Crocodile

'Crocodiles eat more people than any other predator on earth.

And Africa's Nile crocodile kills the most.'

That...is a lot of crocodile.

'Any animal or person near the water's edge is at risk.

This stretch of river in Namibia is reputed to be the croc attack capital of the world.

My name is Mark Evans.

I'm a veterinary scientist with a personal interest in conflict between humans and animals.

I'm here to join crocodile behavior experts attempting a radical new experiment...' - Whoa!

- (Crocodile snarls) '..to try to keep both people - and crocodiles safe.'

'Operation Maneater (MARK) 'The Chobe River.

Africa at its most beautiful and dangerous.

This river is the front line in a deadly conflict between humans and crocodiles.

The Chobe marks the border between Botswana and Namibia.

On the south bank is a national park - perfect croc habitat.

On the north bank, cattle farms and villages, where people wash, fish and fetch water every day.

It's a lethal combination.

In the protection of the park, crocs pose for the tourist cameras... ..until it's time to hunt the easy prey on the opposite bank.

Almost half of the people here have experienced a crocodile attack on a family member.

Most of the victims are children.

I want to find out what happens when crocodiles target humans.

Local villager Cassius witnessed a recent attack.'

So it was right down in here?

Do you think you saw one then?

Cassius, come out of the water.

I don't want a crocodile taking you.

- Come out of there!

- Okay.

So you have children?

Do you let your children come down to...?

'Children have always enjoyed swimming and playing along the river, but attacks are now so frequent parents try to keep their families away from the water's edge.

I want to talk to Liz, the area head of the Ministry of Environment and Tourism.

She's investigating three recent cases - two fishermen and a young girl.'

So why do you think the problem is so bad here now?

So there's more and more need to be using the river.

More cattle...

So it's kind of the conflict between the crocodiles and the human beings is bound to happen.

And were they all fatal?

All deaths?

'I want to explore possible solutions to this problem with Rom Whitaker, one of the world's leading crocodile experts.

When many crocodile species were on the brink of extinction in the 1970s, Rom helped lead the campaign to save them.'

A croc in here?

'Thanks to this work crocodiles are now protected by law.

But as a result, they live longer, grow bigger, and attack more people.'

It's a conservation strategy that has been almost too successful.

Yeah, it gives any one of us who have been working on this kind of thing a sense of responsibility.

That the crocs are coming back so fast that people haven't learnt to adjust to it.

And this is what we've got to deal with now - fast.

'Rom's going to give me an insight into what makes these crocs so dangerous.'

Wow!

That is a beauty.

These guys are obviously very used to people.

Amazing.

Because you'd expect at this distance - it to be back in the water.

- Absolutely.

What's struck me here, it's when you talk to people, the genuine fear and respect of these animals.

Because there's something about a fear of being bitten in human beings, but there's also a bigger fear of being eaten.

- Yeah.

- This croc could end up in this boat, couldn't it?

In about half a second, yeah.

Those hind legs are incredibly powerful.

It could literally leap like a rabbit.

When they're basking like this, are they completely zoned out?

No way.

He's very tuned in.

In fact, let's just see if he's listening.

'To test the croc's response, Rom mimics an alarm call.'

(Deep grunting) - Jesus!

- (Rom laughs) Yeah, he was listening!

'On the other side of the river, we approach Kalala village.'

I mean, this is a potential disaster waiting to happen, and yet it's part of essential everyday life.

- Yep, yep.

- So just take me through... Croc in the river, hungry.

Sees this situation of these three ladies down by the water doing their washing.

With their good eyesight, good sense of hearing and good sense of smell, they're tuning into food potential all over the place.

If a hungry croc is on the move to look for prey, and if he hears water splashing: "Oh, what's splashing?"

When a croc observes a potential prey item he submerges to get closer.

Very often he'll submerge.

But he has recorded where that is and he'll come up even closer.

And like any predator he wants to come as stealthily as possible, very definitely without being seen first.

So it's to his advantage to come up as close as possible.

And with just his eyes above water and his nostrils above water, he may not be detected.

Chances are he won't be, especially if there's a bit of reeds around.

'Nile crocs will wait for days, weeks or even months for the perfect moment to attack.

To target prey they use acute color vision, a much better sense of smell than we have and skin cells that can detect movement in the water.

Muscles in their torso can pull their lungs backwards - altering their buoyancy and allowing them to slip beneath the surface without a ripple.

Once in striking distance, they launch from the water, advancing a whole body length in just a third of a second.

They lock on, drown their prey.

And spin their bodies to tear the victim limb from limb.

Crocodiles are perfectly adapted to hunt mammals at the water's edge - the very spot inhabited by people and cattle along waterways all over Africa.

It's egg-laying season on the Chobe and Rom takes me to a croc nest in the corner of a farmer's field.

The mother is scared off the nest she's guarding as we approach.'

How far would mum be away from here?

Chances are she's very close by.

The interesting thing is the babies have a very strong and loud alarm call.

When they get caught or when they're under stress they make a... (High-pitched cries) - And that is enough... - Can you stop doing that?

I shouldn't do that.

When you're gonna do that, tell me and I'm getting in the boat.

I can at least tell you, that that does attract mother and daddy croc.

It's amazing, isn't it?

Because you've got an apex predator... ..laying eggs, reproducing... more predators, right in the heart of what is a human landscape now.

It's a farmed landscape.

The conflict is just inevitable, isn't it?

It is.

Absolutely.

I mean, this is a perfect illustration, isn't it, Rom, of the problem of human/croc conflict.

It's about people being attacked and killed and injured, but it's about their livelihoods, about their wealth and their survival, because they take their animals.

Yep.

Precisely.

These guys are worth $3,500, a good cow...to these guys.

- Namibian dollars.

- It's a lot of money.

It's a lot of money.

And a bull could be 10,000.

Their wealth is tied up not in cash in the bank.

- It's cows on the river bank.

- Exactly.

Yeah.

And the croc is the main threat right now.

So this is a classic situation, isn't it?

We've got a big herd of livestock here.

They need to drink.

So these guys, the cow herders, have at least made an attempt here.

Yeah.

By pulling in some scrub, some thorn bush, to create a kind of barrier.

Yeah, it would work temporarily.

A croc could get through this, obviously.

There are gaps and stuff.

But if it creates that half a minute, those few seconds, for a cow to get out of the way when a croc attacks, well, that's all that's needed right now.

'Permanent crocodile fences have proved successful in other parts of the world, but here on the Chobe fencing is destroyed by hippos and floodwaters.

Relocation of large crocodiles has also been tried, but they'll travel long distances back to their home territories.

As a last resort, locals are killing crocodiles they feel are a threat.'

I think I see something.

'Rom's friend and colleague, Dr. Pat Aust, is a crocodile conservationist working to tackle the problem.'

It's gone right through the skull.

'He's been invited by the Namibian Government to investigate the conflict.

Sadly, he regularly sees huge crocs like this one, killed for suspected attacks on livestock.'

This is one of the crocodiles that kills my cattle.

One, two, three.

This crocodile's smell is bordering on indescribable.

'Deep inside the croc's stomach, a cow's hoof confirms at least one kill.'

That's all the evidence... We could only say one cow.

Yes.

'I catch up with Pat at a local village meeting.'

- Pat.

- Hi, Mark.

- How are you?

- Very good, thanks.

- It's good to be here.

- Likewise.

Great that you could make it.

'We want to gather information from people who've experienced attacks first hand.'

It will help us if we are able to hear the stories that you have about when crocodiles have attacked.

Please come and find us so that you can share those stories with us.

'I'm told about a small boy who was snatched by a huge maneater four years ago.

I went to meet his father.'

Tell me about what happened to your son.

Were they walking across the stream?

How deep was the water?

So it was a regular crossing point used every day by people?

'The suspected killer was caught and the contents of its stomach examined.'

You must miss him a lot.

Given everything that's happened and your experience are you still okay that there are crocodiles here in such numbers?

'You can understand why.

To avoid widespread slaughter of crocs and save human lives we need to come up with a new solution to the problem.

Rom and Pat think the key is to tap into the innate intelligence of crocs.

Rom tells me about when he first suspected that crocs are smarter than most people imagine.'

I guess you could say for me, it first started when... by remembering a story I was told in Papua New Guinea.

These guys saw a crocodile leaping up to an overhanging tree.

And on a regular basis, over a couple of days.

And it was a tree which was often used by a fisherman.

The guy who saw it said, "We know a fisherman who comes there regularly and fishes.

The croc is gauging how high he has to jump to catch this guy."

And they warned the fisherman, "Hey, this croc..." And the fisherman, of course, says, "Come on, that's ridiculous."

But that croc... That fisherman apparently did not live to tell the tale, because the croc did get him when he was sitting up in that tree.

Okay, it may be apocryphal true, but it sort of rang a couple of bells in my head.

And perhaps this is where it all started.

'One of the handlers at Rom's croc breeding centre in India helped prove how intelligent crocs are.

He used food rewards to train an aggressive Siamese crocodile to be more docile.

Rom shows me how the croc reacted to the handler before the training began.'

This is typical behavior of a Siamese crocodile, okay?

The normal response.

Whoa!

Look at that!

It literally flies straight out of the pond, straight at him!

It's fairly dangerous.

Now check this out.

This is a trained one.

(HANDLER) 'Slow.

Slow.'

Sit.'

This is dog training.

Did he do this all by reward-based training?

Yes.

It took time.

This is over a period of several months and he's done it with several species.

- Five different species.

- 'Sit.

Sit.'

'Sit.

Sit.

Sit!'

- So what was your reaction when you saw that?

- Blown away!

Come on.

No, it made me more amazed at crocodiles and what they are capable of than ever before.

'Crocodiles have one of the smallest brains for their body size in the animal kingdom roughly the size of a walnut in a fully-grown male.

But these small brains have areas highly specialized for social and cognitive processing.

Making crocs the most intelligent of all reptiles.

The speed and level of learning achieved at the Croc Bank took the scientific community by surprise.

'Open your mouth.

Open your mouth.'

These animals now know 30 commands, both visual and auditory, which is more than some pet dogs!

'Jump.

Jump.'

'Pat wants to try to train the crocs here on the river to stay away from humans.

Offering food rewards in the wild is clearly impractical, so Pat wants to try a different kind of conditioning, using punishment rather than reward.

It's a technique nature has used very successfully.'

(MARK) Give me a clue.

What am I looking for?

There's a little animal I'd like to show you.

It's a long, blackish color, and it's something that will help me explain to you what we're trying to do.

'Before we retire to our tents Pat shows me an example of a creature that does this very effectively.'

(PAT) Locally, we call it a Chongololo.

- A Chongololo?

- A Chongololo.

Here we go.

Here's one over here.

Here we go.

- Here we go.

- What, a millipede?

It's a millipede.

Correct.

Hello, matey.

That is so cool.

And that's a favorite children's toy in these parts.

- Really?

- Yeah.

Kids love them.

I remember as a kid playing with those things for hours.

So why bring me out here to find it?

What's the point?

How in any way is this linked to a crocodile?

You can see it's relatively slow.

It's got very few defenses.

Why?

Well...

If I irritate it a little bit and get it... (Sniffs) There you go.

You can smell it.

(Sniffs) Woargh!

It's a fairly noxious little smell, isn't it?

- Really potent.

- Yeah.

Whoo.

He's really going for it now.

Ugh!

Why do you keep sticking it up my nose?

- (Laughs) - It's absolutely revolting.

'Glands in the millipede's body release toxic chemicals.

In some species the gas is hydrogen cyanide.'

You ain't gonna go near it again if it makes you feel sick.

Exactly.

Exactly.

'The stench acts as such an effective deterrent, birds and other predators soon learn to leave these bugs alone.'

The truth of the matter is this little animal actually has very little to fear.

It's just so distasteful and that really puts most predators off.

Very, very few animals that eat this.

But, I mean... You see that across nature.

Absolutely.

It's a well known phenomenon called aposematism.

And basically what happens is animals evolve a particular defense that...gives such a negative response to the predator that's trying to eat it, such a negative sensation, that they actually stop predating on them.

They may try one or two, but in the long term they just stop eating them.

And that's called aposematism?

- I've never even heard of that before.

- Yeah.

Yeah.

- Shall we let this little guy go?

- Yeah.

- He is rather special, isn't he?

- Yeah.

'It's this type of conditioning that Pat wants to try on the crocs here on the river.

He wants to deploy low-tech devices that combine a ringing bell and an electric shock.

That he hopes will train crocs to avoid the sound of a bell.

If it works, the simple ringing of a bell at the water's edge should keep crocodiles away.

But nothing like this has ever been tried before.

Pat needs to prove to the Namibian Government - and the scientific community - that his radical idea could work.

Before we try it in the wild, we're gonna carry out some experiments under more controlled conditions at the Chobe Crocodile Farm, just over the border in Botswana.

Here they breed crocs for larger farms, that rear them for their meat and skins.'

So it's all the newborns in here.

It's like a little maternity unit.

(ROM) It is.

So, I mean, two days old...

They're out, perfectly formed, ready to rock and roll, aren't they?

What's really stunning about these guys is that they are beautifully formed miniature versions of the massive crocodiles you'll see in the Chobe River, aren't they?

- Absolutely.

- It's fair to say, also, extraordinarily cute at this stage.

- They are.

Very lovable.

- Absolutely gorgeous.

What are you gonna turn into, my friend?

Blimey, they're big!

Hello, mate.

What's his name?

(WOMAN) Big Boy.

- Big Boy.

Hello, Big Boy.

That...is a lot of crocodile.

The biology of these guys... is absolutely mesmerizing.

They are hundreds of millions of years of evolution... ..to create... ..what to some people is a monster... ..to me is exquisite.

Some of these jaw-droppingly huge animals are 80 to 100 years old.

Croc farm owner Sue is planning to move a couple of the juveniles to a larger enclosure.'

We're going to be catching some crocs and you are coming to help me.

(Dog barks) It's amazing, isn't it?

You can keep their jaws closed just with electrical insulation tape.

'Though crocs have a bite pressure of 5,000lb per square inch - more than a Great White shark the depressor muscles that open the jaws are tiny compared to the fast-firing muscles that snap shut with such power.'

- They're feisty, aren't they?

- Yep.

They may not be that big, but pretty heavy.

Okay, before you load him I need to check...

Okay.

Somebody want to open that tailgate?

Male.

'Before we transfer this feisty nine-year-old to its new home, it's a rare opportunity to get close to a live crocodile and look at some of the evolutionary features that have put these reptiles at the top of the food chain.'

To be a fantastic predator you need amazing senses.

They've got good eyesight, good hearing.

Hello.

There - that's the ear.

You can see the third eyelid there flick past.

If I just get him to close his eye a little bit there, you'll see... See it open up again?

It's called the nictitating membrane.

But it's completely see-through in the crocodile, unlike in dogs and cats, where it's kind of a whitish color.

And it's thought that maybe it gives it some kind of advantage in being able to see better underwater.

You know what it's like if you dive into a swimming pool.

You can't see clearly.

Well, it's possible that the nictitating membrane may in some way alter the diffraction of light into the eye and help them see better underwater.

But also, in all their scales they have cells which have sensors in which detect heat, movement and pressures, called integumentary sensory organs.

And they're on every scale on their bodies.

Particularly important round the head to detect water currents, water movements when there's prey in the water.

And when they've detected it, it's obviously the teeth that don't chew, but just simply grab and pin whatever they've got that they can then drag it into the water to drown it.

And they've got somewhere between 64, 68 teeth, but they just keep replacing them.

So maybe up to 50 times through their lives they'll be able to replace their teeth completely.

These are two I picked up a minute ago.

These are tiny teeth.

In a big male Nile crocodile, the teeth would be this size.

(Dog barks) - Okay.

- Not by the legs, under the body.

Okay.

Right... Whoa.

Careful, careful.

Oh!

Oh, oh.

Are you okay, Mark?

- Yeah, I'm fine.

- Mind your glasses.

- He's split my lip a bit.

- Oh, we need to sort that out.

No, it's alright.

You carry on, get him in first.

Can I get the gloves from you?

Then we'll sort you out.

Er...

There you go.

That's what happens.

Just one quick swipe of the head... ..knocked into the side of my face.

- Still got your teeth?

- Not his fault.

They might be a bit loose.

- You got him?

- Yep.

We can put him down here.

So there is a lesson for you.

At any moment...

I was holding onto that jaw really tight.

It was up at head level.

And just one quick flick of its head... ..and I just got a little bit of a kind of blunt trauma from its nose on the side of my lip, and it's cut the whole of the inside of my lip up.

Unfortunately, the injury's a little bit worse than I thought.

I've managed now to have a look at it in the mirror and the whole of the lip is split quite badly, so we're trying to find a flight to get me out of here to get to a hospital where they can look at it.

- (Thunder rumbles) - We've now got lightning and a thunderstorm coming, so maybe a plane can't get here.

So...

Happy days.

'Fortunately, I make it out to Johannesburg that night for emergency treatment.'

So, 24 hours later I've just come out of theater, having had a general anesthetic.

I had it stitched up.

I'm sure it looks absolutely ridiculous.

They've let me out!

I've got all my scans.

I've got all my meds antibiotics, ointment, pain killers.

I've got a very, very sore mouth, so I can only eat now like a crocodile, by throwing stuff down the back of my throat and swallowing it.

Now I need to find an aeroplane, to get back to Namibia.

'Here on the Chobe River, Dr. Pat Aust is planning to pioneer shock aversion training as a way of preventing crocodile attacks.

I'm going to help him build an electric shock device that will train crocs to stay away from humans.

We'll begin training on the croc farm before trying it on the river.'

What do you have in mind?

I guess, firstly, we need to deliver the electric shock.

Something to do that.

Secondly, we need something robust enough to withstand an attack by a crocodile.

- Maybe we go with a tire.

- Is there anything out here I should worry about?

- Like... - Snakes.

- Thanks.

- When lifting things, watch out for snakes.

- Poisonous?

- Poisonous and non-poisonous.

Could I not get... No, okay.

'It's important our training device is made from cheap materials easily sourced by locals.'

Incoming!

Brilliant.

Well done, Mark.

Let's go with this little one.

Perhaps you could go find something to hang this up.

- Perfect.

- We've got all our bits now.

Excellent.

'The indoor enclosures provide a controlled area for our crucial first tests.'

So are you fully rigged?

We're rigged and ready to go.

This is our live electrode that's coming from the energizer, through the top of the tire, and that's attached to this cable here.

So that's gonna be live.

We'll attach the meat to this end here.

So what's the objective of this first stage?

The first thing, the main thing we wanna know is, what is their reaction gonna be?

What?

Simply to an electric shock?

Exactly.

We don't know.

Obvious, isn't it?

You've got an electric fence with a cow or sheep in a field.

They go up to the fence.

They touch it.

They go, "Ooh, that hurt."

And they back off.

It's possible these guys might not do that, though.

This is an angry predator with potential...anger at being hurt like this, and may react that way.

- This is all brand-new.

- It is.

It's completely brand-new territory.

Right, we're going - we're live.

'This experiment has never been attempted before.

We simply don't know how they'll react.

We're using an electric fence energizer similar to those routinely used on sheep farms.'

(Ringing) - No shock.

- No shock.

There was no reaction at all.

'What's going on?

They're receiving a shock in the mouth without flinching.

Even when they bite the bare wire it seems to have no effect.

But an accidental zap on the snout does get a reaction.'

What are your thoughts, Pat?

Once their jaws are around the bait, they seem to go into an overdrive and they literally override the pulse, the shock.

When they're in that feeding mode, they just completely go blank to everything else.

(PAT) Exactly.

Over meat they would essentially be grabbing it off each other, so there would be pain inflicted on each other anyway during feeding.

It's true.

We've seen that.

When they catch an animal one would imagine that occasionally they'd get a hoof in the nose and a horn in the side or whatever the case may be.

(MARK) So Plan B?

Try and shock them just before they get hold of the bait.

Okay, so that's gonna need a bit of modification then.

So, Mark, what we do is we don't give them a clear target with the meat.

Maybe what we do is we put the meat in the bottom of the tire.

What we're doing by doing this is we're guaranteeing there's no meat in the mouth when the shock is delivered.

So the senses on the outside about how you find your food... (Hissing) They can smell this food.

You kind of forget there are crocodiles behind you.

After this...

I'm slightly more wary than I used to be.

Yeah, absolutely.

There's nothing wrong with that.

That's about it.

'With the live wire wrapped around the bottom of the tire and the bait inside, we start a second test.'

It's so close underneath there.

It's only gotta lift its head... - (Electrical snap) - Oh!

- (Electrical snap) - Okay.

That's backing off going, "Ooh, that hurt!"

It's the same one.

And now he's decided to turn away.

'Now that we're zapping them on their snouts, the crocs are really taking notice.'

The learning science would say all you've gotta do is have a powerful enough punishment that it generates a negative emotional state.

This one that got shocked is definitely hanging back.

It was forcing its way in before.

That's one of the dominant animals, that dark one.

- (Electrical snap) - Okay.

Didn't like that at all.

- (Electrical snap) - Here goes another one.

(Electrical snap) Pat, a completely different response to when the electrode was inside the mouth.

Totally.

Completely different.

This time round there was an instant retreat back into the water.

'Pat's idea of shocking crocs may seem a bit cruel, but ultimately we want to alert the croc with a sound cue they learn to associate with a shock.

If we can get this to act as a deterrent in the wild, it could save lives - ours and theirs.'

That's stage one.

But for this to work... ..you're only using the electrocution as part of the training.

The big thing is that it learns a cue that predicts you're going to get an electric shock if you carry on doing what you're doing.

Now we're at the stage where we can introduce the cue, which in this case is going to be a bell.

'The sound cue needs to be cheap to produce, just like the shocking device.

Bells are perfect.

But some wild crocs approach cattle when they hear cowbells, so our bells are much smaller and higher-pitched.'

So in that configuration, you'll lower down...

The plan will be, in maneuvering their heads to get the meat inside.

- Bangs the bell... - Bang, bang.

When this bell rings it's a predictor, a reliable predictor of electric shock.

'As it approaches the bait the croc will ring the bell just before it's shocked.

It should learn to associate the sound with pain, until the sound alone is enough to deter it.

Eventually it's hoped that when villagers ring a bell by the river the crocs will shy away.'

Just a wee bit...

Okay.

Down, down.

Down, down, down, down.

- Cool.

- (Bell rings) - Okay, that's a good height.

- (Ringing) So, the bell itself ringing clearly doesn't scare them off.

So...

So, that's a kind of good test, if you like.

Yeah.

(Bell rings, electrical snap) - Perfect.

- Absolutely perfect.

(Bell rings) (Electrical snap) If you're gonna try and get that association with the bell, it has to...

The timing is absolutely critical.

- (Bell rings) - Okay.

(Bell rings) (Electrical snap) You've already got two crocodiles that have got a response to it and others that are wary.

(Ringing) 'The crocs seem to be learning to stay away from the bell, even when there's no shock.'

Interesting that this guy went backwards.

He's very suspicious that there was a reaction from this one.

Mind your hands.

There's a croc right there and these guys jump.

'Pat gives the tire a shake to test the reaction.'

Slow retreat.

Absolutely perfect.

Now a quick jangle of the bell on its own, just in case it's the movement of the tire that scares these small crocs.'

(Bell jangles) There was absolutely no other stimulus coming in to play.

It was just the bell.

And that croc reacted perfectly.

Exactly what we wanna see.

That shows this can work.

This can work.

But what about a really monstrous animal?

I mean, this shock may be a mere tickle to one of those giants.

That's true.

'We now want to find out whether our electric shock deterrent will work on crocs big enough to take a human.

So we're moving to the outside pens, where conditions are more like those in the wild on the river bank.'

- Bit more?

- Yeah.

A little bit more.

Okay.

'Pat has scaled up the shocker using a truck tire.

Will it stand up to the sort of damage these heavyweights can inflict?

- Plug her in.

- All right.

There you go.

She's live.

(MARK) Look at that.

(Ringing) 'The first round definitely goes to the crocs!'

- Rom?

- Yep.

- Will this be heavy enough?

- It should do it.

Tie that device to this truck!

Perfect.

(Bell jangling) It's really interesting, because they're not at all spooked by the bell.

It's going now, and they're not worried about the bell at all, which is a really good thing.

But we have to make sure that bell is ringing when one of them touches their nose on that electrode.

(Bell ringing) (Electrical snap) That's an incredible lesson right there.

We've just learned that they really are affected by it.

That's the very first time any of us have ever seen it.

He doesn't like it at all.

'And now... here comes the champ.

Over five meters long, weighing in at nearly a tonne.

(Bell ringing) (Electrical snapping) 'Even he backs off after a few jolts to the face.'

We've just shocked one of the biggest Nile crocodiles in Africa.

He clearly felt that.

'Round two goes to Pat's shocker!'

That was fantastic.

I'm really chuffed with that.

To prove that it works on a crocodile this big, you know, that in itself is priceless.

(Snarls) 'It seems to take most crocs less than five shocks to learn to stay away.

(Bell ringing) Pat rings the bell to test the response.'

(Bell rings) That was a result.

And that's exactly how it's got to work in the wild.

And it's a croc that size you need to be targeting.

Exactly.

Exactly.

'We've proved an electric shock can be used to train crocs.

But will the shocker work in the wild, where crocs are used to hunting living prey?

We need to find a safe test site away from where villagers come to the water.

I've brought along a piece of kit to help us search for the perfect spot.'

Here we go!

I can see people right on the edge of the water in this little village that I'm going past now.

And, you know, you really get a sense from these pictures of how vulnerable these local people are to croc attack, because these animals are so brilliantly camouflaged.

And the reed beds - if we head off there... As I swoop down... And you can see right in the bottom of the frame there's a crocodile.

I mean, look at that.

You simply would not see that.

You could enter the water totally unwittingly.

'We find a beach with plenty of crocs nearby where we can make sure no villagers can get in.

But before we can deploy the shocker, we need to attract crocodiles to the beach.'

A croc killed a calf nearby but was scared off by the farmer before it could eat it.'

This poor animal.

That's a crocodile.

'We're using the body as bait to try to lure crocs in.

We set remote cameras to monitor our testing zone.'

Line up.

Okay.

'And I've brought something along that's more often found on naval warships.'

This is a sonar, sonic camera if you like.

It's never been used, as far as I'm aware, with crocodiles, so it should be extremely interesting to see whether it can actually pick them up.

Okay.

Sorted, right.

What I want to check before we put it in the water, though, is whether I can move it remotely.

'This bit of hardware will help us find out if there are any really big crocs lurking underwater where we can't see them.'

We switch the cameras to infra-red mode and settle down to wait.

There's no sign of crocodiles on the beach.

That's amazing, isn't it?

'But underwater the sonar reveals a monster approaching.'

He's massive.

I mean, massive.

So that's just in the water here.

You can see the scales on its back.

This might well be the very first pictures of a crocodile that's ever been taken with sonar.

He's still.

He's absolutely still.

- There he goes.

- There he goes!

- Oh, yeah, yeah.

- He's moving away.

- Look at his tail.

- Oh, wow.

That's such a great image, but he's moving away.

He literally just swam off from being on the bottom.

Why?

Not hungry?

It's suspicious, I think.

'The big croc is just the sort of animal we need to attract ashore, but it backed away.

Pat thinks we may be spooking it by being so close to the water, so we decide to go back to camp, leaving the cameras recording.

Daylight reveals something has taken the bait.'

It's a big crocodile.

You can see the bulge...on his neck.

Those jowls.

Hang on, he's giving it a nudge.

He's giving it a nudge.

Okay.

Okay, he's got it.

What you gonna do with it now, matey?

- Oh, my God.

- He's lifting that whole thing off the ground.

Yeah.

He's got the entire back of it.

Look at that.

In fact, his jaws fit all the way around.

Gives you an indication of his huge size.

What's cool about this, we were worried about the infra-red lights but this is pretty normal, natural behavior.

- He's not bothered.

- Three big crocodiles.

Wow.

This is more what you were expecting to see.

Yeah.

And this is the kind of social feeding behavior that you'd absolutely expect to see.

Look at that.

That big one's got that leg.

Do you think, I mean, from a human victim's point of view, if a big croc takes a human being on the river bank, will they tend to dismember it and swallow it, everything themselves?

Or will there still be that kind of... cooperative pulling the human being to pieces?

I think if it just so happens there's another big croc nearby they'll join in.

Everything you hear is, when a human is taken, they disappear.

It's true.

I mean, the fact that our skin doesn't hold together the way a cow skin does, for example.

We're just much weaker animals than they are.

And, I think, we break down into quite nice bite-sized chunks for a big crocodile.

'With the crocs now coming to feed at our beach, we're finally ready to test this training device in the wild.'

Okay, so it's your judgment this, on how high.

'In the croc farm the captive animals reacted strongly to the shock.

But are the wild crocs tougher?

Will the shock trigger the same behavior?

- (Bell jangling) - Bell goes.

Steps on this, puts his head right into there.

Bang!

Electrocution.

Perfect!

That's exactly what we're hoping for.

'Everything hangs on this next test.

Pat will find out whether his croc shock aversion training could work on the river.

Next morning I check the footage to see if our croc shock deterrent has worked.'

That's interesting.

Very cautiously... it's backed off.

'But the crocs aren't approaching.'

What are we doing wrong, Pat?

There's nothing taken out of there, is there?

No.

They loiter about here, on the other edge.

Yeah, you can see them now.

There.

The sort of... the point of that...

Right on the corner there.

I mean, I was, if I'm honest, expecting them to be bolder.

Have I just got the wrong end of the stick and they're shyer than they appear?

Let's give them a bit of time.

They're very patient animals and...

It's worthwhile just giving them another night and see how things go.

Okay.

Frustrating though, isn't it?

It is.

'All we can do is try again the following night and check the footage in the morning.'

So I've got the cards out of the cameras.

I haven't looked through them yet.

Okay, we have eye shine.

We have eye shine.

- Absolutely.

- Which is good.

- So they're right near the edge, aren't they?

- Yep.

Yep.

- Interesting.

- I can see a nose there.

Hang on.

We've still got one there, one there.

A little nose out of the water here.

One there.

- Oh, hang on a second.

- Oh, hello.

He came right out two of them came out!

Oh, look at this walking that is so brilliant!

And here comes this other guy now.

As soon as...

This one's moved in, like, its body length.

Look at that respiration rate from just that little bit of work.

- But he's sniffing, too, no?

- Ah, that's what it is.

- Getting that scent.

- Yeah.

They must wonder, "What the heck is that tire doing there?"

You want that, don't you?

You so want that!

- The other one's moving now.

- Quite fast as well.

With our number one croc just staring straight through the hole in the tire.

He's only inches away from the tire now.

Yep.

Here we go.

Bit more movement.

What are you gonna do, mate?

(Bell rings, electrical snap) - Bingo!

- Yes, he got a zap!

- He got a zap!

- On the bottom jaw.

Whacked on the bottom jaw.

(Laughter) That is very cool.

'It's a great result.

The big river crocs seemed to react even more strongly to one of the others being shocked.

But will we have to shock every croc on the river for it to work?'

The very big one you see out there he's sort of dominated the landscape since he arrived.

And he really sort of protects this whole beach.

You'll see the back coming out of the water?

That's demonstrating to the other crocs he's now the sort of top dog around here and he keeps them that side.

If we train him, we're pretty certain that he will keep all of the other big males out of this territory.

He's probably guarding a kilometer of river and by training him we're effectively training a security guard to maintain this stretch of river free of other big crocodiles.

'As the dominant male, this croc should approach the bait first while others hang back.

He'll naturally be the first to be shocked.'

And he'll stay here because there's still other food here that he can maintain his territory and he'll stay in this place.

Absolutely.

Just on the other side of the river we see plains of small ungulates.

And that essentially is ideal food for them.

So they'll always have that option to focus on those animals.

All we're doing is saying this side of the bank where there are a lot of people and cattle is not a good idea.

'Pat now has preliminary evidence to show shock training could work with wild crocs.

We're going to the nature conservancy office, to meet villagers and officials who are curious to see for themselves.'

You're keen to show them the videos then?

Yeah, absolutely.

What we have thus far is indication of success.

So I think these guys might be quite excited.

Just on the other side of that grass is the river.

You can see they're swimming.

The idea is that when a crocodile comes in... That tire's hanging there from the tree.

It goes "kling, kling".

And then after that, the electricity comes.

(Man speaks in African language) (Speaks in African language) - It works, hey?

Good?

- It works, yeah.

It works.

- Do you think so?

- Yes, because of those bells.

'The villagers and officials seem genuinely encouraged by our results.'

Wow, that went well!

Good job!

- That was fantastic!

- Good job.

Yeah, yeah, I mean...

I had no idea it would go that well.

- You must be well chuffed.

- I'm very chuffed.

And they get that it's only the beginning.

Absolutely.

'We'd really like to build on this success.

Croc shock stations, like the ones we made, could save lives in the future.'

There are many countries in Africa, there are many countries in other parts of the world which have almost identical problems.

What's the vision?

What would you see here?

I'm very confident we can train wild crocodiles to not go into attack mode when they hear a bell.

Crocs do learn, whether they're captive or wild.

They're still crocs.

'It's just the first step, but what excites me is that Pat's shown that training crocs in the wild could work.

He's made a full report of his findings to the Namibian Government.

The idea is to set shockers next to all watering points then later deploy them once or twice a month to keep the lesson fresh in the minds of the crocs.

That way, one day, along the Chobe River, and even across Africa, the ringing of a simple bell at the waterside could warn crocs to stay away, saving the lives of both humans...and crocodiles.'

To learn more about this program visit pbs.org Operation Maneater is available on DVD.

To order, visit shopPBS.org or call 1-800-PLAY-PBS.'