" "Come get it."" "The force of the impact, delivered at over 20 miles per hour, is enough to kill a human instantly." "Two layers of skull protect their brains." "The fight lasts for hours, each ram battering the other dozens of times." "[grumbles]" "By day's end, the young challenger concedes." "But he'll get another chance next year." "The fighting ensures only the toughest genes will be passed on." "Survival in the Rockies demands nothing less." "They say the Rockies have only three seasons, because winter can last for six months." "The animals of Yellowstone National Park live through the worst the mountains can throw at them." "Bitter cold... [howls] ...stinging winds." "And when spring approaches... [caws]" "...avalanches." "By June, the snow should be gone from Yellowstone's valleys." "But this year, winter overstays its welcome." "Herds of elk, which by now should be migrating back up into the mountains, still wait below for the weather to break." "Elk calves are normally born higher up." "But because of the lingering winter, the first ones have to be born down here." "Their arrival doesn't go unnoticed by a young male black bear." "[growls]" "The last storms blow through." "And the skies finally clear." "The elk head for the hills, ascending 4,000 feet up to the good grass on the Yellowstone Plateau." "Most of the calves are born now." "It'll be weeks before his legs are strong enough to outrun predators." "So he must stay hidden and be absolutely quiet." "His mother must leave him now." "Her presence would reveal his location." "His scent is so faint, few predators will even know he's here." "But it drifts toward one of the most sensitive of noses in the animal world." "Not a black bear this time, but a grizzly." "She can track a smell for miles." "After six months of winter sleep, this mother and her two cubs are famished." "[elk squeaking]" "And hidden all around them is a feast." "Hunting season won't last long." "The grizzly has only a few weeks before the elk calves are too fast." "And she's hunting for three." "[heartbeat]" "[heartbeat]" "The wind shifts and saves his life but dooms another." "ln just a month, grizzlies alone kill a third of all new calves." "By late June, the feast is all but over." "Most of the calves have joined the herd and can outrun the fattened-up grizzlies." "But the same young male black bear that hunted the calves in the lower valleys now climbs higher, looking for the few that remain in hiding." "Mothers try to distract him." "But it doesn't work." "He needs to decide now... hide or run." "[growls]" "Enough calves survive to rebuild the herd." "From the Rockies, the great spine leaves North America and runs down to Central America." "Here, the mountains are still being born." "Nicaragua, Central America... one of the most volcanically active countries on Earth." "These cauldrons are inhospitable to life." "The sulfur dioxide they spew out turns to sulfuric acid in lungs." "But, bizarrely, one of these volcanoes provides a home for some very raucous residents." "[birds squawking]" "Parakeets have been coming here to Volcan Nindiri for at least 500 years." "They nest in holes they've dug out of the soft dirt." "A human could barely tolerate such toxic conditions." "Yet, somehow, these birds survive here." "And scientists have no idea how they do it." "One advantage of their noxious neighborhood is fewer predators." "But for fledglings, there is one considerable downside... it's a long way down." "At seven weeks old, they take their first flight." "Unlike birds that nest in trees, they can't flap from branch to branch to test their wings." "Here, it's trial by fire." "Fly or fry... at the bottom of a 1 ,000-foot active crater." "For young parakeets facing such a daunting maiden voyage, a little procrastination is to be expected." "Fortune favors the bold." "Every year the parakeets will return to these crater walls to nest and to learn to fly." "From Nicaragua, the great mountain spine runs down to South America." "Here it rises as the Andes." "At 5,500 miles, it's the longest mountain range on Earth." "Topped by a 23,000-foot peak, they're the highest mountains outside Asia." "ln some places, they're an ice world of massive glaciers." "ln other parts, a desert wasteland." "And here at the equator, tropical cloud forests full of astonishing creatures." "Basking in the warmth of the tropics, mountain life can luxuriate a little here and even show off." "Hummingbirds abound in these forests... some 50 species." "Their names are as pretty as they are." "The violet-tailed sylph... the booted racket-tail the tawny-bellied hermit." "Many have evolved long bills to get to the sweet nectar that powers their flight." "But there's one flower that even they can't reach." "It opens for six days- not a long time for the all-important business of dispersing its pollen and spreading its genes." "It has to find its pollinator quickly, and it does by emitting a powerful musty odor." "An irresistible smell for one creature that, until recently, no one knew existed." "And this is its TV debut." "The tube-lipped nectar bat." "A pool of delicious nectar lies at the bottom of each flower's long flute." "But how to reach it?" "Necessity is the mother of evolution." "This 21/2-inch bat has a 31/2-inch tongue." "The longest, relative to body length, of any mammal in the world." "If human, he'd have a nine-foot tongue." "The bat sates its desire for the high-energy nectar, and the flower gets a courier for its pollen." "As the bat reaches deeper into the flute, his head gets dusted." "At the next flower, the transaction is complete." "He alone is the sole pollinator of this plant." "Without him, the flower simply wouldn't exist." "Some 1 ,500 miles south of the tropics, between Chile and Bolivia, the Andes completely change." "It's called the Altiplano, or high plains." "A place of extremes and extreme contrasts where deserts freeze and waters boil." "More like Mars than Earth, it seems just as hostile to life." "But even here, a few animals tough it out." "And into this barren world comes the Altiplano's most surprising residents... [squawking]" "Flamingos." "They spend their lives up here, commuting from lake to lake looking for their favorite foods algae and tiny shrimp that thrive in the briny water." "But as showy as they are, the flamingos pale in comparison to the real stars of the Altiplano stage..." "The stars themselves." "At 1 2,000 feet, the dry, thin air makes for perfect stargazing." "Some of the world's astronomers have telescopes nearby." "But just looking up with the naked eye, you really don't need one." "After over 9,000 miles, the great mountain spine of the Americas finally ends here, in Patagonia." "Torres del Paine National Park, Chile." "Millions of years of ice, rain and wind have conspired to create one of the most beautiful places on Earth." "[squawks]" "With their 1 0-foot wingspans," "Andean condors rule the skies." "They can travel hundreds of miles in a single day until they find what they're looking for." "[grunting]" "All these scavengers depend on one hunter at the top of the mountain food chain." "It's known by many names." "Mountain lion." "Cougar." "Puma." "From Alaska to California, from Brazil to Patagonia, this big cat is the ultimate icon of the American mountains." "Although it's the most widespread big predator in the Western Hemisphere, it's rare to ever see one." "To see a family in broad daylight is extraordinary." "Three cubs and their mother." "They're not quite cubs anymore, and that's the problem." "It's time to make it on their own." "Their mother has taught them all she knows about hunting their most important prey here..." "Guanacos." "But there's time for one more lesson." "They blow it." "But it's still a valuable exercise- timing is everything." "Ready or not, the time comes for them to go their separate ways." "A brother and sister, not yet prepared to be alone." "They now face the toughest test of their lives." "Fortunately, these young mountain lions are leaving home at the best possible time." "It's spring in Patagonia- guanaco calving season." "They may seem like easy prey, but catching them is a lot harder than it looks especially for beginners." "They need the cover of darkness." "[wind howls] [crickets chirping]" "For novice predators, sometimes it's hard to figure out what's prey and what's not." "It can't seem to decide if this skunk would make a good meal." "And the skunk is in no mood to be eaten." "[mountain lion barking]" "Sometimes it's better to stick with what you know." "Tonight the full moon hands a critical advantage to their prey." "The young hunters will have to work very hard to remain unseen." "But as the night goes on, a change in the weather begins to tip the balance back in their favor." "They have the darkness they need." "[squawking, squealing]" "They pass a vital test, proving they can make it without their mother." "Soon, they will have to go their separate ways." "But now, they're ready." "Each new generation born here faces the same rite of passage- to learn to survive and thrive in these great mountains of ours." "The ones that make it are the toughest of the tough." "Wild... and free." "Only they have earned the right to call the untamed Americas... home."