Original subtitles

DAVID ATTENBOROUGH: Forests, at first sight,

may seem quiet and tranquil.

(SOFT PATTERING)

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.

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...

(DEEP PURRING)

...in a remarkable way, too.

(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 AND PURRING)

Each treehopper species has its own repertoire.

(GENTLE HOOTING AND DEEP RUMBLING)

(HIGH-PITCHED BUZZING)

And every sound...

(DEEP THUDDING)

...has its own particular meaning...

(HIGH-PITCHED WAILING)

...whether it is to attract a mate...

(CLICKING)

...share information about food...

(WHOOPING)

(RASPY CLICKING)

...or warn each other about the arrival of predators.

(RASPY CLICKING)

(PURRING)

(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.

(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)

But with eyes and ears everywhere...

...the deer are soon aware of the dogs' presence.

(SQUAWKING)

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.

(WHISTLING)

Only dholes can understand

these quiet, unobtrusive calls.

(WHISTLING)

Now they take up their hunting positions...

...even though they can't see each other.

(WHISTLING)

(WHISTLING)

With the deer surrounded...

...the dholes wait for the signal to attack.

(WHISTLES)

(YELPS)

Some of the dholes split the herd...

...and drive a stag

towards others waiting in ambush.

(WHISTLING)

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.

(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.

(SQUAWKS)

She, too, is looking for a mate.

This could be his moment.

Oh, dear.

(CHIRPS)

Stage fright.

(SQUAWKING)

And who is this?

A male golden pheasant.

He, too, has come to this clearing...

(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.

Not today.

How deflating.

(CHIRPS)

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 tree's 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.

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 HONKS)

(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.

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)

(WINGS FLUTTER)

They have outstayed their welcome,

and the alpha male decides that it's time to leave.

(SCREECHING)

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.