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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.

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 is 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 world...

..and this is how 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 are 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.

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 they 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 is 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 ultra-violet 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 ultra-violet light.

So she appears even more conspicuous sitting on a flower.

This extra brilliance acts as a kind of super-signal

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 are 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.

But there's another threat on these plains.

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 creates

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 is 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 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 is 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 that 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 long-standing 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 imposter's markings closely mimic those of its nest-mates,

and because it is 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 hard-working 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-back 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 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 all right.

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 for ever.

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-dependant 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, you know.

In what way?

On the Cairngorm Plateau, there's areas where we have snow patches

lasting all the year round,

but if you look at the last sort of 20 years,

there's five, six times where the snow's 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, yes, 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.

But 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.

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 the 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 first-hand.

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 Jorg 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.

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're just beginning to realise

that corals are using colour to fight back.

Jorg is studying how this works.

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.

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.

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.

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.