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Anyone fascinated by the natural world
has probably wondered why some animals
have such strange looking sense organs.
The elephant with its huge ears,
the antennae of a butterfly
which up close look like feathers,
the snake with it's split tongue.
And what about less obvious enhancements,
like the sensory cells on a crocodile skin?
Surely these evolutionary traits are just for decoration.
In fact, the size, shape, and location
of these animal's sense organs are for a purpose.
And just like us, animals rely on their senses
to communicate with each other, find their way around,
stay safe and most importantly, to find food.
When you see how superior some animal senses are
compared to those of humans, you might wonder
how we ever managed to stay on top of the food chain.
Animal super senses.
You won't believe what's possible.
In this episode, we'll explore the animal sense of sight
and you'll see there's a lot more to this
than meets the naked eye.
The human imagination is limited
when it comes to animal senses.
People with good vision are sometimes called eagle eyed,
but eagles can see a fish from many dozen meters away.
Scientists believe that the first sets of eyes
evolved around 540 million years ago
after an extinction event.
Their original purpose
was as straightforward light detecting organs.
With evolution, eyesight has come a long way.
Today vision is a critically important sense.
only you won't believe how some animals see the world.
We often talk about a bird's eye view
without stopping to consider what that means.
But the eyesight of birds, such as eagles, falcons,
and owls is several times sharper than ours.
Eagles can spot rabbits from miles away
while hawks and buzzards scan the earth from heights
of 10 to 15,000 feet looking for tasty rodents.
And once spotted, these birds can dive at speeds
of over 100 miles per hour
and still keep their target and focus.
To match that kind of speed and agility,
humans have to build jet fighter planes.
The eagle eye is among one of the most fascinating
in the animal kingdom.
As an eagle descends from the sky to attack its prey,
muscles in their eyes continually adjust the curvature
of their cornea and lens to maintain an accurate focus
on their target during approach and attack.
The Nanking Kestrel is common in open country in Australia.
It hunts during the day for insects, mice and small birds.
Like all falcons, the kestrel has relatively large eyes.
Not only do they have an elongated strip
of dense light receptors,
they also have two circular fovea as well.
The circular ones are in a pit
and this acts like a telephoto lens, magnifying the image.
The Nanking Kestrel will hover above its prey
from a height of 50 feet,
detecting food that may be only a few centimeters in length.
It's certainly an impressive feat.
This incredible eyesight makes them
extremely effective hunters.
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But kestrels have another weapon in their sensory arsenal.
They can see ultraviolet light.
By following the ultraviolet light naturally reflected
off the scent and urine trails left behind by rodents,
they can track down their prey.
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Now you might take one look at an owl
and think it doesn't look particularly dangerous.
Just be glad you're not a worm.
Owl's eyes are large, often weighing the same as human's.
We also know they have forward facing eyes,
which give owls stereoscopic vision,
very useful in judging distances.
Oddly enough, the best way for small creatures
to stay safe from an owl
may actually be to move towards it and not away.
As it happens, owls are long sighted.
The breed of owl who has the keenest daytime eyesight
is called the eagle owl,
a tribute to just how sharp sighted eagles are.
The Eagle's vision is much sharper than ours,
operating a bit like a telephoto camera lens.
Just imagine being able to see an ant on the pavement
from atop a 10 story building.
That's the eagle way.
One animal that birds of a different feather
must always be on the lookout for is of course the cat,
that'd be cats of all shapes and sizes actually,
because from the mightiest lion
to the most placid domestic cat,
most felines have superb night vision.
But of course it's the big cats such as tigers and lions
which have the most powerful night eyes,
something which enables them to hunt
under the cover of darkness.
Cats also have a reflective layer behind their eyes
known as a tapetum.
It enhances their eyesight in reduced light circumstances.
One visible effect of this are the bright shining eyes
that stare back at you when you point a flashlight at a cat.
Not all cats are nocturnal though.
Cheetahs are fast daytime killers.
They don't need the trickery necessary for nocturnal sight.
The cheetah thrives in areas of open terrain and savannah.
When prey is spotted,
they use their phenomenal speed to give chase.
Their exceptional eyesight along with their speed
allows them to be such effective predators.
But what makes the cheetah's eyes so super powerful?
Mammals have a layer at the back of the eye
where sensory cells respond to incoming light.
On this layer, there is an area that is denser
in sensory cells called the fovea.
And here the cheetah is formidable too.
The elongated shape of the cheetah's retinal fovea
gives it ultra sharp wide angle vision,
enabling them not only to chase their prey
but also make sudden turns with near perfect accuracy.
It is thought that the dark tear marks beneath their eyes
may also enhance their vision
by cutting down on the sun's glare.
Cheetahs just don't go running around
at top speed on a whim.
They deploy their keen eyesight
to scan the environment for signs of prey.
With its distinctive spotted coat providing camouflage
in the high and dry grass,
its speed and agility plus those unforgiving eyes,
the cheetah is one dangerous customer.
Now of course there's one big cat
that seems to rule over all of them,
at least as humans perceive things.
But you don't become known as the king of the animals
unless you have finely tuned senses
and that's where the lion lordes over most other predators.
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Their eyesight is a significant factor,
especially when the sun goes down over the savannah.
While in daylight hours, a lion's sight
is said to be about level with ours.
At nighttime, they shift gear.
You see, lions are believed
to have eight times better night vision than we do.
Lions apparently see things in blues and greens
and while they will be lost
in a completely pitch black room for example,
there's a lot of moonlight and starlight
on the African Plains and it is this which guides them,
usually to their next midnight snack.
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But let's not forget their not so distant cousin, the cat.
This includes feral felines,
such as this particular Australian wild cat,
but also ordinary household domestic cats.
Cats are by far the most active at dawn and dusk.
The term for this is crepuscular in case you ever wondered
if there was a word to describe their frantic activity
at sunrise and sunset.
Night vision comes in useful at these hours
and cat's eyes have six to eight times more Rohn cells,
sensitive to low light, than humans do.
Cats have greater range of peripheral vision too.
So in the corner of their eye
they can spot that trembling mouse hiding in the corner.
The elliptical shape of cat's eyes, larger corneas
and the bright tapestry
make them natural born night stalkers.
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This cat certainly doesn't look
as if he's going to let his prey get away,
and its patience and persistence can be weapons too.
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And now we examine an animal
which seems to break all the rules.
It can change skin color
and look in two directions at the same time.
There are around 160 species of chameleons
dispersed across the globe in rainforests and deserts
from the Middle East to Sri Lanka, though half
of those species live on the island of Madagascar.
These lizard kings vary greatly in size
from a length of just 15 millimeters to 68 centimeters
and have coiled tongues that are sometimes
twice the length of their body and can feed on insects
by using their tongues like ballistic missiles.
To accurately use such a weapon,
chameleons needs superior sight.
Eyes are mounted on conical turrets
that can move independently of each other.
And upper and lower eyelids are joined
with only a pinhole margin for the pupil to see through.
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The structure of their eyes gives the chameleon
360 degree vision working like a tiny telephoto camera lens.
Their eyes focus super fast,
zooming in on targets at phenomenal speeds.
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When prey is spotted,
both eyes can be focused in the same direction
And the result is a combination of sharp stereoscopic vision
and incredible depth perception.
As if that wasn't enough,
chameleons can see both visible and ultraviolet light.
Chameleons exposed to UV light
apparently become more social animals
and even show more interest in reproduction.
Your humble everyday bumblebee
comes with ultraviolet vision.
In all but a very few rare cases,
UV light or ultraviolet radiation
is invisible to the human eye.
These waves come at different frequencies or wavelengths.
They lie on a spectrum from longest wavelengths
to the shortest at the other end.
Our brains interpret the different wavelengths as colors.
But humans can only see a very small part of this spectrum.
Most of the light in the universe is invisible to us,
but not to honeybees.
Bees, like many other insects species,
see from approximately 300 to 650 nanometers.
In simple terms, this means they cannot see the color red,
but at the lower end of the scale
they can see the ultraviolet spectrum, which humans can not.
It is no coincidence that many flowers
have ultra violet color patterns.
These are patterns invisible to the human eye,
but which catch the eyes of the bee.
Bees depend on nectar and pollen
which means they have no choice but to find flowers.
Some of the ultraviolet patterns
actually look a bit like helicopter landing pads.
Its as if they're being directed to landing zones
where they'll find the part of the plant
with the most nectar and pollen.
True, bees have an acute sense of smell,
but the bee's super sight is what detects flowers
at a distance.
Every time a bee drops in,
some of the pollen gets stuck to the little creature
which means it'll probably deposit it later
in another flower.
And so the circle of life continues.
Bee eyesight has evolved to be in tune with flowers,
but also plants and flower have evolved in order
to attract bees, which they need in order
to transmit pollen from one plant to another.
Put succinctly, that's how they reproduce.
So if anyone still talks about the birds
and the bees these days, that's how it all got started.
Polarization is another amazing visual super sense,
one that belongs to one of the most fantastic creatures
to grip the human imagination.
But now we turn to the place even darker and more mysterious
and that's the ocean and the ocean floor.
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For octopi, the super sense of polarized sight is critical,
aiding and abetting their search for prey
but also enabling them to communicate
with their fellow creatures.
The chromatophores and iridescent cells
on the skin of an octopus create visual patterns
that transmit signals from one octopus
to all the other octopi that happen to be in range.
These chromatophore patterns change depending on variables
such as whether it's mating season or for example,
if the octopus is alarmed.
These changes in pattern
are how octopi communicate with one another,
but polarized vision also allows them
and other cephalopods to zone in
on otherwise transparent prey like jellyfish.
The octopus is of course an invertebrate.
It literally has no spine.
It is also a cephalopod, an exclusively marine creature.
Cephalopods are characterized
by their bilateral body symmetry,
which in everyday terms means they look roughly the same
on one side as they do on the other.
They have a prominent head and several large tentacles
attached to their body,
eight of course in the case of the octopus.
Squid and cuddlefish are also cephalopods.
Like the octopus, they too can distinguish
the polarization of light.
The octopus is considered
one of the most intelligent of invertebrates.
The octopus' eye develops an invagination
or in-pocketing of the skin.
Be that as it may, each octopus eye has a retina,
a cornea, an iris, a lens and a fluid filled interior
and is quite a piece of evolutionary engineering.
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And now on super senses, a fish like no other.
The Archer fish, which is usually found in fresh water
is quite unlike any other fish because the Archer fish
finds its prey living outside of the water.
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Insects, butterflies, spiders and other small creatures
are the Archer fish's habitual prey
and it typically searches for victims
resting on branches or twigs just above the water's surface.
The clever Archer fish
then positions itself underneath its prey
and with a pinpoint accuracy of a sharpshooter,
knocks it off the branch and its perch with a blast
from a powerful jet of water shot from its mouth.
Archer fish are remarkably accurate,
usually hitting their intended target
on the very first shot.
The hapless creature then falls into the dip
and the triumphant Archer fish swims to the surface
long enough to retrieve its meal
with the satisfaction of a job well done.
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Their eyes are able to correct
for the way light distorts and bends as it enters the water.
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It's the unique structure of their eyes
that gives them a remarkably accurate aim.
Recent research has found that the Archer fish
has parts of its retina tuned to whether
it's looking at the aquatic or aerial field of view.
The bottom part of the retina looks up,
which means the Archer fish is looking out of the water.
And the top of the retina looks down
as the Archer fish looks below the water surface.
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One of the most peculiar looking animals of land,
sky or sea, the mantis shrimp has possibly
the most complex visual system
on this entire incredible planet.
As it scuttles along looking
like a particularly large incrustaceous caterpillar,
the mantis shrimp's eyes don't miss a trick.
They have compound eyes for one thing.
A compound eye consists of hundreds
or even thousands of individual photo receptor units.
The image perceived by the owners of compound eyes
is a combination of the input from these units.
Just to make things more interesting,
the mantis shrimp's compound eyes are mounted
on mobile stalks, which move independent of each other.
It can detect ultraviolet and infrared
and all of this is achieved the experts reckon
without any intervention from its minuscule brain.
Well, that's just about it for this episode
of animal super senses.
The way animals see the world has offered us
fascinating insight to the richness and complexity of life.
We've seen things from a bird's eye view
and used our ultraviolet vision underwater.
We've had the night vision on while we roamed
the African Plains and met the chameleon
who can see every which way at the same time.
And we'll see too in our next episode
how animal super senses
can take you to some interesting places.
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