DAVID ATTENBOROUGH: Forests at first sight
may seem quiet and tranquil.
But today we can explore them in new ways...
..and from a new perspective.
And, in fact, they're full of unexpected connections,
relationships
and even secret messages.
Only now are we discovering
how strange and complex
forests actually are.
The rainforest of Borneo.
A pair of oriental pied hornbills are renewing their partnership.
They mate for life.
And this year's nesting season is just starting.
Before they face the challenges ahead,
they reaffirm their bond.
And they do so with an unusual ritual...
..at the entrance to a bat cave that they know well.
This rather curious gift
isn't normally on their menu.
But it both demonstrates devotion
and reassures the female that her mate will provide for her.
In the coming weeks, she will depend on him
in the most extraordinary way.
Nesting is a dangerous time for any bird.
The hole in this tree trunk
will provide vital protection.
Just what she wants.
Once settled inside...
..the female does something truly bizarre.
She pulls out her flight feathers.
She is not going to need them
because she will be staying in here for quite some time.
It's not only a little cramped,
it also lacks basic amenities.
Now her partner brings her a beakful of mud.
And she begins to seal herself in.
She has turned the tree hole
into a predator-proof fortress.
But it's also...
..a prison.
Her partner, however, is a regular visitor.
For the next two months, he will deliver all her food
directly to her door.
But she can be fussy.
He's going to have his work cut out.
HORNBILL CALLS
Delicious.
It may seem that he has been doing all the work...
..But she, too, has been fully occupied.
The food he has brought has enabled her to produce
two precious eggs.
She will keep them safe for another six weeks
until the young have grown and fledged.
And then, both she and they
will break out of their confinement.
But until then...
..this devoted couple are going to be very busy indeed.
The warmth and the moisture of rainforests
enables their inhabitants to flourish
in both numbers and variety.
And here, in the Amazon, live many strange species.
SOFT HOOTING
This is a treehopper.
One of hundreds of different types in this forest.
They not only have a bizarre appearance...
..but they also communicate...
RESONANT PURRING
...in a remarkable way.
CLICKING AND PURRING
Vibrating their bodies, they send signals
through the forest plants they live on.
CLICKING AND PURRING
Most of these messages we can only hear by using special microphones.
HIGH-PITCHED TONES
Each treehopper species has its own repertoire.
LOW-PITCHED HOOTING
RESONANT RUMBLING
HIGH-PITCHED BUZZING
And every sound...
PULSING HOOTING
..has its own particular meaning.
SHRILL BUZZING
Whether it is to attract a mate...
..share information about food...
LOW WHOOPING
STUTTERED CLICKING
..or warn each other about the arrival of predators.
STUTTERED CLICKING
SHRILL PURRING
LOW PURRING
This treehopper mother communicates with her young,
encouraging them to stay together
so that she can protect them.
For there are plenty here waiting to eat young treehoppers.
Ants...
..on the hunt.
Treehoppers know how to defend themselves.
But not all threats are so easily dealt with.
An assassin bug.
Armed with piercing mouthparts
and sticky front legs...
...capable of literally sucking the life out of her entire brood.
PURRING AND CLICKING
She can try to block the assassin's path.
But she can't guard them all.
She needs help from friends in high places.
Bees.
They're very aggressive.
This is more than the assassin bug bargained for.
Mission accomplished.
Her brood are safe.
The bees don't protect the treehoppers for free.
A little tickle on a treehopper's back...
..and they exude a sugary liquid.
Honeydew.
A sweet reward for protecting them.
It's just one of the countless ways
in which forest species work together.
In the forests of India,
you can hear a unique and truly extraordinary sound.
RHYTHMIC WHISTLING
These are dholes...
..wild dogs that whistle.
Like treehoppers, they, too, communicate in secret -
but for a different reason.
DEEP RUMBLING
Hunting in a dense teak forest is difficult...
...especially so if your prey is three times your own size.
The only way for dholes to succeed
is to work as a team.
This family has four growing pups.
A chital deer could feed the entire pack.
The pack must get close...
...without being detected.
GRUNTS
CLAMOUR OF ANIMAL CALLS
But with eyes and ears everywhere...
...the deer are soon aware of the dogs' presence.
SQUEAKING AND RATTLING
The pack can't afford to give up.
They may have better luck here.
The vegetation is dense and provides better cover.
But the dholes could easily lose track of one another.
So they use their unique whistles.
SOFT WHISTLING
Only dholes can understand
these quiet, unobtrusive calls.
RHYTHMIC WHISTLING
Now they take up their hunting positions...
...even though they can't see each other.
WHISTLING
With the deer surrounded...
...the dholes wait for the signal to attack.
WHISTLES
SHARP YELP
Some of the dholes split the herd...
..and drive a stag towards others waiting in ambush.
YELPING CALLS
The dholes' ability to communicate so quietly
enables them to stay connected,
and so hunt successfully in the tangle of their jungle.
The mountainous forests of central China.
Until recently, these were among the least known of forests.
They're full of swirling mists,
and few outsiders had any idea
of what they might contain.
THUNDER RUMBLES
Living in such dense vegetation,
it's difficult to make yourself seen...
..even when you want to be.
And that's a problem for this male Temminck's tragopan.
He has lived most of his life alone.
And this is his first mating season.
TRAGOPAN CHIRPS
He needs to make himself conspicuous in the gloom of the forest floor,
and he's found a clearing where he might do so.
A female.
TRAGOPAN SQUAWKS
She, too, is looking for a mate.
This could be his moment.
Oh, dear.
TRAGOPAN CHIRPS SOFTLY
Stage fright.
SHRILL SQUAWKING
And who is this?
A male golden pheasant.
He, too, has come to this clearing...
PHEASANT SQUAWKS
...to attract a female.
And he seems a little more confident.
So that is how it's done.
The tragopan might still have a chance.
Here is a new female.
But is she interested?
It's time to be bold.
RHYTHMIC RATTLING
He pumps up a pair of horns
and a multicoloured bib.
It's a sight to be wondered at.
And it has never before been filmed in the wild.
RATTLING
Not today.
How deflating.
TRAGOPAN CHIRPS SOFTLY
The temperate rainforests of western Canada.
Some of the trees here are 1,000 years old.
It's autumn, and the beginning of a spectacle that each year
transforms this forest and all that lives in it.
After years at sea, thousands of Pacific salmon
are returning to these streams to breed.
SOFT GRUNT
And they attract the forest's rarest resident.
A spirit bear.
A white variant of the black bear.
Fewer than 150 exist,
and they're found only here.
This female has fished for salmon here for 20 years.
Get your timing right...
..and there can be great rewards.
In her youth, she was, in fact, even more successful
than the black bears.
Perhaps her pale coat makes it difficult for the fish to see her
against the bright sky,
and that could give her an advantage.
But now she is old,
and this year she's finding it hard.
Her fishing skills, however, haven't totally deserted her.
This annual feast helps her to fatten,
ready for the winter ahead.
But it also helps the patch of forest where she lives.
This female has an unusual relationship with the forest.
Every fish carcass she leaves behind decays,
releasing nutrients that soak into the soil.
And there...
..they are collected by a network of fungi.
The threads attach themselves to the trees' roots.
And nutrients from the fish, collected by the fungi,
are then passed on to the trees.
As a consequence, the forest around the river
grows three times faster than elsewhere.
And some trees here become as tall as any in the world...
..and provide spirit bears with a healthy forest home.
We now know that such relationships exist in forests all over the world.
At the heart of these many connections
stand giant trees, like this one.
A kapok.
It started life as a seed some 200 years ago.
Now it towers 60 metres above the forest floor...
..and transports 1,000 litres of nutrient-filled water
from its roots up to its canopy every day.
So this giant gives life to others.
A whole community of animals and plants
depends on the wellbeing of this one tree.
CHAINSAW BUZZES
A single cut made in just a few moments
has broken thousands of long-established connections.
Across the world's forests,
this story is being repeated endlessly.
15 billion trees
are cut down every year.
Every one of these trees is, in itself,
an intricate ecosystem.
But here in Brazil, they're being replaced
by plantations of a single species of tree.
Originally from Australia...
..these eucalypts are unable to build relationships
with most of the native plants and animals.
And, worse, these newcomers grow so rapidly
they extract nutrients from the soil
faster than they can be replaced.
And what was once a rich and complex world...
..becomes little more than a green desert.
And at just five years of age...
..their lives are ended.
They're felled and taken away.
Their wood is then pulped to make paper.
And all that remains of the rich rainforest
are a few tiny patches.
Patches so small that few of the original inhabitants
are able to survive in them.
Uganda, East Africa.
This small group of chimpanzees
have a detailed knowledge of the forest territory
that they inherited from previous generations.
They know the best places to shelter,
to raise their young...
..and to feed.
This fruiting tree
cannot by itself sustain the chimps for long.
CHIMPANZEE CALLS
The alpha male signals that it's time to move on.
GRUNTING AND SCREECHING
Where he goes, others will follow.
He leads them not to another fruiting tree...
..but into a new world.
TRAFFIC HUMS
This road, only recently built,
has cut through their territory.
The alpha male is cautious.
His own mother was killed on this road.
HORN BLARES
HORN HONKS
He makes sure it's clear before crossing
with the slower members of his family.
If the group is to get what they need...
..they will have to go against their natural instincts...
..and approach humans.
PIG GRUNTS
But their new neighbours are friendly.
And they allow the chimps to collect...
..jackfruit,
the largest of all tree fruits.
Jackfruit grow all year round in people's gardens.
And they're more nutritious
than the limited amount of wild food
the chimps can now find in what remains of their forest.
But this is a new world...
..and a new relationship.
New boundaries need to be established.
Some of the chimps start to help themselves
to people's crops.
DOGS BARK
SCREECHING AND GRUNTING
CLAMOUR OF ANIMAL CALLS
WINGS FLUTTER
They have outstayed their welcome,
and the alpha male decides that it's time to leave.
CHIMPANZEES SCREECH
The chimps make this dangerous journey every day.
But these highly intelligent animals,
our closest living relatives,
have managed, just about,
to carve out a place for themselves
in this changing world.
Animals have maintained
a long-established relationship with forests.
But as we continue to break our connections with them,
the question is,
for how much longer will they survive?
Surely, the time has come to rebuild them.
DAVID ATTENBOROUGH: Over many years,
I've been lucky enough to watch chimps in their natural home,
such as here in the thick forests of West Africa.
ARCHIVE: Chimpanzees.
A peaceful scene of jungle harmony.
The experienced male...
..is sitting right there.
DAVID: But the lives of many chimpanzees
are now changing dramatically.
Here, in Uganda, over the last decade,
they have lost over 80% of their forest home.
They don't live in a protected area.
To survive here, they have to live alongside
the 200 or so human families who farm here.
The chimps always come from the forest.
They come to eat jackfruit from my land.
They know us by our faces,
as we know them by their faces, as well.
To tell the story of this remarkable chimp group,
the Planet Earth team are working with these residents.
SCREECHING
CREW MEMBER: Who was that, Tom?
This one was Araali.
Tom is part of the Bulindi Chimpanzee and Community Project.
He's been studying the chimps every day for the last 15 years...
..and has seen the change first-hand.
Very many things have changed.
When chimpanzees were seeing people, they would run.
Run very quickly and go.
But now they just stand.
Because everywhere they go,
they find a person.
Chimps are normally tricky to film in the wild.
But in this human world, the crew are surprised
by how easy it is to approach them.
CREW MEMBER: Another one coming up the path.
But back in the forest,
it's a different story.
Here, the chimps seem wary of the newcomers.
CREW MEMBER GRUNTS
There's a ditch there.
All the crew get to see...
..is a lot of bottoms.
This afternoon, the chimps have been taking us on a wild-goose chase.
They've crossed the river and then they've crossed back,
gone past us while we're in the woods,
and then now they've disappeared again.
When we don't have chimps...
..we film goats!
Here, in the chimps' forest home,
it's going to take time to earn the group's trust...
DISTANT SCREECHING
I think they found Moses.
..and get to know one another.
This is Jack.
After two weeks, things are improving on the ground.
But what will the chimps think of the crew up in the trees?
I can see a bunch of chimp faces looking up at me.
This is a new experience for them.
I doubt they've ever seen a human in a tree before.
So, hopefully, they accept me.
After hours of waiting...
..success!
All the chimps that were on the ground looking up at me
are now happily in the tree,
which is a really good sign that they've accepted me.
It's the first time that we've been able to see at their level
while they're feeding.
For the crew, it has taken a long time
to gain the chimps' acceptance.
But, in fact, the chimps here have shown that they can
respond quickly to the presence of people.
Chimpanzees are highly intelligent.
If you cut down the forest,
well, chimps will start eating human crops.
If you divide their range up with roads and, you know...
Well, chimps will end up just learning to cross the roads.
The animals can adapt to an increasingly human environment.
The question is, can people accommodate an animal like a chimp?
LOUD SCREECHING
Chimpanzees can be dangerous.
CHIMPANZEES SCREECH
Living alongside them is a mixed experience.
The local community and the project have been working together
to try to decrease the impact of these problems.
Over the last eight years,
Lilian and her family
have planted native seedlings on her land
and left her patch of forest to regrow.
If we cut it, they come and sleep in our houses,
so we should leave that place for them.
If you leave them and you don't disturb them,
they are peaceful animals.
With other residents following suit,
more of the forest is showing positive signs of return.
There is a long way to go,
and the future for these chimps remains uncertain.
But where peaceful coexistence can be built,
there is hope.
Next time...
..animals battle the elements in a world of extremes...
..where life exists on a knife edge...
..in Earth's greatest natural wonders.
Habitat Explorer brings animals and their habitats to life.
Explore this free interactive, and make origami animals.
Go to bbc.co.uk/planetearth3
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visit the website or call the numbers on the screen.