Original subtitles

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'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 cheetal deer.

Cheetal 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 cheetal 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. Langer 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.

The Langer sounded the alarm before she could get close enough.

If the Langers 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 cheetal, 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 will 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. Or 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'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 spiders hunting grounds are limited. Not

all flowers are yellow. But 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 the 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 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 Masai 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 boldest-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 prey. 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 with the other stripes.

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'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. Lichens 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 a 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

denied 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 denied 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

Earth. 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 blue-striped 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 learned 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 butterfly fish.

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 butterfly fish 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 imposter.

One is significantly bigger than the rest. It hatched from

an egg that was surreptitiously laid in the waxbills' nest

by a pint-tailed wider. Having done so, she flew away,

leaving her young to be cared for by the waxbills. But why

do the waxbills feed this imposter?

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's bigger, it takes nearly

all the food and the young waxbills get little or none.

Two weeks later. And the young wider is much bigger.

By now, however, the adult waxbills have accepted the young

wider as their own. And the more it begs, the more they give

it.

One last meal from its luckless foster parents.

And the young wider leaves its nest. The nest mates behind.

And this is what it will grow up to be. Quite different

from the hard-working waxbills that raised it.

All pint-tailed widers 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 Augrabius 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 sinews.

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.

But others, a good place to hide. Or to get close to the

river, where there's food.

Here on these falls, food is scarce. 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.

Music

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.

Music

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.

Music He's made it. His disguise works, 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.

Music 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. Music

For us, colour in the natural world is a source of beauty

and wonder. But for animals, it's a tool for survival.

Music 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 20 years, there's five, six times

where the snow's completely gone. And over 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? Yes, they're not set up for that, so 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 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 color changes in other parts of

the world.

Including some of the most beautiful,

color-rich habitats on our planet. Coral reefs.

Our Australian team spent months filming on the Great Barrier Reef.

In these sunlit waters, color is everywhere.

Now, this habitat is being subjected to the most drastic

color 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 Joerg Wiedemann 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 color. The algae, when they

photosynthesize during the daylight hours, use sunlight

to grow, excreting sugars as a byproduct, 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 color. 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

colors.

We're just beginning to realize that corals are using color to fight back.

Jörg 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 color, 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 color 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 color they

provide, will disappear from the reefs of the world.