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(soft music)

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Anyone fascinated by the natural world

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has probably wondered why some animals

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have such strange looking sense organs.

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The elephant with its huge ears,

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the antennae of a butterfly

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which up close look like feathers,

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the snake with it's split tongue.

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And what about less obvious enhancements,

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like the sensory cells on a crocodile skin?

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Surely these evolutionary traits are just for decoration.

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In fact, the size, shape, and location

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of these animal's sense organs are for a purpose.

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And just like us, animals rely on their senses

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to communicate with each other, find their way around,

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stay safe and most importantly, to find food.

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When you see how superior some animal senses are

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compared to those of humans, you might wonder

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how we ever managed to stay on top of the food chain.

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Animal super senses.

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You won't believe what's possible.

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In this episode, we'll explore the animal sense of sight

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and you'll see there's a lot more to this

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than meets the naked eye.

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The human imagination is limited

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when it comes to animal senses.

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People with good vision are sometimes called eagle eyed,

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but eagles can see a fish from many dozen meters away.

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Scientists believe that the first sets of eyes

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evolved around 540 million years ago

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after an extinction event.

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Their original purpose

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was as straightforward light detecting organs.

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With evolution, eyesight has come a long way.

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Today vision is a critically important sense.

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only you won't believe how some animals see the world.

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We often talk about a bird's eye view

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without stopping to consider what that means.

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But the eyesight of birds, such as eagles, falcons,

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and owls is several times sharper than ours.

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Eagles can spot rabbits from miles away

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while hawks and buzzards scan the earth from heights

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of 10 to 15,000 feet looking for tasty rodents.

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And once spotted, these birds can dive at speeds

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of over 100 miles per hour

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and still keep their target and focus.

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To match that kind of speed and agility,

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humans have to build jet fighter planes.

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The eagle eye is among one of the most fascinating

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in the animal kingdom.

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As an eagle descends from the sky to attack its prey,

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muscles in their eyes continually adjust the curvature

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of their cornea and lens to maintain an accurate focus

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on their target during approach and attack.

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The Nanking Kestrel is common in open country in Australia.

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It hunts during the day for insects, mice and small birds.

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Like all falcons, the kestrel has relatively large eyes.

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Not only do they have an elongated strip

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of dense light receptors,

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they also have two circular fovea as well.

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The circular ones are in a pit

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and this acts like a telephoto lens, magnifying the image.

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The Nanking Kestrel will hover above its prey

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from a height of 50 feet,

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detecting food that may be only a few centimeters in length.

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It's certainly an impressive feat.

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This incredible eyesight makes them

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extremely effective hunters.

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(intense music)

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But kestrels have another weapon in their sensory arsenal.

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They can see ultraviolet light.

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By following the ultraviolet light naturally reflected

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off the scent and urine trails left behind by rodents,

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they can track down their prey.

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(intense music)

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Now you might take one look at an owl

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and think it doesn't look particularly dangerous.

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Just be glad you're not a worm.

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Owl's eyes are large, often weighing the same as human's.

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We also know they have forward facing eyes,

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which give owls stereoscopic vision,

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very useful in judging distances.

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Oddly enough, the best way for small creatures

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to stay safe from an owl

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may actually be to move towards it and not away.

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As it happens, owls are long sighted.

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The breed of owl who has the keenest daytime eyesight

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is called the eagle owl,

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a tribute to just how sharp sighted eagles are.

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The Eagle's vision is much sharper than ours,

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operating a bit like a telephoto camera lens.

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Just imagine being able to see an ant on the pavement

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from atop a 10 story building.

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That's the eagle way.

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One animal that birds of a different feather

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must always be on the lookout for is of course the cat,

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that'd be cats of all shapes and sizes actually,

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because from the mightiest lion

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to the most placid domestic cat,

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most felines have superb night vision.

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But of course it's the big cats such as tigers and lions

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which have the most powerful night eyes,

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something which enables them to hunt

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under the cover of darkness.

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Cats also have a reflective layer behind their eyes

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known as a tapetum.

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It enhances their eyesight in reduced light circumstances.

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One visible effect of this are the bright shining eyes

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that stare back at you when you point a flashlight at a cat.

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Not all cats are nocturnal though.

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Cheetahs are fast daytime killers.

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They don't need the trickery necessary for nocturnal sight.

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The cheetah thrives in areas of open terrain and savannah.

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When prey is spotted,

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they use their phenomenal speed to give chase.

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Their exceptional eyesight along with their speed

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allows them to be such effective predators.

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But what makes the cheetah's eyes so super powerful?

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Mammals have a layer at the back of the eye

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where sensory cells respond to incoming light.

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On this layer, there is an area that is denser

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in sensory cells called the fovea.

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And here the cheetah is formidable too.

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The elongated shape of the cheetah's retinal fovea

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gives it ultra sharp wide angle vision,

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enabling them not only to chase their prey

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but also make sudden turns with near perfect accuracy.

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It is thought that the dark tear marks beneath their eyes

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may also enhance their vision

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by cutting down on the sun's glare.

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Cheetahs just don't go running around

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at top speed on a whim.

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They deploy their keen eyesight

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to scan the environment for signs of prey.

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With its distinctive spotted coat providing camouflage

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in the high and dry grass,

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its speed and agility plus those unforgiving eyes,

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the cheetah is one dangerous customer.

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Now of course there's one big cat

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that seems to rule over all of them,

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at least as humans perceive things.

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But you don't become known as the king of the animals

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unless you have finely tuned senses

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and that's where the lion lordes over most other predators.

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(intense music)

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Their eyesight is a significant factor,

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especially when the sun goes down over the savannah.

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While in daylight hours, a lion's sight

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is said to be about level with ours.

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At nighttime, they shift gear.

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You see, lions are believed

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to have eight times better night vision than we do.

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Lions apparently see things in blues and greens

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and while they will be lost

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in a completely pitch black room for example,

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there's a lot of moonlight and starlight

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on the African Plains and it is this which guides them,

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usually to their next midnight snack.

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(intense music)

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But let's not forget their not so distant cousin, the cat.

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This includes feral felines,

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such as this particular Australian wild cat,

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but also ordinary household domestic cats.

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Cats are by far the most active at dawn and dusk.

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The term for this is crepuscular in case you ever wondered

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if there was a word to describe their frantic activity

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at sunrise and sunset.

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Night vision comes in useful at these hours

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and cat's eyes have six to eight times more Rohn cells,

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sensitive to low light, than humans do.

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Cats have greater range of peripheral vision too.

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So in the corner of their eye

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they can spot that trembling mouse hiding in the corner.

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The elliptical shape of cat's eyes, larger corneas

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and the bright tapestry

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make them natural born night stalkers.

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This cat certainly doesn't look

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as if he's going to let his prey get away,

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and its patience and persistence can be weapons too.

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(soft music)

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And now we examine an animal

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which seems to break all the rules.

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It can change skin color

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and look in two directions at the same time.

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There are around 160 species of chameleons

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dispersed across the globe in rainforests and deserts

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from the Middle East to Sri Lanka, though half

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of those species live on the island of Madagascar.

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These lizard kings vary greatly in size

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from a length of just 15 millimeters to 68 centimeters

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and have coiled tongues that are sometimes

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twice the length of their body and can feed on insects

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by using their tongues like ballistic missiles.

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To accurately use such a weapon,

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chameleons needs superior sight.

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Eyes are mounted on conical turrets

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that can move independently of each other.

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And upper and lower eyelids are joined

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with only a pinhole margin for the pupil to see through.

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(soft music)

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The structure of their eyes gives the chameleon

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360 degree vision working like a tiny telephoto camera lens.

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Their eyes focus super fast,

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zooming in on targets at phenomenal speeds.

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(soft music)

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When prey is spotted,

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both eyes can be focused in the same direction

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And the result is a combination of sharp stereoscopic vision

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and incredible depth perception.

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As if that wasn't enough,

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chameleons can see both visible and ultraviolet light.

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Chameleons exposed to UV light

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apparently become more social animals

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and even show more interest in reproduction.

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Your humble everyday bumblebee

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comes with ultraviolet vision.

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In all but a very few rare cases,

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UV light or ultraviolet radiation

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is invisible to the human eye.

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These waves come at different frequencies or wavelengths.

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They lie on a spectrum from longest wavelengths

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to the shortest at the other end.

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Our brains interpret the different wavelengths as colors.

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But humans can only see a very small part of this spectrum.

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Most of the light in the universe is invisible to us,

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but not to honeybees.

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Bees, like many other insects species,

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see from approximately 300 to 650 nanometers.

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In simple terms, this means they cannot see the color red,

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but at the lower end of the scale

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they can see the ultraviolet spectrum, which humans can not.

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It is no coincidence that many flowers

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have ultra violet color patterns.

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These are patterns invisible to the human eye,

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but which catch the eyes of the bee.

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Bees depend on nectar and pollen

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which means they have no choice but to find flowers.

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Some of the ultraviolet patterns

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actually look a bit like helicopter landing pads.

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Its as if they're being directed to landing zones

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where they'll find the part of the plant

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with the most nectar and pollen.

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True, bees have an acute sense of smell,

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but the bee's super sight is what detects flowers

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at a distance.

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Every time a bee drops in,

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some of the pollen gets stuck to the little creature

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which means it'll probably deposit it later

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in another flower.

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And so the circle of life continues.

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Bee eyesight has evolved to be in tune with flowers,

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but also plants and flower have evolved in order

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to attract bees, which they need in order

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to transmit pollen from one plant to another.

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Put succinctly, that's how they reproduce.

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So if anyone still talks about the birds

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and the bees these days, that's how it all got started.

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Polarization is another amazing visual super sense,

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one that belongs to one of the most fantastic creatures

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to grip the human imagination.

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But now we turn to the place even darker and more mysterious

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and that's the ocean and the ocean floor.

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(intense music)

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For octopi, the super sense of polarized sight is critical,

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aiding and abetting their search for prey

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but also enabling them to communicate

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with their fellow creatures.

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The chromatophores and iridescent cells

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on the skin of an octopus create visual patterns

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that transmit signals from one octopus

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to all the other octopi that happen to be in range.

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These chromatophore patterns change depending on variables

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such as whether it's mating season or for example,

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if the octopus is alarmed.

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These changes in pattern

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are how octopi communicate with one another,

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but polarized vision also allows them

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and other cephalopods to zone in

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on otherwise transparent prey like jellyfish.

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The octopus is of course an invertebrate.

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It literally has no spine.

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It is also a cephalopod, an exclusively marine creature.

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Cephalopods are characterized

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by their bilateral body symmetry,

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which in everyday terms means they look roughly the same

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on one side as they do on the other.

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They have a prominent head and several large tentacles

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attached to their body,

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eight of course in the case of the octopus.

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Squid and cuddlefish are also cephalopods.

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Like the octopus, they too can distinguish

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the polarization of light.

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The octopus is considered

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one of the most intelligent of invertebrates.

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The octopus' eye develops an invagination

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or in-pocketing of the skin.

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Be that as it may, each octopus eye has a retina,

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a cornea, an iris, a lens and a fluid filled interior

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and is quite a piece of evolutionary engineering.

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(soft music)

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And now on super senses, a fish like no other.

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The Archer fish, which is usually found in fresh water

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is quite unlike any other fish because the Archer fish

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finds its prey living outside of the water.

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(intense music)

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Insects, butterflies, spiders and other small creatures

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are the Archer fish's habitual prey

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and it typically searches for victims

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resting on branches or twigs just above the water's surface.

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The clever Archer fish

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then positions itself underneath its prey

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and with a pinpoint accuracy of a sharpshooter,

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knocks it off the branch and its perch with a blast

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from a powerful jet of water shot from its mouth.

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Archer fish are remarkably accurate,

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usually hitting their intended target

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on the very first shot.

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The hapless creature then falls into the dip

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and the triumphant Archer fish swims to the surface

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long enough to retrieve its meal

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with the satisfaction of a job well done.

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(soft music)

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Their eyes are able to correct

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for the way light distorts and bends as it enters the water.

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It's the unique structure of their eyes

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that gives them a remarkably accurate aim.

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Recent research has found that the Archer fish

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has parts of its retina tuned to whether

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it's looking at the aquatic or aerial field of view.

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The bottom part of the retina looks up,

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which means the Archer fish is looking out of the water.

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And the top of the retina looks down

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as the Archer fish looks below the water surface.

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One of the most peculiar looking animals of land,

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sky or sea, the mantis shrimp has possibly

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the most complex visual system

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on this entire incredible planet.

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As it scuttles along looking

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like a particularly large incrustaceous caterpillar,

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the mantis shrimp's eyes don't miss a trick.

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They have compound eyes for one thing.

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A compound eye consists of hundreds

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or even thousands of individual photo receptor units.

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The image perceived by the owners of compound eyes

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is a combination of the input from these units.

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Just to make things more interesting,

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the mantis shrimp's compound eyes are mounted

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on mobile stalks, which move independent of each other.

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It can detect ultraviolet and infrared

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and all of this is achieved the experts reckon

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without any intervention from its minuscule brain.

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Well, that's just about it for this episode

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of animal super senses.

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The way animals see the world has offered us

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fascinating insight to the richness and complexity of life.

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We've seen things from a bird's eye view

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and used our ultraviolet vision underwater.

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We've had the night vision on while we roamed

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the African Plains and met the chameleon

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who can see every which way at the same time.

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And we'll see too in our next episode

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how animal super senses

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can take you to some interesting places.

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(intense music)

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(soft music)