A Bengal tiger.
She is looking for prey.
One of these deer, perhaps.
But the slightest sound from her...
...could warn them.
She will have to try elsewhere.
The forests of the world
are home to two-thirds of all species of mammals.
For them, it is the most important habitat of all.
Equatorial Africa.
Chimpanzees.
This young chimp has discovered a cloud of bees.
They're coming from a hole in the tree,
and he knows that there could be something sweet in there.
But it's well defended.
The alpha male knows the kind of bee that doesn't sting.
But they live underground.
So, to get their honey, you need a tool.
A straight stick should do the job.
If it's the right length.
A sniff tells him that there is honey down there somewhere.
Got it.
He found it - and the others will have to wait.
Mm!
That looks nice.
Is there enough for two, perhaps?
Apparently not.
Perhaps he's left some behind.
No.
But up in the trees, there is more substantial prey.
Red-capped mangabeys.
The alpha male investigates.
Others stay on the ground
and get ahead of the mangabeys.
And then some quietly climb into the trees.
The trap is set.
The leader charges.
Some hunters return to the forest floor...
...to prevent their prey from coming to the ground.
In panic, the monkeys flee directly towards
the chimps waiting in ambush.
And are caught.
The chimps, young and old,
females and males,
all share in the feast.
Teamwork has won, and is rewarded.
The forests of Madagascar have their own special fauna,
and it's unlike any other in the world.
Among the strangest creatures
are little mammals called tenrecs.
They have poor eyesight,
but a keen sense of smell,
and will eat almost any small creature
they can find in the leaf litter.
And they manage to find food almost anywhere.
One of the smaller members of the family
is having difficulty in keeping up.
And there are dangers around.
The mother realises that one of her family is missing.
She calls to the wanderer using a special instrument -
a patch of stiff bristles on her back
that can be vibrated.
The wanderer recognises the summons
and heads towards it.
But adult and young are separated by a stream.
It's only a metre or so across,
but that is quite a distance for a tiny tenrec.
Oddly, perhaps, tenrecs can swim.
Now it'll have to climb.
Strong toes and hooked claws
enable it to cope with the slippery mud.
Reunited.
Madagascar's rainforests are tropical, hot and dense.
The forests of North America are also thick.
But they are very cold indeed.
This is the home of the forest bobcat.
High in the trees,
a lone female has seen what she's been waiting for.
The meal that will be essential
if she is to survive the coming winter.
The streams are full of newcomers.
Salmon.
Having spent years feeding at sea,
they come back here to spawn.
Otters have been waiting for them
and know how to catch them.
But cats don't have thick waterproof fur, like otters.
And few like getting their feet wet.
She's much more at home on land than in the water.
A fallen tree across the river could help.
She follows the salmon upstream...
...looking for a place where they're forced to swim close
to the river bank.
One of these fish could weigh more than she does.
This is not going to be easy.
It's too big and powerful...
...but these huge fish are worth fighting for.
She follows the river still further upstream.
It's now narrower...
...but swifter.
This could be her chance.
This is the first bobcat ever filmed catching salmon.
It's an extraordinary display of the determination
that she will need if she is to survive the cold months ahead.
As temperatures fall,
some forests have become draped in a thick layer of snow.
Most of the animals that were here in the summer
have long since retreated south.
Those that remain have to dig to reach the vegetation
that lies beneath the snow.
But high in the trees,
one mammal gets about without touching the ground.
A Siberian squirrel.
It...
...can glide.
A furry membrane stretches from its wrists to its ankles.
There could hardly be a more efficient way of travelling.
At this time of the year,
the female squirrels are not only feeding for themselves.
They're also raising families.
A disused woodpecker's nest hole
protects the young squirrels from the sub-zero temperature.
Their mother's precious milk must sustain them
throughout the winter.
Five weeks later...
...the warmth of spring has transformed the forests.
It's time for the young squirrels to leave the shelter of their nest.
But first flights are somewhat daunting.
One of the youngsters seems keen.
And one not quite so confident.
The first climbs up the tree, while the other watches.
The higher up they go, the further they will glide.
And then...
...lift-off!
Made it.
But the other seems to have pre-flight nerves.
Perhaps he'll try... tomorrow.
The warm forests of Costa Rica.
One sound rings out in the dawn.
It can travel for almost three miles in every direction.
It's the loudest call made by any land mammal.
And the singer?
A howler monkey.
A dominant male is proclaiming his family's occupation
of this particular patch of forest.
They eat fruit, but primarily they are leaf-eaters,
and they have already stripped this tree of most of its leaves.
It's time for them to move on.
But they rarely descend to the ground.
Like many South American monkeys,
they have a grasping tail
that they use, in effect, as a fifth limb.
With its help, they manage to bridge great gaps.
Living in such large groups...
...there is always help for the youngsters.
But sometimes, when you're 30 metres up,
you have to take a leap of faith.
Once, they could find great areas
of uninterrupted forest canopy.
But today, they have to venture into towns to find the leaves they need.
The alpha male is the leader.
It's up to him to find food.
This is alien territory.
And up here,
there are dangers.
They don't know exactly what they are...
...but they follow.
Their grasping tails are now particularly valuable...
...and reach cables above them.
But if they touch more than one uninsulated electricity cable...
...the shock will kill them.
In the past three years,
nearly 1,000 monkeys have been electrocuted here.
He keeps a watchful eye on his family.
Once everyone is safely across,
he follows.
At last, they can all feed.
That is not only essential for the howlers...
...but also for many of the trees on which they feed,
which rely on them both for pollinating the flowers
and for distributing the seeds that the fruits contain.
It's a partnership, with rewards for each.
And nowhere is this interdependence
between plants and mammals more impressive...
...than here in central Africa.
These straw-coloured fruit bats
have flown right across the continent
in order to visit this one small particular patch
of forest in Zambia.
Bats are the only mammals that have powered flight.
And this enables them to visit the Zambian forest
at precisely the time that fruit trees are ripening.
The roost is a crowded place.
And bats, like all of us, have things they need to do.
One thing is for certain.
It's better not to be in the lower branches.
The heat of the day has passed,
and as the light fades, the bats start to take off.
Guided by their acute sense of smell,
they head off in search of fruit.
Within just 30 minutes, some ten million bats take to the air.
This is the largest and densest concentration of mammals
to be found anywhere on the planet.
They consume up to 5,000 tonnes of fruit every night.
And within three short weeks,
they will distribute over a billion seeds.
Enough to plant an entire forest.
But today, both these bats and their forest are under threat.
Human beings have claimed the land,
cutting down trees to create farms and build houses.
The delicate natural balance is at risk.
Without our protection, the survival of entire forests
and their remarkable inhabitants are in danger.
But the impact of human activity is not always so obvious.
In Uganda, the warming of the world is changing the landscape.
As temperatures rise,
the cactus-like euphorbia trees are spreading.
And some terrestrial animals are spreading, too.
Not laterally, but upwards.
This pride of lions is starting to claim new territory.
In the branches, it can be several degrees cooler
than at ground level.
It's a nice place to relax...
...if you can find somewhere comfortable to do so.
Lions aren't really suited for life in the trees...
...and they're still trying to get accustomed to it.
But there is little point in getting properly comfortable...
...if there are hungry mouths to be fed.
The dominant female leads the pride...
...followed closely by the cubs.
But instead of starting to hunt,
these lions behave rather strangely.
They start to climb.
It's not only cooler in the branches...
...they also get a better view of what is going on around them.
Up there, their scent is less noticeable than at ground level.
Their prey seem to forget that they are even there...
...and stray ever closer to their tree.
Silently, the adult lions drop into action.
The cubs watch.
Now patience is all-important.
The cubs can't stop playing.
That is too much.
These youngsters still have a lot to learn.
The adult lions are also adapting.
Many things are changing.
The future for the hunters on the savannah
is by no means certain.
India.
Hidden deep in a protected tract of jungle...
...a new generation of tiger cubs
are taking their first steps into the forest.
They are healthy and strong, and growing fast.
Their mother will soon have to go out into the forest to hunt.
The increasing heat of summer
has already scorched the trees and shrubs...
...and the jungle is bare.
Many prey animals have left the forest to look for food elsewhere.
Those that remain are on high alert.
It's increasingly hot.
These deer are cooling off in a forest lake.
In the water, stealth and camouflage will be of no help to her.
But she still needs to hunt.
She gets as close as she can to her prey,
exploiting every last bit of cover.
She splits the herd.
She may be powerful...
...but chasing prey in deep water is exhausting.
She selects an individual near the shore...
...and drives it back into the forest.
Once on dry land, she can use all her power and speed.
Within minutes, the deer is suffocated.
The tiger's great intelligence and physical skills
make it one of the forest's most impressive hunters.
If we protect these rich and diverse forests,
the mammals that live in them will thrive.
Here in India, in the space of just 20 years,
the number of Bengal tigers has doubled.
There are more than 6,000 species of mammals on Earth.
But their fate lies in the hands of just one.
Us.
If we make the right decisions,
we can safeguard the future
not just for our fellow mammals...
...but for all life on Earth.
Over the course of four years,
the Mammals team travelled across the globe...
...filming in a great variety of forests.
But one story took them to an unexpected setting.
In Costa Rica, they found themselves on the streets of Playa Hermosa.
Despite being one of the most forested countries,
even here wildlife is competing for space with humans.
For howlers, living in a fragmented forest has grave consequences.
Close to the...
The team enlisted the help of local howler expert Ines Azofeifa Rojas.
The male from troop two and two males from troop three.
I love the howlers.
They are the gardeners of the forest.
They teach me how to live in one environment
and help another species.
Ines has been researching these howlers for the past seven years,
observing them as they travel in search of food
through the town that cuts across their forest.
When the troop is on the move, just as in the forest,
their instinct is to stay up high.
So when they reach a road, they use power lines.
One male.
Oh, my God. This is so close to the electric cable.
If they touch more than one uninsulated cable at the same time,
they will get a fatal electric shock.
Each death can have a huge consequence for the troop,
and Ines has witnessed this first-hand.
When we found an alpha male in the power lines,
we also lost all the infants before one year,
because the new alpha male kill all of these infants
to produce a new generation.
So this is a big problem
because we don't lost just one individual.
Whilst 80% of howlers that get electrocuted die...
...some survive.
These are often infants.
Attached to their mothers, they are protected from a direct shock.
But there is hope.
There are volunteers and organisations working
across the area to get medical treatment to those affected.
Ines is part of an online response team,
on call day or night to rescue survivors.
Last night, we received a call.
One female was electrocution.
This female have an infant approximately one year.
And this infant I take to the rescue centre.
With their help, these individuals have a chance to survive.
But it's a long road to recovery.
Throughout the region, there are just a handful of vets
primed to treat electrocution victims.
Check the mouth, the teeth, how they're doing.
This is a very big problem
because it's so many of them getting electrocuted
that we can be working with one animal
and be receiving an emergency call right away.
The survival rate is very low.
Maybe 15 to 20% of the patients that arrive to us after an electrocution,
they actually are able to survive
and be able to be released back into the wild.
We're going to do all the regular check-up
that these individuals need.
Check the lungs and the heart.
Mm-hm. Everything sounds good.
She will be with us for at least three to four years.
During the next year that she's going to be with us,
she's always going to be intensive care,
because electrocution can cause severe injuries months,
even years after the trauma.
Hopefully, she's going to be OK and be able to be released.
Back in town, Ines has been identifying hot spots
where most of the electrocutions are happening.
We can have in one accident more than one howler electrocute.
We have some spots that maybe we have five or six individuals
that, in the moment, in the power line.
There is a solution that offers safe passage.
Today, the team are putting up a bridge in a hot spot area,
to give the monkeys an alternative to the power lines.
So, we have a canopy bridge that can connect
these parcels of forest and provide access for more food
and social interaction for the howlers.
For Ines, it's a nervous wait.
They are so curious.
And the howlers are rethinking where they can cross.
Come on, guys.
Oh, my God!
Running, running and running!
Take care, little howler.
Several canopy bridges have now been installed across the town.
Not only has the programme reduced the electrocutions by 90%,
it has also brought more connectivity
to this fragmented forest.
When the humans change the use of land,
we forget that all of this land that we are using
is the habitat of many other species.
Ines's determination to help the howlers has been driven
by reconnecting with the forest.
So, when I began to study the howlers,
I can connect again
with the rights of the forest
and also with all of the other species.
So, my message for many people is,
try to reconnect with whatever species that you want it -
with plants, with trees, with amphibians -
but try to reconnect with this same environment
that we share with other species in the same global planet.
With the knowledge and dedication of local champions, like Ines,
across the series, the production team were able to document
extraordinary moments in the lives of mammals.
As pressure on wildlife increases,
commitment from passionate individuals on the ground...
Here we've got a wolf.
...does make a difference.
Can't ignore how special this place is.
If we continue to share knowledge...
Here's where the den is. Oh, I see.
So, we can connect to that route.
...and protect the environment...
With the education and working together
for common goals, then I be very optimistic.
...there can be hope for the future of all mammals...
Yay!
...including ourselves.
We did it, we did it, we did it!
We did it!