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[Attenborough] Colour can be crucial
in the lives of animals.

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They use it to win a mate,

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to hide…

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and even to warn.

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But to discover
how animals themselves perceive colour

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is not easy.

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Making this series
took ingenious experiments…

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innovative camera systems…

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[man] Look at that! That's extraordinary.

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[Attenborough] …and lots of patience.

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Our camera team's task

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was not only to film colour as we see it,

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but as animals do…

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including colours
that are invisible to our eyes.

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And, as our climate changes,

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we worked with experts
to understand the challenges

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that these changes cause

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and learn that colour can sometimes
be part of the fight to survive.

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Our eyes enable us to see
all the colours of the rainbow,

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from red to violet.

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But many animals
can see colours beyond that spectrum.

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In the ultraviolet.

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To capture their view of the world,
 we needed a highly specialised camera,

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which I was able
to see in action for myself

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in a flower garden near London.

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Cameraman Mark Payne-Gill

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showed me how it works.

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[Payne-Gill] Actually, it's quite simple.

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It's got one camera
that sees in ordinary vision,

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our colour world,

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and the other sees in ultraviolet,
how an insect would see it.

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What's the basis of it?

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So the principle
lies behind this filter here.

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So it's an ultraviolet filter.

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It allows ultraviolet light
to pass through it,

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but the clever bit
is it also reflects white light,

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normal light,
straight into this camera here,

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which can see the world as we see it.

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And the end product is then we can cut
between the two of them as we will?

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Exactly, and see how we see the world
and how the insects see the world as well.

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[Attenborough] Okay, show me it in action.

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[Payne-Gill] Okay, here we go.

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The first picture you'll see
is the white-light view,

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how we see the world.

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[Attenborough] Yeah.

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[Payne-Gill] Then, there you go.

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-[Attenborough] There it is.
-Very different.

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It seems to have black marks
on each of the petals.

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-We can't see those?
-That's right.

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When we look at our white-light view,
it's just pure yellow,

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but hidden in that is the ultraviolet.

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You think there's a lot more
still out there to discover?

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I think there's an awful lot,

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but personally, I quite like the fact
it remains a secret.

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-Leave something for the children.
-Exactly, yeah.

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[Attenborough] Many birds, lizards,
insects, and some fish

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can see ultraviolet,

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so they're often reacting
to things that we can't see.

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Scientists are only
just beginning to reveal

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how animals use these ultraviolet colours.

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Our Australian team joined a scientist

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who has been studying
a small and unassuming butterfly,

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which has a secret trick.

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Cameraman Ben Cunningham
caught up with Dr. Darrell Kemp,

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from Macquarie University,

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at Coffs Harbour, New South Wales.

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[man 1] You got one already?

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-[man 2] I've caught this lovely male.
-Look at that guy.

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Hypolimnas bolina. Yeah.

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Also known as the blue moon butterfly.

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[Attenborough] Darrell studies
mating displays in butterflies,

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and the blue moon butterfly
has something special to show off about.

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[Kemp] That's fantastic
in giving us a really great view

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of the colour patch
that we're interested in here.

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[Attenborough] The butterflies
have iridescent blue patches,

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which certainly look very pretty
to our eyes.

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But their display is even more startling
in the ultraviolet range

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that we can't see.

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[Kemp] We're unfortunate in that regard.

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We miss out on a quarter of the brilliance
of the natural world.

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[Attenborough] Which is where
our ultraviolet camera can help.

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[Kemp] I'm excited to see
what the camera can produce.

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It's almost going to allow us
to get as close as possible

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to understanding
the full brilliance of these butterflies.

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[Attenborough] But first,

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the beam splitter camera
needed to be assembled,

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and that wasn't exactly straightforward.

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Fiddly, fiddly, fiddly.
Where does this one go again?

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[Kemp] It's amazing how complex
a system needs to be

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in order for us to reconstruct
quite simply what a butterfly can do

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with its normal compound eye.

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[Attenborough] Finally,
the camera was up and functioning.

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And it gave Darrell
a view of his butterflies

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that he had never witnessed before.

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[tranquil piano music playing]

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[Kemp] Here, it's almost like
you have a beam of light

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being shone from the wing.

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Because, really, those ultraviolet patches
are little mirrors

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that essentially
reflect the intensity of ultraviolet light

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that's coming from the sun.

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[Attenborough] And, as a consequence,

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Darrell was able to see things

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crucial to his understanding
of his butterfly's behaviour.

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[Kemp] I'm excited by it because
the ultraviolet part of the markings

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of the male of this species

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is really the critical thing
that females are judging

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when they're deciding
who they would ideally mate with.

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[Attenborough]
The brighter the ultraviolet,

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the more attractive the male.

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But this attractiveness comes at a cost.

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[Kemp] And those markings,
being as bright as they are,

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are likely to be equally apparent
to the main predators of this species,

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which are birds.

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[Attenborough]
And birds, with their sharp eyes

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that can see colours that we can't,

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are quick to spot prey.

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[Kemp] In some ways,

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that's both the blessing and the curse
of this colour patch for this species.

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Yes, you need it to impress a female,

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but flying around
with a really bright signal like that,

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visible to birds,

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is almost a handicap
that these guys have to bear.

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[Attenborough] But, for the males,

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it's worth being
the brightest of the bunch.

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[Kemp] It's a male's sole goal
to mate with females

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and perpetuate his genes
to the next generation.

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So, if by being bright,
he's able to achieve two or three matings

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and then die, even at a young age,

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that would be evolutionarily favoured.

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[Cunningham] Even if he meets
a grim death, it's success.

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[Kemp] Absolutely.

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[Attenborough]
The rocky hills of Northern India.

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[menacing instrumental music playing]

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The open forests here
are the hunting grounds

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of one of the world's
most dramatic predators.

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This is the home of the tiger.

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Tigers have to kill at least once a week
if they're not to starve.

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They can't run as fast as a deer,

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their favorite prey,

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so if they're going to catch one,

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they have to get quite close, unseen,

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before they charge.

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Not this time.

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But why are tigers orange
with black stripes?

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At the University of Bristol's
Camouflage Laboratory,

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scientists John Fennell and Laszlo Talas

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have been finding out
how tigers are perceived by their prey.

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To help them test their research,

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they're joined by Max Hug Williams,

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a wildlife cameraman experienced
in filming tigers in the wild.

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I've always wondered,
"Why are they this bright orange colour?"

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You'd think they'd stick out
from the environment.

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There's no form of camouflage at all.

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We tend to think of everything we see
only in terms of our own visual system.

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We're pretty good at picking up colour,

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but many animals don't have that.

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And that's true of most mammals, in fact.

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[Attenborough] Including deer.

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Their eyes lack red receptors,

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so are only sensitive
to blue and green light.

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Deer, in common
with around 5% of human beings,

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are red-green colour-blind,

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and to them,
orange and green look very much the same.

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John and Laszlo are working with glasses

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that allow us to see
in much the same way as deer do.

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They could give Max an idea
of how they view the world.

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Before you look at tigers,
we thought it would be useful

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to do a standard test.

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And your task is to read out the number
that you see.

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So we got a-- That's a 74.

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And in the middle there, 15,
popping out from the orange.

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-How about that one?
-[Hug Williams] Three?

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[Attenborough] Max started well,

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but putting on the glasses
made things much more difficult.

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Wow.

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That's just completely…

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completely disappeared.

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Can't pick out those numbers at all now.
They're just gone.

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Twenty-nine.

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Without the glasses, nothing.

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With the glasses-- Amazing.

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It completely vanishes.
Those numbers have gone.

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[Fennell] The glasses are effectively
filtering out the red lights.

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That's amazing.

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So a deer would not see
these numbers at all.

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[Attenborough] Max's next task
was to look at photographs

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of a tiger stalking in the wild

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and try to point it out
as quickly as possible.

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-Right.
-[Talas] You ready to go?

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Let's go.

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Right, there's one.

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Okay, there's a tiger. Top right.

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That's easy.

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Right bottom. Right there behind the bush.

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Getting my eye in now.

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-So how am I doing?
-[Fennell] You're doing pretty well, Max.

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Your time is probably an average
of about two seconds per frame.

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-Is that good? Sharpshooter?
-[Fennell] It's good.

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[Attenborough]
It's not surprising that Max,

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a wildlife cameraman,
was fast to spot an animal,

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but could he do as well

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with the deer vision glasses,
which render him colour-blind?

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[tense ambient music playing]

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[Hug Williams] Everything's green.
This is just ridiculous.

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-It just completely disappeared.
-[Fennell] Yeah.

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It's amazing.

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So this is what a deer would be seeing?

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[Fennell] Yes, that's right.

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[Hug Williams]
As soon as there's vegetation,

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it's nearly impossible.

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Top… top left.

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Where is the…

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Wow.

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I'm guessing I didn't do well.

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Yes, you were
about half the speed you were

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00:13:24,520 --> 00:13:26,480
when you did this without the glasses on.

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00:13:26,560 --> 00:13:30,480
That time difference might equate
to as much as a seven-metre difference

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for the tiger
when it's attacking its prey.

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[Attenborough]
So tigers don't look orange to deer,

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but why aren't they green?

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All kinds of very different animals,

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birds, reptiles, amphibians, insects,

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are coloured green.

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So why aren't tigers?

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Well, tigers are mammals,

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and the pigments in mammalian hair and fur
come from just two substances,

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eumelanin and pheomelanin.

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It is actually biochemically impossible
for a…

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to manufacture green colour
using these two pigments.

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So we suspect that evolution
came up with the next best thing,

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to make the tiger's fur orange-brown,

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which actually looks the same colour
to its prey.

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Amazing.

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So, while mammals can't be green,
they've evolved alongside the prey

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to become the perfect,
camouflaged killing machine.

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[Attenborough]
Tigers are just as colour-blind as deer.

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So a tiger doesn't even know
that it's orange.

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Luckily, Max does.

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I don't think I'll take these glasses
with me on my next filming trip.

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-You can't see anything.
-[Fennell] That's wise.

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-I think you'd be dinner.
-[Hug Williams chuckling]

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[Attenborough] Whilst tigers use colour
to become inconspicuous,

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00:15:00,000 --> 00:15:04,600
another very different animal
uses colour in a very different way.

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The poison dart frog.

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It's no bigger than a fingernail,

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00:15:11,240 --> 00:15:15,320
and the skin of some species
contains a poison so powerful

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00:15:15,400 --> 00:15:19,040
that local people used it
to tip their blow-pipe darts.

248
00:15:20,880 --> 00:15:24,960
The strawberry poison dart frog 
is not quite so lethal,

249
00:15:25,040 --> 00:15:26,800
but toxic nonetheless.

250
00:15:28,120 --> 00:15:33,080
They live on a remote archipelago
called Bocas del Toro in Panama.

251
00:15:35,720 --> 00:15:37,040
Dr. Yusan Yang

252
00:15:37,120 --> 00:15:40,960
has been researching the function
that colour plays in their lives.

253
00:15:42,680 --> 00:15:45,000
[Yang]
So Bocas del Toro is very interesting

254
00:15:45,080 --> 00:15:47,760
because
the strawberry poison dart frogs here--

255
00:15:47,840 --> 00:15:50,840
On different islands,
you have all kinds of different colour.

256
00:15:50,920 --> 00:15:54,120
They're not slight differences in colour.
They're dramatic differences.

257
00:15:54,200 --> 00:15:57,800
We have red frogs, we have yellow frogs,
we have green, we have blue.

258
00:15:58,640 --> 00:16:00,680
They look different,
but they're the same species.

259
00:16:03,560 --> 00:16:07,640
[Attenborough] These are the most varied
and brightly coloured frogs in the world,

260
00:16:08,440 --> 00:16:11,240
and Yusan has been running experiments

261
00:16:11,320 --> 00:16:14,880
to find out the significance
of their wide colour range.

262
00:16:17,280 --> 00:16:21,640
She's made robot frogs
to test how the territory holders react

263
00:16:21,720 --> 00:16:23,840
to different-coloured individuals.

264
00:16:25,120 --> 00:16:29,520
These are 3D-printed model frogs,
and I hand-painted them,

265
00:16:29,600 --> 00:16:33,640
so that they look like the different
colour types we found on these islands.

266
00:16:34,800 --> 00:16:38,920
[Attenborough] Her equipment enables her
to simulate a territory invasion.

267
00:16:41,440 --> 00:16:45,560
She glues the 3D-printed model
onto a motor arm

268
00:16:45,640 --> 00:16:47,920
so that she can control its movements.

269
00:16:48,000 --> 00:16:49,240
[whirring]

270
00:16:52,280 --> 00:16:54,840
Then she plays the frogs' call,

271
00:16:54,920 --> 00:16:57,360
which is the same on all the islands.

272
00:16:57,880 --> 00:16:59,760
[recording of frog call playing]

273
00:16:59,840 --> 00:17:03,840
A frog will attack any other frog
that enters its territory.

274
00:17:04,360 --> 00:17:06,920
They are famous for their wrestling skill,

275
00:17:07,520 --> 00:17:09,960
but it's a very civilised sport.

276
00:17:10,520 --> 00:17:14,240
[Yang] I always like to describe them
as two gummy bears going at each other,

277
00:17:14,320 --> 00:17:17,840
because they don't have claws or teeth
and can't hurt each other.

278
00:17:17,920 --> 00:17:20,400
They're just trying
to pin each other down.

279
00:17:27,680 --> 00:17:31,120
[Attenborough]
First, she tested an orange frog

280
00:17:31,200 --> 00:17:34,320
on an island
where orange frogs predominate.

281
00:17:34,400 --> 00:17:36,120
[recording of frog call playing]

282
00:17:36,800 --> 00:17:40,840
The males of this species
vigorously defend their territories.

283
00:17:41,600 --> 00:17:44,640
So if one of them hears the calls
of another male,

284
00:17:44,720 --> 00:17:47,320
he will think his territory
is being invaded,

285
00:17:47,800 --> 00:17:49,240
and he won't allow that.

286
00:17:56,160 --> 00:17:58,320
He becomes physically aggressive,

287
00:17:58,400 --> 00:18:01,800
trying to wrestle with the model
and pin it down.

288
00:18:07,400 --> 00:18:10,720
Next,
Yusan tried the orange territory holder

289
00:18:10,800 --> 00:18:12,120
with a blue model.

290
00:18:12,200 --> 00:18:13,840
[recording of frog call playing]

291
00:18:15,400 --> 00:18:18,320
This time, the male reacted to the sound,

292
00:18:18,400 --> 00:18:21,600
but didn't seem to recognise
the blue male as a threat.

293
00:18:24,720 --> 00:18:25,920
[Yang] In the red populations,

294
00:18:26,000 --> 00:18:28,360
the frog will be more aggressive
toward a red model.

295
00:18:28,440 --> 00:18:29,760
And in the blue population,

296
00:18:29,840 --> 00:18:32,200
the frog will be more aggressive
toward the blue model.

297
00:18:32,720 --> 00:18:34,040
But if it's of a different colour,

298
00:18:34,120 --> 00:18:37,560
then a lot of times, the frogs
wouldn't recognise it as a competitor.

299
00:18:39,040 --> 00:18:42,000
[Attenborough]
So if the frogs react only to the colours

300
00:18:42,080 --> 00:18:43,680
with which they are familiar,

301
00:18:43,760 --> 00:18:46,440
what is the function of different colours?

302
00:18:48,040 --> 00:18:49,480
The answer seems to be

303
00:18:49,560 --> 00:18:52,240
that the frogs are not signalling 
to each other,

304
00:18:52,840 --> 00:18:54,000
but to predators.

305
00:18:55,240 --> 00:18:58,280
[Yang] So these poison dart frogs,
as their name suggested,

306
00:18:58,360 --> 00:18:59,360
they are poisonous.

307
00:18:59,440 --> 00:19:02,920
So the bright colour is actually
a warning signal to the predators,

308
00:19:03,000 --> 00:19:04,960
telling them,
"I am poisonous. Don't eat me."

309
00:19:06,800 --> 00:19:09,920
[Attenborough] But the frogs
are not all equally poisonous.

310
00:19:11,600 --> 00:19:15,400
Their poison comes from toxic alkaloids
that occur in their food,

311
00:19:15,480 --> 00:19:17,520
which is largely ants and mites.

312
00:19:19,920 --> 00:19:22,520
The particular diet on some islands

313
00:19:22,600 --> 00:19:25,280
makes some frogs
more poisonous than others,

314
00:19:25,360 --> 00:19:27,440
and this affects their colour.

315
00:19:30,280 --> 00:19:35,600
So researchers have found that the colour
is related to their toxicity,

316
00:19:35,680 --> 00:19:38,960
and the ones that are duller,
that are a more camouflaged colour,

317
00:19:39,480 --> 00:19:40,880
they are actually less toxic.

318
00:19:42,440 --> 00:19:44,880
[Attenborough] Red and orange ones,
on the other hand,

319
00:19:44,960 --> 00:19:46,800
are extremely poisonous

320
00:19:46,880 --> 00:19:49,880
and make that quite clear
before they are attacked.

321
00:19:52,120 --> 00:19:55,600
Most birds and lizards
have excellent colour vision

322
00:19:55,680 --> 00:19:59,280
and are well able
to see these red warning signals.

323
00:20:01,920 --> 00:20:07,000
So whilst the tiger's orange colour
conceals it from colour-blind prey,

324
00:20:07,080 --> 00:20:09,880
the poison dart frog's similar colour

325
00:20:09,960 --> 00:20:12,080
advertises that it's poisonous.

326
00:20:17,160 --> 00:20:20,080
There is yet another equally important way

327
00:20:20,160 --> 00:20:22,880
in which colour is used
in the natural world.

328
00:20:24,320 --> 00:20:25,840
To attract a mate.

329
00:20:29,560 --> 00:20:32,920
The peacock does that on a grand scale.

330
00:20:33,000 --> 00:20:34,440
[jaunty instrumental music playing]

331
00:20:34,520 --> 00:20:37,040
And so does this tiny spider,

332
00:20:37,760 --> 00:20:40,000
in a remarkably similar way.

333
00:20:45,720 --> 00:20:49,840
This one belongs to a group
called the jumping spiders.

334
00:20:54,240 --> 00:20:57,640
Dr. Lisa Taylor,
from the University of Florida,

335
00:20:57,720 --> 00:21:01,360
goes to extreme lengths
to study how they view the world.

336
00:21:02,640 --> 00:21:04,960
There's more than 6,000 species
of jumping spiders,

337
00:21:05,040 --> 00:21:07,680
and we're just now learning a lot
about their colour vision.

338
00:21:10,240 --> 00:21:14,720
[Attenborough] Lisa also studies a group
called the Habronattus spiders,

339
00:21:14,800 --> 00:21:16,600
which can see a range of colours,

340
00:21:16,680 --> 00:21:19,800
from ultraviolet all the way into the red.

341
00:21:21,240 --> 00:21:26,360
The males have bright red faces,
and Lisa is investigating why.

342
00:21:27,400 --> 00:21:30,440
As a starting point for understanding
what those colours are communicating,

343
00:21:31,240 --> 00:21:33,640
one way to do that
is to block out the colours completely

344
00:21:33,720 --> 00:21:35,800
and then ask the females what she thinks.

345
00:21:37,840 --> 00:21:42,040
To block out the male's colours,
we gently apply liquid eyeliner.

346
00:21:44,600 --> 00:21:47,480
We've tested a lot of products
to make sure they're safe for the spiders

347
00:21:47,560 --> 00:21:50,880
and that the spiders behave normally
after the eyeliner is applied.

348
00:21:55,040 --> 00:21:58,200
[Attenborough] By giving some males
a makeover in this way,

349
00:21:58,280 --> 00:22:02,040
Lisa discovered
that a female regards a red face

350
00:22:02,120 --> 00:22:05,360
as a very important quality in a male.

351
00:22:08,360 --> 00:22:10,120
[Taylor]
When the males are courting females,

352
00:22:10,200 --> 00:22:12,120
under
really good quality lighting conditions,

353
00:22:12,200 --> 00:22:14,400
the females were very attentive
to the colour.

354
00:22:16,960 --> 00:22:19,000
[Attenborough]
The red-faced male on the left

355
00:22:19,080 --> 00:22:21,800
is clearly holding the attention
of the female.

356
00:22:23,920 --> 00:22:27,320
But a male with a pale face 
is largely ignored.

357
00:22:30,080 --> 00:22:32,120
There have been a lot of studies
trying to understand

358
00:22:32,200 --> 00:22:35,960
what the brightness of a colour might tell
a female about a potential mate.

359
00:22:36,040 --> 00:22:40,360
Usually, it's the brightest males
that are advertising their good quality.

360
00:22:42,600 --> 00:22:45,080
That's what we've actually found
in the jumping spiders too.

361
00:22:45,600 --> 00:22:48,200
So males with brighter colours
seem to be better quality

362
00:22:48,280 --> 00:22:50,160
than males with darker, duller colours.

363
00:22:51,600 --> 00:22:55,760
[Attenborough] But these male spiders
have an extra need to impress.

364
00:22:56,520 --> 00:22:58,480
So females are really voracious predators.

365
00:22:58,560 --> 00:23:00,240
They go after almost anything that moves,

366
00:23:00,320 --> 00:23:02,960
and they take down prey 
that's a lot bigger than themselves.

367
00:23:03,040 --> 00:23:06,120
So when a male is courting a female,
he has to take that into account.

368
00:23:10,160 --> 00:23:12,840
[Attenborough]
And if she doesn't accept him as a mate,

369
00:23:12,920 --> 00:23:14,360
she will eat him.

370
00:23:16,200 --> 00:23:19,040
The redness of his face
makes all the difference.

371
00:23:22,720 --> 00:23:27,680
Red is a strong, bright colour
that stands out against most backgrounds,

372
00:23:29,640 --> 00:23:32,760
so it's used as a warning of danger
by many animals,

373
00:23:32,840 --> 00:23:34,520
including ourselves.

374
00:23:41,560 --> 00:23:43,320
And in Habronattus,

375
00:23:43,400 --> 00:23:46,480
it could be the difference
between life and death.

376
00:23:47,280 --> 00:23:48,760
When a male encounters a female,

377
00:23:48,840 --> 00:23:51,960
he has a very limited amount of time
in order to impress that female.

378
00:23:52,040 --> 00:23:54,040
So the female could quickly attack him.

379
00:23:54,600 --> 00:23:58,280
So we think that maybe the males
incorporate this red into their display

380
00:23:58,360 --> 00:23:59,680
to give them an extra second,

381
00:23:59,760 --> 00:24:01,320
so they have a little bit more time

382
00:24:01,400 --> 00:24:03,840
before the female pounces on him
and cannibalises him.

383
00:24:04,360 --> 00:24:06,080
[gentle instrumental music playing]

384
00:24:06,160 --> 00:24:09,840
[Attenborough] By adopting the red colour
used by their toxic prey,

385
00:24:09,920 --> 00:24:13,280
a male spider gains
an extra second or two,

386
00:24:13,360 --> 00:24:17,400
during which he can make his case
and win over a mate.

387
00:24:21,120 --> 00:24:24,960
So colour can affect
the way animals hide and display,

388
00:24:25,640 --> 00:24:27,600
but some animals can see light

389
00:24:27,680 --> 00:24:30,400
in a completely different way
to ourselves.

390
00:24:31,280 --> 00:24:35,560
They can detect
and respond to polarised light,

391
00:24:35,640 --> 00:24:38,720
light that vibrates in only one plane,

392
00:24:38,800 --> 00:24:41,880
as it does when it's reflected
from a shiny surface.

393
00:24:47,080 --> 00:24:51,200
Polarised light plays a crucial part
in the lives of some animals,

394
00:24:51,280 --> 00:24:55,960
including these small fiddler crabs
in Darwin, Australia.

395
00:25:02,640 --> 00:25:05,800
Our team worked with Prof. Viktor Gruev,

396
00:25:05,880 --> 00:25:08,200
from the University of Illinois,

397
00:25:08,280 --> 00:25:11,160
to develop a unique
and pioneering camera system

398
00:25:11,240 --> 00:25:13,400
to view this hidden world.

399
00:25:13,480 --> 00:25:14,440
Put it in front.

400
00:25:14,520 --> 00:25:17,760
[Attenborough]
The camera detects areas of polarisation,

401
00:25:17,840 --> 00:25:21,440
such as the light
that passes through polarising sunglasses.

402
00:25:21,520 --> 00:25:23,000
100% here.

403
00:25:23,080 --> 00:25:26,720
[Attenborough] It then combines vertical
and horizontal polarisation

404
00:25:26,800 --> 00:25:30,920
to show the contrast
between polarised and unpolarised light.

405
00:25:33,040 --> 00:25:34,520
With this new camera,

406
00:25:34,600 --> 00:25:38,760
the team hoped to find out
how fiddler crabs use polarised light

407
00:25:38,840 --> 00:25:40,360
to signal to each other.

408
00:25:42,600 --> 00:25:47,080
But this camera had been developed
in sterile, controlled conditions,

409
00:25:47,160 --> 00:25:49,240
and these fiddler crabs live in

410
00:25:49,320 --> 00:25:51,920
one of the least sterile environments
on earth,

411
00:25:52,000 --> 00:25:54,440
Australia's tropical mudflats.

412
00:25:55,880 --> 00:26:01,280
When we designed this technology,
we usually test it in the lab.

413
00:26:01,360 --> 00:26:02,840
And it performs well there.

414
00:26:02,920 --> 00:26:05,200
Taking it out in nature, out in the open,

415
00:26:05,280 --> 00:26:07,080
it's a very different challenge.

416
00:26:07,720 --> 00:26:11,040
[Attenborough] And also a challenge
for the cameraman, Mark Lamble.

417
00:26:11,720 --> 00:26:15,640
That mudflat, it's just
a really extreme environment to work.

418
00:26:16,160 --> 00:26:17,520
Blazing sun overhead,

419
00:26:18,200 --> 00:26:21,520
really high humidity,
and almost no airflow.

420
00:26:22,800 --> 00:26:24,920
[Attenborough]
To make matters even more difficult,

421
00:26:25,000 --> 00:26:30,320
the camera needed to be half buried in mud
to get a fiddler-crab's-eye view.

422
00:26:31,440 --> 00:26:33,120
And there's another problem.

423
00:26:33,760 --> 00:26:37,520
One of the things that's really tricky
about being on the mudflats

424
00:26:37,600 --> 00:26:41,680
is the fact that the water that comes
in there is salt water. It's seawater.

425
00:26:41,760 --> 00:26:43,560
But as the day goes on,

426
00:26:44,560 --> 00:26:47,800
the water evaporates,
leaving it more and more and more salty.

427
00:26:47,880 --> 00:26:50,480
So by the time it's starting to dry out,

428
00:26:51,040 --> 00:26:53,480
it's really, really severe brine,

429
00:26:53,560 --> 00:26:57,360
and if you get your hands in it,
it just literally peels the skin off.

430
00:26:58,200 --> 00:27:00,160
[Attenborough]
Whether the camera would work here,

431
00:27:00,240 --> 00:27:01,720
no one could be sure.

432
00:27:02,800 --> 00:27:04,440
[Gruev] I'm slightly worried.

433
00:27:04,520 --> 00:27:07,320
Hopefully, we're not going to miss
that special moment

434
00:27:07,400 --> 00:27:10,520
as the camera is not going to work,
but I think we'll be okay.

435
00:27:10,600 --> 00:27:12,200
-Good luck.
-Thank you.

436
00:27:15,640 --> 00:27:17,800
[Attenborough]
Once in position, Mark settled down

437
00:27:17,880 --> 00:27:19,400
for an uncomfortable wait.

438
00:27:20,080 --> 00:27:21,560
[Lamble] It's incredibly hot.

439
00:27:22,320 --> 00:27:27,400
The air temperature is somewhere
around about 36 to 37 degrees Celsius.

440
00:27:27,480 --> 00:27:30,520
[whimsical instrumental music playing]

441
00:27:31,160 --> 00:27:33,680
[Attenborough] If the crabs detect
the slightest movement,

442
00:27:34,680 --> 00:27:37,080
they disappear into their burrows.

443
00:27:39,360 --> 00:27:40,320
Again

444
00:27:41,840 --> 00:27:43,080
and again.

445
00:27:45,840 --> 00:27:47,840
I have to be really still, or…

446
00:27:50,360 --> 00:27:52,160
they will not come out at all.

447
00:27:52,680 --> 00:27:54,840
I'd love to be able to have
an umbrella over me.

448
00:27:54,920 --> 00:27:57,560
So, yes, anything over the top of me,

449
00:27:57,640 --> 00:28:00,200
anything higher than me or the camera…

450
00:28:01,760 --> 00:28:04,120
is just not tolerated
by the fiddler crabs.

451
00:28:04,200 --> 00:28:05,480
They just won't come up.

452
00:28:08,520 --> 00:28:09,720
[Attenborough] But amazingly,

453
00:28:09,800 --> 00:28:14,920
the camera survived the heat,
the humidity, and the caustic brine,

454
00:28:15,000 --> 00:28:18,880
and eventually, Mark was able to capture,
for the first time,

455
00:28:18,960 --> 00:28:22,520
a fiddler crab's world in polarised light.

456
00:28:26,680 --> 00:28:30,880
Light reflected
from the crabs' bodies is unpolarised,

457
00:28:30,960 --> 00:28:32,240
so they look dark.

458
00:28:33,360 --> 00:28:36,120
This makes them stand out
against the mudflats,

459
00:28:36,200 --> 00:28:39,000
from which the reflected light
is polarised.

460
00:28:41,320 --> 00:28:43,800
They can see things
that we can only imagine.

461
00:28:44,480 --> 00:28:46,680
When you look up
and you see a bird fly over,

462
00:28:46,760 --> 00:28:49,160
it's a white bird against a white sky.

463
00:28:49,240 --> 00:28:50,720
Whereas when they look up,

464
00:28:50,800 --> 00:28:53,480
it's just this total silhouette
with the polarisation,

465
00:28:53,560 --> 00:28:57,080
and they can see birds coming
from miles away.

466
00:28:57,160 --> 00:28:59,040
And often, I'm filming,

467
00:28:59,120 --> 00:29:01,680
and they'll all bolt down their holes,
and I'll wonder why.

468
00:29:01,760 --> 00:29:04,280
And it's just because
they've spotted a bird

469
00:29:04,360 --> 00:29:06,840
way earlier
than I would've been able to see it.

470
00:29:09,320 --> 00:29:11,520
So polarised light helps the crabs

471
00:29:11,600 --> 00:29:15,280
pick out distant potential mates,
rivals, and predators

472
00:29:15,360 --> 00:29:18,880
more quickly
against their bright polarised background.

473
00:29:19,800 --> 00:29:21,040
And for Viktor,

474
00:29:21,120 --> 00:29:24,920
it was the first time he had seen
the camera he had developed in the lab

475
00:29:25,000 --> 00:29:28,760
revealing the world
in the way these tiny creatures see it.

476
00:29:29,840 --> 00:29:32,320
It's an amazing footage
you've captured, Mark.

477
00:29:32,400 --> 00:29:33,640
It's really amazing.

478
00:29:34,760 --> 00:29:37,920
You really put the system
to its limits today.

479
00:29:41,720 --> 00:29:45,040
[Attenborough] But there was one
even bigger challenge for the camera.

480
00:29:45,560 --> 00:29:48,280
One that lay farther out to sea.

481
00:29:51,200 --> 00:29:56,200
Underwater, only crustaceans,
cephalopods, and a few fish

482
00:29:56,280 --> 00:30:00,280
are known to be able to see
and react to polarised light.

483
00:30:01,000 --> 00:30:02,600
But there is one animal here

484
00:30:02,680 --> 00:30:06,000
that exploits this ability
in a really complex way.

485
00:30:07,440 --> 00:30:09,360
The peacock mantis shrimp.

486
00:30:09,880 --> 00:30:12,960
It's not only able to detect polarisation

487
00:30:13,040 --> 00:30:17,560
but has patches on its body
that reflect light in a polarised form,

488
00:30:18,200 --> 00:30:21,760
and it uses them to signal
to others of their own kind

489
00:30:21,840 --> 00:30:24,160
in ways that we cannot normally see.

490
00:30:26,440 --> 00:30:29,480
Prof. Justin Marshall
of Queensland University

491
00:30:29,560 --> 00:30:33,320
has adapted the polarising camera
to work underwater.

492
00:30:33,880 --> 00:30:34,880
[Marshall] Here we go.

493
00:30:34,960 --> 00:30:37,920
This is the camera
that's gonna show us polarisation.

494
00:30:39,800 --> 00:30:42,680
[Attenborough] Rory McGuinness,
the team's underwater cameraman,

495
00:30:42,760 --> 00:30:45,760
arrived to see
the latest version of the camera.

496
00:30:47,200 --> 00:30:51,200
You've obviously done a lot of work
to get this into an underwater housing.

497
00:30:51,280 --> 00:30:52,280
Yeah, that's right.

498
00:30:52,360 --> 00:30:55,600
You can see in here there's a computer
that runs the camera.

499
00:30:56,080 --> 00:30:59,160
There's quite a lot of engineering
going on in there.

500
00:31:00,080 --> 00:31:02,080
[suspenseful piano music playing]

501
00:31:04,680 --> 00:31:07,760
[Attenborough] Taking the camera
for its first test underwater

502
00:31:07,840 --> 00:31:09,640
was a tense moment.

503
00:31:09,720 --> 00:31:13,520
Computers and salt water
don't usually mix well.

504
00:31:21,920 --> 00:31:23,640
Having found a suitable spot,

505
00:31:23,720 --> 00:31:27,200
it was time
for the camera's first critical test.

506
00:31:32,080 --> 00:31:34,240
A leak could be disastrous.

507
00:31:38,120 --> 00:31:39,400
But all is well.

508
00:31:40,000 --> 00:31:42,160
Now they need a mantis shrimp.

509
00:31:42,240 --> 00:31:44,720
[McGuinness] Looks like
a promising area, Justin.

510
00:31:45,480 --> 00:31:47,200
[Marshall] It looks perfect, Rory.

511
00:31:47,280 --> 00:31:51,800
So we're looking for a hole
with coral around it.

512
00:31:54,360 --> 00:31:55,240
Hey, look.

513
00:31:56,400 --> 00:31:58,320
Is that a mantis shrimp hole?

514
00:31:58,880 --> 00:32:01,320
[Attenborough]
The hole's resident soon appeared.

515
00:32:01,400 --> 00:32:04,360
It was time
for the camera to show what it could do.

516
00:32:05,720 --> 00:32:07,120
As the shrimp turns,

517
00:32:07,200 --> 00:32:08,800
the polarised camera shows

518
00:32:08,880 --> 00:32:13,600
that its tail has a shimmering fringe
invisible in normal light.

519
00:32:14,200 --> 00:32:16,360
[Marshall]
Look at that! That's extraordinary.

520
00:32:17,480 --> 00:32:19,480
Life in polarised light.

521
00:32:21,040 --> 00:32:22,760
Now, this is the first time…

522
00:32:24,880 --> 00:32:29,240
we've been able to do this
with this very special camera.

523
00:32:31,000 --> 00:32:34,240
[Attenborough] The light
on the ocean floor is unpolarised.

524
00:32:34,720 --> 00:32:37,440
So, in complete reverse
to the fiddler crabs,

525
00:32:37,520 --> 00:32:40,200
the mantis shrimps use polarisation

526
00:32:40,280 --> 00:32:43,920
to stand out
against the unpolarised background.

527
00:32:47,840 --> 00:32:52,480
Special pigments polarise the light
reflected from parts of their body,

528
00:32:53,360 --> 00:32:56,240
allowing them to signal to deter intruders

529
00:32:56,320 --> 00:32:58,160
and attract mates.

530
00:33:00,560 --> 00:33:05,120
This camera has revealed to us
a first glimpse into a world of light

531
00:33:05,200 --> 00:33:09,200
that we are only beginning to be aware of,
let alone understand.

532
00:33:13,400 --> 00:33:14,840
Science has shown us

533
00:33:14,920 --> 00:33:18,760
that colour is crucial
for survival for many animals.

534
00:33:19,440 --> 00:33:24,120
So what happens when their world
suddenly changes colour?

535
00:33:25,800 --> 00:33:30,240
That happens, of course,
every year in some parts of the world.

536
00:33:30,320 --> 00:33:32,640
Sometimes, even overnight.

537
00:33:32,720 --> 00:33:35,240
[soaring electronic music playing]

538
00:33:35,320 --> 00:33:37,000
During the making of this series,

539
00:33:37,080 --> 00:33:39,720
we went to the Cairngorm Mountains
in Scotland,

540
00:33:39,800 --> 00:33:43,560
in the middle of winter,
to look for a very special bird.

541
00:33:53,120 --> 00:33:55,520
Here, I met Jim Cornfoot,

542
00:33:55,600 --> 00:33:56,560
a land manager

543
00:33:56,640 --> 00:33:59,920
and an expert
on the natural history of these mountains.

544
00:34:02,120 --> 00:34:04,120
How long have you been here now?

545
00:34:04,200 --> 00:34:07,280
Over 30 years since I started up here, so…

546
00:34:07,880 --> 00:34:10,240
I've seen a lot of different changes.

547
00:34:10,320 --> 00:34:11,160
In what way?

548
00:34:11,240 --> 00:34:12,800
[Cornfoot] On the Cairngorm Plateau,

549
00:34:12,880 --> 00:34:15,920
there's areas where we have
snow patches lasting all year round,

550
00:34:16,000 --> 00:34:17,680
but if you look at the last 20 years,

551
00:34:17,760 --> 00:34:21,720
there's five, six times
where the snow's completely gone.

552
00:34:21,800 --> 00:34:24,440
And, you know,
over sort of 200, 250 years,

553
00:34:24,520 --> 00:34:26,680
there's only been seven times
that that's happened.

554
00:34:26,760 --> 00:34:29,800
Has that had a great effect
on the wildlife?

555
00:34:29,880 --> 00:34:33,880
They're out of kilter, basically,
with what's going on around them.

556
00:34:33,960 --> 00:34:35,960
Things like mountain hare, ptarmigan,

557
00:34:36,040 --> 00:34:38,520
they're standing out with the browns
and the heather behind them.

558
00:34:38,600 --> 00:34:41,800
-And they're still white?
-They're still white, yes.

559
00:34:41,880 --> 00:34:43,720
They're not set up for that,

560
00:34:43,800 --> 00:34:47,360
so if it's a very poor winter,
you know, they're suffering.

561
00:34:49,000 --> 00:34:51,240
[Attenborough]
Ptarmigan, a kind of grouse,

562
00:34:51,320 --> 00:34:54,720
live year-round
in this exposed environment,

563
00:34:54,800 --> 00:34:57,040
where there are few places to hide.

564
00:35:03,600 --> 00:35:05,760
But now, as the world warms,

565
00:35:05,840 --> 00:35:08,280
things are changing dangerously.

566
00:35:10,160 --> 00:35:12,520
The recent decrease in snow cover

567
00:35:12,600 --> 00:35:15,120
has made them only too conspicuous.

568
00:35:19,560 --> 00:35:21,640
Animals like this mountain hare,

569
00:35:21,720 --> 00:35:23,240
also in its winter coat,

570
00:35:23,320 --> 00:35:25,480
can be seen from far away.

571
00:35:27,760 --> 00:35:30,200
And that makes life very hazardous.

572
00:35:32,800 --> 00:35:34,960
These changes are affecting animals

573
00:35:35,040 --> 00:35:37,320
all around the northern hemisphere.

574
00:35:39,520 --> 00:35:40,800
In North America,

575
00:35:40,880 --> 00:35:45,080
the reduced snow cover
has caused snowshoe hares

576
00:35:45,160 --> 00:35:47,120
to be mismatched, on average,

577
00:35:47,200 --> 00:35:48,800
for a week a year.

578
00:35:50,040 --> 00:35:51,360
During this time,

579
00:35:51,440 --> 00:35:56,000
the hare is 10% more likely
to end up as someone else's dinner.

580
00:35:57,520 --> 00:35:59,080
By the end of the century,

581
00:35:59,160 --> 00:36:03,080
the loss of snow cover
is predicted to expose the hares

582
00:36:03,160 --> 00:36:05,160
for up to eight weeks a year,

583
00:36:05,680 --> 00:36:08,320
so increasing their annual mortality

584
00:36:08,400 --> 00:36:09,800
by almost a quarter.

585
00:36:10,880 --> 00:36:12,880
Unless they can adapt rapidly,

586
00:36:12,960 --> 00:36:16,000
they could be
in serious danger of extinction.

587
00:36:20,280 --> 00:36:24,400
While a warming climate
is causing problems in northern habitats,

588
00:36:26,240 --> 00:36:30,200
it's also driving colour changes
in other parts of the world…

589
00:36:34,280 --> 00:36:39,440
including some of the most beautiful,
colour-rich habitats on our planet.

590
00:36:41,200 --> 00:36:42,440
Coral reefs.

591
00:36:48,600 --> 00:36:53,520
Our Australian team spent months filming
on the Great Barrier Reef.

592
00:37:03,200 --> 00:37:05,240
In these sunlit waters,

593
00:37:05,320 --> 00:37:07,160
colour is everywhere.

594
00:37:11,360 --> 00:37:13,920
But this habitat is being subjected

595
00:37:14,000 --> 00:37:17,240
to the most drastic colour change
imaginable.

596
00:37:18,280 --> 00:37:21,560
And our crew witnessed it firsthand.

597
00:37:21,640 --> 00:37:24,320
[melancholy instrumental music playing]

598
00:37:25,200 --> 00:37:29,240
The corals have suddenly
turned into white skeletons.

599
00:37:32,120 --> 00:37:34,160
It's called coral bleaching,

600
00:37:34,240 --> 00:37:37,200
and it's now happening
only too frequently.

601
00:37:41,880 --> 00:37:43,520
On the Great Barrier Reef,

602
00:37:43,600 --> 00:37:47,960
such events have increased
from once in every 25 years

603
00:37:48,480 --> 00:37:51,200
to three events in the last five.

604
00:38:01,400 --> 00:38:04,920
Prof. Jörg Wiedenmann,
from the Coral Reef Laboratory

605
00:38:05,000 --> 00:38:07,240
at the University of Southampton,

606
00:38:07,320 --> 00:38:10,800
has been working to discover
what is behind these changes.

607
00:38:13,200 --> 00:38:18,160
The key is the relationship
between coral and the microscopic algae

608
00:38:18,240 --> 00:38:20,000
that live in their tissues.

609
00:38:22,920 --> 00:38:26,160
These algal partners are called symbionts.

610
00:38:26,680 --> 00:38:29,200
It's they that give the coral its colour.

611
00:38:31,160 --> 00:38:35,320
The algae, when they photosynthesise
during the daylight hours,

612
00:38:35,400 --> 00:38:37,400
use sunlight to grow,

613
00:38:37,960 --> 00:38:40,560
excreting sugars as a byproduct,

614
00:38:40,640 --> 00:38:43,080
which are then absorbed by the corals.

615
00:38:43,160 --> 00:38:45,160
[tranquil piano music playing]

616
00:38:47,400 --> 00:38:52,320
This partnership was established
during the time of the dinosaurs

617
00:38:52,400 --> 00:38:56,360
and has been such a success 
that it has created structures

618
00:38:56,440 --> 00:38:58,240
that are visible from space.

619
00:38:59,520 --> 00:39:03,000
But warming seas
are disrupting this system.

620
00:39:03,560 --> 00:39:07,840
So when the seawater temperatures rise
above a critical threshold,

621
00:39:07,920 --> 00:39:11,440
the photosynthetic machinery
of the algal symbionts

622
00:39:11,520 --> 00:39:12,880
starts to malfunction.

623
00:39:14,880 --> 00:39:17,440
[Attenborough]
They begin to produce toxic compounds,

624
00:39:17,520 --> 00:39:21,000
which cause the corals to expel them
from their tissues…

625
00:39:23,720 --> 00:39:26,760
so the coral loses its colour.

626
00:39:28,480 --> 00:39:29,360
It bleaches.

627
00:39:34,200 --> 00:39:37,000
Sometimes, the bleach corals die,

628
00:39:37,080 --> 00:39:39,360
and then the entire ecosystem,

629
00:39:39,440 --> 00:39:41,600
together with everything it supports,

630
00:39:41,680 --> 00:39:42,800
is lost.

631
00:39:46,400 --> 00:39:49,760
Almost half of the corals
in the Great Barrier Reef

632
00:39:49,840 --> 00:39:53,520
have died this way over the last 15 years.

633
00:39:59,520 --> 00:40:01,400
But, in the last decade,

634
00:40:01,480 --> 00:40:04,280
there have been reports
from various parts of the world

635
00:40:04,360 --> 00:40:08,560
of coral developing
startling neon colours.

636
00:40:14,280 --> 00:40:16,240
We are just beginning to realise

637
00:40:16,320 --> 00:40:19,680
that corals are using colour
to fight back.

638
00:40:24,960 --> 00:40:27,320
Jörg is studying how this works.

639
00:40:28,960 --> 00:40:31,640
[Wiedenmann]
This coral has lost its algal symbionts,

640
00:40:32,280 --> 00:40:34,120
but instead of turning white,

641
00:40:34,200 --> 00:40:36,720
it's producing
these bright neon green pigments.

642
00:40:39,360 --> 00:40:41,320
The coral produces these pigments

643
00:40:41,400 --> 00:40:45,160
to protect the remaining algae
inside of the tissue

644
00:40:45,240 --> 00:40:47,040
from excess light stress,

645
00:40:47,120 --> 00:40:51,000
so they act as a sort of sunscreen
for the symbiont algae.

646
00:40:52,960 --> 00:40:56,320
[Attenborough]
This coral sunscreen makes it more likely

647
00:40:56,400 --> 00:41:00,920
that the bleached coral will be able
to take back its algal partners,

648
00:41:01,000 --> 00:41:05,640
restoring its food supply, its colour,
and helping it to recover.

649
00:41:08,040 --> 00:41:10,760
But even this extraordinary adaptation

650
00:41:10,840 --> 00:41:14,600
is not enough to protect coral
against all the changes

651
00:41:14,680 --> 00:41:15,920
it is now facing.

652
00:41:17,000 --> 00:41:19,840
If corals have been exposed only
to mild stress,

653
00:41:19,920 --> 00:41:21,960
then they can recover from bleaching.

654
00:41:23,800 --> 00:41:26,600
[Attenborough] But if corals 
are subjected to prolonged

655
00:41:26,680 --> 00:41:28,800
or extreme levels of heat stress,

656
00:41:28,880 --> 00:41:32,920
they lose their ability
to create these sunscreen pigments

657
00:41:33,000 --> 00:41:34,560
and are likely to die.

658
00:41:35,760 --> 00:41:39,480
And, unfortunately,
global warming is making this more likely.

659
00:41:41,120 --> 00:41:46,960
There's a severe danger that corals
will be exposed to episodes of stress

660
00:41:47,040 --> 00:41:50,440
where they can't recover,
and they can't use these pigments

661
00:41:50,520 --> 00:41:52,320
to bounce back from bleaching.

662
00:41:54,160 --> 00:41:57,000
[Attenborough] So, although colour
might be helping coral reefs

663
00:41:57,080 --> 00:41:59,000
to tolerate some of the change,

664
00:41:59,680 --> 00:42:04,200
only action to halt global warming
will ensure their survival.

665
00:42:05,080 --> 00:42:07,520
If warming continues, then they,

666
00:42:07,600 --> 00:42:10,840
together with the beautiful array
of colour they provide,

667
00:42:10,920 --> 00:42:13,720
will disappear
from the reefs of the world.

668
00:42:14,600 --> 00:42:16,960
[enchanting orchestral music playing]

669
00:42:17,640 --> 00:42:21,480
Science and technology
are continually unravelling

670
00:42:21,560 --> 00:42:26,320
more and more details of the way
animals perceive colour and use it.

671
00:42:27,640 --> 00:42:29,760
We may marvel at its beauty,

672
00:42:31,200 --> 00:42:32,680
but for many animals,

673
00:42:32,760 --> 00:42:35,280
it's the key to their existence.

674
00:42:36,920 --> 00:42:40,160
The more we understand about its function,

675
00:42:40,960 --> 00:42:44,480
the better we will be able
to protect the natural world,

676
00:42:45,120 --> 00:42:46,560
in all its beauty,

677
00:42:47,120 --> 00:42:48,800
for future generations.