Armoured Giants Life in Cold Blood

For millions of years, before birds evolved,

and long before the rise of the mammals,

cold-blooded animals ruled the world.

In some places, they still do.

Some of these reptiles witnessed the dinosaurs come and go.

Yet in all that time, they themselves remained virtually unchanged.

Among them were some of the most impressive reptiles alive today.

They took that most characteristic of reptilian features, the scale,

to extremes - they turned it into armour.

That increased their weight, but nevertheless some can still move with extraordinary speed.

And although they may appear cold and impassive,

they can nonetheless be passionate...

..and even affectionate.

Among them are the biggest of all reptiles alive today.

They're the crocodiles, the turtles and the tortoises.

This is a giant Galapagos tortoise and it's climbed all the way up

the flank of this great volcano,

and is here wandering around the rim of the crater.

But why should it come to such a bleak and inhospitable place?

Tortoises, being reptiles,

can't generate their own body heat internally as we do.

Instead, they must get it from their surroundings

and these particular ones have come up here to warm themselves

on the hot volcanic rocks among the jets of steam and sulphurous gas.

They live longer than any other animal on earth...

well over 150 years.

They weigh up to a quarter of a tonne and have shells over a metre across.

They really are giants.

Having your body encased in shell obviously brings problems.

One of them is how do you mate?

Making love in a suit of armour is not easy.

But the males have a very ingenious solution.

The underside of their shell is concave,

so it fits neatly over the domed top of the shell of the female,

who is somewhat smaller.

That doesn't make clambering on top of her any easier initially.

But once the male is up there,

it will reduce his chance of slipping off.

The two shells fit together as neatly as two spoons.

So mating can begin,

and once started, it can go on for a long time.

The tortoise's shell is so familiar to us,

it's easy to forget what an extraordinary construction it is.

But how did it originate?

Nearly all reptiles are covered in scales.

And so were the tortoises' ancestors.

But then, as they evolved, a radical change took place.

The ribs expanded outwards

so that they enclosed the hip and the shoulder joints.

They enlarged and fused with other bones beneath the skin.

They widened and eventually, they joined together to form a bony box.

Above, the scales in the skin enlarged

to form a continuous shield of horn on the surface of the box.

And the basic armour was complete.

By developing a shell, tortoises inevitably sacrificed speed.

So they can't sprint off and take shelter in a crack

when danger threatens, but with a shell like that,

they seldom need to.

Some have added deluxe features to the basic model.

This is an eastern box turtle.

In North America, where it lives,

there are plenty of would-be predators...

racoons among them.

And they have very nimble paws.

But these turtles don't have to worry,

because their shell has a special safety feature -

it has a drawbridge. And when danger threatens,

the box turtle just retreats into its shell and pulls it up.

The drawbridge fits so tightly

there is no crack for the racoon to get its teeth into.

After a while, most racoons give up.

Of course, when your head is inside your shell,

you can't see whether your attacker has gone or not.

So it's best to check before you emerge fully.

A shell is an excellent defence against predators,

but there are other dangers against which it provides no protection whatever.

It's midsummer, it's nearly midday and it's very, very hot

and as a consequence, I'm sweating.

Sweating is a direct response to heat that only mammals can do.

No reptile, like this gopher tortoise, has got sweat glands,

but instead, it's got another way of keeping itself cool.

Most reptiles head for the shade when it gets too hot.

To see where this gopher tortoise is heading, here in Florida,

I'm going to use this...

A remotely controlled mini-camera on wheels with its own lights.

It can go pretty well anywhere.

The gopher tortoise is heading for home.

And with luck, I'll be able to follow it - the tortoise -

as it goes down into its burrow.

And that camera has also got a thermometer mounted on it.

And already I can see the temperature is beginning to drop.

The further down the burrow we go, the cooler it gets.

Now, where's the tortoise?

There it is!

We're right behind!

We're now a couple of metres in,

but the burrow could go on for some 50 feet - 17 metres.

And it's all been built by this tortoise.

Well... That is not a tortoise.

That's a rattlesnake!

Obviously taking shelter from the heat, just as the tortoise is.

The tortoise is so well armoured, it's in no danger from the snake.

And gopher tortoises don't seem to mind sharing their burrows.

A-ha!

It's changed its mind. There's its rattle.

Over 100 different species of animal

have been recorded taking shelter inside tortoises' tunnels.

In fact, some can live nowhere else.

But there's another reason why tortoises' homes are so popular.

Tortoises are one of the few animals here that can actually dig.

Each may have more than one burrow within its territory and that's very valuable,

because they have to deal with an even greater danger than sunstroke.

Bush fires.

These are a major and recurrent threat

to all the animals that live here.

Tortoise tunnels are invaluable places in which to take refuge.

Gopher tortoises may seem to be unassuming creatures,

but their engineering skills are essential

for the survival of the whole ecosystem.

The ground is still smoking,

but the flames have passed and the emergency is over.

So by digging tunnels, tortoises save not only their lives,

but the lives of hundreds of other animals.

But tunnels aren't the only place where you can escape extremes of temperature.

There's another environment that's cooler and even more stable...

Water.

Some of the ancestral tortoises started to spend all their time there

and became turtles.

Some still walk slowly along the bottom

in much the same way as their ancestors walked on land.

Water is a good place for a cold-blooded animal to live.

It retains its warmth through the night and stays comfortably cool during the heat of the day.

So turtles are able to keep their body temperature relatively constant without much difficulty.

Many have developed webs between their toes

and have become very efficient swimmers.

The most aquatic of all freshwater turtles is found in New Guinea

and a few rivers like this one in northern Australia.

The pig-nosed turtle.

Its feet have become completely transformed into flippers

and are of little use on land.

And indeed, the pig-nosed turtle rarely comes ashore.

But turtles are descended from land-living ancestors

and so they still need to breathe air.

Females also have to return to land in order to lay their eggs.

Pig-noses nest during the dry season high up on the river bank.

If turtle eggs get wet, the babies inside them will drown.

At least, that is the case with most turtles.

An egg for a turtle represents a huge investment,

as it does for any reptile.

So turtles go to a great deal of trouble

to make sure that they lay their eggs in safe, dry places.

So you would think that dropping one into water would be a disaster.

But watch.

A fully-developed baby turtle.

And it's come from an egg which as far as we know

is unique in the reptile world.

It can not only survive being flooded,

it actually requires to be submerged in water in order to hatch.

This enables the pig-nose to make the hatching of its eggs

coincide with the onset of the rainy season.

A view inside the egg would show the babies to be fully developed.

They can remain there in a kind of suspended animation,

if necessary, for weeks.

THUNDER RUMBLES

When the rains finally arrive, they are torrential.

The river rises swiftly and soon, the nests are flooded.

This would be a disaster for most turtles,

but the unhatched pig-noses are ready for it.

Indeed, its the moment they've been waiting for.

Their unique waiting strategy ensures that no matter how late the rains are,

the young turtles only emerge when the rivers are full

and there's plenty to eat.

They're able to swim immediately.

In due course,

the females among them will return here to lay eggs themselves.

The males however will never set foot on dry land again.

No turtles are better suited to life in freshwater than the pig-nose.

But the most extreme adaptations for swimming

are found in those turtles that went to sea.

Marine turtles have altered their front legs really radically

and turned them into oar-like flippers.

They're so at home in the sea, they even mate while swimming.

A male turtle has special hooks on his front flippers

that enable him to cling on to the female's shell.

And he has to have a firm grip,

for she makes no allowance for him as she swims.

But hanging on to his female is going to get much harder for this male.

A rival has appeared.

The male's armour protects most of his body,

but his rear flippers are exposed

and they are relatively soft and vulnerable.

There can be little doubt that this hurts.

But there's not much that the first male can do about it.

If he lets go with even a single flipper, he will lose his grip

and his female.

The rival tries again and attacks the front flipper.

And now the male's troubles are about to double.

A second rival arrives.

The two challengers join forces and attack the male from both sides.

His only option is to grin and bear it.

Now a third hopeful male joins in.

The female tries to shake them off, but there's no shifting them.

It's going from bad to worse.

Even more males gang up on the hapless couple.

Some of the gang try to force themselves between the mating pair.

The pair have now been submerged for a long time

and both of them are in desperate need of a breath.

If the rivals can prevent the male from reaching the surface,

he will have no choice but to let go.

He's in real danger of drowning.

At last, the determined couple break free

and make a dash for the surface.

With a welcome gasp of air, the pair escape.

One by one, the gang give up.

It was over 200 million years ago that the first turtles took to the water.

But they were not alone.

Another group of reptiles were also making the same move.

And they, too, were armoured giants.

Crocodilians, like turtles and tortoises,

have barely changed since the time of the dinosaurs.

Today, crocodiles, cayman and alligators live in tropical waters throughout the world.

Crocodiles and tortoises are obviously very different,

but they do have one thing in common - armour.

Their bodies are encased by tough, thick scales,

particularly along the back.

In tortoises, that armour is clearly defensive.

But for crocodiles, it has an extra function.

Just below each of these scales lies a network of blood vessels.

A crocodile can control the flow of the blood within them.

When basking, it allows it to circulate freely,

so transferring the sun's warmth from these ridged scales

to the rest of its body.

The crocodile, in short, has rows of very effective solar panels

all down its back.

And a sophisticated solar heating system like that

is a very valuable facility for a cold-blooded creature.

Being cold-blooded brings considerable advantages to a crocodile.

Whereas a warm-blooded predator like a lion would die

if it didn't feed every few days,

a crocodile, if necessary, can go without food for months on end.

And that means that crocodiles can live in places

where no warm-blooded predator could survive

and wait for events that only happen two or three times each year.

And one of those events will occur tonight, right here.

This road in northern Australia is close to the coast

and it floods at the highest tides.

Night falls, and the scene changes dramatically.

The road is now covered in water...and crocodiles.

But this is no random gathering.

The crocodiles are all here for a reason.

We know that some of them have travelled over 60 miles - 100km - to get here.

But how they know when to come here, we have little idea.

There must be some 40 crocodiles

assembled in the river behind me.

And what makes this sight all the more remarkable

is that these are saltwater crocodiles,

which are normally very territorial and intolerant of one another.

So there must be something pretty special happening in the river tonight.

And indeed there is.

This river is tidal.

But it's been crossed by a barrage.

However, at particularly high tides,

the water flows over the barrage.

And that is the moment that all these crocodiles are waiting for.

With the saltwater come fish.

Mullet have been waiting for weeks to migrate up the river to breed.

This high tide is their first chance to cross the barrage.

And the crocodiles are waiting for them.

Remember, it's now pitch dark.

Our infra-red cameras give us a clear view,

but the crocodiles can see virtually nothing.

So they wait with open jaws, ready to snap them shut at the first touch of a fish.

Normally, saltwater crocodiles would not tolerate being so close to each other.

They do compete for the best fishing spots,

but their disputes are settled with the minimum of fuss.

The fish keep coming for over an hour.

But as the tide starts to fall, so their numbers dwindle.

With so many crocodiles competing, some inevitably go hungry.

But for those that stay around, there will be a second bite to this particular cherry.

The next high tide comes during the day, and brings yet more fish.

The crocodiles can now see the fish, but that doesn't seem to make them any easier to catch.

These skilful hunters are surely dramatic proof

that reptiles are certainly not simple-minded creatures.

They've predicted the time of the arrival of the fish

with astonishing accuracy, and they have worked out just what they have to do to catch them.

They have also managed to suppress their normal antagonism

to one another so that they can all take advantage of this bonanza.

The more we learn about crocodiles, the more we realise what complex creatures they are.

Despite what you think, crocodilians are among the most talkative of reptiles and amphibians.

Indeed, they are second only to the frogs in the variety of noises that they make.

The most impressive of these sounds come from the American alligator.

When the breeding season starts, the males begin to proclaim their ownership of territories.

ALLIGATOR BELLOWS

The vibrations in his body are so powerful, they make the water dance along his back.

ALLIGATOR BELLOWS

ALLIGATOR BELLOWS

ALLIGATOR BELLOWS

Sound travels through water even better than it does through air,

and he can be heard by other alligators hundreds of metres away.

This is a clear statement of ownership of territory.

That's fine when he does it lying in his own patch,

but watch what happens when he bellows close to another male.

ALLIGATOR BELLOWS

But the rivals don't come to blows.

They sort out their differences with gestures.

Head slaps and gaping jaws are very obvious signals,

but alligators also send messages in less conspicuous ways.

Raising their backs slightly above the surface of the water is a significant move.

It's a claim to dominance.

Using signals that are almost imperceptible to us, all these individuals are

sending messages to each other, making claim and counter-claim.

Communication between alligators can be very subtle,

quiet, but there are some occasions

when they really want to make their meaning very unambiguously clear.

And one of those is when they're guarding their nests.

As this one is.

I think that was pretty clear!

Anyway, I won't press the point.

Communication between crocodiles starts even before they've hatched.

A tranquil pool in Argentina and in it, a female broad-snouted cayman.

She laid her eggs in a pile of vegetation close to the water almost three months ago.

Now sounds are coming from it.

The eggs are beginning to hatch.

Even while the eggs are still

within the nest, their mother can hear them from some way away.

Back on the nest, she listens intently.

Then, very gently, she starts to take it apart.

She can't know exactly where each of her babies is, and stops every few seconds to listen.

At last, the young are free.

But she doesn't abandon them.

She is going to take them down to the pool that she's selected as their nursery.

Some babies start to make the journey for themselves.

But they continue to call, and that helps their mother locate them.

Cayman jaws are among the strongest in the animal kingdom,

but now she uses hers with the greatest delicacy and gentleness.

So at last, her babies are brought together in the nursery pool.

But their mother's job is still not finished.

Several of the eggs have failed to hatch.

One by one, she takes these in her mouth.

The shell around the egg is quite strong.

The babies must make a considerable effort to free themselves,

and for some it's more than they can manage.

So she starts to crack the unhatched egg with her teeth.

Once the hard shell has been broken away, she has to pierce the leathery inner membrane.

Without her help, this baby might not have hatched at all.

But the female cayman's maternal duties are not over even now.

She will stand guard over her babies for the next few months.

All crocodilians take good care of their young.

But one of them takes parental responsibilities to a really astonishing level.

The Llanos of Venezuela - a lush wetland teeming with wildlife of all kinds.

As well as birds, there are amphibious rodents, capybara and spectacled cayman.

This female is looking after an extraordinarily large number of babies.

But most of these are not, in fact, hers.

This nursery pool is being used by several cayman families.

But instead of all the mothers staying nearby, one of them has taken charge of the whole creche.

Keeping an eye on all these energetic babies is not easy.

There are lots of enemies around.

When danger threatens, the babies all run for protection

to the female, even though she may not be their mother.

There are so many of them that there's not enough room for them all on her back.

Soon these babies will face another hazard, one that's not quite so easy to escape from.

The water that has kept them safe until now is beginning to dry up.

Each year, in the space of a few short months,

the Llanos is transformed from a flooded paradise to a baking oven.

For some babies, the unrelenting heat and the lack of water has already been too much.

Any babies that are left alive will certainly die if they stay here.

So the mother decides to leave.

Calling to her creche, she sets off across the parched land.

In one long cavalcade, they march onwards in search of permanent water.

For the mother, this is certainly exhausting.

For her babies, with their tiny legs, it must be a real marathon.

Some start to fall behind.

But she stops.

The babies call constantly.

She knows exactly where they all are and waits until every single one of them has caught up.

Only when all are with her will she set off again.

At last - safety.

The babies are close to exhaustion.

Without such devotion from the female, few, if any, of these baby cayman would have survived.

And remarkably, most of them aren't even her own.

When parental care was first described in crocodiles,

the reports were dismissed as too extraordinary to be true.

We may call reptiles cold-blooded, but they can show great tenderness.

Reptiles and amphibians are full of surprises.

They can look after their young with as much care as many a mammal.

Their displays can be as colourful as that of any bird.

And they can astonish and enthral us.

Reptiles and amphibians are sometimes seen as simple primitive creatures.

That's a long way from the truth.

The fact that they are solar-powered

means that their bodies require only 10% of the energy that mammals of a similar size require.

At a time when we ourselves are becoming increasingly concerned

about the way in which we get our energy from the environment

and the wasteful way in which we use it,

maybe there are things that we can learn from life in cold blood.

We filmed a lot of different reptiles and amphibians during the making of this series.

We were looking for extraordinary behaviour, preferably for things that had never been filmed before.

To see such wonders, we needed the help of scientists who were working in the field.

They passed onto us their insights and their discoveries,

and then they helped us to interpret the footage that we'd shot. I learnt a lot and had a lot of fun.

But I was also alarmed to discover just how rare some of the subjects of our series have now become.

One of our key locations was the Galapagos Islands.

Here, giant tortoises were going to be among our stars.

The scientists working for the Galapagos National Parks care for the wild animal populations,

but they also look after one extraordinary, unique individual,

with whom I had a special appointment.

This is the rarest living animal in all the world.

There is none rarer.

This is Lonesome George.

He's about the same ages as I am, but his story starts a very long time ago.

In the 17th century, when human beings first came to the Galapagos,

there were about 15 different kinds of giant tortoise,

each living on its own island or its own great volcano,

isolated by impassable lava flows.

There are 13 large islands in the Galapagos and many smaller ones,

and they differ in both age and their vegetation.

The tortoises differ too, because their shells have evolved into

the different shapes best suited for eating the food available on their own particular island.

On islands where there's abundant food on the ground,

the tortoises have dome-shaped shells and short necks that only need reach downwards.

But on islands where tortoises browse on higher bushes, their necks are longer and the shells

are saddle-shaped at the front, so they can stretch their necks upwards.

When the first ships arrived here, there were thousands of each kind of tortoise.

But then people began to slaughter the tortoises for meat.

They discovered the remarkable fact that these creatures could live

for a year without water or food,

so they took them on board their ships and slaughtered them at sea.

The tortoises on Pinta Island were apparently exterminated.

But then, in 1971,

it was discovered that there was one lonely, single survivor.

That was Lonesome George.

This film was taken over 30 years ago by the team

that brought George back to the Charles Darwin Research Station.

The scientists hoped that another Pinta tortoise might be discovered

in some corner of this island or even in a zoo somewhere in the world, but none has ever been found.

So now George lives in his own enclosure, completely safe but entirely by himself.

He's the last of his kind.

It's better news for the other Galapagos tortoises.

Felipe Cruz from the Research Station showed me some of the work being done there.

They take eggs laid by wild tortoises and put them in incubators.

The hatchlings are about the size of apples and have soft shells, so are vulnerable to predators,

especially rats that were accidentally introduced to the Galapagos.

The young ones I saw were only a few months old.

They're kept in special enclosures and given all the foods

they need to enable them to develop hard protective shells.

It takes a few months for their shells to harden,

and it's five years before they're totally predator-proof.

So far, in total, we have repatriated over 3,000 tortoises.

3,000?!

Scientists are also helping to solve another man-made problem.

Domestic goats that have run wild are eating the tortoises' food and destroying the precious plant cover

that they use for shade. So a systematic programme of eradication has started.

I was able to see the effects of this programme for myself.

We visited one island where two years earlier

the goats had been eliminated, and the difference was dramatic. The lush vegetation had returned.

Now the tortoises can find the shade that is so important for them,

and there's plenty of grass for them to eat.

Reptiles are not alone in being under threat.

The amphibians if anything are in even greater danger.

Not since the disappearance of the dinosaurs has a whole group

of the animal kingdom been under such threat.

In Japan, one of the most dramatic amphibians, the giant salamander, has fewer and fewer places to live.

In Panama, we filmed the golden frog.

Since we took this shot, the species has become so rare

that the few survivors have been caught to be protected in zoos, so it's now extinct in the wild.

The gharials that we filmed with their babies were nearly

exterminated in the 1970s when they lost most of their natural habitat, and they're not safe yet.

To try and halt their decline, their eggs are being collected, hatched in incubators

and the babies reared in captivity until they can be released in the wild.

So there may be hope for them yet. The gopher tortoise we filmed in Florida is also in trouble.

The areas where it digs its burrows have become prime real estate

and are now much sought after for building and farming.

By explaining their problems to landowners and developers,

they may yet have a future.

In the great island of Madagascar, there are more species of chameleon

than in all the rest of the world put together.

But the destruction of the island's forests began centuries ago and only a few patches are left.

They too are still being felled, and chameleon species may be lost

even before they've been identified.

We will need to act now if we're not to lose what remains to us

of the reptiles and amphibians that have survived for 200 million years.

Lonesome George, it seems, is doomed to be last of his kind.

But at least he can be a living inspiration for us all to protect the remainder

of the reptiles and amphibians of the world.