Mexico 2 Deadly 60

My name's Steve Backshall.

Whoo!

And this is my search for the Deadly 60.

That's not just animals that are deadly to me,

but animals that are deadly in their own world.

My crew and I are travelling the planet.

And you're coming with me.

Every step of the way.

'Deadly!'

This time, the crew and I are back in Mexico.

Situated between the southern United States and South America.

It's a destination that's been good to us in the past,

but this time, we're hoping to go even deeper,

to prove to you there are deadly demons, even in this paradise.

We're going to be diving to the depths of the ocean in search

of an encounter with a versatile master shark.

And setting up to witness an astonishing gathering of predators.

But first, we're heading to a freshwater lagoon

to look for a particularly Mexican reptile.

It's the Morelet's crocodile,

one of the most beautiful, yet most threatened of all crocodiles.

We're joining a group of scientists who are studying these rare beasts,

and we're hoping to help them catch one.

They're most active after dark - the best time to go looking for them.

While crocodiles can be incredibly tricky to find during the day,

at night, we have one thing that's very much on our side - eyeshine.

That's what Marco's looking for now.

There's a reflective layer of cells at the back of the eye

and when a torch is shone at them,

they reflect back in a glowing, red-hot blaze.

It really gives away the position of the crocodile.

Both Marco and I take turns with the spotlight.

Once you spot them, they can be hard to keep track of.

There it is again. Just there, look.

There. Behind us.

Can you hold this?

Aye!

Just got very soggy and very smelly...

..and failed to catch it.

Oh!

OK.

YELPING

Well, it's not quite what we were hoping for,

but it is our first Morelet's crocodile.

And as soon as it was caught...

..it let rip with what I think

is one of the cutest sounds in the animal kingdom.

Listen to this.

YELPING

That is the juvenile alarm call,

which is common to all crocodiles,

and is usually used to try and attract the attention of the mother.

Um...we have seen, in this area here,

a crocodile that is large enough to be a mature female

and could well be Mum to this one,

so I should probably get back in the boat. Step back a sec, Johnny.

Isn't that beautiful?

Very cute.

But much, much too small for our needs.

So, after getting into some dry clothes,

we continued our mission for a slightly bigger croc.

There we go.

Marco's given the signal that he's spotted something.

It appears it's dived.

It's a good-sized animal.

Probably at least a metre-and-a-half long.

But it moved off at quite a pace in that direction.

Crocodiles are capable of staying underwater for long amounts of time

when they're waiting in ambush for prey. Several hours is not unusual.

They slow their heartbeat right down, they don't use oxygen.

But when they're swimming fast, they're using up a lot of oxygen,

-so they can't stay down for very long.

-We've got him.

This croc hasn't been to the surface for a couple of minutes now

and it's been swimming almost that entire time,

so it will be up to breathe very soon.

After a good ten minutes...

of chasing and evading us extraordinarily well,

we've managed to catch our Morelet's crocodile.

We need to make sure the crocodile's jaws are secured

while the scientists gather data

essential for the protection of this wonder.

I know this probably all seems quite harsh on the animal,

but crocodiles have these scales here behind their head,

they're called scoots, and they're unbelievably strong.

They're like armour plating and protect the crocodile,

so this won't have done it any harm.

I've handled a lot of crocodiles around the world,

but I've never seen one that has

this incredibly silky, almost velvety skin.

It is simply glorious.

It has so many of the attributes

that you'd expect from a crocodile of this kind of size.

It has this broad, paddle-shaped tail with thick muscles at the back.

But it's not just the tail that does the work.

The rear feet are also slightly webbed.

Although generally, when it's swimming,

these will fold back along the side of the body,

making it streamlined in the water, it can use these

to power and propel itself.

It will actually run, literally run along the bottom,

which gives it another means of locomotion.

It can make the most of any opportunity that comes its way,

and that could be anything from fish, from invertebrates,

up to birds and even mammals that come down alongside the shore.

It will get a hold of them in much the same way it's been evading us -

by staying underwater, by staying camouflaged

and at the last minute, attacking with enormous bursts of pace.

I could literally talk about this animal all night long,

but the guys have got some science to do.

It's really important to keep tabs on how the crocodiles are doing.

I'll let them do their work

then return this magnificent animal to the water.

This work is helping to save an animal

that would otherwise probably have gone extinct.

A nearby reptile rescue centre

is also battling to save Morelet's crocs.

Behind me is an enclosure filled with rescued Morelet's crocodiles.

Most of these have turned up in someone's backyard or swimming pool

and been brought here so that they'll be safe.

This...is a pressure gauge.

The way this works is that we have a kind of jelly inside here

which is under pressure,

and when this is squeezed, or in this case bitten,

the exact force is going to come up on this gauge here.

And it'll tell us how powerful the bite is of the animal.

Crocodiles are known for having the most powerful bites of any animal.

Even though the Morelet's is not a massive crocodile,

I'm expecting something impressive.

So what we need to do now

is to get one of these crocodiles into a corner

so that it can't make its way into the water.

OK. We've decided on this one here

that we're going to try and get into that corner.

I need to block his escape route.

Whoo!

-Well, that didn't work very well!

-HE LAUGHS

These animals really aren't naturally aggressive towards people.

In fact, their first instinct is to try and get away.

That doesn't mean we shouldn't have a healthy respect for them

and be very careful where we're putting our feet.

Watch this one.

Ooo!

That was just a little snap and that raised about 500lb.

That was pretty impressive. That was 600lb per square inch.

And that is not a bite

that's actually being used to tear apart prey.

That's purely a show of teeth to try and scare us off. It shows...

the formidable power

in the muscles that drive that jaw.

You can see they do move very quickly over short distances.

And in the swampy habitats that this animal lives in,

this is really, really important.

Whoa! OK.

Well...he's punctured my bite gauge.

HE LAUGHS

That is remarkable.

A fantastic bite...from a two-and-a-half metre long croc.

And that's 800lb per square inch.

Very, very impressive.

The marvellous Mexican Morelet's crocodile.

They're pretty snappy, but they're certainly not a man-eater.

They are, though, an absolute wonder of the swamps.

And for that reason, I reckon they have to go on the Deadly 60.

Dynamic jaw muscles create a formidable bite force.

With tough, protective scales that act like armour plating,

these stealthy, camouflaged crocodiles

ambush their unsuspecting prey.

This Mexican marvel is going on my list.

'Deadly.'

It's all been a bit tough so far,

so I'm breaking out the sunscreen and heading to the beach.

This part of Mexico's east coast

has some of the biggest tourist destinations,

biggest resorts in the whole world.

Every day, thousands of people use these seas,

but if you head out for five minutes,

there is an unbelievable concentration

of one of the most feared animals on Earth.

This is a creature that has a reputation

for being a ruthless man-eater.

So, as appealing as the sand and the sea is right here,

it's going to be much more exciting out there.

It's a shark that just looks like trouble.

The bull shark. They're stocky, pugnacious predators.

Named for their bullish appearance, attitude

and habit of head-butting anything in their path.

Bull sharks have the worst reputation of all sharks.

And are probably more feared than tiger sharks, and even great whites.

They are man-eaters, mostly because they're tremendously adaptable.

They can swim thousands of miles up freshwater rivers

and often hunt in murky waters where humans can be mistaken for prey.

In tropical and subtropical waters like these,

the bull shark absolutely rules.

As an adult, it has no natural predators whatsoever.

We're heading down into the kingdom of the bull shark.

This is a place where humans like us

seem impossibly cumbersome and fragile.

So there really are very few more exciting wildlife encounters

than the one we're about to experience. I hope.

Everything now is down to what the bull shark wants,

so we're just going to keep our eyes open, watch each other's backs

and just hope that they're interested in us.

-OK, guys, let's do it.

-OK.

-OK.

Bull sharks can be dangerous,

so Simon the cameraman and I will have another diver

keeping an eye on us, just in case.

But the danger sharks pose to people is massively sensationalised.

In clear waters, where the sharks can see exactly what we are,

they're highly unlikely to attack.

That doesn't mean my heart isn't racing as we descend.

I know sharks are out there and their senses are so keen,

they'll have perceived us the second we hit the water.

These intriguing fish

are called remoras, or sucker fish.

You can probably see the strange shapes on top of its head.

They're sucker cups, used to attach it to a larger fish

so they can live off the scraps that things like sharks leave behind.

So if you see one of these, there's going to be a shark around.

And our first bull shark is coming towards us right now.

Look at this!

Right, we've got two.

And that one there has an enormous amount of fusiliers.

They're using the sandpaper-like skin of the shark

to rub their own bodies on...

..to remove parasites from their skin.

The bull shark has all of the senses you'd expect from a shark.

They have the ability to pick up electrical signals

from the moving muscles of their prey and, also, to sense vibration.

They can glide along with just a lazy movement of their tail.

But don't be fooled by that.

They can put on explosive bursts of pace when they're hunting.

Bull sharks are real opportunists, eating a massive array of food.

Most of the time, that's fish, but they will feed

on other sharks, mammals, birds at the surface and even turtles.

Just heading along the bottom towards us is a loggerhead turtle.

Look at the size of its head.

Right now, I have to say, I wouldn't want to be this turtle.

Surrounded by animals that could well want to try and eat you.

It's a very, very beautiful creature.

They do need to breathe air,

so it will have to return to the surface at some point.

At which point, it's going to become very, very vulnerable.

Isn't it wonderful!

As the sun sets above us, the sharks' body language changes.

Their movements are less languid and lazy, more mean and menacing.

There must be 10 or 15 of them around us at the moment,

all circling us with real intent.

Look at these three!

Such dramatic animals.

Whoa!

There's no doubt, approaching dusk,

these animals have a totally different attitude about them.

It's clear that now they're ready... to start hunting.

The current's really quite strong.

We're having to hang onto the bottom to avoid being dragged away.

Just another thing you really don't want to be thinking about

when you're surrounded by this lot.

There's something about them now that's truly chilling.

Their noses down, they seem twitchy, poised, ready to explode.

I'm not so worried about the sharks I can see,

it's the ones that I can't.

This is genuinely one of those moments

when you wish you had eyes in the back of your head.

I keep catching something in the edge of my view

and it's a shark and they're coming right in behind you. Like that.

Wow! They are some of the most menacing of all sharks.

It feels like it might be time to head for the surface.

It is kind of incredible that we can be swimming in these seas,

surrounded by bull sharks, and just a few minutes in that direction,

there are tourists splashing around happily on the beaches.

Just goes to show these animals are actually really acutely aware

of everything in their environment. They know we're not food.

Otherwise, you wouldn't stand a chance down here.

Bull sharks move deceptively carefully and slowly,

but they can put on a real burst of pace if they have to.

They're very adaptable. They can hunt here in these coastal waters

or they can move right up inland on freshwater rivers.

This is an unbelievable predator.

An animal that surely has to go on the Deadly 60.

Bull sharks, Deadly!

With the ability to swim in both salt and fresh water,

they can pick up electrical signals and vibrations from their prey

and they're none too fussy about what they eat.

These masters of adapting are remarkable on the inside and out.

'Deadly!'

For our last contender, we're doing something different.

We're not looking for an animal, but a phenomenon.

We'll look at one of the greatest gatherings of predators on Earth.

Oh! Whoa!

Do you know what, I smelt it before I saw it.

Just getting to the edge...

you just get hit by a whiff of ammonia

and centuries-old bat droppings.

Below us is a mighty cavern, a sinkhole.

What will have happened here is a big cave,

the roof will have collapsed in

and now it's just a hole going directly down,

straight into the Earth.

And down there are hundreds of thousands, millions of bats.

And those millions of mouths need feeding.

Soon, they'll explode from the cave

in a gargantuan swarm too vast to appreciate.

In order to see what the swarm's made up of,

we're working with some scientists studying the bats.

They're erecting nets to catch the bats without harming them

so we'll be able to see their attributes up close.

Local people call this the bat volcano.

And the volcano is about to erupt.

We haven't seen any bats yet, but you can hear them.

There's an incredible range of sounds coming up through the cave

and the sinkhole itself is almost functioning like a loudspeaker,

amplifying those sounds.

Then the source of the sound begins to spew out of the cave beneath.

I cannot believe how quickly that started!

From absolutely nothing at all,

a whirlwind of bats has just erupted

and started forming a vortex circling higher.

And...they're level with me.

And pretty soon, they're going to head out into the forest.

One of the greatest hunting machines on Earth.

Any insects around here are in big trouble.

BUZZING

The sound of their wings is just phenomenal!

I actually have to raise my voice

to be heard above the sound of these bats' wings.

And there is a wind being driven out from the hole...

..just purely from their flapping wings.

There are nine different species of bats living inside this cave.

One of them feeds on nectar,

the rest are all insect-feeding bats.

And...this is one of the greatest aggregations,

that is collections of predators,

that you will see on the whole planet.

This is one of the greatest spectacles I have ever witnessed.

From nothing to an eruption of bats.

This really is a volcano of bats.

That is extraordinary!

To see them begin their nightly pilgrimage,

we scramble to a higher viewpoint above the sinkhole.

We just quickly ran up above the sinkhole,

just to catch the last few rays of sunshine

illuminating this cloud of bats,

just heading out almost like tendrils of smoke

over the top of the forest.

It really is one of the most beautiful sights I've ever seen.

Every single one of the bats, their wings are backlit by the sunshine,

so you can see these tiny little phantoms glowing orange

as they hover above the forest.

And look at that now! Just heading across the skyline.

In just great, long, smoky tubes.

It may seem crazy to be looking at something so exquisite

and suggesting it as something that should go on the Deadly 60,

but actually, in terms of scale,

we will never feature anything that is such an epic display

of predatory behaviour as this ever on the series.

I mean, there's anywhere up to two-and-a-half million bats

coming out of these caves.

Each could eat half its bodyweight, perhaps even more, in insects

every single night.

There is no other predator that could do that.

There's no lion that can eat its own bodyweight in gazelle

or orca that can eat its own bodyweight in sea lion.

What these bats are doing is truly extraordinary,

and they're doing it on a massive, massive scale.

It's a sight that you can see in very few places in the world.

In magnitude, this is one of nature's true miracles.

But take a closer look and it's perhaps even more miraculous.

Insect-eating bats perceive their world using echolocation.

This involves sending out high-frequency clicks

from deep in their throat which most of their prey won't detect.

These sounds act as a searchlight,

scanning an area and echoing back as they bounce off objects.

As they get closer to their prey, the time between clicks shortens,

allowing them to pinpoint things with remarkable precision.

The returning echoes are received in their large ears

and give the bats a three-dimensional picture

of everything in the vicinity.

In the darkness, they discriminate between echoes from prey

and echoes from things like twigs and leaves.

It's one of the most complex predator-prey interactions.

The sun has completely set,

yet the bats still pour out unabated from the cavern.

Let's take a closer look at the players in our super swarm.

After rodents, the bats are the most bio-diverse

group of mammals on the planet.

There's well over 1,000 species and I don't know all of them.

But the scientists thankfully do seem to know them all

and they've reliably informed me

that this one here is called Davy's naked-backed bat.

And you can see why. Look at this.

It's all furry down to about here,

and then the whole of the back is just completely naked of fur.

-It looks like it's been shaved.

-HE LAUGHS

This is a hairy-legged myotis bat.

And it just looks like a tiny little miniature teddy bear with wings.

It is just incredible that even at this tiny size,

this animal has probably the most sophisticated

prey-detection system of any creature on Earth.

This is the ghost-faced bat.

And I have to admit, even to me,

that is a face that's pretty repulsive.

Now, it's centred around these whacking great big ears,

and you can see that actually what these do

is almost turn the entire head into a satellite dish.

This is called the common moustached bat.

You can see why, because lying along the length of the upper lip

is what looks like some kind of crazy moustache.

But that's not what's interesting to me.

I think the most remarkable thing is that between the feet here...

is this membrane.

Tail runs down the middle of it

and it acts almost like a baseball catcher's net.

Many species of bat have this tail membrane.

They use it to catch insects that are flying by.

They scoop up their prey, transfer it to their mouths

and consume it whilst still in flight.

The scientists have done their work on this one. He can fly free.

Fantastic!

This is the bat I was hoping to find.

It's called the Mexican free-tailed bat.

And the reason for that is you can see

the tail here is actually free of the wing membrane.

Mexican free-tailed bats roost in truly mammoth colonies.

Their efficiency is absolutely extraordinary.

He has, though, got a fairly fearsome set of gnashers.

The teeth inside there are genuinely needle-sharp.

Capable of munching through the tough exoskeleton of a flying beetle

or munching down a moth that could be the same size as this bat.

It is an absolute wonder.

In fact, every bat here is wonderful.

And they're all truly worth their weight in insects.

So really, I know it's weird,

but I'm going to put all of the bats from the bat volcano

onto the Deadly 60.

With a complex hunting technique

enabling them to locate prey in total darkness,

they catch moving insects on the wing with superb agility.

Collectively consuming more than half a tonne of insects every night.

This mass of munching mammals is definitely...

'Deadly!'

Join me next time as I continue my search for the Deadly 60.

-I can see it! I can see it!

-Go, go, go, go, go!

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