Original subtitles

Narrator: Ever wondered?

Why goats would risk life and limb

To climb the vertical face of a dam?

These must be some of the most daring animals I have ever seen.

What would happen if a zebra had no stripes?

It's this zebra that looks totally unlike any other zebra.

Narrator: And why is this diver surrounded by a fishy aura?

If I was the diver, I would be very confused.

Narrator: Nature is awe-inspiring.

But sometimes it just doesn't make sense.

Man: I have never seen anything like this.

Narrator: Our team of experts investigates

The weirdest animal behavior...

That's amazing.

Narrator: ...And the most unexpected events...

What is causing that?

Narrator: ...Ever caught on camera.

Woman: My god!

Narrator: These are...

♪

May 2017.

Cingino in the italian alps.

This 160-feet-tall wall is a hydroelectric dam in Italy.

Narrator: Italian photographer roberto bianchetti

Is using a drone to film the landscape

When he spots some curious specks moving across the dam.

♪

As he gets closer, he reveals these specs are actually goats,

And they appear to be defying the laws of gravity.

[ goats bleating ]

These must be some of the most daring animals

I have ever seen.

♪

Nelson: There is almost no place to get a foothold,

And yet they're scaling the edge of that cliff.

Narrator: The question is, what could possibly possess

These anti-gravity goats to risk life and limb like this?

These crazy goats. What are these goats doing?

[ laughs ]

Narrator: Could they have got there by accident?

Now, it may sound a bit silly,

But it isn't uncommon for animals to get stuck.

So maybe these goats got stuck

Trying to cross to the other side of the river.

[ cat meows ]

Nelson: A lot of animals will do things

That overestimate their physical abilities.

I mean, everybody's familiar with cats climbing up

And getting stuck.

Narrator: Cats have curved claws,

Which are great for climbing up

But not so useful

For when it comes to climbing down headfirst.

Better to descend butt-first, which is not instinctive.

Though this cat has got it all figured out.

The thing is, these goats don't really look like they're stuck.

If you look at the footage, they are perfectly at ease

On the face of this dam.

I mean, they don't seem uncomfortable at all.

Narrator: Turns out these are not your average goats.

[ man yodeling ]

♪

They're alpine ibex.

Living high in the mountains,

They're used to life on the edge.

Males have large horns which they use to defend territories,

Compete for females,

And make for a great back-scratcher.

These animals have evolved in this environment,

And they're mountain specialists.

They constantly scale cliffs and vertical cliff faces.

♪

Narrator: But how are these daredevil goats

Able to achieve these incredible feats of climbing?

Daly: Ibex have short legs.

A low center of gravity, and strong muscles,

As well as split pincer-like hooves which help them grip.

Nelson: These hooves are nice and pointy.

But they're also soft and flexible,

Enough that they essentially grab

The edge of that cliff face.

Burke: So these split hooves allow them to perch

And balance on tiny, little cliff ledges.

[ goat bleats ]

Narrator: Okay. We know what makes these goats

Such elite mountaineers,

But this dam is really upping the stakes.

One wrong move on this sheer surface,

And it could be game over.

So why risk it?

[ echoing ] time to look into the mind of a goat.

Goats are probably one of the most underrated animals around.

These are really hardy creatures.

And they're not just hardy.

They'll go anywhere where there's food.

Narrator: These moroccan goats climb the argan tree

To feast on leaves and fruit.

Burke: It almost defies logic and explanation

How these goats are actually able to climb up into the trees,

But clearly they do, and they do very well.

Narrator: So, could food be what's inducing

This foolhardy stunt?

The real key in this mystery

Is looking at what they're doing on the dam.

They're actually licking it.

Narrator: We all know goats will eat practically anything.

But rocks?

Daly: It turns out

The bricks of the wall contain mineral salts.

Narrator: As water leaches through the face of the dam

And evaporates, it leaves behind deposits of salt --

Vital minerals for the ibex.

A lot of animals need nutrients from the environment to survive.

♪

Narrator: Butterflies in the amazon

Will even drink the tears of turtles

To meet their salt needs.

♪

Predators often get their salt from eating other organisms,

But in this case, they're herbivores.

They eat nothing the plants.

So if they're eating nutrient-poor vegetation,

They need to supplement their diet with salt.

You'd think all alpine ibex would do this,

But it turns out it's only females and their young.

Narrator: That's because salts are essential

For the healthy development of muscle and bone.

It's especially important for ibex mums when they're feeding,

As these minerals are passed to their young through their milk.

Narrator: So the reason these goats risk life and limb

On this vertical dam

Is to ensure their kids get a healthy diet.

This footage here absolutely made my stomach turn

When I watched it.

But for them, this is just another day at work.

♪

Narrator: July 2010.

Etosha national park, namibia.

A land of salt and crusted dry lake beds

Where animals gather at scattered oases.

Wildlife filmmaker pete cayless is tracking a herd of zebra

When he notices a misfit.

Riskin: It's zebra, zebra, zebra.

W-wait a second. What was that one?

And it's this zebra that looks totally unlike any other zebra.

It's black.

Burke: So here's a real curiosity.

Why doesn't this zebra have stripes?

Sometimes nature reveals itself with the exceptions to the rule.

This zebra is a perfect example of that.

Narrator: Perhaps the case of the black zebra

Can help us solve a mystery

That's been plaguing scientists for years.

Burke: Why do zebras have stripes?

There's obviously some kind of advantage that this confers,

But what exactly that is, well, that's a mystery.

Narrator: First, we need to tackle

A really important question.

Are zebras black with white stripes

Or white with black stripes?

See, that part still confused me,

And none of my zebra guys knew that.

Narrator: It's okay. We have zebra guys, too.

As a fetus, they are all-black,

And then, early on, white stripes start to develop.

So they are black with white stripes

Rather than white with black stripes.

Narrator: Why didn't our black zebra -- let's call her lucky --

Get her stripes?

Riskin: There's a word for this black coloration.

It's called melanism.

Which is basically an inherited trait

That creates a dark pigment.

Narrator: Lucky isn't alone in her bizarre coloration,

As other misfits have been spotted,

Including squirrels, wolves...

And the black jaguar.

But what does an unconventional coat mean for lucky?

One of the defining features of zebra are their stripes.

So when you see a genetic mutation like that,

You sort of wonder whether they might have

Negative consequences that come from that.

Narrator: So are stripes essential for survival

Or just cosmetic?

♪

Narrator: In namibia, a rare black zebra nicknamed lucky

Is spotted, prompting the question,

Why do zebra have stripes at all?

Could it be something to do with where they live?

Across the african continent in the warmer parts,

You see zebra with much bolder stripes than in the cold parts.

Narrator: And in namibia, where lucky was seen,

Temperatures regularly reach 90 degrees fahrenheit,

Or 30 celsius.

Burke: One thought was the stripes are creating

A kind of cooling system along the zebra's hides.

The color black and the color white

Have very famous properties.

Black absorbs heat really well and white reflects it.

And if you take infrared photography of a zebra,

You can see that the black stripes

Are clearly warmer than the white stripes.

So what you might get is heat

Being pumped off the black stripes

And falling back down on the white stripes,

And so you might get these little micro air currents

Flowing against the skin.

Narrator: Lucky has a black coat thanks to her melanism.

So is she roasting without her white stripes?

Scientists in hungary recently set out

To investigate the air-conditioning theory.

They took some barrels,

And they wrapped them in animal hides,

And some of them were black and some of them were white,

And some of them had black-and-white stripes.

And they found absolutely no differences

In the internal temperature of these drums.

There was just no evidence from that study

That the black and white stripes help with heat.

Narrator: Good news --

Lucky isn't overheating because of her black coat.

Do stripes protect zebras in other ways?

One of the original theories about why zebras have stripes

Was to do with evading predators.

And one thought was the stripes might be confusing predators.

When a lion is going after zebras,

It wants to pick out one individual

That it's going to tackle,

And if the zebras are running close to each other,

Maybe it's hard for the predator to tell which one's which,

And it gets confused.

Perhaps the stripes sort of fuse together

In that you can't really tell

When one zebra starts and one zebra finishes.

Maybe that just gives the zebras

A little bit of an edge for escape.

Narrator: If stripes do help zebra to evade predators,

Lucky could be an easy target.

But predator eyesight isn't the same as ours.

How: We find it very easy to see the stripes of animals,

But a lion would only be able to see the zebra stripes

When they're in relatively close range.

The resolution of the predators' eyes is a lot lower than ours.

Narrator: So from a distance, a lion wouldn't spot the difference

Between lucky and the other zebra.

And once lions get closer, they're using other senses.

Caro: They'll probably hear or smell the zebras,

And, furthermore, zebras are an integral part

Of the diet of lions.

So if striping was a form of confusion,

It really works badly.

Midcap: The stripes of the zebra may not be deterring land predators.

There's a whole different predator

That this may be affecting.

Narrator: For many animals on the african savanna,

Flies are a menace.

[ flies buzzing ]

Could the zebra's stripes be a solution to this problem?

♪

So, there's an easy way to test this idea,

And that's just to dress up some horses.

Narrator: Oh, this sounds fun.

♪

Narrator: In namibia, lucky the black zebra

Is surviving without stripes.

But she might be at a disadvantage

When it comes to flies.

[ flies buzzing ]

Martin how studies the ways animals view the world.

He's come up with a test to see whether flies could be confused

And therefore repelled by stripes.

Zebra can be stubborn subjects,

So he uses the next best thing -- horses.

We printed out lots of different patterned rugs

That we could place over horses.

These rugs were either a solid color like a black or a gray,

Or they had stripes.

Narrator: Martin uses cameras

To track flies as they approach the horses.

He then maps their paths with a red line.

First up, the gray rug.

We've got a fly that comes in from the side here,

Slows down, hovers around a little bit,

Touches down, and then it decides actually

It's going to land here,

So it's a really nice controlled landing.

Narrator: No problems with plain colors like gray.

But how do flies react to stripes?

The fly comes in from the side here.

It comes in really fast,

And then it does this abort behavior at the end,

And it flies off in the other direction.

So it's a really clear difference in behavior.

Now, why would a fly get freaked out by stripes?

Narrator: Well, flies perceive the world

Very differently to us.

Their resolution is much lower than ours,

But they're very interested in movement.

They have a very fast lifestyle,

Flying around, landing on objects,

And avoiding things,

And so their eyes have to work extremely quickly.

Midcap: They can see four times faster than the human eye,

So they essentially see everything in slow motion,

Which is why it's so difficult

To swat at a fly that's been bugging you all afternoon.

Narrator: But what effect might stripes have on fly sight?

To find out, martin has mocked up

What a zebra looks like to a fly.

From a distance, it's like a blurry gray horse.

But as it gets closer...

So, we can simulate the approach of our fly

As it's coming to land on a zebra.

As the fly comes in closer, these stripes suddenly appear

Within the resolution of the fly's eyes.

We think the stripes are having an illusion effect

On the motion vision of the flies.

Midcap: You can see this for yourself when you look at a barber's pole.

Now, these have diagonal stripes that are moving horizontally,

But they look like they're moving upwards.

Narrator: So trying to land on a zebra is a pretty weird

And disorienting experience for flies.

For the flies, it's like an optical illusion.

It's all trippy and crazy

And makes it feel like the whole room is spinning,

And it's just too much for the fly to handle,

And it doesn't land there.

It's unbelievable, but it's true.

Flies get confused by stripes.

Burke: So it seems the most likely explanation

As to why zebras have stripes

Is to avoid getting bitten so frequently by flies.

Narrator: The question now is, why isn't the savanna covered

With other stripy animals?

Zebra are quite susceptible to attack by biting flies,

Given that they have much shorter fur

Than most of the other animals on the savanna.

Narrator: So what happens to a zebra with no stripes?

Caro: Most biting insects

Are attracted to large, dark objects,

And that's what they home in on.

Narrator: Uh-oh. Sounds like someone we know.

Looks like our black beauty, lucky,

Might be more popular with flies than the other zebra.

But she's managing to survive without her stripes.

Things aren't always so black-and-white after all.

♪

August 2018. Hurgarda, egypt.

Underwater enthusiast rene thies

Is on a scuba-diving excursion with his family.

♪

Nosal: This is the red sea,

A diverse, unique area with hundreds and hundreds

Of species of fish and corals.

Narrator: As the group heads toward the open sea,

Rene suddenly spots a strange swarm

Around his stepson tobias.

Nelson: Oh, my goodness.

It's like he's surrounded by a force field of fish.

The big mystery here is, why are all of those fish

Circling the diver?

Nosal: If I was the diver, I would be very confused.

♪

Narrator: In the red sea, a diver finds himself

Surrounded by a mysterious sphere.

Clearly, there's something fishy going on.

♪

Nelson: Could the diver have found himself

In the middle of some elaborate mating ritual?

We know that a lot of fish form giant schools to mate.

Parrotfish do it.

Surgeonfish do it. Groupers do it.

They'll go off of a reef,

And at one time, they'll start mating.

Narrator: During these mass mating, or spawning, events,

Females release eggs into the water

And males release sperm.

But if this was a spawning event,

You'd see a milky cloud of sperm and eggs,

And we're not seeing that here.

Nelson: Could these fish just be looking for some kind of shelter?

In the open ocean, you can think of it like a giant desert,

And then here you are as a fish and you got predators around.

So you have to find a way to hide from them.

Nosal: If these fish come across

Anything that resembles a shelter,

It's going to be a hot commodity.

They are going to be attracted to it.

This is why fish like to gather

Underneath peers and peer pilings

Because it provides them some shelter.

Narrator: Perhaps the fish in the clip

Are attracted to the diver

Because they see him as shelter.

But in this case, the fish are not under the diver.

They're swimming all around him.

Narrator: And they appear to be moving in a coordinated way,

Rippling around the diver while staying in a tight ball.

Other animals like starlings and also wildebeest

Will gather together for safety in numbers.

Could the fish be using a similar tactic?

♪

Nelson: A lot of fish that are being preyed upon by larger fish

Will form a giant swirling mass.

Now you're not just one fish that a predator's going after.

You're this mass, and it can kind of confuse

A predator diving in

Because you have fish going everywhere.

Narrator: And that looks a lot like

The sphere of fish around our diver.

Galante: What you're seeing here is a bait ball.

There's safety in numbers,

So these fish are all congregating

And getting as tightly packed as they can.

Basically to dilute the risk of an individual being eaten.

Narrator: The shoal of fish contracts, expands,

And even parts before coming back together

Without missing a beat.

There's no leader.

Each fish coordinates with its neighbor,

Who coordinates with its neighbor, and so on.

And the movement is synchronized in the blink of an eye.

But why did these fish form a bait ball to begin with?

There's an interesting twist,

Because if you watch the entire video,

You see that out of nowhere a large whale shark appears.

Nelson: At the beginning, we didn't realize

There was a big predator around.

The fish knew it, but we couldn't see it yet.

Nosal: So could these fish have formed the bait ball

Because they were afraid of the whale shark?

Narrator: These giant fish swim with their mouths open wide

To scoop up plankton and small fish.

Oddly, the whale shark does not try to target the fish.

It doesn't react to the fish in any way.

Just lazily swims on by.

Narrator: Perhaps it's already had dinner,

Which is lucky for these fish.

The fish, they had to take evasive action,

So they formed a bait ball around the diver.

Narrator: The fish didn't see the diver as a threat,

And he offered some rare shelter in the open sea.

Nosal: And even though there was a risk of everybody

Being in the same place at the same time,

It was a gamble worth taking.

Narrator: The whale shark wasn't the only threat here.

On closer inspection, there are other predatory fish

Looking for an easy meal.

So forming a bait ball was the right call.

-- Captions by vitac -- www.Vitac.Com

Captions paid for by discovery communications