0:00:05 > 0:00:07Our planet is a place of constant change.
0:00:09 > 0:00:12Each year, the seasons shift and life is transformed.
0:00:15 > 0:00:19But there are places where the changes are so epic in scale
0:00:19 > 0:00:20they can be seen from space.
0:00:23 > 0:00:24In this series,
0:00:24 > 0:00:27we reveal three of the most miraculous transformations.
0:00:30 > 0:00:33The islands of Svalbard - within a few weeks,
0:00:33 > 0:00:36frozen wastelands burst into life.
0:00:38 > 0:00:41The African Okavango -
0:00:41 > 0:00:44a desert transforms into a magical waterworld.
0:00:46 > 0:00:49And the mysterious forests of New England -
0:00:49 > 0:00:52erupting in a blaze of seasonal colour.
0:00:56 > 0:01:00Life finds the most ingenious and surprising ways to thrive...
0:01:02 > 0:01:05..in the world's fastest-changing landscapes.
0:01:18 > 0:01:22New England - home to the most colourful forest in America.
0:01:24 > 0:01:26Stretching across six states...
0:01:29 > 0:01:34..from Maine in the north to Connecticut in the south.
0:01:36 > 0:01:40Every year, millions of people flock here to witness
0:01:40 > 0:01:43one of the planet's greatest spectacles,
0:01:43 > 0:01:45known here as the fall...
0:01:47 > 0:01:53..when billions of trees explode into a riot of red, orange and gold.
0:01:57 > 0:02:00There's nowhere else on Earth quite like it.
0:02:04 > 0:02:07But despite this beauty, there's a battle raging.
0:02:10 > 0:02:14One that holds the secret to this magical forest's most
0:02:14 > 0:02:16flamboyant display.
0:02:42 > 0:02:44The story of the fall begins
0:02:44 > 0:02:47while winter still has a grip on the forest.
0:02:51 > 0:02:5517 billion trees, rich with maples and oaks,
0:02:55 > 0:02:57wait in suspended animation.
0:03:01 > 0:03:02Amongst them,
0:03:02 > 0:03:05many of New England's animals are hibernating from the cold.
0:03:10 > 0:03:13But America's tallest mammal remains at large.
0:03:19 > 0:03:22Moose survive by chewing on twigs.
0:03:30 > 0:03:32Their calves will be born in just two months...
0:03:33 > 0:03:36..and their survival will depend on the same
0:03:36 > 0:03:40chain of events that will fuel the forest's climax of colour.
0:03:46 > 0:03:49As the weather warms, water courses through every tree...
0:03:52 > 0:03:55..and it picks up sugar stored in the wood.
0:03:57 > 0:04:01This liquid energy is the life force of the entire forest.
0:04:04 > 0:04:07It's so rich with sugar that maple syrup is made from it.
0:04:13 > 0:04:17The spring sunshine warms the land...
0:04:19 > 0:04:21..and the sugar surges faster...
0:04:24 > 0:04:27..fuelling the growth of nutrient-rich buds.
0:04:34 > 0:04:39These tiny packages contain everything needed to build a leaf.
0:04:45 > 0:04:49But from this point on, each tree faces a battle.
0:04:56 > 0:05:00All across New England, twigs are coming to life.
0:05:11 > 0:05:15These creatures spend the winter disguised as twigs.
0:05:18 > 0:05:19Looper caterpillars.
0:05:26 > 0:05:31They awake with the warmth and immediately begin to seek out
0:05:31 > 0:05:34the freshest buds, on a hunt for sugar.
0:05:40 > 0:05:43Nearby, hundreds of baby tent caterpillars
0:05:43 > 0:05:45hatch from their winter eggs.
0:05:50 > 0:05:54Each smaller than a grain of rice. They join the feast.
0:06:00 > 0:06:04Swarming along the branches, a torrent of bud destruction.
0:06:09 > 0:06:13This is just the first wave in a battle that will escalate
0:06:13 > 0:06:14through the year.
0:06:18 > 0:06:21The buds race to open before they can be attacked.
0:06:26 > 0:06:30Gradually, the first flush of green spreads across the forest.
0:06:35 > 0:06:38But it will be a few weeks before the leaves are fully expanded...
0:06:42 > 0:06:44..and they will need a constant supply of sugary
0:06:44 > 0:06:46sap from under the bark.
0:06:47 > 0:06:51In some trees, that sap is also at risk.
0:06:57 > 0:07:01The warming spring weather attracts an animal with a serious
0:07:01 > 0:07:02sugar addiction.
0:07:06 > 0:07:08TAPPING
0:07:08 > 0:07:11All the way from Mexico,
0:07:11 > 0:07:14he's one of the first to come back after the trees wake.
0:07:21 > 0:07:23The yellow-bellied sapsucker.
0:07:26 > 0:07:28His beak hammers six times a second...
0:07:32 > 0:07:33..wounding the tree deeply...
0:07:35 > 0:07:38..and chiselling into the vessels carrying the precious sugar.
0:07:47 > 0:07:51His feathery tongue quickly laps up the weeping liquid.
0:08:00 > 0:08:04On this tree last year, he dug hundreds of holes,
0:08:04 > 0:08:07but now, all the wells are dry.
0:08:13 > 0:08:16It's not enough to deter a determined sapsucker.
0:08:17 > 0:08:20He can dig as many as 1,000 holes in a season.
0:08:27 > 0:08:30And on another tree, he's excavating a nest.
0:08:33 > 0:08:36If he finishes it and keeps his wells running sweetly,
0:08:36 > 0:08:39he could attract the attention of a female.
0:08:42 > 0:08:45But there's another bird that could scupper his plans.
0:08:47 > 0:08:49A ruby-throated hummingbird.
0:08:53 > 0:08:57He's followed the sapsucker all the way from Mexico.
0:09:06 > 0:09:09His wings beat 80 times a second,
0:09:09 > 0:09:11putting him on a calorific knife edge.
0:09:21 > 0:09:25The weeping sap is the best source of sugar currently available,
0:09:25 > 0:09:29and feeding at 15 sips a second, he can quickly drain a well dry.
0:09:33 > 0:09:35He's too fast for the sapsucker to chase off...
0:09:41 > 0:09:44..so the sapsucker opens more and more wells.
0:09:58 > 0:10:01Eventually, despite the interruption,
0:10:01 > 0:10:05he finishes off his nest, creating a deep hollow in the tree.
0:10:07 > 0:10:09Now, everything is prepared.
0:10:21 > 0:10:24Despite relentless attack from birds and insects,
0:10:24 > 0:10:29the warming weather keeps the trees pumping sap,
0:10:29 > 0:10:33and, as the day length increases, the leaves continue to inflate.
0:10:38 > 0:10:42As the leaves grow, they start to shade the forest floor.
0:10:46 > 0:10:50In anticipation, the plants down below wake from their stupor.
0:11:04 > 0:11:07The flowers must attract a pollinator before all
0:11:07 > 0:11:08the light is stolen.
0:11:12 > 0:11:16Now, hummingbirds can feed on their favourite source of sugar.
0:11:17 > 0:11:18Nectar.
0:11:21 > 0:11:24In turn helping to pollinate the flowers.
0:11:39 > 0:11:43A looper caterpillar feeds amongst the flowers, too.
0:11:44 > 0:11:47He's no longer hiding amongst the twigs.
0:11:47 > 0:11:51This master of disguise has a different trick up his sleeve.
0:11:56 > 0:12:01Swaying back and forth, he mimics a flower moving in the breeze.
0:12:04 > 0:12:09He sticks petals to his back so that he can feed unnoticed by predators.
0:12:15 > 0:12:19And there's a whole army of flower arrangers sporting the latest
0:12:19 > 0:12:20spring fashion!
0:12:28 > 0:12:30As the sun strengthens,
0:12:30 > 0:12:34the building sap finally forces the leaves to fully unfurl.
0:12:45 > 0:12:49As many as 200,000 leaves on every tree.
0:12:56 > 0:13:00Together, they grow enough foliage to blanket an area six times
0:13:00 > 0:13:02the size of New England.
0:13:08 > 0:13:10As the leaves expand,
0:13:10 > 0:13:13they produce one of nature's most powerful chemicals.
0:13:17 > 0:13:18Chlorophyll.
0:13:19 > 0:13:22This green pigment catches the sun's energy to power
0:13:22 > 0:13:24a reaction crucial to all life.
0:13:28 > 0:13:32Photosynthesis - creating sugar from sunshine.
0:13:38 > 0:13:42This sugar is essential for the tree to grow,
0:13:42 > 0:13:46but it's now in easy reach of New England's hungriest animals.
0:13:58 > 0:13:59A moose.
0:14:04 > 0:14:09Named by the Native Americans as moosu, "he who strips off",
0:14:09 > 0:14:11they are leaf-eating machines...
0:14:14 > 0:14:16..and can strip a branch clean in seconds...
0:14:20 > 0:14:23..but the trees can defend themselves.
0:14:25 > 0:14:29In response, they flood their leaves with a repulsive chemical
0:14:29 > 0:14:30called tannin.
0:14:33 > 0:14:36So moose must constantly roam to seek out fresh ones.
0:14:39 > 0:14:42But this female doesn't want to travel far.
0:14:45 > 0:14:48She has twins and they're just two weeks old.
0:14:50 > 0:14:56Until now, they've remained hidden in the shade of the forest.
0:14:56 > 0:14:59With the leaves now loaded with unpleasant tannins,
0:14:59 > 0:15:03she needs to find an alternative food source.
0:15:13 > 0:15:16She leads the twins away from the cover of the trees
0:15:16 > 0:15:18for the very first time.
0:15:35 > 0:15:38Out here, it's a big, new world.
0:15:44 > 0:15:45The mother must stay close.
0:15:52 > 0:15:56Another cow and her calf are already enjoying the coolness of the lake.
0:16:01 > 0:16:04Moose have the longest legs in North America,
0:16:04 > 0:16:09which allows her to reach something that other animals can't get to.
0:16:09 > 0:16:12It's what makes this lake irresistible.
0:16:17 > 0:16:18Water plants.
0:16:21 > 0:16:24Just what this mother needs to enrich her milk...
0:16:31 > 0:16:33..because they're packed with nutrients
0:16:33 > 0:16:35washed out of the leaf litter.
0:17:03 > 0:17:07The twins will increase in weight tenfold over the next few months.
0:17:13 > 0:17:16It's not just the females who need the nutrients.
0:17:20 > 0:17:23Big bulls are here to feed for a different reason.
0:17:27 > 0:17:31To grow their antlers, one of the fastest-growing animal organs.
0:17:46 > 0:17:48They keep a safe distance.
0:17:48 > 0:17:51Neither wants to damage his prized possessions.
0:17:52 > 0:17:55Because their racks are not just for fighting.
0:17:57 > 0:18:01Male moose concentrate on looking good...
0:18:01 > 0:18:03and attracting females.
0:18:07 > 0:18:10With females watching on, it's a chance to show off.
0:18:22 > 0:18:25A good try, but at this time of the year,
0:18:25 > 0:18:28this female's attention is still fully on her calves.
0:18:33 > 0:18:36It won't be until the fall that she will be
0:18:36 > 0:18:39back on the market for a mate.
0:18:58 > 0:19:01Late spring, the busiest time
0:19:01 > 0:19:04for the forest's most notorious tree-eater.
0:19:13 > 0:19:16Signs of his appetites surround almost every lake.
0:19:25 > 0:19:29The beaver, New England's most industrious animal.
0:19:33 > 0:19:37His lodge is his castle, built of sticks and hardened by mud.
0:19:40 > 0:19:43But his masterpiece is his dam.
0:19:45 > 0:19:49Over 50 metres long and built of thousands of logs and branches.
0:19:51 > 0:19:55For 20 years it has held back the water to create a moat -
0:19:55 > 0:19:57a defence against predators.
0:19:59 > 0:20:02But this security comes at a price.
0:20:05 > 0:20:07The dam needs constant maintenance.
0:20:09 > 0:20:10A leak.
0:20:11 > 0:20:13He's going to need supplies.
0:20:20 > 0:20:22To avoid being spotted by predators,
0:20:22 > 0:20:25beavers work under the cover of darkness.
0:20:38 > 0:20:42There iron-infused teeth make powerful tools with which they can
0:20:42 > 0:20:46fell a tree ten inches wide in just a couple of hours.
0:20:52 > 0:20:54SNAPPING
0:21:03 > 0:21:06Fixing a leak can take all night
0:21:06 > 0:21:07and into the morning.
0:21:29 > 0:21:33He stirs up mud, using this mortar to seal the cracks.
0:21:38 > 0:21:42But fix one leak... and another is sure to spread.
0:21:48 > 0:21:50A beaver's work is never done.
0:21:58 > 0:22:02All this work isn't just for his own security.
0:22:04 > 0:22:06MEWING
0:22:08 > 0:22:12In spring, a beaver's lodge is busy with the activity of baby
0:22:12 > 0:22:16beavers and their sounds as they call for milk.
0:22:16 > 0:22:18MEWING AND PURRING
0:22:38 > 0:22:41This is a crucial time to practise using their teeth before
0:22:41 > 0:22:44they too are unleashed onto the forest.
0:22:46 > 0:22:48PURRING
0:22:54 > 0:22:58The beavers of New England fell millions of trees every year.
0:23:00 > 0:23:05But surprisingly, it's this that makes them heroes of the forest.
0:23:08 > 0:23:10By removing softer trees,
0:23:10 > 0:23:15they create large open spaces where red maple saplings can take root.
0:23:17 > 0:23:20And they leave bigger hardwoods standing, like maples
0:23:20 > 0:23:24and oaks, with space to spread their branches.
0:23:33 > 0:23:38With more leaves to create sugar, trees can grow ten times faster,
0:23:38 > 0:23:42and their colours in the fall will be much brighter.
0:23:47 > 0:23:51Beavers have helped to create a forest rich with maples and oaks.
0:23:53 > 0:23:57But 400 years ago, something happened that was to rapidly
0:23:57 > 0:24:00speed up what the beavers had started.
0:24:06 > 0:24:10Clues to this event can be seen threading through the forest.
0:24:11 > 0:24:12Stone walls.
0:24:15 > 0:24:17240,000 miles of them.
0:24:19 > 0:24:20Enough to reach the moon.
0:24:25 > 0:24:29In 1620, British settlers landed on these shores.
0:24:30 > 0:24:33Attracted by tales of green and pleasant lands...
0:24:35 > 0:24:38..they had hoped to create a prosperous life.
0:24:44 > 0:24:48What they encountered was an ancient dark forest,
0:24:48 > 0:24:50creaking with giant trees.
0:24:55 > 0:24:58And haunting sounds they had never heard before.
0:24:58 > 0:25:00BIRDS SQUAWK
0:25:03 > 0:25:06The trees towered above them,
0:25:06 > 0:25:09far higher than any they had seen in Britain.
0:25:12 > 0:25:15The biggest of them all was the white pine,
0:25:15 > 0:25:18said to have reached as high as 200 feet.
0:25:23 > 0:25:27By royal decree, the King of England claimed every one with
0:25:27 > 0:25:31a diameter greater than 24 inches.
0:25:31 > 0:25:34They were shipped across the Atlantic for use as the masts
0:25:34 > 0:25:35of the Royal Navy.
0:25:37 > 0:25:39The rest were left for settlers.
0:25:48 > 0:25:53They felled trees to build homes, churches and mills.
0:25:57 > 0:25:59Many animals, like mountain lions
0:25:59 > 0:26:03and wolves, were wiped out as the wilderness was tamed.
0:26:07 > 0:26:10By 1850, almost all of New England's
0:26:10 > 0:26:12forest had been chopped down,
0:26:12 > 0:26:15and much of this was turned to farmland,
0:26:15 > 0:26:18surrounded by stone walls.
0:26:20 > 0:26:22But then everything changed
0:26:22 > 0:26:27as richer farmland and gold was discovered in the west...
0:26:28 > 0:26:32..and many of the settlers chased their fortunes elsewhere.
0:26:37 > 0:26:41Towns like Livermore disappeared as quickly as they had been formed.
0:26:46 > 0:26:50Slowly, the trees of New England grew around the ruins
0:26:50 > 0:26:52and reclaimed the land.
0:26:57 > 0:27:00This new forest was very different.
0:27:00 > 0:27:03By chopping down the old-growth trees,
0:27:03 > 0:27:08people had given fast-growing maples and oaks a chance to claim the land.
0:27:11 > 0:27:14They grew back in greater numbers than ever before,
0:27:14 > 0:27:17and today they dominate this forest.
0:27:22 > 0:27:26From now on, there would be nowhere else more colourful in the fall.
0:27:28 > 0:27:32Today those stone walls are highways
0:27:32 > 0:27:34for one of New England's busiest animals.
0:27:38 > 0:27:40The chipmunk.
0:27:46 > 0:27:51There can be as many as 15 living in every acre...
0:27:51 > 0:27:53because New England is a chipmunk paradise.
0:27:58 > 0:28:02The stone walls help them to get around the forest
0:28:02 > 0:28:03and keep an eye out for predators.
0:28:08 > 0:28:11And the new forest provides all the acorns and maple seeds
0:28:11 > 0:28:13a chipmunk can eat.
0:28:25 > 0:28:28Today the forest is treasured,
0:28:28 > 0:28:32and 80% of New England is covered in trees,
0:28:32 > 0:28:35ensuring the fall remains rich and colourful.
0:28:44 > 0:28:47Because vast areas are uninhabited,
0:28:47 > 0:28:51in many places the sky is dark with little light pollution.
0:28:54 > 0:28:57New England is further south than the UK.
0:28:57 > 0:29:00But it's dark enough that on special nights
0:29:00 > 0:29:04the distant northern lights can be seen shining.
0:29:27 > 0:29:30The growth of the new forest paved the way
0:29:30 > 0:29:33for wildlife to move back in,
0:29:33 > 0:29:37and animals that were once persecuted now thrive here.
0:29:39 > 0:29:41DISTANT ANIMAL CALL
0:29:55 > 0:29:57It's the beginning of summer.
0:29:57 > 0:30:01And with daytime temperatures now in the mid-20s,
0:30:01 > 0:30:06it's warm enough to draw out New England's most misunderstood animal.
0:30:07 > 0:30:10RATTLING
0:30:13 > 0:30:15A timber rattlesnake.
0:30:18 > 0:30:21A creature at home hiding amongst the trees.
0:30:31 > 0:30:35It was once so feared, a bounty was placed on its head.
0:30:39 > 0:30:42But the timber rattlesnake is making a comeback,
0:30:42 > 0:30:45with a few hundred now living in these forests.
0:30:54 > 0:30:59Using his tongue, a large male seeks the scent of a potential meal.
0:31:02 > 0:31:06He's detected a log heavy with the scent of rodents.
0:31:13 > 0:31:16Coiled like a spring, he waits.
0:31:20 > 0:31:23FAINT RUSTLING
0:31:27 > 0:31:29FAINT PATTERING
0:31:40 > 0:31:43Even one of the fastest hunters on the planet
0:31:43 > 0:31:46can sometimes be off target.
0:31:54 > 0:31:56But he's patient.
0:32:03 > 0:32:0715 hours later, he's still in position.
0:32:14 > 0:32:17FAINT RUSTLING
0:32:18 > 0:32:20PATTERING
0:32:26 > 0:32:28MOUSE SQUEAKS
0:32:28 > 0:32:31He instantly withdraws his fangs,
0:32:31 > 0:32:33eager not to damage them.
0:32:38 > 0:32:41It won't take long for the venom to kill.
0:32:46 > 0:32:50He follows the mouse's scent to claim his prize.
0:32:53 > 0:32:56This should satisfy his hunger for a few weeks.
0:33:06 > 0:33:08It's the height of summer,
0:33:08 > 0:33:11and the trees' leaves are working at maximum capacity
0:33:11 > 0:33:14to turn sunlight into sugar.
0:33:17 > 0:33:20This is when they face their greatest battle.
0:33:20 > 0:33:23CHOMPING
0:33:23 > 0:33:26Billions of bugs are on the attack.
0:33:29 > 0:33:33The trees do everything they can to resist the onslaught.
0:33:37 > 0:33:40They increase the concentration of repulsive tannins
0:33:40 > 0:33:42in the surface of their leaves.
0:33:49 > 0:33:53But even this isn't enough to stop one hungry insect.
0:33:56 > 0:33:58Only a few millimetres long,
0:33:58 > 0:34:01this leaf miner is tunnelling under the skin,
0:34:01 > 0:34:03where he can avoid the bitter tannins
0:34:03 > 0:34:06and get to the juicy, sweet bits.
0:34:12 > 0:34:14Under the safety of the leaf itself,
0:34:14 > 0:34:17he devours so much green chlorophyll
0:34:17 > 0:34:21that the leaf can no longer produce the sugar it needs to stay alive.
0:34:29 > 0:34:32In just two days, he leaves a trail of destruction,
0:34:32 > 0:34:35and his appetite shows no signs of slowing.
0:34:45 > 0:34:48Most insects are too big to squeeze inside a leaf,
0:34:48 > 0:34:51so they must be more selective in how they attack.
0:34:57 > 0:34:59Many eat carefully between the veins,
0:34:59 > 0:35:03avoiding areas with higher concentrations of tannins...
0:35:05 > 0:35:08..leaving the leaf skeletonised in their wake.
0:35:19 > 0:35:21The bigger caterpillars get,
0:35:21 > 0:35:25the more they can process the leaves' unpleasant chemicals.
0:35:28 > 0:35:33And working en masse, caterpillars can devour a leaf in minutes.
0:35:35 > 0:35:39But they themselves could easily fall prey to birds.
0:35:40 > 0:35:43So disguise is the key to their success.
0:35:48 > 0:35:53Some mimic dangerous New England animals to deter their predators.
0:35:54 > 0:35:58Swallowtails have eye spots to look like snakes.
0:36:01 > 0:36:05The hag moth caterpillar resembles a big spider.
0:36:08 > 0:36:11And the fur of this one makes it tricky
0:36:11 > 0:36:13for a predator to get to the soft bits.
0:36:17 > 0:36:19But the most cunning disguise of all
0:36:19 > 0:36:23is to mimic the parts of the leaf that they've already eaten.
0:36:27 > 0:36:32Many New England caterpillars look like nothing more than leaf damage.
0:36:35 > 0:36:37Filling in the gaps with their bodies
0:36:37 > 0:36:40makes them less visible to birds.
0:36:43 > 0:36:47New England is swarming with undercover caterpillars.
0:36:49 > 0:36:53But there's one predator that caterpillars can't hide from.
0:36:55 > 0:36:59Because here the trees have an ally.
0:36:59 > 0:37:02An army is being mobilised.
0:37:06 > 0:37:09These are the Allegheny mound ants,
0:37:09 > 0:37:12and the trees are their hunting grounds.
0:37:23 > 0:37:27Like lions in the leaf litter, they hunt in a pack...
0:37:30 > 0:37:32..efficiently trimming the hairs
0:37:32 > 0:37:35so they can get to the sugary juices...
0:37:36 > 0:37:39..draining the caterpillar dry.
0:37:42 > 0:37:44But this isn't food for THEM to eat.
0:37:48 > 0:37:51In the warm interiors of their mounds,
0:37:51 > 0:37:54the summer heat is incubating the next generation.
0:37:58 > 0:38:03Caterpillar juice is the perfect nourishment for a growing soldier,
0:38:03 > 0:38:07supercharged with sugar that the caterpillars stole from the leaves.
0:38:13 > 0:38:16Soon they will be ready to help the colony expand.
0:38:25 > 0:38:29Every year ants dig miles of tunnels
0:38:29 > 0:38:32and excavate as much as 12 tonnes in every acre.
0:38:44 > 0:38:47This aerates and breaks down the leaf litter,
0:38:47 > 0:38:49which fertilises the soil.
0:38:57 > 0:39:00Trees with rich soil and ant protection
0:39:00 > 0:39:02produce more sugar,
0:39:02 > 0:39:03they're brighter,
0:39:03 > 0:39:07and they will hang on to their leaves for longer during the fall.
0:39:16 > 0:39:19Despite the battles raging through the forest,
0:39:19 > 0:39:22billions of leaves continue to produce sugar.
0:39:30 > 0:39:32This is transported down the trunk,
0:39:32 > 0:39:37where it's stored to replace the tree's reserves.
0:39:37 > 0:39:42Each will gain as much as 100kg in weight before the end of the year.
0:39:49 > 0:39:51FAINT TAPPING
0:39:51 > 0:39:54BIRD CALLS
0:39:54 > 0:39:57The yellow-bellied sapsucker has attracted a female,
0:39:57 > 0:40:01and in their nest they have four young chicks just a few days old.
0:40:01 > 0:40:03CHICKS CHEEP
0:40:12 > 0:40:15Their parents bring back food 20 times every hour.
0:40:18 > 0:40:19BIRD CALLS
0:40:22 > 0:40:24It's exhausting, keeping up with the demand.
0:40:28 > 0:40:29CHICK CHEEPS
0:40:29 > 0:40:31The summer sap is sweeter,
0:40:31 > 0:40:34and it attracts a swarm of insects.
0:40:40 > 0:40:45This is why the father has been obsessively digging wells -
0:40:45 > 0:40:48because the sap leaking from them is now bait.
0:40:54 > 0:40:57And not even the trees' allies, the ants,
0:40:57 > 0:41:00can resist a nibble of the free-flowing sugar.
0:41:02 > 0:41:03CHICK CHEEPS
0:41:03 > 0:41:06For the chicks to grow, they need protein.
0:41:09 > 0:41:13Sugar-coated bugs make up two-thirds of their summer diet.
0:41:18 > 0:41:22Because of the constant supply of insects,
0:41:22 > 0:41:25the chicks increase in weight by 16 times
0:41:25 > 0:41:26in just four weeks.
0:41:30 > 0:41:32CHICKS CHEEP
0:41:36 > 0:41:40And they're already learning the art of tapping for themselves.
0:41:40 > 0:41:42CHICKS CHEEP
0:41:44 > 0:41:46In three months' time,
0:41:46 > 0:41:49they will depart the cooling forest for warmer climates in the south.
0:41:51 > 0:41:53This will give the trees a chance
0:41:53 > 0:41:57to repair the damage before the summer ends.
0:42:11 > 0:42:16This female rattlesnake has spent three months basking in the sun,
0:42:16 > 0:42:18but daytime temperatures
0:42:18 > 0:42:23are now dropping as low as 14 degrees Celsius.
0:42:23 > 0:42:26Being cold-blooded, she is the first in the forest
0:42:26 > 0:42:30to feel a chill in the air as the days draw in.
0:42:33 > 0:42:36She's getting too big for her skin,
0:42:36 > 0:42:40but yawning widely helps to loosen it.
0:42:49 > 0:42:53And snags in the leaf litter help her to undress,
0:42:53 > 0:42:55peeling away the scaly layer.
0:43:09 > 0:43:12This lethal hunter is now ready.
0:43:28 > 0:43:32In a safe and secure place, specially adapted for filming,
0:43:32 > 0:43:34she waits.
0:43:50 > 0:43:54Through the night, months of preparation comes to an end.
0:43:59 > 0:44:03She's given birth to seven tiny rattlesnakes.
0:44:06 > 0:44:09Only 20 centimetres long,
0:44:09 > 0:44:11and already their sharp fangs
0:44:11 > 0:44:13are fully loaded with potent venom.
0:44:17 > 0:44:19Unlike most other snakes,
0:44:19 > 0:44:20timber rattlesnakes
0:44:20 > 0:44:24carry their babies inside their bodies to keep them warm.
0:44:26 > 0:44:28And there's one more on the way.
0:45:06 > 0:45:11The mother's work doesn't end there. Her maternal bond is strong.
0:45:15 > 0:45:18Having the fiercest mother in the forest,
0:45:18 > 0:45:21there's very little that could threaten these baby snakes.
0:45:26 > 0:45:30One by one, they snuggle into the safety of her coils.
0:45:40 > 0:45:43It won't be long until the cooling fall weather
0:45:43 > 0:45:46forces New England's rattlesnakes to lead their babies
0:45:46 > 0:45:48to underground dens,
0:45:48 > 0:45:51where they will hibernate as families until the spring.
0:46:04 > 0:46:06The shortening days and cooling weather
0:46:06 > 0:46:10trigger a change in the behaviour of New England's biggest animal.
0:46:14 > 0:46:18Male moose have been growing their antlers all year,
0:46:18 > 0:46:20and now they're dressed to impress.
0:46:26 > 0:46:29And finally, the females are open to their advances.
0:46:29 > 0:46:31FAINT BELLOW
0:46:33 > 0:46:35But some moose have more luck than others.
0:46:39 > 0:46:40SPLASHING
0:46:42 > 0:46:46This younger male has been following a female for weeks
0:46:46 > 0:46:48in the hope of getting her attention.
0:46:51 > 0:46:53It's tiring work,
0:46:53 > 0:46:55and to make matters worse,
0:46:55 > 0:46:57she's still caring for a calf.
0:47:05 > 0:47:09But with antlers like this, how could she possibly resist?
0:47:14 > 0:47:17He decides to make a bolder move before a bigger bull shows up.
0:47:19 > 0:47:21MOOSE SMACKS LIPS
0:47:21 > 0:47:25Lip-smacking makes his intentions clear.
0:47:32 > 0:47:34Her scent is irresistible.
0:47:44 > 0:47:47Not the response he was hoping for.
0:47:50 > 0:47:54Urination gives him a sign that she's still not in the mood.
0:47:57 > 0:48:00Even after weeks of trying to court her,
0:48:00 > 0:48:03persistence doesn't always pay off.
0:48:06 > 0:48:08THUNDER RUMBLES
0:48:08 > 0:48:12Fortunately, every year, thanks to the nutrition from the forest,
0:48:12 > 0:48:14a moose grows a bigger rack.
0:48:16 > 0:48:17THUNDER RUMBLES
0:48:17 > 0:48:19And next time,
0:48:19 > 0:48:23maybe his antlers will be big enough to impress the choosy female.
0:48:37 > 0:48:40With the temperature now constantly below ten degrees,
0:48:40 > 0:48:43the leaves can no longer work efficiently.
0:48:43 > 0:48:46And with less than 12 hours of sunshine a day,
0:48:46 > 0:48:49they have less time to create sugar for the trees.
0:48:51 > 0:48:55There comes a point when they are no longer earning their keep,
0:48:55 > 0:48:58and the tree must start to close down for the winter.
0:49:05 > 0:49:08At first, the effects are subtle.
0:49:08 > 0:49:11Individual leaves start to turn yellow.
0:49:15 > 0:49:18Like tiny factories closing down,
0:49:18 > 0:49:22the green pigment inside each cell is dismantled.
0:49:26 > 0:49:28The tree salvages all that it can,
0:49:28 > 0:49:32carrying it down in the sap to be stored in the tree's trunk.
0:49:34 > 0:49:37The cooling weather quickens the process,
0:49:37 > 0:49:42until the Midas touch of fall turns entire forests golden.
0:49:56 > 0:49:59But this is only just the beginning
0:49:59 > 0:50:01of the most magical transformation of all.
0:50:03 > 0:50:05The fall in New England.
0:50:08 > 0:50:11While most trees are already preparing for the winter...
0:50:13 > 0:50:18..some also take this opportunity to secure a future for their offspring.
0:50:22 > 0:50:26They drop millions of winged maple seeds and acorns.
0:50:36 > 0:50:40Many will soon be safely hidden beneath leaf fall
0:50:40 > 0:50:43to await the nourishing warmth of spring.
0:50:49 > 0:50:51But they've been spotted.
0:50:51 > 0:50:54Despite the cover, there's one animal
0:50:54 > 0:50:57who is able to sniff out a fresh nut amongst the leaf litter.
0:50:59 > 0:51:00A chipmunk.
0:51:03 > 0:51:08His small size means that he's unable to pile on enough body fat
0:51:08 > 0:51:11to survive hibernation through the winter.
0:51:13 > 0:51:16And just when reserves are looking a little thin...
0:51:17 > 0:51:20..a new air drop is delivered by the trees.
0:51:25 > 0:51:26Perfect timing...
0:51:27 > 0:51:31..if he can stockpile enough in his secret caches.
0:51:38 > 0:51:41He can squeeze four acorns into his cheek pouches,
0:51:41 > 0:51:44allowing him to collect up to 160 a day.
0:51:49 > 0:51:52It takes a lot of work to amass a big stash.
0:51:54 > 0:51:57But there's always one who's less prepared to put in the hours.
0:52:01 > 0:52:03A lazy chipmunk.
0:52:04 > 0:52:08He's spotted his neighbour's acorn and where it's being hidden.
0:52:10 > 0:52:12It's too tempting.
0:52:16 > 0:52:19But it's not an easy steal.
0:52:19 > 0:52:21SQUEAKING
0:52:38 > 0:52:42This is one chipmunk determined to protect his stash.
0:52:45 > 0:52:48The chipmunk is a hero of the forest -
0:52:48 > 0:52:50because even after all that work,
0:52:50 > 0:52:54he will forget where he's buried some of his hard-earned treasure.
0:52:56 > 0:53:00And protected underground, the seeds have a better chance of germinating.
0:53:04 > 0:53:06Whether they are a tree's enemy or an ally,
0:53:06 > 0:53:09the animals of New England have conspired
0:53:09 > 0:53:12to make the fall a season of beauty.
0:53:12 > 0:53:14And one thing is for sure -
0:53:14 > 0:53:17in the end, it's the entire forest that wins.
0:53:19 > 0:53:23And as the trees make their final preparations for winter,
0:53:23 > 0:53:25the best is yet to come.
0:53:35 > 0:53:38As the temperature drops towards freezing,
0:53:38 > 0:53:39the trees increase the speed
0:53:39 > 0:53:42at which they drain the leaves of their goodness.
0:53:44 > 0:53:46A magical new chemical is conjured up
0:53:46 > 0:53:49from within the leaves of the maple and oak trees.
0:53:52 > 0:53:54Red anthocyanin.
0:53:57 > 0:54:01It keeps the sap flowing for longer as the temperature plummets,
0:54:01 > 0:54:04so the trees can hold on to their leaves
0:54:04 > 0:54:07and extract every last drop of sugar.
0:54:13 > 0:54:16The reds and oranges join the golds,
0:54:16 > 0:54:19and together they set the forest ablaze.
0:54:23 > 0:54:27From an ocean of green, every tree becomes an individual.
0:54:33 > 0:54:37Red maples and oaks burn in shades of red.
0:54:47 > 0:54:50Sugar maples glimmer in orange.
0:54:53 > 0:54:55And for just a few weeks every year...
0:54:56 > 0:54:59..New England is a wonderland of colour.
0:55:22 > 0:55:25These colours can be seen from space,
0:55:25 > 0:55:29spreading across this corner of America like wildfire.
0:55:33 > 0:55:36The spectacle is intense, but brief.
0:55:38 > 0:55:42As the last of the nutrients and sugars are extracted by the trees,
0:55:42 > 0:55:45billions of leaves hang on tenterhooks.
0:55:48 > 0:55:50All it takes...is a breeze.
0:56:02 > 0:56:05It's the last chance for their most persistent enemy to feast.
0:56:05 > 0:56:07CHOMPING
0:56:14 > 0:56:18Caterpillars... in a hungry race against time.
0:56:29 > 0:56:34Leaf miners are still feeding as the leaf changes around them.
0:56:35 > 0:56:38They eat all that they can before a quick getaway.
0:56:41 > 0:56:45Some caterpillars chase the colour through the fall.
0:56:47 > 0:56:51The spicebush swallowtail swaps the green costume of summer
0:56:51 > 0:56:53for a golden coat.
0:56:58 > 0:57:00And, having had her fill,
0:57:00 > 0:57:04she sheds this new skin to form an overwintering pupa that,
0:57:04 > 0:57:07like a leaf, fades to brown.
0:57:15 > 0:57:19Many other caterpillars turn red and orange in the fall.
0:57:20 > 0:57:24And as the leaves lose the last of their sugar,
0:57:24 > 0:57:26they climb to the edge of a leaf...
0:57:26 > 0:57:29and take a leap of faith.
0:57:36 > 0:57:40Amongst the leaf litter they seek out a refuge from the winter.
0:57:43 > 0:57:45In the spring, they will emerge as moths
0:57:45 > 0:57:49and unleash a new generation of caterpillars onto the forest.
0:57:56 > 0:57:58It's the end of October,
0:57:58 > 0:58:02and the planet's most colourful forest fades
0:58:02 > 0:58:04as the last leaves fall.
0:58:04 > 0:58:08They have given the trees all that they need to survive...
0:58:12 > 0:58:15..until the battles begin again next year.