Original subtitles

Narrator: Ever wonder what could swallow

50-foot trees in seconds?

That's huge.

Narrator: What mystery creature could transform

An entire landscape?

It's just -- it changes everything.

Narrator: And what's the point of the world's weirdest tusk?

This is the first time this behavior

Is ever been caught on camera.

Narrator: Nature is awe-inspiring.

But sometimes it just doesn't make sense.

Man: I have never seen anything like this.

Our team of experts investigate the weirdest animal behavior...

That's amazing.

...And the most unexpected events...

What is causing that?

...Ever caught on camera.

My god!

Narrator: These are...

♪

June 2016 -- a team of scientists

And wildlife filmmakers

Are on an expedition to study narwhals.

Their mission -- to try and solve

One of the greatest mysteries of the natural world.

So, the big question is, why on earth

Have they evolved this extraordinary structure?

Narrator: On a routine drone flight,

They capture narwhals doing something very strange

With their most distinctive feature -- their tusk.

It wasn't till we got the drone back

That we looked at the footage

And we realized we had something special.

♪

Narrator: Narwhals usually glide smoothly through the water,

But look closely, and these ones are not.

They seem to be shaking their heads.

Narwhals have never been filmed doing this before.

♪

Could this activity help us crack the age-old mystery

Of what their tusks are for?

It's got to be there for something, but what?

Narrator: Well, historically,

It's been thought that narwhals use their tusks as ice picks.

♪

So, narwhals are whales, they're mammals,

They breathe air, and they live in the arctic,

So it's very possible that they could get trapped under ice.

Could that extremely long tusk be used to find holes in the ice

Through which they can breathe?

Narrator: Finding air holes in the pack ice

Is a common problem for arctic mammals.

Seals, for example,

Play russian roulette with polar bears

When coming up to breathe.

♪

They've never been seen, actually,

Doing this sort of behavior.

The narwhal uses the back of its melon

To actually break ice that's thicker.

The last thing that this whale wants to do is endanger its tusk

Because if it breaks, it's not going to repair very well.

And so, it seems unlikely that this is, at least,

The primary purpose for the tusk.

So, they're not ice picks, but they are very strong.

Another theory is if it looks like a sword

And it moves like a sword, maybe it's a sword, right?

Maybe the males are using these tusks

To have sword fights to try to win females.

Is this footage of a narwhal showdown?

Could these tusks be used to face down competitors?

♪

Cooke: Is it like the antlers of a deer

And used by males in dominance battles?

[ grunts ]

♪

[ grunts ]

♪

Narrator: Could be, but look closely

And there doesn't seem to be any direct contact,

And previous arctic narwhal expeditions

Have reported that narwhals are a gentle species.

When you look at footage of these tusks

Touching each other, it's very gentle,

So it really doesn't seem like

They're fighting with them at all.

Narrator: It seems narwhals are naturally gentle,

But this might still be a display of dominance.

Is the tusk there to attract females?

Sometimes, just looking gorgeous is enough.

All male narwhals have tusks, so that would suggest

That it could be something that's evolved

As part of sexual selection and dominance behavior.

♪

Riskin: Maybe females think those tusks

Are just darned sexy,

And so the longer the tusk, the more attractive the male is.

That would certainly be sufficient to make them evolve.

Narrator: So, is this a male narwhal beauty pageant?

Well, it could be, except...

Females, in about 15% of cases, also have a tusk.

Narrator: ...Some ladies have them, too.

Nice gigantic spikes, girls.

If you look closely, you can also just make out

Some baby narwhals with their moms.

Narwhals give birth in July,

And that means it's too late for mating.

There's something else going on,

And it could relate to what the tusks are made of.

♪

Turns out, the narwhal tusk is a tooth.

It's actually an elongated canine tooth

That just sticks out of the mouth.

I mean, if you look carefully,

It doesn't come out of the middle,

It comes out of the side.

It's just a really weird tooth.

That tooth can get 9 feet long.

Narrator: And the perfect person to study a tooth?

A dentist, of course.

I would basically be a marine mammal tooth specialist,

Or odontologist, if you would.

Narrator: We'll stick with tooth specialist.

Narwhals are born with only two teeth,

And usually one stays completely hidden in their jaw.

So this single extended lopsided tusk

Is their most prized possession.

So apart from being the only straight,

Spiraled 9-foot tooth in the animal kingdom,

What else makes it so special?

♪

Nweeia: Hard to believe,

But along the surface of this tusk, or tooth,

Are millions of little tubes that connects the inner nerve --

Which runs the full length of this, by the way --

To the outside environment.

And just like people have sensitivity in their teeth

To hot, to cold, to certain flavors like sugar,

This long tooth is basically sensitive

To these sorts of things, as well.

It can basically taste the water.

If you can believe it,

This tooth can measure how salty the water is.

Narrator: So, is the narwhal tusk a giant antenna,

A secret weapon for sensing its surroundings?

And if so, could that hold the answer

To what's happening in the footage?

Scientists have been arguing over

What the tusk does for centuries,

But martin thinks that as well as detecting salinity,

It can gauge other things, like temperature, pressure,

And concentrations of different particles.

Because we think this tusk has other attributes,

It may play into the role of hunting

By detecting certain gradients of water

Where fish that the whale wants are.

Narrator: And once they've found fish with their tusks,

These amazing sense organs could be repurposed to attack them.

Is that what they're doing in the drone footage?

If you look very carefully, they're whacking fish with them.

♪

Ravetch: The narwhal are clearly

Knocking those fish over their heads.

They're clubbing them, and it's repeated hits,

And then they slurp it up.

We have feeding,

We have something that no one's ever captured before.

It was the holy grail.

Narrator: But like all good scientific mysteries,

The debate is still raging.

The video footage shows some of the fish

Being tapped by the tusk

And implying that they're stunned by the tusk,

When in fact, the tusk may be just the way of it

Knocking the food into their mouth.

The food may likely have already been stunned.

Narrator: Whether multipurpose narwhal tusks

Are for clubbing fish or for guiding them to their mouths,

This footage of narwhals using their tusks to feed

Is a world first,

And it's helped crack a centuries-old mystery --

What is the purpose of the most unique,

Incredible tooth in the whole of the animal kingdom?

♪

The northern range --

Yellowstone national park, u.S.A.

Satellite images reveal a rapidly changing landscape.

Lakes are forming and rivers are shifting course.

Down on the ground, trees are growing

Where they haven't for years,

And something else weird has happened.

For six decades, this has been elk paradise.

In the mid '90s, elk populations were booming.

Narrator: Back then, there were over 19,000 elk here,

But today, only around 6,000 remain.

They've been spooked.

The question is, what's happened to yellowstone's elk?

♪

♪

Narrator: In yellowstone national park,

The landscape has been transforming,

And elk numbers have shrunk by nearly 70%.

They've started behaving very oddly.

Instead of hanging out in giant groups

In the middle of the fields,

They started moving into small groups in the woods.

So the question is,

What is changing yellowstone national park?

Narrator: What has changed in yellowstone

Over the past 20 years

To cause the elk to move to new pastures?

♪

Elk are one of the resident grazers in the national park.

They eat willows, berry bushes, aspen cottonwood --

A variety of plants.

Narrator: All of these plants grow in the river valleys,

Which used to be prime real estate for elk.

But now, there's another furry critter

Taking over the waterways,

And they've seen a surge in population.

Are they what made the elk move?

Are beavers what's changed yellowstone national park?

Baker: Since the mid '90s,

As the elk numbers have been going down,

The beaver numbers have been going up.

Narrator: Beaver business has been booming in yellowstone,

And they've been going to town on their favorite food --

Willow, which is also the elks preferred dinner.

So, have they starved the elk out of the area?

Well, beavers are effectively hydro engineers.

♪

They will build dams,

They will cut down trees that line the rivers,

And they will change the entire ecology of a river system

Based on their needs.

♪

Narrator: Since the mid '90s, beaver numbers have grown,

But contrary to what you might expect,

So have the willow trees.

These beavers pay back more than they take.

Creating a dam actually creates habitat for more willows.

♪

Beaver dams raise the water level,

Which create mud flats.

Mud flats are the perfect environment

For willow trees to grow.

So, it's kind of this weird process

Where even though the beavers are eating willows,

They're creating habitat for more willows.

Galante: The very same food that the beavers need to eat

And use as building materials.

It's a perfect cycle.

♪

Narrator: The beavers have actually increased

The amount of food available for the elk.

So why did the elk leave?

Both the beavers and the elk are intrinsically connected,

Linked to the changes in the landscape

And also to a predator even higher up the food chain.

♪

The answer to this has to do with an experiment

That was run in the 1990s,

Where biologists brought an animal back to yellowstone

That had previously been killed out.

[ howling ]

♪

Narrator: In yellowstone national park,

The entire landscape, rivers,

And trees have been transforming,

And it's down to a very unlikely culprit.

To understand what happened, we need to rewind by a century.

♪

[ howling ] smith: Wolves were begun

To be eradicated in 1872, when the park was established,

And the last wolf was killed in 1926.

Riskin: People tend to hate wolves.

They've always had a bad rap,

And this ultimately spelled the demise

For the whole species in yellowstone, originally.

They're a carnivore, so that means they kill for a living,

But most everything kills for a living in some way or another.

So singling the wolves out as the demon

Has been unfair through time.

♪

Narrator: No wolves in yellowstone

Meant an elk explosion.

♪

Their numbers shot up to over 19,000 individuals.

All those hungry mouths overgrazed the land

And stopped the trees from growing.

That meant no berries for the bears

And no habitat for the birds.

The ecosystem became sick and animals

Moved out of yellowstone.

In 1995 is when everything started to change.

Officials decided to reintroduce wolves

Into yellowstone national park.

[ howls ]

Bringing the wolves back to yellowstone

Was as an emotional moment as you'll get.

I mean, when they came through the arch,

Which is the entrance to yellowstone,

It was almost like crossing the threshold.

Narrator: Back in their natural habitat,

The wolves settled in and bred.

The results were dramatic.

♪

Smith: We reintroduced a total of 41 wolves,

And now we have about 100 wolves in 10 packs.

Wolves change everything because they're apex predators.

They're the keystone species in this whole thing.

Narrator: First in the wolves' sights were the elk.

So, you put wolves in -- wolves like elk an awful lot,

Elk don't like wolves very much.

Nelson: Elk love willows, so most of their time

Was spent down in the lowland areas where these willows lived.

Baker: Wolves go to where the elk are hanging out,

And immediately, without even catching an elk,

The elk have moved.

They stirred them up.

So now, all of a sudden, the elk are in smaller groups.

They're hiding in the woods.

That means that all these plants are growing up

That couldn't grow before.

♪

Narrator: More willows meant beavers could return.

More fish, more things that eat fish.

Birds are back because they've got somewhere to breed.

The bears have got berries to feed on.

They never would have predicted the positive outcomes

Of just putting these apex predators

Back where they belonged.

Narrator: The wolves that were once seen as the demons

Have rebalanced the entire ecosystem.

♪

♪

August 2013 --

Assumption parish, louisiana.

On a normally placid lake,

The water begins to move towards the center.

The trees begin to sink faster and faster,

Until all 50 feet of them are completely swallowed.

♪

What is going on?

♪

♪

Narrator: In assumption parish, louisiana,

50-foot trees are swallowed

Into the belly of apparently placid water.

So how is it possible that this area in louisiana

Has trees that within seconds

Just completely sucked under water

Into this lake.

Narrator: This area is marshy swampland.

The water is way too shallow to absorb these trees.

So what's happening beneath the surface

That could consume them from the roots up?

The first thing that comes to mind

Is probably some sort of sinkhole opening up...

...And swallowing these trees.

♪

♪

So all across the u.S.,

There are these things called sinkholes...

...Where all of a sudden, the ground just falls down,

Revealing a cave that nobody knew was there,

And this could be what's happening in louisiana.

These cavities in the rock can be massive.

I mean, we're talking about hundreds of meters across,

Hundreds of meters deep.

Sinkholes form in various ways,

One of which is that you have a source of water

Running underneath the ground

And it's eroding the soil, the bedrock,

Leaving an open space, leaving a vacuum.

Nelson: The cavity forms underground,

And then the roof gets destabilized

And the roof of the cavity collapses, causing a sinkhole.

Narrator: Generally, it's limestone

Or other carbonate rocks that give way to sinkholes,

But there's something about this area that doesn't add up.

The problem with the idea of a sinkhole

Is that this area doesn't have limestone.

The bedrock is not limestone.

We're in a bayou in louisiana.

So this is something else

That's causing those trees to go down.

Narrator: This area might not be known for limestone,

But it is known for a different mineral,

One that you wouldn't expect to be hiding under

Miles of swampy, wet mississippi bayou.

Salt.

♪

And that could be the key to the disappearing trees.

♪

150 million years ago,

Huge natural salt deposits formed in this area

When an ancient salty ocean evaporated,

And we've been extracting that salt for over 150 years.

The way you mine for salt is to find a deposit

Where there is really salty soil,

You spray it with water, turning it into this briny liquid,

And then you suck it up a straw.

When you do that, you leave a cave behind.

♪

Unfortunately, this cave got big enough

That it couldn't support the land above it,

And what the video's showing is the land collapsing down

Into this empty salt mine.

♪

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

Captions paid for by discovery communications