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{\an8}The Amazon rainforest.

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There's more life here
than anywhere else on Earth.

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The calls of tens of thousands
of different species

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make this the richest soundscape
on the planet.

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With the airwaves so packed,

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the biggest challenge here

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is how to make yourself heard
above the competition.

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And one way of doing this
is to pump up the volume.

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Meet the loudest of all land animals.

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The howler monkey.

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Howlers live in small troops

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and they spend their days
feeding in the canopy.

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Their favorite trees
have the tastiest fruit.

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Life here is pretty relaxed.

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Apart from once a day

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when Dad claims
his family's feeding spot by howling.

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At 140 decibels,

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his call is as loud as a jet engine.

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It can be heard from three miles away.

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The secret to this ear-splitting howl
is his huge throat sac.

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It contains a hollow bone
known as the hyoid.

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This acts like an echo chamber,
deepening and amplifying his voice.

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Usually, this long-range warning
is enough to keep other groups away...

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but not today.

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Another troop is closing in...

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and want the feeding tree for themselves.

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Dad challenges them
to the jungle's loudest shouting contest.

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As the competition builds,
he swaps to shorter barks.

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A sign of increased aggression.

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But when the rivals still don't back down,

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howlers have one final acoustic strategy.

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Mum and Dad join forces.

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A duet that sends the intruders packing.

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Howling uses huge amounts of energy,

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but it's worth it, as these monkeys can
size each other up through sound alone,

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so rarely come to blows.

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While in the treetops
it may pay to be loud,

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on the forest floor,
it's a different story.

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Deep in the jungle,

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we can now eavesdrop
on the Amazon's most elusive creatures...

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using remote cameras and microphones.

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Here, animals are drawn to clay licks,
a vital source of minerals.

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But surprisingly, no one makes a sound.

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Even the howler monkeys are hushed.

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Down here, they battle in silence.

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A behavior never filmed before.

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And there's a good reason
for their stealth.

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A jaguar.

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The Amazon's apex predator.

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As he prowls,

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the alarm calls of birds
follow his every move.

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It's the rainforest's neighborhood watch.

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Every animal is listening out
for these warnings.

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All it takes is one shrill alarm...

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and everyone scarpers.

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South America's biggest cat foiled by
the rainforest's remarkable alarm system.

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The soundscape of the Amazon not only
changes from forest floor to canopy,

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but also throughout the day.

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Around dawn, the cool, still air
means sound travels further.

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The perfect time for primates
to broadcast long-range calls.

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It's why birds also sing
in the cooler mornings.

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As humidity builds during the day,
sound doesn't travel as far.

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Larger animals stop calling,
leaving the airwaves open for insects.

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At dusk,

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one of the last birds to call
is the great tinamou.

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At night, a new chorus takes over.

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Frogs call in the dark.

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Some even sound like racing cars.

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Perfectly timed,

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this is nature's most intricate
animal orchestra.

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Fine-tuned over millions of years.

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But not all jungle dwellers stick to this
carefully choreographed daily schedule.

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The three-fingered sloth,
the slowest mammal on the planet.

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To avoid predators, they stay hidden
and quiet most of the time.

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But once a month, to attract a mate,
female sloths break their silence...

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with the rainforest's
most piercing love song.

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For male sloths, life is laid back.

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But the female's shrill invitation
is a real wake-up call.

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Irresistibly drawn towards her song,
this male begins an epic journey...

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descending from the safety of the treetops
in pursuit of love.

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On the ground, he's not the fastest...

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and being shortsighted doesn't help.

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As he gets closer,

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he ups his speed
to nearly one mile an hour.

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Not that you'd notice.

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Finally, he makes it to the female's tree.

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But now he's got competition.

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Another male.

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The jungle's slowest race is on.

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The rivals are on a collision course.

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Microphones capture the close-up sounds
of the rare sloth fight.

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Our male throws a fierce left hook

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and his rival lets out a whimper.

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It's a sign that he's giving up,

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leaving our male to complete his mission
and join the female.

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Their final coming together
takes less than a minute.

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It seems it's the only thing
sloths do quickly.

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United through sound,

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the world's slowest mammals
find love in the canopy.

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But in the battle
for the Amazon's airwaves,

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there's one daily event that drowns out
even the most piercing call.

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Every afternoon,

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the patter of each raindrop...

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falling on different-sized leaves...

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creates different notes...

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and builds to a complex beat.

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In a single storm,

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over a trillion raindrops can fall...

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producing a background din so loud...

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most animals simply stop calling.

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After a storm,
the birds soon restart their chorus.

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And one little bird has come up
with a unique way of making itself heard.

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The club-winged manakin.

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This handsome young male is keen
to attract a partner.

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But in the dense undergrowth,
his bright feathers can be hard to spot.

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So, he's come up with a nifty way

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of getting the attention
of any female nearby.

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Instead of singing,

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he uses his wings...

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as a musical instrument.

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It's known as stridulation,

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and manakins are the only birds
that do it.

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By slowing their sound down...

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we can show the secret
to his performance.

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The feathers slide over each other like
a bow playing the strings of a violin.

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But unfortunately for this youngster,
he isn't the only one performing today.

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Up to ten different males
have gathered in this patch of forest.

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To outplay the competition,

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our male needs to put on
a virtuoso performance.

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With a female nearby,
now is his time to shine.

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It seems to be going well.

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But when he plays off-key...

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there are no second chances.

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Practice makes perfect.

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In time, he'll become a musical maestro.

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But of all the unusual ways animals
make themselves heard in the Amazon,

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surely the strangest takes place
deep in the undergrowth...

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where there's a hidden acoustic world
beyond our hearing.

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A treehopper.

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These insects make sounds
in a highly unusual way.

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By quivering their abdomen,

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they send out a wave of vibrations

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that travel down through their legs

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and along the stems of the plants
like their own telephone lines.

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Now using technology
that transforms vibrations into sound,

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we can eavesdrop
on their secret conversations.

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And treehoppers sound as weird
as they look.

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They're calling for mates

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and to let each other know
they found food.

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Communication in some treehoppers

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has reached even more remarkable levels
of complexity.

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This green treehopper is a caring mother.

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She looks after her nursery of nymphs.

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Each only the size of a grain of rice.

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Treehoppers are some of the only insects
that show maternal care.

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And it's just as well,
because the forest is full of dangers.

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An assassin bug, a venomous predator.

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As soon as the nymphs sense its footsteps,

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they send out an alarm.

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A series of vibrations
that ripple through the nursery.

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Mum detects their alarm call.

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The nymphs' Mexican wave...

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alerts her
to exactly where the danger is.

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She follows their signals.

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Mum now has a fight on her hands.

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But those legs that are so good
at sending and receiving messages

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are also pretty handy
at a spot of kung fu.

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With the assassin bug defeated,

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Mum returns to the nursery and sends
soothing vibrations to her young.

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The secret language of treehoppers
is so complex,

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scientists believe it rivals
that of some vertebrates.

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A hidden world of sound
deep within the forest.

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Just one of the thousands
of amazing voices

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that make the Amazon
the richest soundscape on the planet.

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To capture the complex sounds
of the world's largest rainforest,

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sound recordist Ellie Williams
traveled deep into the jungles of Peru.

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To experience the Amazon at its best,
she would have to get up high.

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My sound world
is very much the level of my own ears

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and there is so much
that goes on up in the canopy,

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so I was really keen to get up.

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With her microphone dangling below,

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Ellie headed upwards.

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But this is not for the fainthearted,

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especially when you find
you're giving a lift

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to the Amazon's
most painful stinging insect.

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I'm not very good with heights.

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- And stop.
- Wanna stop there?

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But the thing that scared me
was I was about ten meters off the ground

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and I noticed a bullet ant.

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I've got a bullet ant on my lap
right under my bag.

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I can't see it. It's really--
No, it is a bullet ant. It's massive.

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I've been hearing about
how you get eight hours worth of pain

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from one bite.

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Oh, I can see it.

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Yeah.

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Yeah, I knocked it off.
I knocked it off. It was massive.

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That's--

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Oh, my God.
That's way more scary than big heights.

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Are you ready to go up, Ellie?

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Oh, yeah.

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Do you think it was on its own
or do you think it had a girlfriend?

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Holy moly.

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Oh, my God.

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With no more stowaways,

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Ellie could now focus on her recording,

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and she soon discovered that the forest
soundscape is made up of distinct layers.

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I was kind of going up a few meters
and then stopping for a minute.

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Can you go a little bit higher, Ollie?

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We can, Ellie. Yeah.

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The sound seemed to change
quite a lot

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as I was moving up through the tree.

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Great. Thanks. Amazing.

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With the canopy
towering 190 feet above the ground,

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Ellie could hear a whole new world.

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There seemed to be more going on
higher up because I think--

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because I was at the top of the canopy,

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the sounds from all around
were coming from further away

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and I was able to hear them.
So, it felt really rich up there.

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And for Ellie,
one canopy sound soon became her favorite.

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I love the crested oropendola,

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which sounds like it's from Star Wars.

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It sounds almost robotic and I just--
I absolutely love it.

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With up to 90%
of all life here found in the canopy,

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climbing high gave Ellie a chance

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to record the noisiest part
of the rainforest,

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and the most biodiverse place on Earth.