In the frigid valleys of Japan’s Shiga Highlands, a troop of snow monkeys make their way and raise their families in a complex society of rank and privilege where each knows their place. Their leader is still new to the job and something of a solitary grouch. But one little monkey, innocently unaware of his own lowly social rank, reaches out to this lonely leader, forming a bond with him that manages over time to warm his less than sunny disposition. It is a rare and remarkable gesture that alters both their lives. Changing seasons bring new babies to care for, a profusion of insects and blossoms to eat, family disagreements to squabble over and tragedies to overcome. Mating season brings competition for females as the days grow shorter and colder in a rush toward winter. But with their now confident leader to guide them and their families to shelter and care for them, this troop of snow monkeys is ready to face the world.
NARRATOR: In a place called Hell Valley, an ancient tribe relies on each other to survive.
A monkey's position in the group is inherited from its mother.
Bloodline determines rank, and every member knows their place.
But in this world of tradition, there are opportunities to change your fate.
One quiet moment can have great significance, when a young monkey bonds with the leader of the troop.
In this clan, nothing goes unnoticed -- it's all part of the drama unfolding deep in the Japanese Alps.
NEESON: Long ago, one hearty tribe made an epic journey... Traveling thousands of miles, crossing treacherous mountain passes and deep snowbound valleys.
By the time they finally settled down, these macaques had traveled farther North than any other primate on Earth -- aside from us.
Over time, they adapted to the extremes of the seasons and rightfully earned their name, 'snow monkeys.'
To this day, the descendants of that ancient tribe still roam the mountains of central Japan.
And this is where our story begins.
It's early winter in the Japanese Alps, but already the temperature is well below freezing.
Here, boiling volcanic waters feed the Yokoyu River, keeping it ice-free all winter long.
Snow monkeys take advantage of the subterranean heat by huddling over thermal vents.
Higher up in the trees, families cling tightly together.
In the frigid morning air, no one is quick to rise.
Well, almost no one.
Hiro is just eight months old.
And as he watches the juveniles play, he's anxious to start his day as well.
Hiro and his friends are determined to get the rest of the troop on their feet.
No easy task in a family this size.
The troop is 160 members in all, mostly females and their offspring.
Males usually leave home before they reach sexual maturity.
But a handful of adult males may stick with the troop, ensuring its safety.
Hiro's mother is a lower-ranking female, a status he'll likely share until he's old enough to leave the troop and chart his own path.
His rambunctious play has even roused the troop's leader.
Kuro-san has a reputation for being ill-tempered, with little tolerance for youngsters.
The clan roosts high in the mountains, but every morning they heed a familiar call.
A whistle from the valley below beckons them down the mountain.
[Whistle in distance] Hiro and his cousin are still busy playing, while the rest of the family is already on the move.
And this is why they're in such a hurry -- grain has been scattered to supplement the troop's meager winter diet... And no one wants to be late for breakfast.
But someone is missing.
Hiro and his cousin have lagged behind.
[Hiro calls] And his cousin is no help at all.
Just one familiar face is all it takes, and they are back on track.
Keeping up with the troop is vital.
For snow monkeys, family is survival.
But there's something else drawing them down the mountain.
Jigokudani, or Hell Valley, is famous for its hot springs.
And some 50 years ago, one was built exclusively for the Hell Valley troop.
It became an overnight sensation, and snow monkeys have been soaking up the warm volcanic waters ever since.
It's a communal affair, open to all regardless of rank.
Every member of the troop is a unique individual... some a little more unique than others.
Take Bubbles, for example.
She loves making bubbles on the water's surface... and seems completely engrossed in the task.
And there's Shiro-san.
He's a lover of the hot spring, even earning the nickname, Hot Springs Uncle.
He's supposed to be Kuro-san's right-hand man when trouble breaks out... But he spends most of his days lounging with the ladies.
Kuro-san rarely enters the hot spring.
Instead, he spends his days alone.
He's still new to the job of troop leader, and perhaps the added stress has made him more withdrawn than normal.
But that doesn't stop Hiro.
Maybe it's the bitter cold, or maybe he thinks Kuro-san needs a little company.
Kuro-san ignores Hiro's gesture.
He'd rather be alone.
Yet it seems no matter where he goes, he is surrounded by little ones.
As evening approaches, the troop must seek shelter deeper in the forest.
But Kuro-san seems reluctant to lead.
Maybe, it's all too much for him.
The late day flurries are a reminder -- the worst of winter is yet to come.
A fresh bed of snow fills the forest floor and the troop takes to the trees to avoid the deep drifts.
On a steep hillside, a gang of juveniles is playing 'king of the mountain.'
Play-fighting is how young monkeys test each other's strengths and weaknesses, sorting out a delicate balance of power.
This is not a battle yet, but a dance.
One young gang leader decides to turn this into a more serious contest.
The juveniles caught downhill feel threatened by his aggression... and call for reinforcements.
[Calling] But their brother at the top of the hill is unaware the game has changed.
The belligerent youngster tries to assert his dominance, but the lower hill gang refuses to back down.
Now, as back-up arrives, the troublemaker realizes he may have overplayed his hand.
With all forces converging on him, his only option is to flee.
Finally, he wriggles free and makes a dash for safety.
But the point of this battle has already been made.
This little gang of juveniles has a new leader -- at least for now.
In a family more than 100 strong, learning to play with others is the most important thing.
Hiro's made a snowball and tries to get his cousin to play along.
The relationships he forges through this simple act may one day tip the scales in a more serious game.
But for Hiro, being playful comes as naturally as the newly-fallen snow.
It's getting late, and the snow is growing thicker by the minute.
Suddenly, Hiro's game is cut short.
There is a sense of urgency in the air.
A storm is coming.
The troop must seek shelter for the night, and this time, Kuro-san leads the way.
But as they climb, Hiro falls farther and farther behind.
His mother scans the area for her son as the others move on.
[Hiro cries] Hiro's desperate calls are swallowed up by the wind.
His mother continues her search, but fast-moving snow has erased his tracks.
[Hiro crying] [Hiro crying] Finally, his mother hears his faint cries.
Now, Hiro holds on tight.
He was lucky this time -- second chances don't come along often in Hell Valley.
Storms like this can last for days.
During winter, more snow falls on the Japanese Alps than almost anywhere else on Earth.
Snow monkeys have learned to keep friends and family close.
It is truly a matter of survival.
Without the warmth and companionship of others, the bitter cold sinks into their bones.
The troop is drawn down the mountain, knowing the hot spring awaits them.
One by one, families gather in the water to soak, each seeking the warmth so desperately needed.
Shiro-san was one of the first to arrive, but now the little pool is getting packed.
Kiko is a lower-ranking female, but a regular to the hot spring.
In her eagerness to squeeze in, she's managed to annoy higher ranking Tomano.
Kiko tries again, but Tomano won't budge.
Shiro-san is hoping this little spat doesn't get out of hand.
But finally he steps in to break up the fight.
As things settle down, Kiko takes a different tack, and finds an opening behind her sister.
Yet, Tomano isn't ready to leave Kiko alone.
But strangely, she's not back to fight.
She slides over and grooms Kiko.
For snow monkeys, grooming is an act of reconciliation, a way of making up after a fight.
In a community that depends upon one another for survival, grooming is the glue that binds the troop together.
It's partly a free meal, partly good hygiene -- beneficial all around.
In fact, it may be better to give than receive -- the very act of grooming leads to many benefits.
And the more equally you distribute this act of kindness, the calmer and healthier you become.
Kuro-san, the troop leader, sits alone.
He huddles with no one as he shivers in the cold.
But with his less than sunny disposition, most of the troop have given up on him.
The only one who still seeks him out is Hiro.
So far, Kuro-san doesn't seem to mind him hanging around too much.
It's possible that Hiro's plucky nature is slowly chipping away at Kuro-san's icy facade.
For on this quiet, snowy afternoon, something is about to happen that will surprise everyone.
Suddenly, Kuro-san folds Hiro into his arms -- though he isn't quite sure he's made the right move.
Well, at least they are both a little bit warmer... and honestly, that's how some relationships begin.
It's always sort of a dance, really... An awkward... jerky... odd looking dance.
But eventually, every pair figures out the moves.
And then, they're on their way.
This is all highly unusual.
Seeing any male with a youngster perched on his back is odd enough.
But for a reclusive leader like Kuro-san it's even more surprising.
And the spectacle isn't lost on the rest of the troop, either.
Now, as Kuro-san leads the troop, Hiro has a first class ticket -- a chance to see the world through the eyes of a leader.
Hiro watches his new mentor intently.
As they shred bark together, Hiro's confidence grows.
And with his air of loneliness lifted, Kuro-san has new energy.
Kuro-san has found a spot to bask peacefully in the sun... well, sort of.
With Hiro now at his side, the days never seem to slow down much.
But will this fragile relationship last?
Or melt away with the winter snow?
It won't be long now -- spring is on its way.
With help from the troop, the ornaments of winter are taken down one by one.
The river surges with the new snow melt.
The warm rains wash the forest clean and fill the river to its banks.
Slivers of spring, like fiddleheads and peat moss, are peeking out, preparing their takeover.
Snails emerge from hibernation, stretching out from their shells to search for young green shoots.
The troop moves through the forest like explorers of a new and verdant land -- stopping now and again to soak up the warm air laden with the intoxicating scents of spring.
In Japan, cherry blossoms are the symbol of the ephemeral nature of life.
The troop takes advantage of these sweet flowers while they last.
The forest is a buffet, and Hiro hardly knows where to begin.
After eating bark and twigs all winter, this is paradise.
But an unfamiliar cry has gotten his attention.
Rina has a brand new baby boy, just hours old... And she's not the only one.
The forest has been turned into a nursery, with babies everywhere.
Newborn snow monkeys are small enough to fit in the palm of your hand.
But these little bundles of energy can't be contained for long.
For mum, keeping them safe is a full-time job.
They're intensely curious, but are blissfully unaware of troop politics.
Wandering up to a stranger can be a dangerous lesson... unless she's your aunt.
But this constant exploration is how babies learn about their world, so it's a good thing snow monkeys are such patient mothers.
Both Rina and her sister have given birth, just a week apart.
During the short spring, the troop will have around 20 infants.
Rina's sister is an experienced mum, and her eldest daughter is always close at hand, keeping a watchful eye on her little brother... especially now he's beginning to wander.
With mum's busy schedule, it's always good to have a little help around.
Every day is a new lesson, and by sticking close to mum, all the tiny secrets of the forest will be revealed -- like how to find insect larvae under the bark of cedar trees.
This time of year a monkey's diet is mostly greens, so it's important to look for protein wherever they can find it.
It's a bit like rummaging through the kitchen cabinets -- eventually, you find what you're looking for.
Like all kids, they learn by watching others, and Hiro, now one year old, is eager to do everything grown-ups do.
Like most things, there's a bit of a learning curve.
Clearly there's a skill to this peeling business that Hiro has yet to master.
Maple trees are a troop favorite, and Rina's sister is busy plucking fresh new shoots.
Now four weeks old, the babies are already learning to climb.
But confidence... well, that comes with practice.
[Baby squawking] There you go, safe and sound.
On the valley floor, the troop relaxes in the sunshine.
[Squawking] But a cry of distress is upsetting the calm of the forest.
It's a brand new baby -- with no mother in sight.
Rina forages with her young baby clutched to her, just steps from the infant.
Uncertain what to do, Rina minds the first rule of snow monkey motherhood -- look, but don't touch.
But clearly something is wrong here, and she can't ignore the desperate baby in front of her.
The new infant is still a bit shaken, but is slowly realizing she is no longer in danger.
Rina, on the other hand, may not appreciate what she's taken on.
Having two mouths to feed is quite a challenge.
The new baby can't see much beyond her reach just yet, but somehow she seems to know she's found a new mum.
[Thunder rolling] Summer rains come early to Hell Valley.
For the babies, the downpour is something entirely new.
While Rina nurses her adopted baby, her son is busy exploring with a new playmate.
And Bubbles is transfixed as rain creates magic on the water's surface.
Kuro-san's unusual relationship with Hiro continues to blossom.
While all around them, Japanese Wisteria is in full bloom.
As Kuro-san gently grooms his little buddy, the juveniles... well, they're up to their usual antics.
In a sly move, they have commandeered the hot spring.
Instead of the heated waters of winter, cool river water is now piped into the pool.
It's the perfect summer swimming hole.
Maybe it's just the weather, or maybe it's Hiro's influence... Whatever the case, Kuro-san seems more relaxed than ever.
But while the juveniles are playing, the mothers have their hands full.
For Rina, the job is twice as hard.
With each passing day, nursing and carrying two infants is becoming more of a burden.
She can barely manage to keep up with her sister.
While her son is growing stronger every day, her adopted baby remains weak, struggling just to keep a grip on mum.
As the days pass, it becomes clear that there is something very wrong with Rina's adopted daughter.
It's possible Rina could not produce enough milk to feed both infants, or maybe the adopted baby was already ill.
There is nothing Rina can do now.
Rina's son has yet to realize his adopted sister is gone.
Summer gives way to autumn.
[Animals calling] Once again, Hell Valley is transformed.
But it's not just the color of the leaves that has changed.
The usually quiet, reserved Kuro-san is now loud and aggressive.
Hiro takes refuge with his mother.
Kuro-san's face is flush, his body taut, his eyes wild.
This is not the affectionate leader that gently groomed him in the summer sun.
It's mating season in Hell Valley, and Kuro-san has only one thing on his mind.
But he's got competition.
Males from outside the troop have come to Hell Valley to mate, and they're making their presence known.
Kuro-san keeps a close eye on the intruders, but each day, they edge a little closer.
Autumn days are short in Hell Valley, and bulking up for winter is the going concern.
Some strip bracket fungi from the trees, while others dig up the last of the season's chestnuts.
As the troop is busy foraging, one of the outside males silently slips past Kuro-san.
He's tracking down a female crossing the valley.
When she tries to run, he gets aggressive.
He tries to separate her baby from her, but she rushes in to protect it as the baby makes a dash for safety.
Her eldest daughter tries to help, but she is pushed aside by the large male.
Kuro-san and the other males rush in, and the intruder makes a run for it.
But Kuro-san and Shiro-san are hot on his tail.
They pin him down at the river's edge, but the intruder breaks free and uses the river as a shield.
With the icy river between them, the male scales the steep cliff to make his escape.
His scar will be a permanent reminder of the troop's strength.
His comrade watches from the cliff above.
If he wants to mate, he'll need a different approach.
Kuro-san now turns towards Hiro's mum, grooming her affectionately.
Hiro wants to nurse, but for once, it's her turn to be pampered.
Mating is a dance, and the females often lead.
One of the outside males has made an impression on Hiro's aunt.
She's chosen a secluded patch of forest for a romantic rendezvous.
The cries are mating calls.
Attraction is a difficult thing to define, but her interest in this exotic foreigner does makes genetic sense.
He represents fresh genes from outside of Hell Valley.
By breeding with this male, she will ensure that her own troop will stay strong.
Wind sweeps across the mountains, taking with it autumn's colors.
Soon, the valley will be under a blanket of snow.
With autumn behind them, the troop settles in to their winter routine... a diet of twigs and bark.
Hiro nibbles on the buds of a maple.
Not far away, Kuro-san is doing the same.
Even after the trials of autumn, it's clear their relationship hasn't skipped a beat.
In fact, it seems stronger than ever.
The troop moves across the valley, each member keeping close tabs on their mothers and sisters, ensuring no one is left behind.
And like family, Hiro and Kuro-san stick close as they brave the winter together.
Their unusual relationship may have started out of convenience -- Each seeking comfort that first hard winter -- but it has grown into something more... A friendship that has lasted through the seasons.
By the following spring, Kuro-san has grown into a confident and caring leader.
And Hiro is always by his side.
He's already two years old and even has a brand new baby sister.
Like every spring, there's new life in the troop.
Last year's babies are now the curious one-year-olds Hiro once was.
Hiro may have come from humble beginnings, but this bright-eyed youngster has lit a spark in a once lonely leader.
Their unlikely friendship has already begun to reshape their future.