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00:30For millions of years, before birds evolved and long before the rise of the mammals, cold-blooded
00:46animals ruled the world. In some places, they still do.
01:00Some of these reptiles witnessed the dinosaurs come and go.
01:11But in all that time, they themselves remained virtually unchanged.
01:21Among them were some of the most impressive reptiles alive today. They took that most
01:27characteristic of reptilian features, the scale, to extremes. They turned it into armour.
01:36And to increase their weight. But nevertheless, some can still move with extraordinary speed.
01:48And although they may appear cold and impassive, they can nonetheless be passionate. And even
01:57affectionate.
02:04Among them are the biggest of all reptiles alive today. They're the crocodiles, the turtles
02:11and the tortoises.
02:20This is the giant Galapagos tortoise. And it's climbed all the way up the flank of
02:27this great volcano. And it's here, wandering around the rim of the crater. But why should
02:33it come to such a bleak and inhospitable place?
02:38Tortoises, being reptiles, can't generate their own body heat internally as we do. Instead,
02:47they must get it from their surroundings. And these particular ones have come up here
02:52to warm themselves on the hot volcanic rocks among the jets of steam and sulphurous gas.
03:01They live longer than any other animal on earth, well over 150 years.
03:10They weigh up to a quarter of a tonne and have shells over a metre across. They really
03:15are giants.
03:25Having a body encased in shell obviously brings problems. And one of them is how do you mate?
03:33Making love in a suit of armour is not easy.
03:38But the males have a very ingenious solution.
03:47The underside of their shell is concave, so it fits neatly over the domed top of the shell
03:52of the female, who is somewhat smaller.
03:57That doesn't make clambering on top of her any easier, initially. But once the male is
04:02up there, it will reduce his chance of slipping off.
04:20The two shells fit together as neatly as two spoons.
04:29So mating can begin. And once started, it can go on for a long time.
04:41A tortoise's shell is so familiar to us, it's easy to forget what an extraordinary construction
04:48it is. But how did it originate? Nearly all reptiles are covered in scales, and so were
04:56the tortoise's ancestors. But then, as they evolved, a radical change took place.
05:06The ribs expanded outwards so that they enclosed the hip and the shoulder joints. They enlarged
05:15and fused with other bones beneath the skin. They widened, and eventually they joined together
05:23to form a bony box.
05:28Above, the scales in the skin enlarged to form a continuous shield of horn on the surface
05:33of the box. And the basic armour was complete.
05:42By developing a shell, tortoises inevitably sacrifice speed. So they can't sprint off
05:48and take shelter in a crack when danger threatens. But with a shell like that, they seldom need
05:54to.
05:59Some have added deluxe features to the basic model. This is an eastern box turtle.
06:16In North America, where it lives, there are plenty of would-be predators. Raccoons among
06:23them. And they have very nimble paws.
06:35But these turtles don't have to worry, because their shell has a special safety feature.
06:42It has a drawbridge. And when danger threatens, the box turtle just retreats into its shell
06:48and pulls it up.
06:59The drawbridge fits so tightly, there is no crack for the raccoon to get its teeth into.
07:21After a while, most raccoons give up.
07:29Of course, when your head is inside your shell, you can't see whether your attacker has gone
07:34or not. So it's best to check before you emerge fully.
07:44A shell is an excellent defence against predators. But there are other dangers against which
07:49it provides no protection whatever.
07:56It's mid-summer, it's nearly midday, and it's very, very hot. And as a consequence, I'm sweating.
08:04Sweating is a direct response to heat that only mammals can do. No reptile like this
08:11gopher tortoise has got sweat glands. Instead, it's got another way of keeping itself cool.
08:21Most reptiles head for the shade when it gets too hot. To see where this gopher tortoise
08:26is heading here in Florida, I'm going to use this. A remotely controlled mini-camera on
08:34wheels with its own lights. It can go pretty well anywhere. The gopher tortoise is heading
08:43for home. And with luck, I'll be able to follow it, the tortoise, as it goes down into
08:56its burrow. And that camera has also got a thermometer mounted on it. Already, I can
09:05see the temperature is beginning to drop. The further down the burrow we go, the cooler
09:13it gets. Now, where's the tortoise? There it is. I'm right behind. We're now a couple
09:28of metres in, but the burrow could go on for some 50 feet, 17 metres. And it's all been
09:35built by this tortoise. Well, that is not a tortoise. That's a rattlesnake. Obviously,
09:53taking shelter from the heat, just as the tortoise is. The tortoise is so well armoured,
10:01it's in no danger from the snake, and gopher tortoises don't seem to mind sharing their burrows.
10:13Changed its mind, and there's its rattle.
10:19Over a hundred different species of animal have been recorded taking shelter inside tortoises' tunnels.
10:26In fact, some can live nowhere else. But there's another reason why tortoises' homes are so popular.
10:36Tortoises are one of the few animals here that can actually dig. Each may have more
10:44than one burrow within its territory, and that's very valuable, because they have to
10:48deal with an even greater danger than sunstroke.
10:56Bush fires.
11:04These are a major and recurrent threat to all the animals that live here.
11:10Tortoise tunnels are invaluable places in which to take refuge.
11:15Gopher tortoises may seem to be unassuming creatures, but their engine is one of the
11:45skills are essential for the survival of the whole ecosystem.
11:57The ground is still smoking, but the flames have passed, and the emergency is over.
12:07So by digging tunnels, tortoises save not only their lives, but the lives of hundreds
12:13of other animals. But tunnels aren't the only place where you can escape extremes of temperature.
12:20There's another environment that's cooler and even more stable. Water.
12:31Some of the ancestral tortoises started to spend all their time there, and became turtles.
12:43Some still walk slowly along the bottom, in much the same way as their ancestors walked
12:50on land.
12:54Water is a good place for a cold-blooded animal to live. It retains its warmth through the
12:59night and stays comfortably cool during the heat of the day. So turtles are able to keep
13:04their body temperature relatively constant without much difficulty.
13:13Many have developed webs between their toes, and have become very efficient swimmers.
13:30The most aquatic of all freshwater turtles is found in New Guinea, and a few rivers like
13:38this one in northern Australia.
13:43The pig-nosed turtle.
13:48Its feet have become completely transformed into flippers, and are of little use on land.
13:55And indeed, the pig-nosed turtle rarely comes ashore.
14:00But turtles are descended from land-living ancestors, and so they still need to breathe air.
14:16Females also have to return to land in order to lay their eggs.
14:22Pig-noses nest during the dry season, high up on the river bank.
14:29If turtle eggs get wet, the babies inside them will drown. At least, that is the case
14:35with most turtles.
14:39An egg for a turtle represents a lot of energy.
14:43At least, that is the case with most turtles.
14:48An egg for a turtle represents a huge investment, as it does for any reptile.
14:55So turtles go to a great deal of trouble to make sure that they lay their eggs in safe, dry places.
15:03So you would think that dropping one into water would be a disaster.
15:08But watch.
15:13A fully developed baby turtle.
15:15A fully developed baby turtle.
15:42And it's come from an egg which, as far as we know, is unique in the reptile world.
15:47It can not only survive being flooded, it actually requires to be submerged in water
15:53in order to hatch.
15:56This enables the pygmos to make the hatching of its eggs coincide with the onset of the
16:02rainy season.
16:05A view inside the egg would show the babies to be fully developed.
16:15They can remain there in a kind of suspended animation, if necessary, for weeks.
16:21When the rains finally arrive, they are torrential.
16:35The river rises swiftly and soon the nests are flooded.
16:52This would be a disaster for most turtles, but the unhatched pygmos are ready for it.
17:00Indeed, it's the moment they've been waiting for.
17:22Their unique waiting strategy ensures that no matter how late the rains are,
17:28the young turtles only emerge when the rivers are full and there's plenty to eat.
17:38They're able to swim immediately.
17:45In due course, the females among them will return here to lay eggs themselves.
17:53The males, however, will never set foot on dry land again.
17:59No turtles are better suited to life in fresh water than the pygmos,
18:05but the most extreme adaptations for swimming are found in those turtles that went to sea.
18:15Marine turtles have altered their front legs really radically
18:21and turned them into oar-like flippers.
18:27They're so at home in the sea, they even mate while swimming.
18:34A male turtle has special hooks on his front flippers that enable him to cling on to the female's shell,
18:40and he has to have a firm grip, for she makes no allowance for him as she swims.
18:50But hanging on to his female is going to get much harder for this male.
18:57A rival has appeared.
19:03The male's armour protects most of his body, but his rear flippers are exposed,
19:09and they are relatively soft and vulnerable.
19:16There can be little doubt that this hurts,
19:22but there's not much that the first male can do about it.
19:28If he lets go with even a single flipper, he will lose his grip,
19:34and he'll have to get used to it.
19:41If he lets go with even a single flipper, he will lose his grip and his female.
19:54The rival tries again and attacks the front flipper.
20:11And now the male's troubles are about to double.
20:17A second rival arrives.
20:28The two challengers join forces and attack the male from both sides.
20:41His only option is to grin and bear it.
20:50Now a third hopeful male joins in.
20:56The female tries to shake them off, but there's no shifting them.
21:11It's going from bad to worse.
21:17Even more males gang up on the hapless couple.
21:23Some of the gang try to force themselves between the mating pair.
21:30The pair have now been submerged for a long time,
21:36and both of them are in desperate need of a breath.
21:42If the rivals can prevent the male from reaching the surface,
21:48he will have no choice but to let go. He's in real danger of drowning.
22:00At last, the determined couple break free and make a dash for the surface.
22:15With a welcome gasp of air, the pair escape.
22:30One by one, the gang give up.
22:45It was over 200 million years ago that the first turtles took to the water,
22:51but they were not alone.
22:56Another group of reptiles were also making the same move,
23:02and they too were armoured giants.
23:13Crocodilians, like turtles and tortoises,
23:17have barely changed since the time of the dinosaurs.
23:26Today, crocodiles, caiman and alligators
23:31live in tropical waters throughout the world.
23:36Crocodiles and tortoises are obviously very different,
23:42but they do have one thing in common, armour.
23:47Their bodies are encased by tough, thick scales,
23:52which are hidden in the middle, along the back.
23:56In tortoises, that armour is clearly defensive.
24:00But for crocodiles, it has an extra function.
24:05Just below each of these scales lies a network of blood vessels.
24:10A crocodile can control the flow of the blood within them.
24:15When basking, it allows it to circulate freely,
24:19from these ridged scales to the rest of its body.
24:23The crocodile, in short, has rows of very effective solar panels,
24:28all down its back.
24:33And a sophisticated solar heating system like that
24:37is a very valuable facility for a cold-blooded creature.
24:44Being cold-blooded brings considerable advantages to a crocodile.
24:49Whereas a warm-blooded predator, like a lion,
24:52would die if it didn't feed every few days,
24:55a crocodile, if necessary, can go without food for months on end.
25:00And that means that crocodiles can live in places
25:03where no warm-blooded predator could survive,
25:07and wait for events such as an earthquake
25:11and wait for events that only happen two or three times each year.
25:17And one of those events will occur tonight, right here.
25:24This road in northern Australia is close to the coast
25:28and it floods at the highest tides.
25:32Night falls, and the scene changes dramatically.
25:41The road is now covered in water, and crocodiles.
25:52But this is no random gathering.
25:55The crocodiles are all here,
25:57We know that some of them have travelled over 60 miles,
26:01a hundred kilometres, to get here.
26:15But how they know when to come here,
26:18is a mystery.
26:22But how they know when to come here, we have little idea.
26:39There must be some 40 crocodiles
26:43assembled in the river behind me.
26:46And what makes that sight all the more remarkable
26:49is that these are the water crocodiles,
26:52which are normally very territorial and intolerant of one another.
26:57So there must be something pretty special happening in the river tonight.
27:02And indeed, there is.
27:05This river is tidal, but it's been crossed by a barrage.
27:11But it's been crossed by a barrage.
27:15However, at particularly high tides,
27:19the water flows over the barrage.
27:22And that is the moment that all these crocodiles are waiting for.
27:30With the salt water, come fish.
27:33Mullet have been waiting for weeks to migrate up the river to breed.
27:37This high tide is their first chance to cross the barrage.
27:47And the crocodiles are waiting for them.
27:57Remember, it's now pitch dark.
28:00Our infrared cameras give us a clear view,
28:03but the crocodiles can see virtually nothing.
28:06So they wait with open jaws,
28:09ready to snap them shut at the first touch of a fish.
28:29Normally, saltwater crocodiles would not tolerate being so close to each other.
28:37They do compete for the best fishing spots,
28:41but their disputes are settled with the minimum of fuss.
29:07The fish keep coming for over an hour.
29:11But as the tide starts to fall, so their numbers dwindle.
29:23With so many crocodiles competing, some inevitably go hungry.
29:30But for those that stay around,
29:33there will be a second bite to this particular cherry.
29:42The next high tide comes during the day and brings yet more fish.
29:54The crocodiles can now see the fish,
29:57but that doesn't seem to make them any easier to catch.
30:03They're on the move.
30:23These skillful hunters are surely dramatic proof
30:26that reptiles are certainly not simple-minded creatures.
30:30They've predicted the time of the arrival of the fish with astonishing accuracy,
30:34and they have worked out just what they have to do to catch them.
30:39They have also managed to suppress their normal antagonism to one another
30:44so that they could all take advantage of this bonanza.
30:49The more we learn about crocodiles,
30:52the more we realise that they are not just a game,
30:55but a real creature of nature.
30:58They have also managed to suppress their normal antagonism to one another
31:03so that they could all take advantage of this bonanza.
31:15The more we learn about crocodiles,
31:18the more we realise what complex creatures they are.
31:29Despite what you might think,
31:31crocodilians are among the most talkative of reptiles and amphibians.
31:36Indeed, they're second only to the frogs
31:39in the variety of noises that they make.
31:42The most impressive sounds of all come from the American alligator.
31:48When the breeding season starts,
31:50the males begin to proclaim their own territory.
31:54When the breeding season starts,
31:55the males begin to proclaim their own territory.
32:18The vibrations in his body are so powerful
32:21they make the water dance along his back.
32:24Sound travels through water even better than it does through air, and he can be heard by
32:50other alligators hundreds of metres away. This is a clear statement of ownership of
32:57territory. That's fine when he does it lying in his own patch, but watch what happens when
33:06he bellows close to another male.
33:36But the rivals don't come to blows. They sort out their differences with gestures.
33:47Head slaps and gaping jaws are very obvious signals, but alligators also send messages
33:56in less conspicuous ways. Raising their backs slightly above the surface of the water is a
34:03significant move. It's a claim to dominance. Using signals that are almost imperceptible to
34:13us, all these individuals are sending messages to each other, making claim and counterclaim.
34:19Communication between alligators can be very subtle and quiet, but there are some occasions
34:32when they really want to make their meaning very unambiguously clear. And one of those
34:37is when they're guarding their nests, as this one is. I think that was pretty clear.
34:57Anyway, I won't press the point.
35:02Communication between crocodiles starts even before they've hatched.
35:13A tranquil pool in Argentina, and in it a female broad-snouted caiman.
35:26She laid her eggs in a pile of vegetation close to the water almost three months ago.
35:34Now sounds are coming from it. The eggs are beginning to hatch.
35:40Even while the eggs are still within the nest, their mother can hear them from some way away.
35:49Back on the nest, she listens intently.
36:14Then, very gently, she starts to take it apart.
36:30She can't know exactly where each of her babies is, and stops every few seconds to listen.
36:40At last, the young are free. But she doesn't abandon them.
37:02She is going to take them down to the pool that she's selected as their nursery.
37:20Some babies start to make the journey for themselves, but they continue to call and
37:26that helps their mother locate them.
37:40Caiman jaws are among the strongest in the animal kingdom, but now she uses hers with
37:46the greatest delicacy and gentleness.
38:13So at last, her babies are brought together in the nursery pool.
38:26But their mother's job is still not finished.
38:32Several of the eggs have failed to hatch.
38:41One by one, she takes these in her mouth.
38:52The shell around the egg is quite strong. The babies must make a considerable effort
38:57to free themselves, and for some it's more than they can manage.
39:03So she starts to crack the unhatched egg with her teeth.
39:21Once the hard shell has been broken away, she has to pierce the leathery inner membrane.
39:47Without her help, this baby might not have hatched at all.
40:04But the female caiman's maternal duties are not over even now.
40:10She will stand guard over her babies for the next few months.
40:16All crocodilians take good care of their young, but one of them takes parental responsibilities
40:22to a really astonishing level.
40:29The Llanos of Venezuela, a lush wetland teeming with wildlife of all kinds.
40:43As well as birds, there are amphibious rodents, capybara, and a spectacle caiman.
40:57This female is looking after an extraordinarily large number of babies.
41:05But most of these are not in fact hers.
41:15This nursery pool is being used by several caiman families, but instead of all the mothers
41:21staying nearby, one of them has taken charge of the whole creche.
41:32Keeping an eye on all these energetic babies is not easy.
41:37There are lots of enemies around.
41:52When danger threatens, the babies all run for protection to the female, even though
41:57she may not be their mother.
42:03There are so many of them that there's not enough room for them all on her back.
42:18Soon these babies will face another hazard, and one that's not quite so easy to escape
42:24from.
42:27The water that has kept them safe until now is beginning to dry up.
42:32Each year, in the space of a few short months, the Llanos is transformed from a flooded paradise
42:39to a baking oven.
42:42For some babies, the unrelenting heat and the lack of water has already been too much.
43:00Any babies that are left alive will certainly die if they stay here.
43:06So the mother decides to leave.
43:29Calling to her creche, she sets off across the parched land.
43:36In one long cavalcade, they march onwards in search of permanent water.
43:59For the mother, this is certainly exhausting.
44:03For her babies, with their tiny legs, it must be a real marathon.
44:17Some start to fall behind, but she stops.
44:27The babies call constantly.
44:29She knows exactly where they all are, and waits until every single one of them has caught
44:34up.
44:58Only when all are with her will she set off again.
45:23At last, safety.
45:36The babies are close to exhaustion.
45:52Without such devotion from the female, few, if any of these baby caiman, would have survived.
45:59And remarkably, most of them aren't even her own.
46:13When parental care was first described in crocodiles, the reports were dismissed as
46:18too extraordinary to be true.
46:25We may call reptiles cold-blooded, but they can show great tenderness.
46:35Crocodiles and amphibians are full of surprises.
46:57They can look after their young with as much care as many a mammal.
47:09Their displays can be as colourful as that of any bird.
47:17And they can astonish and enthrall us.
47:34Reptiles and amphibians are sometimes seen as simple, primitive creatures.
47:40That's a long way from the truth.
47:43The fact that they're solar-powered means that their bodies require only 10% of the
47:48energy that mammals of a similar size require.
47:53As a time when we ourselves are becoming increasingly concerned about the way in which we get our
48:00energy from the environment, and the wasteful way in which we use it, maybe there are things
48:06that we can learn from life in cold blood.
48:33We filmed a lot of different reptiles and amphibians during the making of this series.
48:46We were looking for extraordinary behaviour, preferably for things that had never been
48:50filmed before.
49:02To see such wonders, we needed the help of scientists who were working in the field.
49:12They passed on to us their insights and their discoveries, and then they helped us to interpret
49:17the footage that we'd shot.
49:19I learnt a lot and had a lot of fun.
49:23But I was also alarmed to discover just how rare some of the subjects of our series have
49:27now become.
49:33One of our key locations was the Galapagos Islands.
49:36Here giant tortoises were going to be among our stars.
49:40The scientists working for the Galapagos National Parks care for the wild animal populations,
49:46but they also look after one extraordinary, unique individual, with whom I had a special
49:51appointment.
49:53This is the rarest living animal in all the world.
49:58There is none rarer.
50:01This is Lonesome George.
50:05He's about the same age as I am, but his story starts a very long time ago.
50:11In the 17th century, when human beings first came to the Galapagos, there were about 15
50:19different kinds of giant tortoise.
50:22Each living on its own island, or its own great volcano isolated by impossible lava
50:29flows.
50:30There are 13 large islands in the Galapagos, and many smaller ones, and they differ in
50:38both age and their vegetation.
50:41The tortoises differ too, because their shells have evolved into the different shapes best
50:46suited for eating the food available on their own particular island.
50:51On islands where there's abundant food on the ground, the tortoises have dome-shaped
50:55shells and short necks that only need reach downwards.
51:00But on islands where the tortoises browse on higher bushes, their necks are longer and
51:05the shells are saddle-shaped at the front, so they can stretch their necks upwards.
51:11When the first ships arrived here, there were thousands of each kind of tortoise.
51:17But then people began to slaughter the tortoises for meat.
51:23They discovered the remarkable fact that these creatures could live for a year without water
51:31or food.
51:33So they took them on board their ships and slaughtered them at sea.
51:38The tortoises on Pinta Island were apparently exterminated.
51:43But then, in 1971, it was discovered that there was one lonely single survivor.
51:55That was Lonesome George.
52:00This film was taken over 30 years ago by the team that brought George back to the Charles
52:04Darwin Research Station.
52:06The scientists hoped that another Pinta tortoise might be discovered in some corner of his
52:10island or even in a zoo somewhere in the world, but none has ever been found.
52:20So now George lives in his own enclosure, completely safe but entirely by himself.
52:26He's the last of his kind.
52:29It's better news for the other Galapagos tortoises.
52:33Felipe Cruz from the research station showed me some of the work being done there.
52:38They take eggs laid by wild tortoises and put them in incubators.
52:43The hatchlings are about the size of apples and have soft shells, so are vulnerable to
52:48predators, especially rats that were accidentally introduced to the Galapagos.
52:56The young ones I saw were only a few months old.
53:00They're kept in special enclosures and given all the foods they need to enable them to
53:05develop hard, protective shells.
53:09It takes a few months for their shells to harden, and it's five years before they're
53:13totally predator-proof.
53:22So far, in total, we have repatriated over 3,000 tortoises.
53:273,000?
53:28In the different islands.
53:31Galapagos are also helping to solve another man-made problem.
53:36Domestic goats that have run wild are eating the tortoises' food and destroying the
53:41precious plant cover that they need for shade.
53:44So a systematic programme of eradication was started.
53:56I was able to see the effects of this programme for myself.
53:59We visited one island where, two years earlier, the goats had been eliminated, and the difference
54:04was dramatic.
54:05The lush vegetation had returned.
54:09Now the tortoises can find the shade that is so important for them, and there's plenty
54:14of grass for them to eat.
54:25Reptiles are not alone in being under threat.
54:28The amphibians, if anything, are in even greater danger.
54:32Not since the disappearance of the dinosaurs has a whole group of the animal kingdom been
54:37under such threat.
54:39In Japan, one of the most dramatic of amphibians, the giant salamander, has fewer and fewer
54:45places to live.
54:52In Panama, we filmed the golden frog.
54:55Since we took this shot, the species has become so rare that the few survivors have
55:00been caught to be protected in zoos, so it's now extinct in the wild.
55:07The gharials that we filmed with their babies were nearly exterminated in the 1970s when
55:12they lost most of their natural habitat, and they're not safe yet.
55:18To try and halt their decline, their eggs are being collected, hatched in incubators,
55:23and the babies reared in captivity until they can be released in the wild.
55:28So there may be hope for them yet.
55:31The gopher tortoise we filmed in Florida is also in trouble.
55:35The areas where it digs its burrows have become prime real estate and are now much sought
55:40after for building and farming.
55:44By explaining their problems to landowners and developers, they may yet have a future.
55:55In the great island of Madagascar, there are more species of chameleon than in all the
55:59rest of the world put together.
56:04But the destruction of the island's forests began centuries ago and only a few patches
56:09are left.
56:10They too are still being felled, and chameleon species may be lost even before they've been
56:15identified.
56:21We will need to act now if we're not to lose what remains to us of the reptiles and amphibians
56:27that have survived for 200 million years.
56:32Lonesome George, it seems, is doomed to be the last of his kind.
56:38But at least he can be a living inspiration for us all to protect the remainder of the
56:45reptiles and amphibians of the world.