0:00:05 > 0:00:07In the heart of the Americas,
0:00:07 > 0:00:11where continents collide,
0:00:11 > 0:00:15there's a land full of natural riches.
0:00:15 > 0:00:17BEAR GRUNTS
0:00:19 > 0:00:22BIRDS CALL
0:00:27 > 0:00:29HOWLING
0:00:34 > 0:00:37A land of towering giants...
0:00:39 > 0:00:42..scorching sands...
0:00:44 > 0:00:46..and secret rivers...
0:00:53 > 0:00:55..where great civilisations rose...
0:00:57 > 0:00:59..and fell.
0:01:00 > 0:01:03MAN WHOOPS, HORSE WHINNIES
0:01:03 > 0:01:06To succeed here takes passion and spirit.
0:01:13 > 0:01:16This is a country rich in colour and culture.
0:01:21 > 0:01:23A festival of life.
0:01:34 > 0:01:37This is Mexico.
0:01:44 > 0:01:46BIRD CALLS
0:01:59 > 0:02:03BIRD CRY ECHOES
0:02:03 > 0:02:07In the far north-east of Mexico is an ancient mountain world...
0:02:09 > 0:02:12Serranias del Burro.
0:02:23 > 0:02:26It's home to an abundance of creatures.
0:02:36 > 0:02:40And its most surprising resident
0:02:40 > 0:02:42is the black bear.
0:02:44 > 0:02:47This mother has three young cubs, just eight months old.
0:02:50 > 0:02:52BEAR GRUNTS SOFTLY
0:03:08 > 0:03:11It's autumn and the family needs to fatten up
0:03:11 > 0:03:14before the winter hibernation.
0:03:15 > 0:03:18This year, the oak trees are laden with acorns -
0:03:21 > 0:03:23an important source of fat.
0:03:31 > 0:03:33The bears have plenty to eat,
0:03:33 > 0:03:36but their challenge here is finding enough to drink.
0:03:39 > 0:03:41CATTLE LOWING ECHOES
0:03:41 > 0:03:44The limestone mountains soak up the rain,
0:03:44 > 0:03:46so there are no permanent streams.
0:03:52 > 0:03:56Fortunately for the bears, there is another source of water.
0:04:07 > 0:04:10CATTLE LOW
0:04:14 > 0:04:19Serranias del Burro is prime cattle country and the ranchers provide
0:04:19 > 0:04:24year-round water for their herds by tapping into underground springs.
0:04:48 > 0:04:52The water tanks are a magnet for all.
0:04:52 > 0:04:56Mother bear, with her young cubs, must approach with caution.
0:05:05 > 0:05:08CATTLE LOWING ECHOES
0:05:10 > 0:05:14Bears occasionally kill cows,
0:05:14 > 0:05:18so the ranchers let their cows' horns grow long
0:05:18 > 0:05:20as a natural bear deterrent.
0:05:36 > 0:05:40The family gets the message -
0:05:40 > 0:05:42loud and clear.
0:05:53 > 0:05:58The cattle have had their fill, now it's the family's chance.
0:06:00 > 0:06:03BIRDS CALL
0:06:05 > 0:06:08But someone else has got his eye on the tank.
0:06:08 > 0:06:10BEAR GROWLS
0:06:15 > 0:06:18A big male.
0:06:18 > 0:06:20He's best avoided.
0:06:26 > 0:06:29CUBS CALL OUT
0:06:40 > 0:06:43This male wants more than a drink,
0:06:43 > 0:06:47he wants to cool off in his tub.
0:06:57 > 0:07:00At last...
0:07:28 > 0:07:32Mexico's black bears were once on the brink of extinction,
0:07:32 > 0:07:38but they clung on in mountain hideaways like Serranias del Burro.
0:07:38 > 0:07:41The ranchers here don't just tolerate the bears,
0:07:41 > 0:07:45they help them out, even providing a leg up for the cubs.
0:08:04 > 0:08:06The population is flourishing,
0:08:06 > 0:08:11making this mountain world an important stronghold for bears in
0:08:11 > 0:08:13North America.
0:08:31 > 0:08:36Mexico is a vast country, around 2,000 miles long...
0:08:38 > 0:08:42..dominated by a great range of mountains, the Sierra Madre...
0:08:43 > 0:08:47..stretching all the way from the country's northern border
0:08:47 > 0:08:53with the United States, down to its southern border with Guatemala.
0:08:55 > 0:08:58Travel down Mexico's rocky spine -
0:08:58 > 0:09:02and there are many more diverse mountain worlds.
0:09:31 > 0:09:37The grandest of them all is found in the north-west of the country,
0:09:37 > 0:09:40in a region known as Copper Canyon,
0:09:40 > 0:09:43covering 25,000 square miles.
0:09:48 > 0:09:50A maze of gorges,
0:09:50 > 0:09:53some even deeper than the Grand Canyon.
0:10:13 > 0:10:17In the 16th century, Spanish conquistadors came here,
0:10:17 > 0:10:19hunting for gold and silver.
0:10:22 > 0:10:25But they weren't the first to arrive.
0:10:30 > 0:10:36The Raramuri have lived in these mountains for over 2,000 years.
0:10:41 > 0:10:45To escape slavery in Spanish mines,
0:10:45 > 0:10:49many sought refuge in the most inaccessible places.
0:10:53 > 0:10:57To navigate the canyon's vast terrain quickly,
0:10:57 > 0:11:00the Raramuri became skilled long-distance runners...
0:11:03 > 0:11:06..able to cover 200 miles without stopping.
0:11:20 > 0:11:24Centuries of running at high altitude has made them
0:11:24 > 0:11:26unrivalled endurance athletes.
0:11:34 > 0:11:38THEY SPEAK IN SPANISH
0:11:39 > 0:11:43Today, the Raramuri still live in remote regions of the Copper Canyon
0:11:43 > 0:11:46and running remains an important part of their culture.
0:11:50 > 0:11:54Sisters Carmen, Mequejilda and Elida
0:11:54 > 0:11:57are from a proud family of runners.
0:11:59 > 0:12:04Their brother, Santos, is already a champion, winning several marathons.
0:12:07 > 0:12:10But today, it's his sisters' turn.
0:12:17 > 0:12:21Their traditional running sandals called huaraches,
0:12:21 > 0:12:26once fashioned from animal hide, are now made from old car tyres.
0:12:28 > 0:12:30Wearing them from childhood
0:12:30 > 0:12:31strengthens the foot muscles
0:12:31 > 0:12:34and stiffens the arches of the feet.
0:12:37 > 0:12:43Preparing this new generation of Raramuri for a life on the move.
0:12:47 > 0:12:50They are heading to the nearest town for a race.
0:13:24 > 0:13:26Here in the town of Porochi,
0:13:26 > 0:13:31a race day is a chance for distant neighbours to catch up.
0:13:34 > 0:13:37BUZZ OF CHATTER
0:13:43 > 0:13:45The girls' race is the first of the day.
0:13:48 > 0:13:50HE SPEAKS IN SPANISH
0:13:50 > 0:13:53They will be competing over three miles.
0:13:53 > 0:13:58Uno, dos, tres...
0:13:58 > 0:14:01fuera!
0:14:13 > 0:14:15In this traditional team event,
0:14:15 > 0:14:19the girls toss a hoop, called an arihueta, for the first lap.
0:14:30 > 0:14:33One lap down, one to go.
0:14:35 > 0:14:38Sister Elida now takes the arihueta.
0:14:40 > 0:14:43THEY SHOUT ENCOURAGEMENT
0:14:50 > 0:14:53The first hoop to cross the finishing line wins.
0:15:06 > 0:15:08At last, the home straight.
0:15:08 > 0:15:11MEN SHOUT
0:15:15 > 0:15:18Elida is first to cross the finish line...
0:15:18 > 0:15:21CROWD APPLAUDS
0:15:23 > 0:15:26..upholding her family's winning record.
0:15:26 > 0:15:29THEY SPEAK IN SPANISH
0:15:30 > 0:15:33The races continue long into the night.
0:15:49 > 0:15:54Mexico has one of the largest indigenous populations in Latin America.
0:15:56 > 0:16:01More than 25 million people and 68 different languages.
0:16:09 > 0:16:14Living in the Copper Canyon has moulded the Raramuri's whole way of life.
0:16:22 > 0:16:26All of Mexico's mountain worlds
0:16:26 > 0:16:29shape life in profoundly different ways.
0:16:39 > 0:16:45Nowhere is this more apparent than among a very unusual group of mountains...
0:16:47 > 0:16:491,000 miles to the south,
0:16:49 > 0:16:54where ancient tectonic events have crumpled the land...
0:17:05 > 0:17:10The Sierra Gorda, or opulent mountains.
0:17:10 > 0:17:14Here, the temperate and tropical collide,
0:17:14 > 0:17:16creating a mosaic of different habitats.
0:17:16 > 0:17:19BIRDS CALL
0:17:33 > 0:17:37In this one region, there are more than 2,000 different types of plant...
0:17:40 > 0:17:43..over 340 bird species...
0:17:43 > 0:17:46BIRDS CALL
0:17:46 > 0:17:49..and 800 kinds of butterfly.
0:18:01 > 0:18:05Fairy tale oak forests are a secret garden
0:18:05 > 0:18:08for more colourful tropical species.
0:18:20 > 0:18:23The most bewitching of all,
0:18:23 > 0:18:26orchids.
0:18:29 > 0:18:31Over millions of years,
0:18:31 > 0:18:35these flowers have developed an unusual relationship
0:18:35 > 0:18:37with a very colourful character...
0:18:39 > 0:18:43..the orchid bee.
0:18:43 > 0:18:47For just a few months each year, when the orchids are in bloom,
0:18:47 > 0:18:50the orchid bees visit them in droves.
0:18:52 > 0:18:55Not to sip their nectar -
0:18:55 > 0:18:59but to sweep up fragrant oils using brushes on their front feet.
0:19:01 > 0:19:05They scrape the oils into a special pouch on their hind legs.
0:19:05 > 0:19:08BEE BUZZES
0:19:09 > 0:19:12These orchid bees are mixing their own cologne...
0:19:13 > 0:19:17..made from up to 80 different scents collected from the forest.
0:19:18 > 0:19:22This complex fragrance helps the males attract the females.
0:19:22 > 0:19:25BEES BUZZ
0:19:27 > 0:19:32The most fragrant oils are produced by one very special kind of orchid...
0:19:35 > 0:19:37..Stanhopea.
0:19:39 > 0:19:43This orchid blooms for just one day each year.
0:19:45 > 0:19:50In this crucial 24 hours, it must spread its pollen far and wide.
0:19:55 > 0:19:57As soon as it opens,
0:19:57 > 0:19:59the flower emits a hypnotic perfume...
0:20:01 > 0:20:04..that smells like freshly ground cinnamon...
0:20:06 > 0:20:10..sending the orchid bees into delirium.
0:20:20 > 0:20:23BEES BUZZ INTENSELY
0:20:25 > 0:20:30But Stanhopea's sweet smell belies a cunning purpose.
0:20:33 > 0:20:37Its petals are covered in slippery oil droplets.
0:20:43 > 0:20:47And their intricate shape forces the bee to walk backwards.
0:20:48 > 0:20:51The bee slips
0:20:51 > 0:20:54and the orchid sticks a packet of pollen onto its back...
0:20:56 > 0:21:01..which it will unwittingly carry to other Stanhopea flowers.
0:21:06 > 0:21:09With its pollen distributed in just a single day,
0:21:09 > 0:21:11the flowers' job is done.
0:21:18 > 0:21:20As the sun sets,
0:21:20 > 0:21:23the petals wilt and die.
0:21:39 > 0:21:42BIRD CALL ECHOES
0:21:44 > 0:21:48Travel further south down Mexico's spine and ancient peaks give way to
0:21:48 > 0:21:52younger mountains in the fertile heart of the country.
0:21:55 > 0:21:59Much of this land is over 6,000ft above sea-level.
0:22:03 > 0:22:07A landscape of extensive farmland and pine oak forest.
0:22:14 > 0:22:19The soils here are especially rich because this is the home
0:22:19 > 0:22:23of restless giants.
0:22:45 > 0:22:49Popocatepetl is Mexico's second-highest peak...
0:22:50 > 0:22:54..over three miles above sea-level - and still growing.
0:22:57 > 0:23:00It's the country's most active volcano.
0:23:08 > 0:23:11LOW RUMBLING
0:23:37 > 0:23:41Mexico is one of the most volcanically active places on earth
0:23:41 > 0:23:46because it lies at the collision point of three tectonic plates,
0:23:46 > 0:23:51producing a great chain of mountains that stretch right across central
0:23:51 > 0:23:55Mexico, known as the Transvolcanic Belt,
0:23:55 > 0:23:59with more than 20 active volcanoes.
0:24:11 > 0:24:14They can cause death and destruction
0:24:14 > 0:24:17but they're also givers of life.
0:24:25 > 0:24:29Their volcanic ash enriches the soil,
0:24:29 > 0:24:32making this a highly productive region of Mexico...
0:24:37 > 0:24:40..and the most inhabited.
0:24:46 > 0:24:49The country's capital, Mexico City,
0:24:49 > 0:24:53lies on a high plateau in the shadow of volcanoes.
0:24:56 > 0:24:59People first settled here almost 10,000 years ago.
0:24:59 > 0:25:02DISTANT DOGS BARK
0:25:06 > 0:25:09It's a riot of colour...
0:25:09 > 0:25:10CAR HORNS BEEP
0:25:10 > 0:25:12..noise...
0:25:12 > 0:25:15and culture.
0:25:15 > 0:25:18CROWD CHEERS
0:25:20 > 0:25:27This sprawling mega-city is home to over 20 million people
0:25:27 > 0:25:32and 80% of all the food consumed here comes from a single place...
0:25:35 > 0:25:38..the largest wholesale food market in the world...
0:25:39 > 0:25:42..La Central de Abasto.
0:25:50 > 0:25:5430,000 tonnes of produce changes hands every day...
0:26:00 > 0:26:03..much of it grown on Mexico's volcanic belt.
0:26:09 > 0:26:12NOISY CHATTER
0:26:31 > 0:26:37The country's most iconic foods, chillies, maize and avocados,
0:26:37 > 0:26:40all originate in Mexico's Highlands.
0:26:42 > 0:26:46Many are exported worldwide
0:26:46 > 0:26:51and there's one product that's earned a formidable reputation.
0:26:51 > 0:26:55BELL TOLLS
0:26:59 > 0:27:02TRANSLATED FROM SPANISH:
0:27:26 > 0:27:3216-year-old Martin is a sometime bull rider but a full-time jimador,
0:27:32 > 0:27:36a farmer who harvests the blue agave plant...
0:27:39 > 0:27:42..the essential ingredient of tequila.
0:28:12 > 0:28:17Agave plants can take a decade to mature before the plant is cut down.
0:28:17 > 0:28:20DOGS BARK
0:28:23 > 0:28:29By slicing away the spiky leaves, the jimadores expose what they're after,
0:28:29 > 0:28:33the sugar rich heart, the pina.
0:28:34 > 0:28:39Martin toils in the shadow of Volcan de Tequila,
0:28:39 > 0:28:43which last erupted 220,000 years ago...
0:28:44 > 0:28:49..its ancient ash fertilising the rich red soils.
0:28:55 > 0:29:01This one region of Mexico, Jalisco, produces 80% of the country's tequila,
0:29:01 > 0:29:04crafted in special distilleries.
0:29:14 > 0:29:19The pinas are first roasted and then crushed, squeezing out the sugar-rich juices.
0:29:23 > 0:29:25These are then fermented.
0:29:26 > 0:29:28Yeast turns the sugar into alcohol.
0:29:31 > 0:29:34Finally, it's distilled...
0:29:34 > 0:29:37producing the highest grade tequila.
0:29:39 > 0:29:42MEN SPEAK IN SPANISH
0:29:43 > 0:29:46To improve the quality of their crops,
0:29:46 > 0:29:49some farmers are trying something new.
0:29:50 > 0:29:53For the first time in 200 years,
0:29:53 > 0:29:58they are letting a proportion of their agave go into flower.
0:30:02 > 0:30:07The plants funnel all their sugars into towering blooms...
0:30:09 > 0:30:12..rendering them useless for tequila
0:30:12 > 0:30:16but offering a lifeline for a threatened species.
0:30:21 > 0:30:26Thousands of female lesser long-nosed bats migrate along
0:30:26 > 0:30:30Mexico's mountains to reach their breeding caves in the north.
0:30:33 > 0:30:39They can fly over 60 miles a night and need frequent sips of sugar-rich nectar.
0:30:46 > 0:30:50The agave provides them with a critical source of food.
0:31:03 > 0:31:07The bats also benefit the farmers by pollinating their crop.
0:31:07 > 0:31:09MEN CHAT IN SPANISH
0:31:10 > 0:31:14If their agave is exposed to a greater mix of pollens,
0:31:14 > 0:31:20the plants will be stronger and more resilient to disease.
0:31:20 > 0:31:23THEY SPEAK IN SPANISH
0:31:23 > 0:31:26THEY LAUGH
0:31:26 > 0:31:30By helping the bats, the agave farmers are safeguarding their own future...
0:31:32 > 0:31:37..and ensuring the continued legacy of Mexico's most iconic drink.
0:31:50 > 0:31:54Central Mexico's mountains have attracted people for millennia.
0:32:06 > 0:32:10Immense empires grew in this volcanic heartland...
0:32:11 > 0:32:15..and the remnants of some of their cities still stand.
0:32:19 > 0:32:251,500 years ago, Teotihuacan was a thriving metropolis,
0:32:25 > 0:32:29home to over 100,000 people.
0:32:32 > 0:32:37But perhaps the most famous ancient empire here
0:32:37 > 0:32:39was the Aztecs.
0:32:45 > 0:32:49They dominated central Mexico in the 15th and 16th centuries.
0:32:51 > 0:32:55Aztecs believed mountains connected Earth to the heavens
0:32:55 > 0:32:57and the underworld.
0:33:00 > 0:33:0750 miles south of Mexico City is the Temple of Tepozteco.
0:33:07 > 0:33:10This shrine was abandoned long ago
0:33:10 > 0:33:14but a very resourceful animal has since made it home...
0:33:14 > 0:33:17SOFT GRUNTING
0:33:18 > 0:33:21..coatis.
0:33:26 > 0:33:29They are the most social of the raccoon family...
0:33:31 > 0:33:33..forming bands up to 30 strong.
0:33:35 > 0:33:41They normally live in tropical woodlands and open forest.
0:33:41 > 0:33:43COATIS SNUFFLE AND SQUEAL
0:33:47 > 0:33:49Coatis are omnivores.
0:33:50 > 0:33:54They can eat pretty much anything.
0:33:59 > 0:34:02Here at Tepozteco, there are plenty of options.
0:34:22 > 0:34:27This important archaeological site attracts many visitors,
0:34:27 > 0:34:30and tourists bring opportunities.
0:34:39 > 0:34:42This is no ordinary coati clan.
0:35:05 > 0:35:09These adaptable animals have become artful thieves.
0:35:19 > 0:35:23The coatis are thriving thanks to teamwork
0:35:23 > 0:35:25and a shameless streak.
0:35:25 > 0:35:27COATIS SQUEAK
0:35:46 > 0:35:48Below the volcanic heartland,
0:35:48 > 0:35:53Mexico's Sierra Madre stretches on south towards the tropics.
0:35:59 > 0:36:02At its southernmost tip,
0:36:02 > 0:36:04where it meets the Pacific Ocean,
0:36:04 > 0:36:08the mountains catch the moisture from clouds rolling in off the sea.
0:36:23 > 0:36:2710% of all of Mexico's rain is captured here,
0:36:27 > 0:36:33helping to create a lush cloud forest known as El Triunfo.
0:36:45 > 0:36:47The combination of humidity,
0:36:47 > 0:36:53altitude and warmth makes the perfect conditions for life to flourish.
0:36:53 > 0:36:56BIRDS CALL, INSECTS BUZZ
0:36:58 > 0:37:03This secret mountain world is home to an abundance of rare creatures,
0:37:03 > 0:37:06many found nowhere else on earth.
0:37:10 > 0:37:13High in the canopy,
0:37:13 > 0:37:17100ft off the ground, lives the alligator tree lizard...
0:37:21 > 0:37:24..and the horned guan.
0:37:24 > 0:37:27GUAN MAKES DEEP-THROATED CALL
0:37:27 > 0:37:29The last survivor of an ancient bird family,
0:37:29 > 0:37:34it's been evolving independently for more than 30 million years.
0:37:34 > 0:37:38BIRDS CALL VOCALLY
0:37:43 > 0:37:48In forest clearings, male long-tailed manakins dance to entice females,
0:37:48 > 0:37:51a ritual that may take a decade to perfect.
0:38:02 > 0:38:07Travel deeper into the heart of this cloud forest,
0:38:07 > 0:38:11and you might discover the true spirit of El Triunfo...
0:38:13 > 0:38:16..a mythical creature rarely seen.
0:38:21 > 0:38:24Sacred to the ancient Aztecs,
0:38:24 > 0:38:27who treasured its feathers more than gold.
0:38:31 > 0:38:36It's considered the most beautiful bird in the Americas...
0:38:36 > 0:38:40BIRDS CALL
0:38:43 > 0:38:49..the aptly named resplendent quetzal.
0:39:04 > 0:39:09It's the mating season and these males' three-foot-long tail feathers
0:39:09 > 0:39:12have helped him successfully attract a mate.
0:39:19 > 0:39:22Now he has a young family to feed.
0:39:27 > 0:39:32He works tirelessly for a month to satisfy his brood's voracious appetite.
0:39:38 > 0:39:44His lush Mexican home is brimming with fruit and insects.
0:39:53 > 0:39:55At the end of the mating season,
0:39:55 > 0:39:59he will drop his spectacular tail feathers,
0:39:59 > 0:40:02but the quetzal grows a new train every year.
0:40:07 > 0:40:13Only in such a rich mountain habitat can animals afford to devote so much
0:40:13 > 0:40:16energy to looking this good.
0:40:29 > 0:40:34From north to south, all of Mexico's mountain worlds are unique.
0:40:36 > 0:40:38And some are so inviting,
0:40:38 > 0:40:42they compel creatures to journey vast distances to reach them.
0:40:49 > 0:40:54Every winter, one creature travels nearly 3,000 miles
0:40:54 > 0:40:55from as far as Canada,
0:40:55 > 0:40:59to this special place, high in the mountains of central Mexico.
0:41:07 > 0:41:11The trees seem to be draped in leaves, but in fact,
0:41:11 > 0:41:15they are coated in millions of delicate creatures.
0:41:18 > 0:41:22Silent, unmoving...
0:41:24 > 0:41:26..monarch butterflies.
0:41:32 > 0:41:35In their hundreds of millions.
0:41:39 > 0:41:43These oyamel fir forests are their perfect winter sanctuary.
0:41:46 > 0:41:49The low temperatures slow their metabolism,
0:41:49 > 0:41:52putting the butterflies in a trance for five long months.
0:42:04 > 0:42:07Mountain mists prevent them from drying out.
0:42:09 > 0:42:13And the towering firs help protect them from winter storms...
0:42:15 > 0:42:17..ensuring they don't freeze.
0:42:21 > 0:42:23For thousands of years,
0:42:23 > 0:42:29these monarchs have had a special significance for the people of Mexico's mountains,
0:42:29 > 0:42:34who believe the butterflies to be the spirits of the dead,
0:42:34 > 0:42:36returning to Earth from the heavens.
0:42:37 > 0:42:42And their arrival in winter coincides with one of the most
0:42:42 > 0:42:44important events in the Mexican calendar.
0:42:53 > 0:42:56MAN SINGS IN SPANISH
0:43:06 > 0:43:11Dia de Los Muertos - The Day of the Dead.
0:43:14 > 0:43:17CHIMES TINKLE
0:43:19 > 0:43:22SHE SPEAKS IN SPANISH
0:43:22 > 0:43:25In villages across the Sierra Madre,
0:43:25 > 0:43:30families like Catalina's are remembering those who have passed on.
0:43:31 > 0:43:34TRANSLATED FROM SPANISH:
0:43:40 > 0:43:43THEY SPEAK IN SPANISH
0:43:57 > 0:44:01Catalina and her family gather around her husband's grave.
0:44:36 > 0:44:39THEY CHAT AND LAUGH
0:44:50 > 0:44:54The family keep their candles burning until first light.
0:44:55 > 0:44:57But they are not alone.
0:45:00 > 0:45:04Tonight, millions of candles are lit throughout Mexico...
0:45:09 > 0:45:12..helping to guide the spirits of loved ones back home.
0:45:21 > 0:45:25The party for the dead has only just begun.
0:45:25 > 0:45:28FIREWORKS WHISTLE
0:45:30 > 0:45:33WHOOPING AND CHEERING
0:45:34 > 0:45:37Many Mexicans do not believe death is an ending.
0:45:40 > 0:45:44They embrace it as an essential part of a natural cycle.
0:45:54 > 0:45:58The people here have been celebrating the Day of the Dead
0:45:58 > 0:46:00for more than 3,000 years.
0:46:07 > 0:46:10Generation after generation.
0:46:18 > 0:46:21But the spirits of the dead cannot stay for long.
0:46:24 > 0:46:27Just as the spirits must return to the heavens...
0:46:30 > 0:46:33..the butterflies will also leave.
0:46:57 > 0:47:02This is Mexico's greatest natural spectacle,
0:47:02 > 0:47:05up to a billion butterflies take to the wind.
0:47:13 > 0:47:16These monarchs will never return to Mexico.
0:47:16 > 0:47:19Their short time on this earth is almost over.
0:47:22 > 0:47:24But they will lay their eggs on the journey north.
0:47:32 > 0:47:36And next year their descendants will continue this ancient ritual...
0:47:39 > 0:47:44..by making the same epic pilgrimage along Mexico's rocky spine,
0:47:44 > 0:47:47back to this unique mountain world.
0:47:56 > 0:48:00It's no coincidence that Sierra Madre means Mother Mountains.
0:48:04 > 0:48:08Her great ranges nurture an incredible diversity of life...
0:48:11 > 0:48:15..and helped give birth to some of the greatest civilisations on earth.
0:48:22 > 0:48:25The Aztecs believed mountains brought you closer to the heavens.
0:48:28 > 0:48:31In Mexico's Mother Mountains,
0:48:31 > 0:48:33you can see why.
0:48:46 > 0:48:51Of all the animals the mountains team wanted to feature,
0:48:51 > 0:48:54one creature was top of the list.
0:48:54 > 0:48:58Rarely seen, little-known, hardly ever filmed.
0:49:01 > 0:49:02Mexico's black bear.
0:49:05 > 0:49:07Filming them would be a great achievement.
0:49:10 > 0:49:13To stand any chance of even finding them,
0:49:13 > 0:49:18the team relied on Mexico's foremost bear scientist,
0:49:18 > 0:49:20Diana Doan-Crider,
0:49:20 > 0:49:24a Mexican American who has been studying and protecting these bears
0:49:24 > 0:49:25for 25 years.
0:49:29 > 0:49:32My mother's Mexican and my father's American.
0:49:32 > 0:49:36When I was a kid, my grandfather, he would tell me stories of seeing bears.
0:49:38 > 0:49:42As I grew up, I knew I wanted to study wildlife in Mexico.
0:49:57 > 0:49:59Since the 1980s,
0:49:59 > 0:50:03Diana's extensive research in the Serranias del Burro
0:50:03 > 0:50:07has shown that these mountains are an essential stronghold
0:50:07 > 0:50:08for black bears.
0:50:14 > 0:50:18She has worked closely with ranchers and landowners to help protect
0:50:18 > 0:50:20this important habitat.
0:50:25 > 0:50:28But five years ago, disaster struck.
0:50:31 > 0:50:34Five years ago, it quit raining for eight months.
0:50:34 > 0:50:36So it dried up all of that fuel.
0:50:36 > 0:50:39And then, in March, while I was here, a fire started.
0:50:42 > 0:50:43That fire didn't stop until May.
0:50:45 > 0:50:47And it burned 350,000 acres.
0:50:50 > 0:50:54I will be honest, I was traumatised by what I saw because...
0:50:54 > 0:50:55I'm sorry.
0:50:57 > 0:50:58We saw a lot of dead bears.
0:51:07 > 0:51:10I think a lot of us were, like, "Man, this is it. It's over."
0:51:13 > 0:51:16The fires also ravaged the oak forests,
0:51:16 > 0:51:20whose acorns are a critical source of food for the bears.
0:51:25 > 0:51:30This is Diana's first time back to find the bears since the fire,
0:51:30 > 0:51:33so the shoot takes on extra significance.
0:51:36 > 0:51:39After decades of conservation effort,
0:51:39 > 0:51:43she is desperate to see if they have managed to survive,
0:51:43 > 0:51:47and whether this fragile ecosystem has fully recovered.
0:51:48 > 0:51:54This is my first time back, and this place here was completely devoid
0:51:54 > 0:51:56of vegetation.
0:51:56 > 0:51:59So this was a dead tree.
0:51:59 > 0:52:02And what's really great is that we have acorn production now.
0:52:02 > 0:52:04And that's what we were most concerned with,
0:52:04 > 0:52:07was how long was it going to take for these patches,
0:52:07 > 0:52:10especially severely burnt patches, to start producing acorns.
0:52:12 > 0:52:15The mountains team have timed their visit carefully.
0:52:17 > 0:52:21It's autumn, and the bears should be around,
0:52:21 > 0:52:23fattening up on the flush of food.
0:52:26 > 0:52:30Diana takes the team, along with landowner David,
0:52:30 > 0:52:33to look for signs of bear activity.
0:52:33 > 0:52:36What we have is branch breakage by the bears.
0:52:36 > 0:52:38They climb up in here and they pack it down and then they sit up there
0:52:38 > 0:52:41and feed. And this is a really good example.
0:52:42 > 0:52:45There is further evidence, if a bit unsavoury.
0:52:46 > 0:52:48How old would that be?
0:52:48 > 0:52:51This is probably just a couple of days old because it has been
0:52:51 > 0:52:53very hot and it is still moist on the inside.
0:52:55 > 0:52:57I'd have to taste it to be sure.
0:52:57 > 0:52:58LAUGHTER
0:53:00 > 0:53:04Great news - proof that the bears are around.
0:53:05 > 0:53:07But this is a vast landscape,
0:53:07 > 0:53:11more than 1,000 square miles of wilderness.
0:53:13 > 0:53:16The team need to know where they should focus their effort.
0:53:17 > 0:53:19And Diana knows the right people to ask.
0:53:22 > 0:53:26Ranchers. They know this land like the back of their hands...
0:53:28 > 0:53:30..and the bears better than anyone.
0:53:33 > 0:53:36I came in kind of with an attitude of telling them what I was going to do,
0:53:36 > 0:53:39what I was going to learn about bears and, you know,
0:53:39 > 0:53:41give them all the answers that they needed.
0:53:41 > 0:53:44I remember the first meeting I had with them, and it was a group
0:53:44 > 0:53:46of ranchers, and they sat down and they gave me a list.
0:53:46 > 0:53:49And they told me, "This is what the bears do in the spring,
0:53:49 > 0:53:53"this is what the bears do in the fall, this is how many cubs they have.
0:53:53 > 0:53:54"This is what they eat."
0:53:55 > 0:53:59And I can tell you this, every one of those things on that list were true.
0:54:01 > 0:54:04There have been recent bear sightings.
0:54:06 > 0:54:09And ahead of the shoot the ranchers set up some camera traps for
0:54:09 > 0:54:14the team, hoping to find out where the bears are most active.
0:54:15 > 0:54:17Oh, man. I can't believe it.
0:54:18 > 0:54:19Look what he did.
0:54:21 > 0:54:24A bear just came and knocked over the whole rock.
0:54:26 > 0:54:27There's two down.
0:54:33 > 0:54:35LAUGHTER
0:54:35 > 0:54:38Look here. He made a hole.
0:54:38 > 0:54:40This isn't exactly what they were hoping for.
0:54:42 > 0:54:46These animals, they can't, like, not totally trash it.
0:54:46 > 0:54:49Bears four, me zero.
0:54:49 > 0:54:52We'll see if we have anything that's useful on these cameras.
0:54:55 > 0:54:58I guess it's the best way we can work out where to concentrate our
0:54:58 > 0:55:00efforts, as long as it hasn't been eaten up.
0:55:02 > 0:55:03Can you see anything?
0:55:03 > 0:55:09For the first time in five years, Diana sees her bears again.
0:55:09 > 0:55:12- What are they doing? - They are just goofing around.
0:55:13 > 0:55:16And they both have chest blazes which makes me think that they
0:55:16 > 0:55:18- are siblings.- Siblings.
0:55:18 > 0:55:21These two show up and they start romping around,
0:55:21 > 0:55:24- playing with each other.- It would be great if we could film them because
0:55:24 > 0:55:26they are very playful.
0:55:26 > 0:55:30What's interesting about this is you see the truck go by.
0:55:30 > 0:55:33And not even four minutes later the bear comes back.
0:55:33 > 0:55:38At least now we know which are the most active pools to concentrate on.
0:55:38 > 0:55:41I'll be honest with you, I never knew this number of animals were
0:55:41 > 0:55:43visiting these water sources.
0:55:47 > 0:55:50With this information from the camera traps,
0:55:50 > 0:55:54the team now concentrate on a few key water tanks.
0:55:55 > 0:55:58It's really good cos we've just seen our first bear.
0:56:02 > 0:56:06There is a mother bear and a baby there just feeding on some acorns.
0:56:19 > 0:56:23For the first time since the fire, this is a bumper year for cubs.
0:56:39 > 0:56:41- That's a wonderful jump. - Oh, my gosh.
0:56:41 > 0:56:43This is so amazing.
0:56:43 > 0:56:44That's great stuff.
0:56:46 > 0:56:49Today has been great. The dam broke, we've got some great play behaviour.
0:56:49 > 0:56:51I mean, as good as I've filmed anywhere,
0:56:51 > 0:56:53Canada or North America.
0:56:53 > 0:56:55So it has been great.
0:56:59 > 0:57:02Diana has been an absolute godsend to the shoot.
0:57:02 > 0:57:08Having her wisdom and her 25 years' experience and her relationship
0:57:08 > 0:57:14with the ranchers, she has opened the door to us, to tell, I think,
0:57:14 > 0:57:16the most magical black bear story.
0:57:16 > 0:57:21I quit coming for a long time and now I've come back, five years later,
0:57:21 > 0:57:26and I'm actually floored over the recovery of the ecosystem.
0:57:28 > 0:57:31And not just that, but the recovery of this bear population.
0:57:37 > 0:57:41This place demonstrates how people can coexist with wildlife.
0:57:41 > 0:57:43It's a really unique relationship.
0:57:45 > 0:57:48The ranchers have learned to coexist with the bears.
0:57:48 > 0:57:50The bears have learned to coexist with the cattle.
0:57:50 > 0:57:53I love that. That's Mexico's heritage -
0:57:53 > 0:57:55us living on the land.
0:58:01 > 0:58:05Next time, we travel to Mexico's southeast,
0:58:05 > 0:58:07and a unique peninsula.
0:58:08 > 0:58:10The Yucatan,
0:58:10 > 0:58:14the birthplace of the once-mighty Maya civilisation...
0:58:20 > 0:58:24..where mysterious forests hide a secret underworld.