All language subtitles for Natures.Strangest.Mysteries.Solved.Series.1.Part.21.Bug.Mathematician.720p.HDTV.x264.AAC.MVGroup.org.eng

Narrator:
How do a million high-speed bats
avoid crashing into each other?

It's an absolute wonder
to behold.

Narrator: What did this dolphin
want with this diver?

I was blown away that it
just swam right up to me.

Narrator: And how is one bug
a secret mathematician?

It's always some weird number.

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 investigates
the weirdest animal behavior...

That's amazing.

...And the most
unexpected events...

What is causing that?

...Ever caught on camera.

My god!

These are...

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

Captions paid for by
discovery communications

In downtown austin, texas,

Crowds gather to watch
a breathtaking nightly display.

This is one of the greatest
natural phenomena

You can see
anywhere on the planet.

The mexican free-tail bats
come out from under the bridge

In austin, texas,

And fly out
in these massive clouds

To go eat insects
across the countryside.

Narrator: Many bat colonies
number in the thousands,

But crammed under
congress avenue bridge

Are over 1.5 million.

This is the biggest
urban bat colony in the world.

Narrator:
That means in summer, bats
outnumber people in this city.

They're almost like
a plume of smoke.

It's an absolute wonder
to behold.

What's amazing
about this spectacle

Is these millions of bats
emerge,

Yet there's no congestion.

They don't even seem to collide
with one another.

Narrator: So, how do they manage
to fly out at the same time

Without flying into each other?

So, one possible explanation

Is that
they're using their echolocation

To see where everyone is
and avoid bumping into them.

Cooke: Well, we've all heard
of echolocation.

It's the incredible system

Whereby bats can navigate
in the dark.

They send out high-frequency
sounds,

And then they listen
for their reflection back.

Narrator:
Is it possible the texas bridge
bats are using echolocation

To minimize the number
of deadly mid-air collisions?

It's really hard to imagine,
with that many bats,

Millions of bats,
all whirling around,

That they simply
have this perfect system

Where the echolocation means
they avoid one another.

You're shouting
and listening to your echoes,

But everybody around you is also
shouting as loud as they can.

So, how do you tell your echo
from that bat's or that bat's

Or the one coming right at you?

So, something else
is going on here.

Narrator: If echolocation is not
the answer, what is?

Is there a clue in the way that
british daubentons bats fly?

Scientists in the u.K.

Discovered that bats will choose
a wing man, a leader to follow.

Narrator: Thermal imaging
cameras revealed that these bats

Tend to forage in pairs

And seem to obey a simple
set of traffic rules.

It goes left, you go left.

If it goes right, you go right.

And as long as everybody
cooperates,

That should keep everyone safe.

Narrator:
Could the bats in texas
also be playing a giant game

Of follow the leader to
avoid catastrophic collisions?

The problem with that theory,
though,

Is that these bats are all
changing position all the time,

And it's really not clear that

There's any particular leader
in these clouds.

Narrator: So, how do they
fly out from under this bridge

In their millions
without getting injured?

Burke: Bat biologists are
so intrigued by this behavior

That they film bats
with ultra high-speed cameras

That slow the action right down.

♪

Narrator: When scientists
analyzed the footage,

They were amazed to discover

That, actually, thousands
of collisions do occur,

Many more than expected.

Yet incredibly, the bats
carry on flying

Without missing a wing beat.

So it seems bats really do
go bump in the night.

The question now is
how are they able to recover

From mid-air collisions
so quickly?

Could the answer lie in the
unique structure of their wings?

Boerma: They're mammals
just like we are,

And so their anatomy
is really similar to ours, too.

And so their wings are made
from an arm and a hand.

I can look at my arm
and my hand,

And I can see the same joints
in my body

That a bat has in their wings.

Not only that, but they actually
have muscles

Embedded
within the wing membrane

That can control
the stiffness of the wing.

That affects the aerodynamics.

Narrator: A bat's flexible wings
can change shape during flight

To a much greater extent
than those of insects or birds.

And this may give them
superior aerial agility.

The beauty of bat wings is that
they can handle a bump.

They can deform.

They're made out of a flexible
membrane,

So it's not like when
two airplanes hit each other,

And they both crash
to the ground.

If bats smack wings a little,
they're okay.

Narrator: And that's why it's
not raining bats every night

In austin, texas.

♪

January 2013.

Kona, hawaii.

Dive instructor keller laros

Is leading a busy nighttime
scuba dive at garden eel cove.

There are 50 snorkelers
and divers in the water

At this manta ray hotspot.

Many have underwater cameras

To film the wildlife
they encounter.

We're sitting, and we're
watching the manta rays

As they swoop back and forth

And feed on the plankton
attracted to our light.

All of a sudden,
I heard a really loud,

Piercing sonic burst.

[ animal squeaking ]

It sounded like a dolphin,
and as I turned,

A bottlenose dolphin
was right behind me.

[ dolphin squeaking ]

It was all alone.

Normally, they travel in pairs
or threes or sixes.

Narrator: A bottlenose dolphin
is a rare sight

At this shallow dive location.

At night, they usually head out
to deeper waters to hunt.

But then, as keller watches
the unexpected guest,

He spots something ominous.

I notice that there's a fishing
line hanging out of his mouth

And was wrapped around
his pectoral fin.

It was obviously in distress,
and I sensed the urgency.

I'd seen fishing lines seriously
cut and injure manta rays

And see them actually
lose fins from fishing line.

And it's that important
that you get it off.

Narrator:
Using his dive knife, he starts
to cut away the fishing line.

Dolphins are known
for playing with humans,

But this animal could be
in a lot of pain,

And most injured wild animals
will avoid human contact.

So, what is this dolphin doing?

Is it possible that the dolphin
panicked after it approached

Keller,
and now it's scared stiff?

When an animal is caught
and handled by a human

And then an animal
is unable to get away.

Sort of almost goes into a --
almost like a trance-like state.

Sort of safety shutdown,
I guess.

Essentially, the stress hormones
pumping through their body

Are so overwhelming that,
instead of trying to fight back,

They just freeze,
and they go motionless.

Narrator: But keller's
dolphin encounter is different.

The dolphin actually chooses
to approach the diver.

It's not being
approached itself.

Laros: I looked up, and I said,

"oh, you've got
a fishing line, come here."

And I literally gestured
like that.

And then dolphin just swam
straight up to me.

You know, when you say
to your dog,

"come here,"
you expect the dog to come.

But when I said, "come here"
to the dolphin,

I was blown away that
it just swam right up to me.

That animal is completely

And utterly happy
in the presence of keller.

Narrator:
As he works on the dolphin's
fin, it stays close by,

But then, without warning,

And before the fishing line
is removed, it leaves.

If the dolphin really has
approached keller for help,

Why would it swim away
mid-rescue?

Narrator: In kona, hawaii, a
dolphin tangled in fishing line

Approaches diver
keller laros for help.

Mid-rescue, it suddenly leaves
and swims to the surface,

But why?

This dolphin clearly needed to
surface for air, which it did.

But as soon as it had
enough air,

It went straight back down.

Narrator:
It picks keller out again
from the group of 50 divers

And swims right up to him.

Yeah, there I am in a wetsuit
at night, you know, with a mask,

And the dolphin came back
and found me again.

Narrator:
But how did it single keller out
from such a large group?

Could it be that the dolphin
actually recognized him?

Well, there are many examples
of dive sites

And even boat safaris where
the same individual dolphins

Will appear in response
to a boat

Or a diver
being present in the water.

It's possible
that this what was going on,

That this dolphin
actually knew the diver.

Narrator: But did the diver
know the dolphin?

Well, it turns out that keller

Is more of a manta ray
specialist.

I can tell manta rays apart
by the spots on their abdomen.

It's like a fingerprint.

But dolphins?

They all pretty much look
alike to me.

Narrator:
As far as he was concerned,

This was just any old dolphin
that came by to say hi.

That is, until he got back home
and reviewed the footage

When he realized
something astonishing.

Narrator: On a routine
night dive off kona, hawaii,

Scuba instructor keller laros
encounters a dolphin

In need of his help.

It approaches, and keller works
to cut away

A tangled fishing line.

But why did the dolphin
single out keller in particular?

I noticed that it had
a white scar,

Kind of a rectangular-shaped
scar behind its left eye.

And I realized, that makes
this dolphin look different

Than all the rest.

The previous summer,
keller had taken his son

On a snorkeling trip
with school friends,

And they'd taken
some underwater photos.

So, when my son's senior
yearbook came out,

We were looking at the pictures.

And one of the pictures
he'd used was him

Snorkeling with this dolphin.

It was the same dolphin.

White scar behind its eye.

So, I'd actually met this
dolphin the previous summer.

Narrator: Whether it not
it remembered him,

The dolphin certainly
does seem to have known

That keller could help it out.

Laros: I think the first sign
of trouble

Was that the dolphin
squeaked really, really loud.

Very sharp, focused sonar blast.

[ dolphin squeaks ]

It was almost like a call
for help.

It came up and sort of leaned
into me.

It was so intent and so focused

On getting this
fishing line removed.

So, it was no accident.

This dolphin was clearly
trying to make sure

That the diver understood
what needed to be done.

Baker: Somewhere along the line,
that dolphin has worked out

That keller is the solution
to its problem.

That's the incredible thing.

Narrator:
But how did it figure out
that humans were the answer?

Or that keller and the other
divers were safe to approach?

It seems to me
what's happening here

Is some form of habituation.

Oh, my god.

Narrator:
Habituation is when wild animals
repeatedly interact with humans

And learn not to
be fearful of them.

It's not always a good thing.

It can put them at risk,
but in this unique case,

It may have saved
the dolphin's life.

Laros: I think that dolphin came
to find humans

Because it knew that humans
would be in a position

Where we could help it,

And I was just lucky enough that
I recognized the dolphin's need.

As I cut the line off, I really
think the dolphin felt relief,

And it took off.

We see that dolphin to this day,
and it's doing well.

Narrator: This distressed
dolphin knew it was in trouble

And sought out humans
for help.

Fortunately, keller was on hand
to make sure

This mystery
had a happy ending.

♪

June 2013, east coast, america.

In nine different states,
from new jersey to virginia,

Millions of cicadas emerge
all at the same time.

Nelson: Imagine one acre.

That's maybe a large plot
of land for a house.

We're talking about 1.5 million
cicadas an acre.

Narrator: These cicadas were
laid and hatched 17 years ago.

They've been biding their time,

Developing underground
ever since.

They're known as
periodical cicadas,

And for a very good reason.

Riskin: The mystery around them

Is why they only come out
every 13 or 17 years.

Not every 10, not every 5.

It's always some weird number.

Narrator:
What's the reason for their
strangely timed appearance?

Is there a clue in the actions
of other swarming insects?

So, one possibility is that
the cicadas

Are just moving around
in search of food.

Nelson: Desert locusts,
from the biblical plague,

They form these huge
populations of individuals

Which can destroy crops.

These come up in their billions,

And when they do,
they form these vast clouds.

Narrator: Hungry locusts
must travel up to a mile a day

To find enough food
to support the swarm.

But adult cicadas barely feed,
drinking only a little tree sap,

Causing minimal damage
to plants.

Burke: They emerge en masse,

But they seem to stay
put and die in one place.

So, something else is going on.

Narrator:
If they're not looking for food,

Why else might these cicadas
have suddenly turned up?

Riskin: Another possibility
is that they're all coming out

At the same time
for safety in numbers.

They don't want to be eaten,
so if there's zillions of them,

The predators
will be overwhelmed,

And so individual cicadas
are more likely to survive.

The theory is you're simply
flooding the market.

♪

So, if there is more animals
in the market,

Then the native
predators can tackle --

You simply cannot eat
all those animals in one go.

Then some, by definition,
get away and succeed.

Narrator: If this mass emergence
is all about safety,

Wouldn't a less risky strategy
be to just stay put underground?

There's another reason why
animals might emerge en masse,

And that's to mate.

Narrator:
So, is this huge gathering a
periodical cicada mating frenzy?

So, over a period of just
a couple weeks,

All these adult cicadas
push up through the soil.

They've been
waiting for the cue,

And they all come out
of the soil together.

These are mating machines.

They don't really feed
as adults.

It's all about sex.

♪

Narrator:
Cicadas come out en masse
to maximize their chances.

Like speed dating.

The more potential partners
there are,

The likely they are to be
lucky in love.

Nelson: So maybe that's what
we're seeing here.

A timed event

Where they're all coming
out of the ground to mate.

Riskin: The problem
with that theory, though,

Is that it doesn't explain
why they would only come out

In such weird numbers of years.

Nelson: And I think the solution
to this is found

When you actually look
at those numbers.

13 and 17
are very unique numbers.

They're prime numbers.

What that means is the only
thing that divides into them

Is itself and one.

Riskin:
And you would think that that is

Just something you learn
in math class,

And it has no bearing
at all on the natural world.

But it turns out
that prime numbers

Are very important for cicadas.

Narrator:
Across the eastern usa,

Periodical cicadas emerge
every 13 or 17 years.

They all come out
at the same time

So they can mate en masse,
but why the strange timings?

It turns out their long,
prime number population cycles

Help the cicadas to avoid
as many predators as possible.

Think of it from
a predator's perspective.

They also have
population cycles,

With their numbers
rising and falling,

Depending on how much food
there is to go round.

If their boom in population
matched that of the cicadas,

They could almost wipe them out.

Imagine a predator with a two-
or three-year life cycle.

If the cicadas came out, say,
every 6 or 12 years,

The peak in predator numbers
would coincide

With the cicadas every time.

But 13 and 17?

Nothing divides into that.

If you have a predator that
comes out every other year,

It's never going to match
the cycle of the cicadas.

Narrator: There are no
predator life cycles

That synch up with
the prime number boom years

Of the periodical cicada.

As a strategy for the cicada,
it works really, really well

'cause it is near impossible
to time your own life cycle,

If you're a predator,
to hit those mass emergences.

It's an amazing strategy.

It's a bizarre strategy,
and I believe a unique one.

But the question is
how do they know

When 13 years or up
or 17 years are up?

How do they know when to emerge?

Narrator: Are cicadas secret
mathematicians?

Potentially, because somehow,

They're tracking
the passage of time.

Nelson: Well, what we think
happens is that the cicadas

Are actually keeping
track of the sugar

Flowing through the tree.

The sugar only flows
through the tree

When the leaves are out.

Narrator:
Track the sugars, and the
cicadas can track the seasons.

Now, as every spring goes by,

They can taste when the sugars
spike as the trees go into leaf,

And it's this way
that they're able to monitor

Each passing year,
each passing spring.

Narrator:
The cycles of tree sap probably
affect how cicadas develop.

In readiness to emerge en masse
every 13 or 17 years.

♪