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The deserts of Southern Africa.

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{\an8}This is a world where silence is golden.

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But listen carefully...

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and these hushed lands are alive
with secret conversations

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we're only beginning to understand.

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And for one little desert dweller,

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hidden messages are key
to keeping their family safe.

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Meerkats.

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These chatty creatures
spend most of their waking hours

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digging for insects and grubs.

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Some more carefully than others.

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But with their heads buried in the sand,
it's impossible to spot danger.

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So meerkats have evolved

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an ingenious alarm system.

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Their squeaks may sound simple,
but slowing them down...

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reveals different chirps
made without moving their mouths.

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They combine these
to build 30 distinct phrases.

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This sophisticated language,
more complex than that of many primates,

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allows them to alert each other
to specific predators.

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A martial eagle.

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Africa's largest bird of prey,

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and just one of the perils meerkats
come across every day.

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This young male is on lookout duty.

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He's spent six months
learning meerkat language,

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and must now use it to let his family know
what's going on around them.

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This is the all-clear call.

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It means, "Keep digging.
Nothing to worry about."

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But when you're just one foot tall,

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danger doesn't only come from above.

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A Cape cobra.
Its venom could kill a meerkat.

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The lookout barks the snake warning,

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but surprisingly, the family doesn't
run away from the threat.

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They run towards it.

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By continuing to call,

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more and more join the assault.

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Safely seen off...

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and once again,
the lookout gives the all-clear.

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But scientists
are discovering meerkat language

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is far more complex
than just identifying different predators.

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Amazingly, they can also communicate
the urgency of a threat.

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The martial eagle is on the hunt.

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It's still a long way off,
and may just pass them by.

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The lookout sounds
the low-urgency aerial alarm.

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But the eagle is edging closer.

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Time to shift things up a gear.

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A medium-urgency alarm.

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No need to panic,
but everyone in earshot now stops.

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And puts eyes on the eagle.

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Finally, the high-alert call.

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Everyone makes a dash for the burrow.

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Today,
the whole family lives to tell the tale.

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And it's all thanks
to our young lookout's mastery

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of meerkat language.

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Far more sophisticated
than we ever realized.

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Bordering the meerkat's home

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in the arid Kalahari...

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lies the oldest desert on the planet.

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The Namib.

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A vast sea of dunes,
some a thousand feet tall.

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A stage where the faintest footsteps...

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can give you away.

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But out here, it's not
only animals that make secretive sounds.

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When the desert winds
blow over the crests of the dunes...

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they trigger an avalanche of sand.

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Microphones capture the tiny sounds

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as the grains tumble over each other...

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and start to vibrate.

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Trillions of sand particles
vibrating together

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cause the surface of the dune to resonate
like a giant speaker.

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Known as the singing dunes of the Namib,

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this planetary hum has been buzzing
for more than a million years.

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But there are some noises out here
that are beyond our hearing.

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Secret channels of sound
that animals use to keep in touch

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over vast distances.

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The African elephant...

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as loud as a jumbo jet.

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Their bellowing trumpets
reach 120 decibels.

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But they also use low-pitched rumbles

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to keep in touch with distant herds.

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Deeper sounds travel further,

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but we only hear a fraction
of what they're saying.

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Using cutting-edge technology,

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we can tune in to the very lowest rumbles
of elephants like never before.

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Known as infrasound...

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we're now hearing the parts
of their calls usually inaudible to us.

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They create these lowest of sounds

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by blowing air across giant vocal cords

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eight times larger than ours.

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These can broadcast
for over 100 square miles.

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It allows herds to keep
in touch across these vast plains.

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And more importantly,
to join forces when they sense danger.

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This is lion country.

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The largest prides
can take down young elephants.

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In the desert,
Africa's biggest predators gather close

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to the few water holes...

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where they know
all prey must eventually come to drink.

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To get to water, the herd must figure out

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how many lions there are,

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and whether they pose a risk
to their calves.

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They can do this simply by listening.

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Elephants eavesdrop
on lions' territorial calls.

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And have even learned to count.

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Huddling around youngsters
if they feel threatened...

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the wisest and oldest elephants
over 60 years of age

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can also distinguish
between the calls of lionesses...

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and the deeper,
louder roars of more dangerous males.

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If there are too many lions,
the elephants will avoid the water hole.

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But when they outnumber the predators,

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they're not afraid
to show them who's boss.

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With the lions sent packing,
the herd gets to drink.

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By dialing into a world of sound that
we're only just beginning to understand,

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elephants keep their families safe
across these vast planes.

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For other desert inhabitants,
success comes not from listening

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to distant sounds...

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but to minuscule murmurs
just beneath their feet.

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The bat-eared fox.

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No prizes for guessing
how they got their name.

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Their outer ears, known as "pinna,"
are five inches tall

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and act like satellite dishes

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making these dainty little foxes
the desert's ultimate acoustic predators.

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In the last light of day,
this family is getting ready to hunt.

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And that means
tuning into the desert's quietest sounds.

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Harvester termites,
the fox's favorite snack.

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No bigger than an ant,

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strangely, a termite's footsteps
are 100 times quieter.

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They may seem impossible to detect.

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But the bat-eared fox
has a sonic superpower

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and uses its oversized ears
to amplify the tiniest sounds.

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Ultra-sensitive microphones give
an insight into how a fox hears its prey.

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Listening for termites in the day
is hard enough.

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But bat-eared foxes are largely nocturnal.

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And when the sun goes down,
they face a deafening problem.

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As they patrol,

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the desert's amazing night chorus
turns up to full volume

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downing out
the tiny sounds of termite footsteps.

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The cacophony is created
by amorous bush crickets

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that belt out
their 90-decibel mating calls

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by rubbing modified wings together.

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But the clever fox
can filter out their din.

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They cock their heads

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and aim their satellite dish ears
to the ground

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blocking out the background noise...

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and just listening in to their quarry.

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Their hearing is so acute

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a single fox can eat 3,000 termites
a night.

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As the sun rises,
the nocturnal chorus fades.

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And the fleeting burst
of life fills the airwaves.

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But of all Africa's desert dwellers,

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there's one that's pushed secret sounds
to a whole new level.

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The ostrich.

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This young couple
are expecting their first chicks.

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Thirteen of them.

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But to bring their family
safely into the world,

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they'll have to listen out

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for the faintest of messages
from their unhatched offspring.

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The eggs appear dormant,

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but there's a world of sound
inside the shells.

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At around ten days old, the developing
chicks' tiny hearts start beating.

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After 40 days we can hear them
take their first gasps of air

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through pores in the eggshell.

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The parents-to-be take it in turns
to incubate the eggs

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all the while listening out
for another secret sound

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using ears at the back of their heads.

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And after 42 days on the nest...

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Mum hears what she's been waiting for.

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A gentle cheeping from within the eggs.

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It's a sign the chicks are just hours away
from hatching.

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And for the parents,
it's a cue to get ready for action.

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They now stay close together
guarding the nest

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and won't leave
until every egg has hatched.

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And before long...

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the proud parents
welcome their first baby into the world.

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But this is a dangerous time.

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The smell of freshly hatched egg
will soon attract desert predators.

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Black-backed jackals.

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The parents need to get the others out

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and leave the nest site
as quickly as possible.

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Now Mum starts making a sound of her own.

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She beak claps to her eggs...

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as if she's telling them to get cracking.

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And incredibly, the first hatchling
also helps speed things along.

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Every time he calls,

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it triggers a burst of energy
from his siblings...

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helping them to break out of their shells.

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One by one,
others join in the hatching chorus.

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Soon,
the family is complete and ready to roll.

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Just in time.

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Ostriches make a noisy entrance
into the world.

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But it won't be long
before the chicks stop chirping

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and tranquility returns to the deserts
of Southern Africa.

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To capture the secret conversations
of elephants like never before,

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the <i>Earthsounds</i> team ventured
to the northern reaches of the Kalahari.

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Sound recordist Sebastian Dunn
is tasked with an unusual challenge.

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To record the infrasonic rumbles

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of elephants completely undetectable
to human ears.

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{\an8}So, inside this little ball of fluff
are two microphones.

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{\an8}The one microphone is a stereo microphone

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{\an8}that will record the sounds
that us humans can hear.

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But the other microphone in there

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is able to record sounds
that we cannot hear.

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His first recordings
aren't quite what he was hoping for.

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Little bit of flatulence, but

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it's pretty much all that I'm getting
so far.

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But it's not long
before he starts capturing

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the elephants' deepest vocalizations.

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That is amazing.

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And I can hear that rumble, but I know
there's so much more that I can't hear.

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Wow.

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Almost 90% of elephant calls
contain sounds below our hearing.

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But listening to his recordings,
Sebastian discovers that elephants

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aren't the only ones
producing low-frequency sounds.

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I can hear vehicles.

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The low-level rumbling of a car
really travels far on the ground.

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Even in the middle of the desert,

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the distant drones from car engines
can travel over a mile.

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Scientists are discovering
that low-frequency noise pollution

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from human activity
can disrupt elephant behavior

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and may affect their ability
to hear each other over long distances.

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To capture clean elephant rumbles
without the background noise of vehicles,

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Sebastian sets his microphones
to record overnight.

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But come morning,
the elephants have a surprise for him.

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Oh, no. Guys.

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This used to be one long cable.

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This is a small price to pay
if Sebastian has managed

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to record the infrasonic sounds
of the nighttime raiders.

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That's a lovely rumble.

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Wow, that is amazing.
I've never heard that. That's fantastic.

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These recordings reveal a whole new side

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to elephant communication
we're only beginning to understand.