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The Himalayas.

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{\an8}The highest mountain range on Earth.

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With peaks rising over five miles
into the clouds.

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Here, deep canyons create
the world's largest echo chamber,

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where the slightest noise
ricochets through the valleys.

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For the few extraordinary animals
that live here,

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sound is key to their survival.

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A snow leopard.

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The ghost of the mountains,

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and the Himalayas'
ultimate stealth hunter.

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This male is searching for a meal.

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To get close to his prey,

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it's vital that he avoids being seen.

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But in the silence of the mountains,

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it's just as important
that he's not heard either.

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With prey scattered far and wide,

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snow leopards take advantage
of the unique high-altitude soundscape.

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Their hearing is three times
more sensitive than ours.

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Allowing them to pick out faint noises
from miles away.

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And they listen out
for one particular animal.

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Himalayan ibex.

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As the hunter closes in,
he switches to stealth mode.

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An ambush predator,
he needs to get within just a few feet.

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The long fur between the pads of his toes

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helps soften his footsteps,
allowing him to sneak closer.

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All it takes is one loose rock...

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and the ibex will be spooked.

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Cover blown.

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He's forced to attack from a hundred feet.

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In the thin mountain air,
every stride uses precious energy.

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On the sheer cliffs,
all it takes is one slip...

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and the chase is over.

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This time, he goes hungry.

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But in just a few weeks,
he'll use the mountains echo chamber

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for a very different type of pursuit.

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Beyond the peaks
lies a whole new soundscape,

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where the acoustic rules
are turned upside down.

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The Tibetan plateau.

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On these flat, featureless planes,

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sound doesn't echo around
but dissipates into the cold, dry air.

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So up here, you've got to shout
to make yourself heard.

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The chiru, perhaps the world's
strangest antelope.

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Each winter, herds of these curious
creatures gather to breed.

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This male guards a harem of ten females.

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And to keep them close...

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he struts his stuff.

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He needs to watch out

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as he's not the only male
with mating on his mind.

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Rivals are gathering
and fighting amongst themselves.

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The winner will get to challenge
our male for his harem.

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So he sends them a blunt reminder
of who's boss.

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Deep sounds travel further.

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So chiru use low, loud growls to broadcast
their warnings for nearly a mile.

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But not every male is intimidated.

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A rival roars in reply.

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It's a direct challenge our male
will have to silence.

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And so begins the battle of the bellows.

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Possibly the world's worst
singing contest.

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On most occasions, these growl-offs
are enough to settle any dispute.

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But today our male has met
his vocal match.

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Now, with his harem at stake,
he must see the intruder off.

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Even with little oxygen in the air,
chiru can run at 50 miles an hour.

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This time, his rival is all talk.

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In the Himalayas,
conditions can change in an instant...

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shifting the soundscape.

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A fresh fall of snow muffles sound,

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making the mountains quieter.

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Now, to hear any signs of life,
you must listen even more carefully.

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Beneath the surface, microphones
pick up the secretive chatter

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of one of the Himalayas'
cutest-looking creatures.

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The plateau pika.

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These social little mammals
live in family groups around 20 strong.

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They use a repertoire of seven different
calls to keep in touch...

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and to settle disputes with neighbors.

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But all this chatter
attracts unwanted attention.

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A Tibetan fox.

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Foxes have excellent hearing,
six times more sensitive than our own.

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They're tuned in to high-frequency sounds
like the squeaking of pika.

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Honing in, the fox starts to stalk.

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Keeping a low profile and moving slowly

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to minimize making any noise.

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Their ears can rotate independently,

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helping them pinpoint the slightest sound...

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and creep in close.

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This unsuspecting pika
is just inches from the fox's jaws.

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But luckily, pika have a
neighborhood watch scheme like no other.

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Their squeaky alarm calls
are highly directional,

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helping them pinpoint
where the warning is coming from...

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so they can make their escape.

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But the wily fox doesn't give up easily.

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Once back in their burrows,
the pika start chatting again.

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And the hunter listens in from above.

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He starts to dig.

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He can burrow three feet into the ground.

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Now, it seems the pika
are in serious trouble.

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But these smart little mammals
are one step ahead.

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Because their tunnels have emergency exits

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so they can escape
even the most determined fox.

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The pika live to squeak another day.

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In the Himalayas,
the loudest sounds of all

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come from the peaks themselves.

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Weather fronts collide with mountains,
weakening rock faces.

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Glaciers groan as they carve deep valleys.

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And avalanches thunder down slopes.

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Every year,
these peaks get half an inch taller.

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The sounds of the world's highest
mountains growing even higher.

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But in the foothills,
one noise can be heard above all others.

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Fueled by meltwater and monsoon rains,

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fast-flowing mountain rivers
charge with white water...

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creating a background din
as loud as a jet engine.

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This drowns out any other sounds
and makes communication a challenge.

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But one little bird has found a way
to cut through the chaos.

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A Himalayan dipper.

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This female is hunting
for aquatic insects...

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to feed her hungry chick.

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Even though he's just a few days old,

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he's already a whopper
with an appetite to match.

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When close by,
they easily call to each other.

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But to hunt for food,
Mum must travel far along the river.

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And that makes keeping in touch
much harder.

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Especially if your chick
is a little clumsy.

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He's swallowed up by the torrent
and washed downstream.

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When Mum returns,
her chick is nowhere to be seen.

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So she produces a high-pitched call.

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By blocking out the background noise...
we can tune into it.

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The dipper's vocalizations
are way above the range of the water.

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A bandwidth that scientists term
"the silent window."

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It's their own communication channel
that cuts above the background din

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so her chick can still hear her.

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Even at such a young age, he's already
found his voice and calls back.

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High-pitched sounds are easier to locate.

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So, from his call alone,
Mum can track him down.

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And the pair are reunited.

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But for Mum, there's no time to rest.

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Of all the sounds in the Himalayas,

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there's one special call that's rarer
than any other.

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The love song
of the ghost of the mountains.

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For two years,
a remote surveillance network

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eavesdropped on the highest peaks.

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And recorded rare footage
of elusive snow leopards.

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Each spring, for a few weeks,
females begin an annual search for a mate.

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A seemingly impossible challenge
given the vastness of the mountains.

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The first step is to leave a scent trail.

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Wandering huge distances,
they mark across their territories

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of over a hundred square miles.

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And this is what they're hoping for.

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A young male.

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As he rolls in the scent,

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we can hear his intimate call,
known as a chuffle.

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Having drawn a male close...

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the female now switches
from scent to sound.

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Her song can travel for miles.

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For a male, it's an irresistible draw.

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And just inches from our camera,

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his reply is the closest ever recording
of a snow leopard's call.

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Their haunting duet lasts
for just a few minutes.

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But it's enough to bring
two solitary cats together.

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Having spent most of their lives alone...

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this new couple appears a little nervous.

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Their tender courtship
is a rarely seen moment.

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Thanks to the mountain's
unique soundscape,

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snow leopards are able to find love...

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in the vastness of the Himalayas.

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To capture the mountain's rarest call,

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the <i>Earthsounds</i> team traveled
to Ladakh in northern India.

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At over 15,000 feet.

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{\an8}Where's the chairlift?
They said there'd be a chairlift.

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They hope to record the sound

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of one of the world's
most elusive animals,

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the snow leopard.

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These secretive big cats only call during
the few weeks of their breeding season.

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So being in the right place at
the right time would be a huge challenge.

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They'd need the help of expert guide,
Khenrab Phuntsog.

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The landscape is so vast.

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You'll have to be exactly in a place
where they make the call.

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Which is very difficult to predict.

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Their first task was to find the cats.

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Not an easy job
in the world's largest mountain range.

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Yeah.

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But for Khenrab,
these peaks are full of hidden signs

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that snow leopards leave behind.

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So it went down this way.

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- It's very clear, isn't it, in snow?
- Yeah.

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Good sign that cats are around.

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But finding the snow leopards
is just the start.

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To capture their vocalizations, the team
has to rely on remote camera traps.

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{\an8}Here we're burying it in the ground
with the hope that we'll get the--

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{\an8}one of the snow leopards
walking over the top of it.

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And I guess I would just stop about here.

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Yeah.

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And then I'd walk over the top.

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- And then there's that tail's trail--
- Yeah.

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That'd be cool.

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And to guarantee
they get the sound they've come for,

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Nick has a plan.

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Just looking for somewhere to place
this little remote sound recorder.

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This is like a camera trap,
but it's just for the sound.

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Dot these around and bug the mountain.

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Once everything is set and tested...

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It's good. It's okay.

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...all the team can do
is head back down the mountain and wait.

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After three weeks, it's time
to check whether they've struck lucky.

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Something is coming.

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And the team
get their first glimpse of a snow leopard.

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But despite getting closer to these
mysterious cats than they ever imagined...

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Nick's sound recordings were silent.

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I've been doing this too long
to get too disappointed.

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You take the rough with the smooth
when you're camera trapping.

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But it is disappointing.

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Capturing the rarest call in
the Himalayas was never going to be easy.

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Maintaining all the traps
would require the equivalent effort

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of the crew climbing Everest four times.

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Finally, two years later,
Khenrab hits the jackpot.

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A male snow leopard triggers the camera.

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And as he leaves the shot,
he begins to call.

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The clearest and closest ever recording
of a wild snow leopard call.

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The extraordinary love song
of the ghost of the mountains.