Original subtitles

Narrator: Ever wondered which animals get the giggles?

[ laughter ]

People have probably been tickling rats

For hundreds of years and not known that

The rats were laughing.

Narrator: What would cause the sea lions of san francisco

To mysteriously swim away all at once?

It's rather shocking.

And I need to ask myself why.

Why would they do that?

Narrator: And what's made three manta rays

Synchronize their swimming?

An awful lot of what they do is still a bit of a mystery.

Which makes them even more magical to me.

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...

Berlin, germany.

November 2016.

Scientists researching brain development

Are conducting a study,

Tickling rats.

And the craziest thing,

Is that when rats are tickled,

They laugh!

[ high-pitched squeaking ]

That is just loopy.

But it's definitely making some giggling noises.

[ high-pitched squeaking ]

They laugh really really high pitched,

So you have to be listening with a special detector

That hears in the ultrasound, to hear the giggles.

[ high-pitched squeaking ]

Narrator: Yep, there it is.

The actual sound of a rat laughing.

So when tickled, the rats do laugh.

And they love it.

And we know they love it because they actively go

For the hand to be tickled again.

And it even goes further than that.

There's a button that they can press,

That if they suddenly want to be tickled,

They can push with their nose

To let the scientists know,

"I would love a tickle right now, please."

Narrator: Which begs the question...

Why are some animals ticklish, and other animals not ticklish?

♪

Narrator: To find out, we visited humboldt university

In berlin,

Where the phenomenon of rat giggling

Is being investigated.

We don't have a very systematic understanding of

Which animals are ticklish.

It's clear that pretty much

All primates tested are ticklish.

With other mammals, it's not so clear.

One of the challenges here is to define what a laugh is, right?

How do you know this is what an animal's laugh sounds like?

[ laughing ]

If you look at primates, they're making sounds that, you know...

[ mimics chimpanzee laughing ]

[ laughing ]

Not exactly human, but close enough

That it sounds like a laugh.

Narrator: And the rat giggling

Has the same signature rhythmic, repetitive sound.

[ high-pitched squeaking ]

Which, along with the playful behavior,

Tells us they really are laughing.

So how is it that some animals are ticklish?

Could it be that they are just more sensitive to touch?

One possibility is that if you touch an animal,

And it feels all that stimulation,

It's gonna laugh.

[ laughing ]

We all know that from tickling kids, the reaction

Is pretty much involuntary.

Even when kids beg you to stop,

If you keep tickling them, they're gonna keep laughing.

[ laughing ]

Perhaps this is just an involuntary reaction

To being touched.

[ laughing ]

Narrator: This meerkat is another animal

Prone to a chuckle when tickled.

[ laughing ]

♪

But michael has discovered

That when it comes to rats,

They will only laugh under certain conditions.

Brecht: The rat needs time to learn to be tickled.

So they need to accustom to the experimenter.

So fearful animals are very non-ticklish.

So for rats, it's not just about touch.

They need to be comfortable to laugh.

♪

So what do primates and rats share

That might give them the giggles?

Is it just basic intelligence?

Rats are renowned for being

Extremely smart animals who excel at learning.

These rats have even figured out how to play basketball.

Could it be that intelligent animal's brains

Are just hardwired to laugh when tickled?

While some animals might have a sense of humor,

If you're an orangutan,

A magic trick can be a real hoot.

This primate fell for the oldest gag in the book.

The disappearing act.

[ laughter ]

Galante: This amazing footage shows animals laughing by choice.

Something that they are seeing is disrupting their reality.

For them to be able to process what's going on,

And realize that it's something out of the ordinary,

And convert that into laughter,

Means you have a very smart primate.

But rats, while being intelligent,

Might not be smart enough to get a joke

Like our primate friends.

So why are they laughing,

Even when they're not being tickled?

I think the key to understand where this

Laughter stuff comes from,

Is that you only see this laughing and this tickling,

In social species.

So laughter might be really about communication.

♪

There's further evidence that laughter

Is all about social stuff.

For one thing, if you look at humans,

We are 30 times more likely to laugh

If we're around other people.

Narrator: And scientists think laughing might be how animals

That live in groups encourage play and learning.

The most intelligent animals are social beings.

They're mammals with an immense mental ability.

All of the animals have an advanced social structure,

And playing is a big part of learning for them.

Michael's work tickling rats confirms this theory.

Brecht: We think ticklishness and the vocalizations,

Is something that makes it fun for animals

And humans to interact.

So it is something that encourages

The playful interaction.

It's really a trick

That gets animals or humans together.

Schreiber: So scientists think that the reason

The rats enjoy being tickled,

Is because it's helping them to learn to be more social.

Narrator: And why does this research matter?

Schreiber: We're taking this knowledge and applying it to humans.

We're showing that if you do play with a young child

More and more when they're younger,

It is gonna help their social interaction

When they're older.

And the burning question,

In case you ever wanna tickle a pet rat yourself --

Where's the sweet spot?

Rats are most ticklish on their bellies,

And on their backs.

Narrator: They're not quite rodents,

But will our experts share where they're most ticklish?

I'm not telling you were I'm ticklish.

I mean, if you tell somebody where you're ticklish,

That's like giving the plans to the death star.

You don't do that.

Where am I most ticklish?

Pretty much everywhere.

You just shouldn't try and tickle me,

I don't like it. [ laughs ]

♪

Narrator: August 2016.

Oahu, hawaii.

A drone operator spots some unusual behavior.

Manta rays are normally solitary.

So the question is, why are these three together?

And why does their swimming look synchronized?

Can't help but be mesmerized watching them swim

In a tighter and tighter circle.

This looks like fighter jets in formation.

Narrator: So why have these mantas met up?

And just what are they doing?

♪

♪

Narrator: August 2016.

Oahu, hawaii.

Manta rays usually swim solo,

But these three are together,

And their swimming looks synchronized.

Why?

Maybe these rays have joined ranks to talk to one another?

Across the animal kingdom,

A lot of animals have found very innovative ways

To communicate with other members of their species.

[ high-pitched barking ]

[ chirping ]

From vocal communication to reading facial expressions,

Different animals exhibit different behaviors

To communicate.

For example, peacock spiders.

The males will put on an elaborate dance to attract

Their female mates.

Narrator: And mobula rays,

A close relative of the manta ray,

Have an extraordinary way of communicating.

Mobula rays are known for jumping out of the water.

And this happens when they form very large aggregations,

With hundreds of other individuals.

It's generally accepted that the jumping behavior

By mobula rays has to do with communication.

Narrator: Their belly flop landings

Send sound waves through the water to others nearby.

Saying, I'm here!

And so it might follow that the circling behavior

By manta rays also has to do with communication.

Could these mantas be having a chat?

Galante: When you look at this clip,

And they way that the rays are swimming,

They can all see each other,

And there's no other rays in sight.

So I don't think they're trying to communicate.

Narrator: Maybe there are two males courting a female,

Hoping to win a chance to mate.

This idea of like, kind of mating chases

Or kiss chases in nature, is not a strange one.

Lots of animals do it.

Narrator: Could our three synchronized swimmers

Be in a similar courtship ritual?

Baker: The whole ritual of a chase

Is a way of deselecting your suitors.

So if you are a female and you're swimming away

From a group of males, by the end of the swim,

The fittest male is the one left.

And that's the one you want to mate with.

Squirrels are very good at it.

You'll see them haring through the trees

Like a furry tornado,

Shooting around the branches.

And that's basically the female, leading on males.

Narrator: Mantas spend most of their lives alone.

When they do meet up, it's usually for courtship.

Nosal: Mantas have sometimes been observed

Forming trains of up to 20 individuals,

Where males are following females

In order to mate with them.

Narrator: And they'll form lines to follow her.

Nosal: Whereas, the behavior we're seeing here,

Are mantas circling in a tight formation.

And there's no other mating behavior seen,

So it must be something else.

Galante: Circular swimming has been seen in one other piece

Of manta behavior, and that's feeding.

They're filter feeders,

Meaning they gape their mouths and filter water

Through their gills to pick up as much zooplankton as possible.

Narrator: Zooplankton are tiny animals such as krill

That drift along with water currents.

Nosal: In some locations where there is just a ton

Of food in the water, mantas will actually form

Foraging chains, where they'll follow behind each other.

And this a way of actually maximizing

The rate of food intake.

It's the most efficient way to feed.

By swimming in formation,

The mantas create a feeding vortex,

Which keeps their food bunched together.

So what looks like synchronized swimming

Is actually a kind of social foraging behavior.

The leader gets the biggest plankton prize.

But they'll switch places,

And each manta gets a turn up front,

And a share of the meal.

Similar synchronized circular behavior,

And that's a mouthful,

Has been observed like this before in the maldives.

What happens is an upwelling of currents

Push a ton of krill into a singular area.

And in that area,

Up to 200 mantas will gather,

And they begin to chain feed in groups of 50 or more,

And they do it in circles.

Nosal: So these three mantas, instead of swimming in a line,

They're swimming in a tight circle,

Because they've hit on a dense area of food.

And what they're doing is basically cooperating

To get the maximum rate of food intake.

Narrator: When food brings these solo swimmers together,

They're surprisingly social

And use synchronized teamwork

To score supper.

♪

San francisco, california.

Tourists flock to this coastal city each year.

When you think of san francisco, you think of alcatraz.

And for many people, they also think of pier 39.

♪

[ sea lions barking ]

Nosal: The sea lions of pier 39

Have become a must-see tourist attraction.

And they've been like that for decades.

You could watch these things for hours,

Playing and fighting and growling at each other

And pushing each other off the platforms.

Narrator: But then something strange happens.

Nosal: All of the sea lions just disappear

Seemingly overnight in June 2014.

It was really shocking.

Narrator: No one was more stunned than sheila chandor,

The harbor master at pier 39.

So all of the sudden there was sea lions here,

And then there weren't any.

Where were they? And why had they gone?

Nosal: It's one thing for a bunch of animals

To disappear slowly overtime.

But for them to all basically follow each other at once,

It's rather shocking.

And I need to ask myself why.

Why would they do that?

♪

♪

Narrator: June 2014.

San francisco, california.

The city's famous sea lions all mysteriously disappear

Overnight.

Wildlife biologist, forrest galante,

Sets out by boat to get closer to a group

Of california sea lions

To check out what might make them move en masse.

Galante: We might not have invented smellovision yet,

But as you pull up to see a sea lion rookery,

There is a very distinct, very pungent smell.

And if you ate nothing but fish your entire life,

I think your poop would smell pretty bad too.

[ groans ]

[ bell clangs ]

So these sea lions are doing what's called a haul-out,

Where they'll jump up on land and rest

To take a break from swimming.

But they're also in a safe space.

And the reason being, when they're in the water,

They are susceptible to predation.

Narrator: So maybe predators showed up,

And pier 39 stopped being a safe space

For the san francisco sea lions.

They're has actually been an incident where a sea lion

Was attacked and killed in front of some tourists

At alcatraz.

Narrator: In an incredible ambush attack,

The 3,000 pound shark explodes out of the water.

[ dramatic music ]

Sharks can jump 10 feet into the air.

And this one caught the sea lion completely off guard.

♪

But that attack happened more than a mile away

From pier 39,

In the deep waters off alcatraz.

Great white sharks do not come into the marina,

Or within the proximity of the marina,

Because they like deep water,

And they are afraid of the boats and the activity.

[ sea lions barking ]

Narrator: If the sea lions weren't evading predators,

Perhaps their seasonal summer break holds clues,

As there's something surprising

About the san francisco sea lions --

They're an all boys club.

Most of what you see here at pier 39,

The majority, are males.

The majority of the females

Stay down in the breeding grounds in the channel islands.

And every year, mature male sea lions

Must head off to hook up with them.

So did the sea lions swim away

To mate with their sweethearts?

Perhaps, as the mating season seems to match up

With when the sea lions checked out of pier 39

In June 2014.

The mating season is normally June and July.

Narrator: Every summer, these ocean athletes

Swim over 300 miles south from san francisco

To the channel islands.

Meaning the males leave pier 39

Every summer to pair up.

So the answer to our sea lions 2014 disappearance is mating.

Mystery solved.

[ sea lion barking ]

Well, almost.

What we're used to is even at the height

Of the breeding season when the majority have gone south,

There's always a few of the younger ones left

On the docks because they can't swim the distance.

This means some sea lions always stick around.

But something changed this time.

2014, the big difference for us was they were all gone.

♪

That had never happened,

And actually has never happened since.

Narrator: What occurred in June 2014

For all the sea lions to vanish at the same time?

♪

♪

Narrator: June 2014.

San francisco, california.

The city's famous sea lions are missing.

There are usually some sea lions at pier 39,

Even during the mating season.

So why'd they all vanish at once?

Like most animals,

One of the sea lions' biggest priorities is food.

Could food be behind their disappearance?

California sea lions feed on salmon, krill, anchovy,

Just about any fish that's out there in the bay.

Narrator: They need to eat

At least 15 pounds of fish every day.

If they need this much food,

What happens when lunch runs out?

Certainly, food availability is gonna drive animal movement.

If there's no food somewhere,

The animals are gonna move to where there is food.

Narrator: And a strange weather event in 2014

Could hold clues.

We experienced what's called an el niño,

When the water temperature changes.

And it gets warmer.

And what that does is it effects what's available

For the california sea lion to eat in the bay.

So el niño caused a food shortage.

Limited food came at a bad time,

Since it was during the sea lions' mating season.

Chandor: So, in 2014,

Because clearly there was not enough food in the bay area,

They had to go further afield

In order to get ready to go on that long journey down south

To the channel islands to breed.

Narrator: As a result, the sea lions followed the food.

Remember, they'll eat 15 pounds of fish a day.

But in the run up to mating,

Males can add on an extra 300 pounds of body weight.

Meaning these titans can weigh in at half a ton.

♪

This extra fat, called blubber,

Gives them the energy they need to defend their territories,

Known as rookeries, in the pinniped world.

The male needs to stay in his rookery as long as possible

To ensure that he gets more females.

So the bigger the male, the more blubber,

The longer he can stay.

If he gets hungry and has to leave to go find food,

Another male could take his spot.

So, they have to fast for up to 27 days

During the mating season.

Narrator: So, males must pile on the pounds before breeding

To win over the ladies.

This makes food the key to our story.

A food shortage in the bay, triggered by el niño,

Coincided with the mating season.

That's why every single sea lion vanished in 2014.

Nosal: Any year you visit pier 39,

Especially during the months of June and July,

You won't see a ton of these male sea lions,

Because some of these have already left

To go and find their mating grounds.

But in June of 2014, because of the shortage of food,

Almost all of them had left to go find food elsewhere.

♪

Narrator: But as soon as the fish returned and the breeding season ended,

The sea lions came home.

Much to the relief of the san franciscans.

And fortunately for us, as you can see,

They came back.

And we're very happy about that.

[ laughs ]

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

Captions paid for by discovery communications