The deserts of Southern Africa.
This is a world where silence is golden.
But listen carefully...
and these hushed lands are alive with secret conversations
we're only beginning to understand.
And for one little desert dweller,
hidden messages are key to keeping their family safe.
Meerkats.
These chatty creatures spend most of their waking hours
digging for insects and grubs.
Some more carefully than others.
But with their heads buried in the sand, it's impossible to spot danger.
So meerkats have evolved
an ingenious alarm system.
Their squeaks may sound simple, but slowing them down...
reveals different chirps made without moving their mouths.
They combine these to build 30 distinct phrases.
This sophisticated language, more complex than that of many primates,
allows them to alert each other to specific predators.
A martial eagle.
Africa's largest bird of prey,
and just one of the perils meerkats come across every day.
This young male is on lookout duty.
He's spent six months learning meerkat language,
and must now use it to let his family know what's going on around them.
This is the all-clear call.
It means, "Keep digging. Nothing to worry about."
But when you're just one foot tall,
danger doesn't only come from above.
A Cape cobra. Its venom could kill a meerkat.
The lookout barks the snake warning,
but surprisingly, the family doesn't run away from the threat.
They run towards it.
By continuing to call,
more and more join the assault.
Safely seen off...
and once again, the lookout gives the all-clear.
But scientists are discovering meerkat language
is far more complex than just identifying different predators.
Amazingly, they can also communicate the urgency of a threat.
The martial eagle is on the hunt.
It's still a long way off, and may just pass them by.
The lookout sounds the low-urgency aerial alarm.
But the eagle is edging closer.
Time to shift things up a gear.
A medium-urgency alarm.
No need to panic, but everyone in earshot now stops.
And puts eyes on the eagle.
Finally, the high-alert call.
Everyone makes a dash for the burrow.
Today, the whole family lives to tell the tale.
And it's all thanks to our young lookout's mastery
of meerkat language.
Far more sophisticated than we ever realized.
Bordering the meerkat's home
in the arid Kalahari...
lies the oldest desert on the planet.
The Namib.
A vast sea of dunes, some a thousand feet tall.
A stage where the faintest footsteps...
can give you away.
But out here, it's not only animals that make secretive sounds.
When the desert winds blow over the crests of the dunes...
they trigger an avalanche of sand.
Microphones capture the tiny sounds
as the grains tumble over each other...
and start to vibrate.
Trillions of sand particles vibrating together
cause the surface of the dune to resonate like a giant speaker.
Known as the singing dunes of the Namib,
this planetary hum has been buzzing for more than a million years.
But there are some noises out here that are beyond our hearing.
Secret channels of sound that animals use to keep in touch
over vast distances.
The African elephant...
as loud as a jumbo jet.
Their bellowing trumpets reach 120 decibels.
But they also use low-pitched rumbles
to keep in touch with distant herds.
Deeper sounds travel further,
but we only hear a fraction of what they're saying.
Using cutting-edge technology,
we can tune in to the very lowest rumbles of elephants like never before.
Known as infrasound...
we're now hearing the parts of their calls usually inaudible to us.
They create these lowest of sounds
by blowing air across giant vocal cords
eight times larger than ours.
These can broadcast for over 100 square miles.
It allows herds to keep in touch across these vast plains.
And more importantly, to join forces when they sense danger.
This is lion country.
The largest prides can take down young elephants.
In the desert, Africa's biggest predators gather close
to the few water holes...
where they know all prey must eventually come to drink.
To get to water, the herd must figure out
how many lions there are,
and whether they pose a risk to their calves.
They can do this simply by listening.
Elephants eavesdrop on lions' territorial calls.
And have even learned to count.
Huddling around youngsters if they feel threatened...
the wisest and oldest elephants over 60 years of age
can also distinguish between the calls of lionesses...
and the deeper, louder roars of more dangerous males.
If there are too many lions, the elephants will avoid the water hole.
But when they outnumber the predators,
they're not afraid to show them who's boss.
With the lions sent packing, the herd gets to drink.
By dialing into a world of sound that we're only just beginning to understand,
elephants keep their families safe across these vast planes.
For other desert inhabitants, success comes not from listening
to distant sounds...
but to minuscule murmurs just beneath their feet.
The bat-eared fox.
No prizes for guessing how they got their name.
Their outer ears, known as "pinna," are five inches tall
and act like satellite dishes
making these dainty little foxes the desert's ultimate acoustic predators.
In the last light of day, this family is getting ready to hunt.
And that means tuning into the desert's quietest sounds.
Harvester termites, the fox's favorite snack.
No bigger than an ant,
strangely, a termite's footsteps are 100 times quieter.
They may seem impossible to detect.
But the bat-eared fox has a sonic superpower
and uses its oversized ears to amplify the tiniest sounds.
Ultra-sensitive microphones give an insight into how a fox hears its prey.
Listening for termites in the day is hard enough.
But bat-eared foxes are largely nocturnal.
And when the sun goes down, they face a deafening problem.
As they patrol,
the desert's amazing night chorus turns up to full volume
downing out the tiny sounds of termite footsteps.
The cacophony is created by amorous bush crickets
that belt out their 90-decibel mating calls
by rubbing modified wings together.
But the clever fox can filter out their din.
They cock their heads
and aim their satellite dish ears to the ground
blocking out the background noise...
and just listening in to their quarry.
Their hearing is so acute
a single fox can eat 3,000 termites a night.
As the sun rises, the nocturnal chorus fades.
And the fleeting burst of life fills the airwaves.
But of all Africa's desert dwellers,
there's one that's pushed secret sounds to a whole new level.
The ostrich.
This young couple are expecting their first chicks.
Thirteen of them.
But to bring their family safely into the world,
they'll have to listen out
for the faintest of messages from their unhatched offspring.
The eggs appear dormant,
but there's a world of sound inside the shells.
At around ten days old, the developing chicks' tiny hearts start beating.
After 40 days we can hear them take their first gasps of air
through pores in the eggshell.
The parents-to-be take it in turns to incubate the eggs
all the while listening out for another secret sound
using ears at the back of their heads.
And after 42 days on the nest...
Mum hears what she's been waiting for.
A gentle cheeping from within the eggs.
It's a sign the chicks are just hours away from hatching.
And for the parents, it's a cue to get ready for action.
They now stay close together guarding the nest
and won't leave until every egg has hatched.
And before long...
the proud parents welcome their first baby into the world.
But this is a dangerous time.
The smell of freshly hatched egg will soon attract desert predators.
Black-backed jackals.
The parents need to get the others out
and leave the nest site as quickly as possible.
Now Mum starts making a sound of her own.
She beak claps to her eggs...
as if she's telling them to get cracking.
And incredibly, the first hatchling also helps speed things along.
Every time he calls,
it triggers a burst of energy from his siblings...
helping them to break out of their shells.
One by one, others join in the hatching chorus.
Soon, the family is complete and ready to roll.
Just in time.
Ostriches make a noisy entrance into the world.
But it won't be long before the chicks stop chirping
and tranquility returns to the deserts of Southern Africa.
To capture the secret conversations of elephants like never before,
the Earthsounds team ventured to the northern reaches of the Kalahari.
Sound recordist Sebastian Dunn is tasked with an unusual challenge.
To record the infrasonic rumbles
of elephants completely undetectable to human ears.
So, inside this little ball of fluff are two microphones.
The one microphone is a stereo microphone
that will record the sounds that us humans can hear.
But the other microphone in there
is able to record sounds that we cannot hear.
His first recordings aren't quite what he was hoping for.
Little bit of flatulence, but
it's pretty much all that I'm getting so far.
But it's not long before he starts capturing
the elephants' deepest vocalizations.
That is amazing.
And I can hear that rumble, but I know there's so much more that I can't hear.
Wow.
Almost 90% of elephant calls contain sounds below our hearing.
But listening to his recordings, Sebastian discovers that elephants
aren't the only ones producing low-frequency sounds.
I can hear vehicles.
The low-level rumbling of a car really travels far on the ground.
Even in the middle of the desert,
the distant drones from car engines can travel over a mile.
Scientists are discovering that low-frequency noise pollution
from human activity can disrupt elephant behavior
and may affect their ability to hear each other over long distances.
To capture clean elephant rumbles without the background noise of vehicles,
Sebastian sets his microphones to record overnight.
But come morning, the elephants have a surprise for him.
Oh, no. Guys.
This used to be one long cable.
This is a small price to pay if Sebastian has managed
to record the infrasonic sounds of the nighttime raiders.
That's a lovely rumble.
Wow, that is amazing. I've never heard that. That's fantastic.
These recordings reveal a whole new side
to elephant communication we're only beginning to understand.