All language subtitles for The Life of Mammals 9of9 Social Climbers 720p HDTV x264 AAC MVGroup org_Subtitles01.ENG

Monkeys, together with apes,
are our closest relatives.

They have the richest social life
of all mammals,

and much of their time is spent
establishing relationships

and climbing the social ladder.

And that has had
some remarkable consequences.

South America,

and a few capuchin monkeys
are having a morning get-together.

Capuchins are very like the earliest
of all monkeys, judging from fossils.

The basic pattern, you might say.

With grasping hands and gripping
tails, they race through the forest

with astonishing speed and agility.

But it's their big brains
that really give them an edge.

If there is one thing
that is characteristic of monkeys,

it is their ability to spot
an opportunity and then exploit it.

That's especially true of capuchins.

Of course, they'll grab a ripe fruit,

but they investigate everything
in their path. Little escapes them.

But it's their inquisitiveness
that really impresses you

when you follow them.

They look for food everywhere.

Their colour vision is excellent.

Their sense of smell, however,
is no better than ours,

so to find food that is hidden from
view, they use brains - not noses.

They can, clearly, imagine what
might be lurking beneath dry leaves.

Out of sight
is by no means out of mind.

A good memory must also help.

Recalling a previous experience

could make the difference between
getting stung and getting honey.

The troop
is just entering these mangroves.

Most mammals
wouldn't find much to eat here,

but monkeys' big brains enable them
to find things that others miss.

Only the bolder ones
chance their hand with crabs.

It's quite brave to tackle
sharp claws with delicate fingers.

A retreating tide exposes shellfish.

But eating those poses more problems.

The clams are full of meat, but it's
all locked up behind closed doors.

However, grasping hands guided by a
big brain can deal with that problem.

These clams are very tough.

I would have a lot of difficulty
in opening them myself,

but these monkeys have learned
that if you hit them hard enough,

the clam relaxes,
the shells can be opened,

and they can get at
the juicy meat inside.

The whole troop is in on the trick,

and now at least 20 of them are busy
giving the clams the treatment.

Ten minutes on, and the shells of
the clams are still tightly clenched.

This is hardly fast food.

The young watch attentively.

Most will eventually learn
how to do it,

so the clam-cracking technique
will pass to the next generation.

But it takes years for a young monkey
to get it absolutely right.

Patience is important.
Unfortunately, so is technique.

Capuchins, just like us,

have varied personalities
and abilities,

and some never really get to grips
with clam-cracking.

Those with a good technique
AND perseverance

are now beginning
to collect their rewards.

Although some aren't exactly thrilled
by what they find.

It's not just food
that monkeys collect from the forest.

The two bunches of leaves
may look very much the same,

but this kind is used
by the local people

as an antiseptic
and insect repellent,

whereas this one
has no medicinal qualities at all.

If I put them both down, I think I
know which the monkeys will choose.

Those are pipa leaves - the ones
with the insect-repelling sap.

Pipa is hard to find, so this big
bunch will cause a lot of excitement.

Like many things in monkey life,

pipa rubbing is a major social event.

Those taking part
disregard the differences

they might have had at other times
and everyone joins in.

Do these capuchin really know
that this behaviour

protects them against
skin infections and mosquitoes?

Well, of course,
it's impossible to say.

But they do it more frequently
during the rainy season

when there are more skin infections
and mosquitoes around

than at any other time
during the year.

Not all capuchins use pipa. But once
one discovers the plant's properties,

the knowledge quickly spreads,

so pipa-leaf rubbing
becomes a group tradition.

Capuchins eat most things.

Some monkeys, however,
have particular specialities.

These are uakaris, and they
will eat fruit of an unusual kind.

The colour of their faces
indicates their social position.

The brighter the scarlet,
the more senior the animal.

The good colour vision that enables
them to tell where they are socially,

also helps them to select fruit.

Unusually, they will eat fruits that
are a vivid green and not yet ripe.

The monkeys in this forest
can all eat slightly different foods,

allowing many species
to live together side by side.

The saki has special teeth

which enable it to eat nuts
that no other monkey can crack.

The spider monkey
has long limbs and a grasping tail

which enable it to collect
the very ripest fruit.

But there are foods in this forest

that not even a spider monkey
can get to.

There is food for monkeys
in every part of the rainforest,

but some of it
is very difficult to reach.

I have only got up here
into the canopy in a special crane,

and I am 120 feet above the ground.

And here, on the outermost
twigs of the trees,

the stems are too thin
to support a normal-sized monkey.

And yet,
there is a lot of food up here.

Underneath these leaves -

a cocoon, a caterpillar,
another leaf-eating insect.

But there is one kind of monkey that
can get up here and eat these things.

It's a pygmy marmoset -
the smallest monkey in the world,

no bigger than my hand.

Its feet are too small to grasp
anything but the thinnest twigs.

Their needle-sharp claws
prevent them from slipping.

As it stalks its insects
it has to move with great stealth,

lest any vibration
should scare them off.

But these hunters are so small

that not even the thinnest branches
tremble under their weight.

All monkeys have forward-pointing
eyes so that they can judge distance.

That's invaluable
when moving around in the trees.

But this tiny little hunter
uses that ability also to pounce.

But their staple diet
is altogether more extraordinary.

You might think that the lumps
on this tree are a natural feature,

but, in fact, they are wounds
inflicted by pygmy marmosets

that come to this tree trunk
every day.

It's eating gum,

which it has forced the tree
to produce by gnawing its bark.

And what's more, it is making sure
that there will be gum tomorrow,

because it is also re-opening the
wounds that the tree has healed up.

The marmosets
keep opening these wounds

and the tree keeps closing them

until so much scar tissue builds up
that circular mounds appear.

Generations of pygmy marmosets have
done that on this particular tree,

resulting in these huge columns
of lumps running right up the trunk.

A well-managed gum tree is an asset
for a group of marmosets,

making it a tempting target
for thieves.

And a rival group
is preparing to invade.

The intruders charge
and the owners flee,

leaving their precious gum
undefended.

While the invaders steal the gum,

the displaced residents start
scent-marking in the trees nearby.

This seems to reinforce the bonds
between them

and stiffen their resolve
to mount a counter-attack.

It works.
The home team are back on their tree.

But you can share a food resource
that is cropped by others

without having
a face-to-face confrontation.

You might think
that when the sun goes down,

all monkeys
would be settling down to sleep.

That's almost true, but not quite.

There's only one monkey in the world
that collects its food at night.

And precisely because
it IS nocturnal,

it is very seldom seen
and still little known.

But there is a family of them
living in this tree behind me.

They are douroucoulis.

They are also known,
for obvious reasons, as owl monkeys.

Their eyes may be huge,

but, in fact, their night vision
is not particularly good,

suggesting that their ancestors
lived by day

and that douroucoulis
became nocturnal relatively recently.

During the day, the nectar-rich
flowers on which they feed

are guarded aggressively
by other monkeys.

By coming out only at night,

douroucoulis avoid having to fight
for a share and can feed in peace.

Day breaks.

The douroucoulis retire

and a new set of fruit-
and nectar-feeding monkeys awake.

Tamarins set off
to collect their share.

But this forest
is not rich in such food,

and though they live in small groups,
finding all they need takes time.

The female always produces twins,
which travel with the family.

But she has two male partners
and she uses her tongue to signal

that it's time that one of them
took over the twins.

Both are eager to do so,
for both mated with her

and so each has cause
to regard the babies as his.

But the twins have other ideas.
They want to stay with Mum.

She gets rid of them at last,
and it is important that she does so.

She has to provide them with milk,
so she must eat much more than usual

and she would find that difficult

if she were burdened by her babies
all the time.

The situation is made harder,

because there are other kinds
of tamarins here as well.

This is one of them -
a saddleback tamarin.

Monkeys usually guard their food
ferociously,

but these two kinds of tamarin
often feed side by side.

And when one leaves,
the other follows.

The emperors go first,
and the saddlebacks -

with their shorter, stumpier legs -
try hard to keep up.

The travelling party
shares a quick refuel.

Both kinds of tamarin, being small
and energetic, need frequent snacks.

They share another thing, too.
They have a common enemy.

They give alarm calls
that both species understand.

TAMARIN SHRIEKS

A tayra - a kind of giant weasel.

Not the most dangerous predator
in this forest,

but deadly to a bite-sized monkey.

It's certainly safer to travel
in groups, but having to share food

is a high price
to pay for a warning system.

There is, however,
another rather more subtle advantage.

Each flower needs time
to refill its reservoir of nectar

after a visitor has drunk from it.

after a visitor has drunk from it.

If either kind of tamarin
foraged separately,

they might make a hazardous journey,

only to reach a tree that had
recently been emptied by the other.

That would be disastrous for an
animal that has to feed so regularly.

It's far better for tamarins
to travel together

and then share the food
when they arrive.

Howler monkeys -
ten times the size of a tamarin.

They also eat flowers,
given the chance,

but these are not always available.

In tropical forest, at least
leaves can be found all year round.

Howler monkeys specialise on these.

The best leaves are up in the canopy,

so that's the best place to go if
you want to watch howlers close-up.

Leaves are not all the same.

Some are poisonous,
even to a howler monkey.

Of those that are edible,
some are nicer than others.

But, once again, that monkey ability
to see in colour is a great help.

These red ones
are young and succulent,

and would be very good to eat,
if they weren't protected by poisons.

These mature ones are green
and the poison in them has faded,

but they're fibrous and woody
and NOT very good to eat.

A leaf-eater wants something
in between, like this.

Imagine how difficult it would be
to pick the right one

if you didn't have colour vision.

Even the best leaves
are not easy to digest,

so, although howlers spend
a short time collecting food,

they spend a long time digesting it.

In fact, they spend half
of every day just lying around,

like cows, chewing the cud.

Even after all that digestion,
leaves are not very nutritious,

so howlers can't waste energy
chasing rivals through the treetops.

They use a rather more
labour-saving way of doing that.

GRUNTING

Howlers have a specially enlarged
bone in the throat, the hyoid,

that enables them
to make this extraordinary song.

It's one of the loudest noises
made by any animal

and the whole family joins in
almost every evening.

They work themselves into a frenzy,

but since neither they, nor their
rivals actually move anywhere,

it's very hard to say who's winning.

It may be that this howling serves
to strengthen family solidarity

and deter intruders.

RASPING GRUNTS

That may sound
a bit like a howler monkey,

but I've left South America
and I'm in Africa.

The howler's African equivalent
is the black and white colobus.

Many different kinds of monkeys
are able to share the same forest,

because they find their food
in different ways.

Red colobus' stomachs allows them
to eat unripe fruit and leaves,

whereas sooty mangabeys,
like saki monkeys,

have powerful jaws that
can break open really tough foods.

The rest of the monkeys have a more
general diet, like capuchins,

and belong to a group
called the guenons.

All guenons eat fruit and insects,

but each looks for them
at its own level in the forest.

There are 17 different kinds
of guenon in Africa.

They all have similar-shaped bodies,

but each has its own colours
and patterns

that serve as signals allowing
them to recognise friends and rivals.

They are the most colourful
group of monkeys in the world.

But colour signals are not a good
way of sending urgent messages

in places where
the visibility is poor,

and that's certainly the case here
in the Tai Forest in West Africa.

Failing to spot another monkey is
one thing, but if you miss a warning,

the consequences could be fatal.

So how do monkeys
keep out of harm's way?

I'm travelling with
one of the most extraordinary

anti-predator alliances
in the world.

Around me is a troop
of sooty mangabeys and mongooses.

They're keeping an eye out
for danger on the ground.

In the branches above me, there are
at least five species of monkey,

all ready to detect a threat from
the sky or from within the canopy.

In this alliance, monkeys
of many kinds travel side by side.

It's a huge safety network

that extends from the canopy
right down to the forest floor.

With so many pairs of eyes
at every level,

someone is sure to spot a threat,
no matter where it comes from.

There's little squabbling over food
between different species

because each finds it
in a different way.

Visibility is so poor here that they
communicate almost entirely by sound.

Unlike visual signs, a sound reaches
every monkey in a split second.

It's the best means of staying
in contact or warning of danger.

Diana monkeys forage
near the top of the canopy,

so they're usually first
to spot danger from the air.

Crowned eagles are never far away
here, but if one comes too close,

a specific alarm will be sounded,
telling monkeys to drop for cover.

Danger above! Monkeys plummet down
without even looking up.

The alliance has saved
another member.

All these monkeys have different
alarm calls for different predators.

Watch this!

SQUEALING

GRUNTING

That's the leopard alarm call
of the Diana monkey.

GRUNTING
That different one is the spot-nose.

But the important point is that all
species of monkey in the alliance

recognise one another's call
and know the nature of the enemy.

That's important

because each predator requires
its own particular response.

All these monkeys know
there's a leopard around

and you might think, therefore,
that they would flee,

but they don't -
they're advancing towards it,

and that's because the leopard
is an ambush predator.

Once it's spotted,
it usually gives up and goes away.

Monkeys are drawn by the call
from a large area.

They even drop lower, so they
can keep the cat in full view.

And here they will stay,
on maximum alert,

until the leopard finally gives up
and leaves them in peace.

The ancient city of Polonnaruwa
in Sri Lanka.

The civilisation that built it 1,000
years ago has long since crumbled,

but one society that lived here then
is still here now and thriving.

Toque macaques have walked
these walls for centuries,

but only in the last few decades

have we started to understand
their complex society.

This is one of the most studied
monkey groups of all time.

For 30 years, their daily existence
has been recorded in detail.

That has given us great insight
into their private lives.

These youngsters
are playing as equals,

but they have very different futures
ahead of them.

There's a ruthless class system
in monkey society.

Those born in high-ranking families
have a massive head-start in life.

Emelda is one of them.
She is highborn.

Others have been feasting on berries,
but she's come too late to get any.

The berries are stashed
in the cheek-pouches of others.

Emelda spots Poppin. She is far
larger and older than Emelda,

but she is from
a lower-ranking family,

entitling Emelda to take anything
of Poppin's that she wants,

including the food
right out of her mouth.

Poppin makes it as hard for Emelda
as she dare,

but if she resists too strongly,
she risks a beating from the rest.

In monkey society,
it helps to be highborn.

It also helps to be intelligent,

and that is particularly apparent
during the mating season.

Toque macaques try to attract
one another's attention

by fluttering their mauve eyelids
and flashing their teeth.

But although there are willing males
everywhere you look,

there is a shortage of females
ready to mate.

Females are only fertile
for a few weeks in the year.

During this short period, lots
of males want to mate with them,

but hierarchy does not allow that.

This male in front of me,

after years of political manoeuvring
and a good deal of muscle,

has become alpha male,
and he has first pick,

but there are always some young males
who try to beat the system.

Booster has a lesser rank

and that prevents him from
openly mating with a fertile female.

His best chance is a secret liaison,

but the alpha male
has recruited many allies,

and these males will stop any female
who tries to sneak away

and reprimand her, if necessary.

This security team
allows the alpha to concentrate

on the privileges of his position.

But Booster's chance has come.

The alpha male's allies don't have
eyes in the backs of their heads,

and females, like Shanti here,
see Booster as a future alpha.

Allowing him to father their young
could be a shrewd investment.

First, she needs to attract
Booster's attention.

Shanti is flirting.

Her glances are subtle, because
she doesn't want to get caught,

but they're unmistakable,
if you know what you're looking for,

and Booster certainly does.

He needs to signal his intentions
to Shanti,

but feign disinterest should
the alpha male look in his direction.

But the alpha
has other females to attend to

and his allies
are nowhere to be seen.

Shanti gives Booster the eye.

They must be discreet and quick.
Shanti's absence may be noticed.

If Booster DOES take over, he may
look favourably on Shanti's young.

They might, after all, be his.

A big brain certainly helps you
to take advantage of others,

and the larger the group you live in,
the bigger your brain needs to be.

But it was a dramatic change
to the Earth itself

that allowed monkeys to climb up to
the next rung of the social ladder.

10 million years ago,
the climate of the world changed.

Many places became much drier.

The rainforests shrank

and were replaced by scrub
and open grassland.

But there was a lot to eat
in this new terrain.

Some of the monkeys
came down from the branches

and went out to find it in the open.

The first monkeys to walk out here
would have found some familiar foods,

flowers and seasonal berries,

but today baboons collect
all kinds of other things -

bulbs, cactus,

even rabbits.

The grasslands are a great place
for an opportunist.

Baboons use their fingers and brains

to collect
an extraordinary variety of foods.

Insect grubs can be picked up

from the edge of a soda lake
in Kenya's Rift Valley.

Flamingos gather in vast numbers
and generate a rich layer of compost

that contains plenty of food
for those patient enough

to pick through it.

But a few baboons
have become more ambitious.

Only this troop of baboons
catch flamingos.

It's just five years since the first
of them discovered this new food

and worked out how to get it,

but the skill has spread quickly

and now the whole troop
are dedicated flamingo hunters.

Life in the open
has its disadvantages, too.

There are more big predators around,

so baboons protect themselves
by assembling in large groups.

As among macaques, living in big
groups causes social problems.

And here there's an even more
complex social structure,

within which
males compete for females.

When a female
becomes sexually available,

her bottom swells
and turns bright pink.

All the males can read the message,
but she only offers herself

to males that have looked after her
during the rest of the year.

This male
is attempting to join the troop,

but it may be some time
before he can father any offspring.

First, he has to learn the social
order in this complex community

and a good way to start is to
befriend one of the senior females.

The ledge can get very crowded,

and the presence of the alpha male
is intimidating.

Even deciding where to sit
is a political decision.

The new male inevitably invades
the personal space of others.

Tempers flare.

SHRIEKING AND CHATTERING

Life for a new arrival
can be very stressful.

Established males rely on
a network of allies for support.

The most successful of them invested
heavily in such social relationships.

But knowing who to build them with
takes intelligence.

Grooming is a good way
to maintain friendships.

Looking after babies
will also score you points.

Child-caring brings another benefit.

Babies are protected
in baboon society,

so no-one will hit you
if you're carrying one.

That allows smart baboons
to use infants like shields

when they feel threatened.

It takes time and brain power

to rise to the top in a large group.

It's easy to imagine how a big brain
could help you in baboon society.

But if social complexity
IS the driving force

behind the growth
of the primate brain,

then it SHOULD be
that brain size in primates

corresponds closely to group size.

This is the skull of a baboon

and this lump of Plasticine

represents the brain
which the skull once contained.

This represents
the brain of a bush baby.

It's essentially a solitary animal,

but even allowing for its
small body size, its brain is tiny.

This, slightly larger, is the
brain of a colobus - group size 15.

This, bigger still, a guenon -
group size 25.

And back to our baboon -
group size 50.

The relationship is so close,

that were you to give a skull to
a researcher who works with monkeys

even though they didn't know what
kind of monkey it belonged to,

they could accurately predict
the size of group in which it lived.

500 miles away
in the highlands of Ethiopia

live the largest monkey groups
of all.

Geladas -
the world's only grazing monkeys.

There's a lot of grass up here

so geladas flourish
and gather into enormous herds.

They don't have nipping teeth
like sheep or rabbits

so they have to collect their grass
by hand.

This is done best by sitting down

and they spend much of their lives
shuffling along on their backsides.

Because they sit down so much,

their sexual displays
have moved to their chests,

where other geladas can see them.

These indicate strength and virility

and allow individuals to assess
each other's status at a glance,

so avoiding
unnecessary confrontations.

Within these herds
are smaller groups,

like those formed by other monkeys.

Related females are the core and a
male harem leader watches over them.

And he has to be very vigilant.

A pack of bachelor males
with one goal in mind -

to displace the holder of a harem.

The bachelors avoid males
with the brightest chests -

they are in their prime and will have
the full support of their family.

But less impressive males will
have to prove their worth in battle.

A lip-flip from one of the bachelors
is a threat. Flip answers flip.

There's going to be trouble.

These fights are largely for show
and rarely result in injury,

but they do waste
valuable grazing time.

Eating grass is time-consuming
and also occupies your hands,

so it's hard to find time
for grooming.

So geladas maintain
their friendships in another way -

they chatter to one another.

CHIRPS AND MURMURS

These noises are, in effect,
VOCAL grooming

and enable geladas to communicate
with many individuals at once.

And this is the secret of their
ability to live in huge groups.

Their continuous chatter
SOUNDS like a language,

but we have no idea what sort
of information they are exchanging.

One thing, however, IS likely -

it was the need to communicate
detailed social information

between many individuals

that led to the evolution
of language in our own species.

So although monkeys living in the
tree tops have rich and varied lives,

it's the ones that came down to
the ground and formed large groups

that have the most complex
and communicative societies of all -

a fact not without significance
for our own ancestry.

Those monkeys cracking shellfish
and anointing themselves

with a natural insecticide

were showing a kind of behaviour
that, not so long ago,

was thought to be exclusively human.

But over the past 40 years,

intensive studies have shown that
monkeys have a surprising complexity

in their tool use, in their language,
and in their societies.

Primatologist Jane Goodall

is famous for her ground-breaking
studies of wild chimpanzees,

but in 1960, she also began one of
the first field studies of monkeys -

the olive baboons of Tanzania's
Gombe Stream National Park.

Many monkey species
have large, heavily armed males.

They seem to be constantly fighting

and soon the researchers identified
the rank of different males

in a turbulent hierarchy
of threats and challenges.

It is the young, prime male,
entering a new troop

and eventually
confronting the existing leader

who becomes the new,
undisputed ruler of a troop.

Here, a male's rank
depends on his dominance,

with the alpha male at the top.

Across Africa, biologists revealed
baboon troops as complex,

highly-ordered and stable societies,
containing long-term relationships.

This includes a key role
for the females in the species

studied by Chadden Hunter -

the gelada baboon.

We have about 600 here
filling up this valley,

so just this ocean of fur.

It's really hard to see just how
many monkeys are here in one place.

Family groups are basically
sisters who stick together -

say, four or five sisters.

They'll pick a male,
he comes into the family,

has to toe the line with them -

basically protect them, protect
the kids whenever they want him to.

On the side of the group

is this tight-knit kind of street
gang of mean-looking bachelors

and if the sisters aren't happy
with their male

then they'll chuck him out
and get a new guy.

Even when there's
relative stability,

males are constantly under pressure.

The alpha male can never relax.

By measuring hormone levels,

Professor Bob Sapolsky has shown
that, just like humans,

baboons suffer from stress
and stress-related diseases.

Baboons and us are very similar.

WE don't get ulcers cos we have to
wrestle somebody for a parking spot.

We don't have the physical stressors
most animals do.

We're psychologically
sophisticated enough

to invent nonsense in our heads
and we get sick with it.

And largely
that's what baboon society is about.

They've got enough free time
and enough food

that they can spend a lot of time
making each other miserable

with social stress.

Here's one really stressful thing
you can do if you're dominant -

some lower-ranking guy is in
a sexual consortship with a female.

She's in heat, she's reproductively
accessible, they're hanging out.

What does the dominant guy do?

He doesn't attack. He's just AROUND.

He's six feet away, just being
on the scene harassing the pair.

No fights, no threats, no nothing.

The guy who's being harassed
picks up and walks away voluntarily.

This is psychological stress,
straight out of the dictionary.

So we know that monkeys live complex,
even stressful, social lives.

To maintain cohesion, they
constantly send and receive messages.

Monkeys are excellent communicators.

If it is possible
to get inside the mind of a monkey,

then the squeals and chatters that
accompany almost everything they do

perhaps hold the key.

Right from the beginning
of these studies,

it was clear monkeys had something
important to say to one another.

These vervet monkeys
are warning each other of a snake.

RAPID CLICKING

The first detailed study
of primate communication,

by Robert Seyfarth
and Barbara Cheney,

revealed the true meaning
of vervet alarm calls.

We did a series of experiments
in 1977 and '78

where we'd wait until the monkeys
were foraging in a certain area

and then we would hide a loudspeaker
in a bush nearby.

We'd recorded the alarm calls
in natural encounters.

We took one of these alarm calls
and played it from the loudspeaker

when there were no predators around.

The monkeys responded by running up
into the trees at a leopard alarm,

looking up or running into bushes
at an eagle alarm,

or looking on the ground around
them in the case of a snake alarm.

This means that the alarm call
almost functions like a word.

Vervet infants
have to learn these words.

They start
with broad classes of danger.

The eagle alarm
covers all birds and flying objects.

As they grow,
they become more precise

and, quite simply, those
that can't learn don't survive.

So we now know
that vervet monkeys use words

and have the rudiments of language.

Different vocalisations
mean different things

and must be learned
by the young members of the troop.

Recent studies have shown
that that applies

to other species of monkeys as well.

And monkeys don't just call out
warnings of danger.

Professor Mark Hauser's experiments
with these rhesus macaques

show that they're constantly
discussing food.

COUGH-LIKE GRUNTS

They tell each other
about mundane food items

using a grunt that Mark refers to as
"the boiled-potato call".

But they use "the caviar call"
when the food is more interesting.

WHISTLES

Experiments show some monkeys even
recognise the calls of other species.

They've become bilingual.

The monkeys of the Tai forest
are hunted by eagles and leopards,

but in the wet season the greatest
threat is a primate - the chimpanzee.

They are expert climbers that
can follow monkeys into the trees

and they hunt cooperatively.

So their prey - red colobus monkeys -

form a partnership
with Diana monkeys.

Klaus Zuberbuhler plays chimp calls

and the red colobus
immediately look for Diana monkeys.

THEY are the most likely to spot
the chimps and raise the alarm.

What is interesting when looking
at inter-species communication,

between one monkey species
to the next,

you find that each species
possesses their own repertoires.

A Campbell's monkey has a
particular alarm call for a leopard

which is completely different
from the leopard alarm call of, say,

a Diana monkey

and it's quite obvious they do
understand each other's alarm calls.

That tells us they must learn it
at some point.

They aren't born with the knowledge
of all these other species' calls.

So as it grows up, a young monkey
learns the calls of other species.

It's a bit like learning
a second language.

It also seems that groups of calls

may carry a greater meaning
than single ones

with call-groups that are equivalent
to adding an adjective to a noun.

For example, Campbell's monkeys
also have multifier calls

that seem to affect subsequent
meaning of alarm calls

and it's this way of combining
calls that has caught our attention.

And that's an important step.

If adding one call to another
creates a new meaning,

there's a fascinating parallel
with human language.

One thing is for sure -
the more we listen to monkeys,

the more they'll tell us about
their complex, highly social lives.