01x02 - Hiding in Colour

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SIR DAVID ATTENBOROUGH:

The natural world is full of colours

that we often take for granted.

There are few animals

more brilliantly coloured

than these scarlet macaws.

Animals can use colour

for all kinds of different reasons

and some have colours

that we ourselves can't even see.

But not all colours

are what they seem.

Some animals also use colours

to hide.

Colours that make them disappear.

Colours that create

optical illusions.

And colours that are used

to trick and deceive.

To understand how

these colours work,

we need to see them

from an animal's perspective.

With the help

of our specialist cameras,

we can now do that

..and discover how some animals

have become masters of disguise.

The Indian subcontinent is home

to some truly spectacular animals.

PEAFOWL CALL

Most, like these peafowl,

use colour to attract attention

and the kinds they've developed

are influenced by the way

they see the world.

But flashy colours can

also come at a cost,

and sometimes it's better

to remain out of sight.

So some animals use their colours

to help them hide

and disappear into the background.

One such animal lives here

in the forests of central India.

It's one of the most formidable

hunters on earth.

A Bengal tiger. A female.

She's one of the world's

biggest cats,

and remaining out of sight

is not easy

when you are as large as she is.

Her orange and black coat

is crucial to her success.

To have any chance

of catching a meal,

she has to get to within

a few metres of her prey.

She keeps to the cover of the trees

and slowly makes her approach.

She may appear conspicuous

to our eyes,

but not so to these chital deer.

Chital have only two types

of colour receptors in their eyes,

compared to our three,

which means that they are

effectively blind to red and orange.

So to the deer,

the tiger isn't orange at all.

This is how we see the world

..and this is how the deer do.

The tiger's orange coat to them

is a muted shade of green,

so it's nearly impossible

for the deer to register.

She creeps closer.

The chital don't see her.

The odds appear stacked

in the tiger's favour.

But the deer aren't

entirely defenceless.

They have help from an unusual ally.

Langur monkeys.

They're known as

'the eyes of the forest'

and their colour vision

is excellent.

Their eyes, like ours,

have three types of colour receptors

and they CAN see orange.

MONKEY GROWLS

The langurs sounded the alarm

before she could get close enough.

If the langurs can easily spot her,

why then is the tiger orange at all?

Why isn't she green?

That's because mammals are unable

to develop green pigments,

so it seems the next best solution

for the tiger is to have orange fur,

which appears green

to her main prey.

She will have to find a new target.

Down by the water, she finds one

sambar deer.

Sambar don't keep company

with monkeys.

They are on their own.

They have the same limited eyesight

as the chital,

but ears like satellite dishes.

If she treads on a twig

and it snaps,

the hunt will be over

before it began.

The deer seem to sense danger.

They still can't see her.

Despite her effective camouflage,

most hunts end like this.

Less than 10% of her attacks

are successful.

But without her orange fur,

her chances would be even lower.

It is her colours that are key

to her survival.

The Cairngorm Mountains in Scotland.

Here there are special problems

for the hunted.

Some animals have developed

camouflage of such perfection

that they are virtually invisible

against their surroundings.

But what happens

when those surroundings change?

Well, then, of course,

the animals have to change too.

These mountains are home

to a particular kind of grouse

called the ptarmigan.

Their mottled brown feathers

make them inconspicuous

among the rocks and heather.

But in winter,

these mountains are hard places

in which to live.

Temperatures drop

and the land can overnight

be covered by a blanket of snow.

Most birds by now have gone south

to warmer parts of the world,

but not the ptarmigan.

When winter comes, they undergo

the most extraordinary change.

They replace their brown feathers

with pure white ones.

They do so for a simple reason

they must go unnoticed.

They need to hide.

This open habitat

makes the ptarmigan

very vulnerable to predators.

Being the right colour is crucial.

Now they are invisible

even to a keen—eyed eagle.

Ptarmigan are not the only animals

to use this disappearing act.

So does the arctic fox

..snowshoe hares

..and weasels.

All, with the coming of winter,

change their coats

and vanish from sight.

Their transformation is triggered

by the decreasing daylight,

and over several weeks,

they replace their brown costumes

with white ones.

So, changing colour with the seasons,

for some animals,

is the only way to avoid

becoming a meal.

But many plants, of course,

do the reverse.

In spring, they produce colour

to declare that are

providing food — nectar.

Bees and many other insects love it.

In spring and summer,

they travel busily from flower

to flower collecting it.

And when the bees leave

to look for more,

they inadvertently take pollen

with them,

which then fertilises

the next flowers they visit.

But there's a hunter here

that exploits this relationship.

A crab spider.

She's tiny —

no bigger than a fingernail

and she's waiting for her prey.

Almost the same colour

as her background,

she's virtually invisible.

No more honey for her.

But of course, the spider's

hunting grounds are limited.

Not all flowers are yellow.

When she sits on a pure white petal,

she immediately becomes obvious.

She will never catch a bee

while she's so conspicuous.

So she changes.

She breaks down the yellow pigments

in the outer layer of her skin

to expose special crystals

underneath

that act like tiny mirrors

and reflect the light.

It may take a few days,

but she turns from yellow to white.

Changing colour isn't

the spider's only trick.

There's more to this story

than meets the eye.

Bees can see colours that we cannot.

They can see ultraviolet colours.

As they come in to land on a flower,

they use special sensors that can

detect ultraviolet patterns

on the flower's petals.

We can see them too

with our special UV camera.

There are dark lines on the petals

that mark the landing strips

for the bees,

guiding them to the nectar.

The spider, however, has developed

a way to exploit these signals.

Watching her with our UV camera,

we can see that she reflects

ultraviolet light,

so she appears even more conspicuous

sitting on a flower.

This extra brilliance

acts as a kind of supersignal

which the bee can't resist.

And the spider benefits.

In fact, the bees are more than

three times as likely

to visit flowers

with UV—reflecting spiders on them

than those without.

The crab spider uses

a sophisticated range of colours

to deceive its prey.

But colour can also be used in

a simpler, even more surprising way

to confuse the enemy.

And on the plains

of Kenya's Maasai Mara,

there's one animal

that uses just two colours

to outwit its predators.

The zebra.

Its black and white coat

makes it extremely obvious

as it grazes

out on the open grasslands.

Other grazers have softer,

gently varied colouration,

which blends with their background.

So, it seems strange that zebras

apparently do quite the opposite.

Particularly as they live in a world

where there are so many hunters.

Lions

..hyenas

..and cheetah.

The boldly—striped zebra

seem to be asking for trouble.

How do they get away with it?

The question has been hotly debated

by naturalists for centuries.

New research is now

suggesting an answer.

To understand how it might work,

we need to consider

the particular colours involved.

Black and white are two of

the most contrasting colours

and no two animals have

exactly the same pattern,

so each has a unique

whole—body fingerprint.

But when the zebras move,

the stripes create confusion.

It's known as motion dazzle

..and it makes it difficult

for a predator

to keep focused

on one particular target.

The cheetah, looking for a meal.

To make a successful strike,

they must judge the distance accurately

and time it perfectly.

So if a zebra's stripes

can confuse the cheetah

just for a few crucial seconds,

it may escape.

ZEBRAS CALL

But there's another threat

on these plains.

BUZZING

Flies.

They are a real pest here.

They're not just a nuisance —

they carry diseases,

some of which are particularly nasty,

even deadly.

Despite the huge numbers of flies,

the zebras appear

remarkably untroubled by them.

There are plenty of flies around

..but few actually land

on the zebra.

One theory is that

the black and white stripes

make it difficult for flies

to judge the distance.

To test this idea,

scientists counted

how many flies landed

on animals with

gently graded colours

and how many landed

on the zebra's stripes.

They found that four times fewer flies

landed on zebras

than on their more

plainly—coloured neighbours.

Why should that be?

It seems it's another consequence

of those stripes.

They confuse the flies as they make

their final approach to settle.

Perhaps this creates

a visual blurring for the flies,

much as it does for a cheetah.

So, it seems that

the zebra's patterns of stripes

create an optical effect

that helps protect them

from enemies both large and small.

While zebras use different patterns

to confuse their enemies,

on the island of Cuba

there are smaller

and rather slower—moving creatures

that do a similar thing.

This is Polymita picta,

a Cuban painted snail.

You might think that this one is

an exceptionally lovely,

eye—catching individual.

But it's not by any means

the only snail

that is so beautifully decorated.

No two individuals are

exactly the same,

yet all these belong

to the same species.

There are also five other species

of Polymita here.

Each snail has

its own unique combination

of colours and stripes.

Their colours come from their diet

lichen and mosses rich in minerals

that give the shells

these stunning colours.

They differ according to

the particular mix of plants

that each snail has been eating.

Variations of individuals

within a species

is not uncommon

in the natural world.

It's called polymorphism.

But it's particularly marked

among Cuban snails.

Some scientists believe

that the variation in itself

may be a kind of defence

against predators.

But how could that work?

Most animals looking for prey

have a search image in their minds.

They scan their surroundings

looking for a victim

that matches their expectations.

If they see something they recognise,

they'll go for it.

And that's where the snail's

varying colours may come in.

The great range of different

tints and patterns,

it seems, confuses the birds.

He's never seen one

quite like this before.

And while the bird is wondering

whether it's edible or not,

the snail can — slowly —

make a getaway.

So, it seems that colour can

both conceal and confuse.

And sometimes it's used in yet

a third, quite different, way.

Some poisonous animals,

like this little ladybird,

use colour as a warning.

It's bright red,

and that's a message which says,

"Keep away. I'm poisonous."

Red, black and yellow are

widely understood as warnings,

so the ladybird's message is

a truthful one

it is poisonous.

But some animals

that are in fact harmless

have found it profitable to develop

these warning colours themselves.

This African queen butterfly,

like the ladybird,

is indeed very poisonous.

But this is

a different species entirely

a danaid butterfly.

It has almost exactly

the same colouration,

yet it's perfectly edible.

It is, you might say,

using its colours and patterns

to tell a lie.

To our eyes

and to that of the predators,

poisonous and non—poisonous

individuals look almost identical

and that's the point.

The danaid mimics the colours

and patterns of the African queen

and so it isn't eaten.

Mimicry like this occurs

quite frequently among insects.

The yellow and black stripes

of this harmless hoverfly

resemble the warning colours

of bees and wasps that sting,

so it's left alone.

Other animals use mimicry to hide.

This moth resembles a broken twig.

A kind of mantis closely matches

the shape and colours of a leaf.

Another mantis is shaped

and coloured like a flower

..and gets a reward

for the resemblance.

And one particular caterpillar

has come to look like a tiny snake.

While this butterfly's wings take on

the appearance of dead leaves.

But there are some animals

which use mimicry

for a rather more sinister purpose.

And one such creature lives here

on Australia's Great Barrier Reef.

Just beneath the surface,

the reef is a riot of colour.

But that means there are great

opportunities for deceptions.

A bluestriped blenny.

It lives close to

a cleaning station

a place on the reef

where large fish come

to get their parasites picked off

by smaller fish

that feed on what they remove.

This little wrasse

is one of these cleaners.

It has a longstanding relationship

that relies on trust.

The big fish get a health treatment

and the little fish get a meal.

But the blenny has learnt how to

exploit this trusting relationship.

It leaves its hole

and starts looking for a meal.

But the big fish

don't seem to trust it.

It's time for a change of costume.

Filmed close up

under controlled conditions,

we can see how the blenny's

brown stripes turn black.

The pigment cells in its skin

expand and contract

to bring about this subtle change.

But it's enough to do the trick.

The blenny now looks very similar

to a juvenile cleaner wrasse.

It's a devious disguise

and one that will help it

take advantage of the arrangement

the cleaner wrasse has developed

with its clients.

It's spotted a target

a butterflyfish.

The blenny hangs back,

allowing an established

cleaner wrasse to start work.

Now the blenny slowly moves in,

as if to offer the same service

as the wrasse.

But once within range

..it strikes!

Its razor—sharp teeth have removed

not just dead skin

but a chunk of flesh.

This isn't the treatment

the butterflyfish was expecting.

The blenny's deceit

may work for a time,

but eventually it has consequences.

Reef fish begin to associate

the distinctive colours

of a cleaner wrasse

with the pain of the bites

of a blenny.

Then they will eventually stop

coming to this cleaning station.

And that is bad for business

for the blenny too.

So it's time to let things cool off.

A quick change back to brown

and its deception is over — for now.

All the while, it keeps its eye

on the cleaning station

and waits for its next target.

Some animals change colour

for short periods of time

in order to deceive others,

but some use colour mimicry

permanently

as a method of persuading

a different species

to rear their young.

One such creature lives here on

the grasslands of southern Zambia.

A nest hidden in the grass.

It belongs to a pair

of common waxbills.

They are busy feeding their chicks.

The hungry youngsters

open their beaks

to display

a conspicuously patterned gape

which says, in effect,

"Food here, please!"

And the parent obeys.

But among them, in this nest,

there is an impostor.

One is significantly bigger

than the rest.

It hatched from an egg

that was surreptitiously laid

in the waxbills' nest

by a pin—tailed whydah.

Having done so, she flew away,

leaving her young to be cared for

by the waxbills.

But why do the waxbills

feed this impostor?

The parent birds

recognise their young

by the pattern of their gapes.

And the black and white markings

are characteristic of their species.

But the impostor's markings closely

mimic those of its nest—mates,

and because it's bigger,

it takes nearly all the food

and the young waxbills

get little or none.

Two weeks later,

and the young whydah is much bigger.

By now, however,

the adult waxbills have accepted

the young whydah as their own,

and the more it begs,

the more they give it.

One last meal from

its luckless foster—parents

..and the young whydah

leaves its nest—mates behind.

And this is what

it will grow up to be

quite different from the hardworking

waxbills that raised it.

All pin—tailed whydahs

are reared like this.

Mimicry wins.

Deceiving a different species

is one thing,

but in South Africa, one animal

uses mimicry to fool its own kind.

The Orange River,

the largest in South Africa,

and on it, the Augrabies Falls.

These are the main home

of a particular species

of flat—backed lizards.

The males are brilliantly coloured.

The females, on the other hand,

are very different.

They are plain and drab.

The brilliance of a male's colours

is an indication

of its physical fitness

and strength.

The higher their status,

the more colourful they are.

And they're not afraid

to make their seniority quite clear.

A side—shuffle dance

showing off their colours

is usually quite enough

to settle who is the boss.

But if that doesn't work,

they fight.

Their disputes are

all about location.

Sometimes they want a vantage point

from which to show off.

At others, a good place to hide,

or to get close to the river

where there's food.

Here on these falls,

food means flies.

The river is a breeding ground

for blackflies.

There are huge swarms of them.

And they are the favourite food

of the lizards.

They have acrobatic skills

needed to catch them.

While the colourful males

are busy feeding,

a different kind of male appears.

He is brown, rather like a female.

There's just a hint of blue

on his throat

that gives him away as a male.

He's fully mature,

but not yet strong enough to compete

with his flashier neighbours.

To avoid fighting, he delays

the development of his colours

and so mimics a female.

One in ten young males

behave in this this way.

But he still needs to eat,

and to do that, he's got to get down

to the river where the flies are.

That means getting past

the powerful, highly—coloured males.

One thing could reveal

the deception

he may look like a female,

but he smells like a male.

As long as he keeps his distance,

he'll be alright.

The big male hasn't noticed

that he's not a female.

Almost there.

Only one male now stands in his way.

The most dominant and aggressive

of the lot.

He's made it.

His disguise worked

and now he can feast on the flies.

He won't be able

to keep this up forever.

Ultimately, all males have to

put on their glad rags

and develop those bright colours

if they are to breed.

For now, though, he's developed

a disguise that enables him to cheat

in one of nature's most

colour—dependent mating systems.

So, animals of all kinds use colour

in a multitude of different ways.

New discoveries are giving us

fresh insights

into the lives of these animals,

and new cameras are allowing us

to see into a world of colour

as never before.

We're only just beginning

to understand

the many different ways

in which animals use colour,

particularly those colours

that we can't even see.

For us, colour in the natural world

is a source of beauty and wonder,

but for animals,

it's a tool for survival.

We've seen in this series that

colour is crucial for survival.

So what happens to animals

when their world changes colour?

The experts we've worked with

in the field

have been helping us to find out.

In the Cairngorms in Scotland,

I met Jim Cornfoot,

a land manager and an expert

on the natural history

of these mountains.

How long have you been here now?

Over 30 years

since I started up here,

so I've seen a lot

of different changes.

In what way?

On the Cairngorm plateau,

there's areas where we have

snow patches lasting all year round,

but if you look at

the last, sort of, 20 years,

there's five, six times

where the snow has completely gone,

and in over, sort of,

200, 250 years,

there's only been seven times

that that's happened.

Has that had a great effect

on the wildlife?

You know, they're out of kilter,

basically,

with what's going on

around them.

So, things like mountain hare,

ptarmigan,

they're standing out with the browns

and the heather behind them.

And they're still white?

And they're still white, yeah,

so they're not set up for that.

So if it's a very poor winter,

you know, they're suffering.

Ptarmigan, a kind of grouse,

live year round

in this exposed environment,

where there are few places to hide.

And now, as the world warms,

things are changing dangerously.

The recent decrease in snow cover

has made them only too conspicuous.

Animals like this mountain hare,

also in its winter coat,

can be seen from far away.

And that makes life very hazardous.

BIRDS CAW

These changes are affecting animals

all around the Northern Hemisphere.

In North America, the reduced

snow cover has caused snowshoe hares

to be mismatched on average

for a week a year.

During this time,

the hare is 10% more likely

to end up as someone else's dinner.

By the end of the century,

the loss of snow cover is predicted

to expose the hares

for up to eight weeks a year,

so increasing their annual mortality

by almost a quarter.

Unless they can adapt rapidly,

they could be in serious danger

of extinction.

While a warming climate

is causing problems

in northern habitats

..it's also driving colour changes

in other parts of the world.

Including some of the most

beautiful, colour—rich habitats

on our planet

..coral reefs.

Our Australian team spent months

filming on the Great Barrier Reef.

In these sunlit waters,

colour is everywhere.

But this habitat is being subjected

to the most drastic colour change

imaginable.

And our crew witnessed it firsthand.

The corals have suddenly turned

into white skeletons.

It's called coral bleaching

and it's now happening

only too frequently.

On the Great Barrier Reef,

such events have increased

from once in every 25 years

to three events in the last five.

Professor Jörg Wiedenmann

from the Coral Reef Laboratory

at the University of Southampton

has been working to discover

what is behind these changes.

The key is the relationship

between coral

and the microscopic algae

that live in their tissues.

These algal partners

are called symbionts.

It's they that give the coral

its colour.

The algae, when they photosynthesise

during the daylight hours,

use sunlight to grow,

excreting sugars as a by—product,

which are then absorbed

by the corals.

This partnership was established

during the time of the dinosaurs

and has been such a success

that it has created structures

that are visible from space.

But warming seas are

disrupting this system.

So, when the seawater temperatures

rise above a critical threshold,

the photosynthetic machinery

of the algal symbionts

starts to malfunction.

SIR DAVID:

They begin to produce toxic compounds

which cause the corals to expel them

from their tissues.

So the coral loses its colour.

It bleaches.

Sometimes the bleached corals die,

and then the entire ecosystem,

together with everything

it supports, is lost.

Almost half of the corals

in the Great Barrier Reef

have died this way

over the last 15 years.

But in the last decade,

there have been reports

from various parts of the world

of coral developing

startling neon colours.

We are just beginning to realise

that corals are using colour

to fight back.

Jörg is studying how this works.

JÖRG: This coral has lost

its algal symbionts,

but instead of turning white,

it's producing

these bright neon green pigments.

The coral produces these pigments

to protect the remaining algae

inside of the tissue

from excess light stress,

so they act as a sort of sunscreen

for the symbiont algae.

SIR DAVID:

This coral sunscreen makes it more likely

that the bleached coral will be able

to take back its algal partners,

restoring its food supply,

its colour,

and helping it to recover.

But even this extraordinary adaptation

is not enough

to protect coral against

all the changes it is now facing.

If corals have been exposed

only to mild stress,

then they can recover

from bleaching.

SIR DAVID:

But if corals are subjected

to prolonged or extreme levels

of heat stress,

they lose their ability

to create these sunscreen pigments

and are likely to die

and unfortunately, global warming

is making this more likely.

There's a severe danger

that corals will be exposed

to episodes of stress

where they can't recover

and where they can't use

these pigments

to bounce back from bleaching.

SIR DAVID: So although colour might be

helping coral reefs

to tolerate some of the change,

only action to halt global warming

will ensure their survival.

If warming continues, then they,

together with the beautiful array

of colour they provide,

will disappear

from the reefs of the world.