Life in Colour (2021) s01e02 Episode Script

1
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.