Reptiles and amphibians are sometimes thought of
as primitive dull and dim-witted.
In fact of course they can be lethally fast
spectacularly beautiful
surprisingly affectionate and very sophisticated.
They have remarkably varied ways of catching their prey
and of defending themselves.
They can produce a great turn of speed
and fight with impressive zest.
Some have spectacular colours and show off to one another.
They communicate with calls...
(CROAKING)
(HIGH-PITCHED CROAKING)
...and with gestures.
And there. That's it.
The full works.
Reptiles have scaly skins
and amphibians soft moist ones.
None of them live at a uniform pace
but switch from the fast to the slow lane
within a year or an hour.
Unlike us they get their energy directly from the sun
and although being called "cold-blooded"
might suggest they are unemotional
they can be touchingly warm-hearted as mates...
(GRUNTING)
...and as parents.
And that's just the beginning.
There are a whole lot of other warm-hearted truths to be discovered
that give the phrase "life in cold blood"
a completely new meaning.
The Galapagos Islands.
Some of the reptiles that live here are particularly skilful at solving
the problems of getting their energy directly from sunshine.
Marine iguanas face a major thermal challenge
every morning of their lives.
During the night their bodies cooled
and now they must warm up quickly
in order that they can become active and start feeding.
Their bodies and skins are black
which is very efficient at absorbing heat
and they bask with their black flanks broadside to the sun.
The rate at which they absorb warmth
is invisible to the naked eye
but very clear indeed to a thermal camera.
First thing they are cold and purplish blue.
But slowly as they warm up
a golden glow spreads through their bodies
and eventually after half an hour or so
they become as hot as the rocks beneath them.
Once they are thoroughly warmed up
marine iguanas can maintain their body temperature
just about as constantly as I can
and what's more at about the same level
or indeed slightly higher around 37 degrees centigrade.
Now they need to feed.
There is nothing to eat on or around these barren rocks except seaweed
and to get that they will have to swim.
But the sea around here is surprisingly cold
around 15 to 16 degrees centigrade
and only the bigger iguanas can absorb enough heat
to power the dives to enable them to go to the seaweed at any depth.
However their bodies are now thoroughly warmed up.
The thermal camera shows them as golden yellow
as they clamber down over the cold blue rocks
and dive into the sea.
Although their islands lie almost exactly on the equator
the sea here is permanently chilled
by a cold current that sweeps up from the depths of the ocean
so they won't be able to stay in the water for very long.
They have no time to waste.
In the shallows close to the shore the seaweed has been heavily cropped.
To get a good meal they may have to dive to at least
15 feet five metres.
They are able to reduce the chilling effect of the cold water
by closing down the blood supply to their limbs
and the outer part of their bodies.
But even so their body temperature may drop
by 10 degrees or so.
A cooling like that would kill a human diver.
After five to 10 minutes on the sea floor
most iguanas have had enough
and they return to the surface
and the life-saving warmth of the rocky shore.
A recently emerged iguana is black.
Its chilled to the bone.
Now they need heat in order to be able to digest
that meal of seaweed and they get that
by spread-eagling themselves on these black hot sun-baked rocks.
Their image warms from black
to purple
and then from red to orange.
In the evening the temperature falls
and they huddle together to retain their warmth as long as possible.
They will have to wait until the following morning
before they can re-warm themselves sufficiently to feed again.
Most kinds of lizards have this daily schedule.
Side-blotched lizards in California certainly do.
You can see from the colour of my face that my body is warm.
That's because Ive got a central heating system
which I have fuelled with my breakfast.
In fact, about 80% of what I eat
is used in keeping my body temperature high and steady.
These lizards however squander very little of the energy
they get from their food on warming themselves.
They like the marine iguanas get nearly all they need for that
by basking on the warm rocks.
And so important is the need for warmth
that the females actually choose their males
on the basis of which has the best under-floor heating.
Each male sits on his pile of boulders doing press-ups
to signal his ownership and to warn off other males.
Intruders are confronted immediately and if necessary attacked.
And the victor returns to sit on his wonderfully warm throne.
Look at his rocky kingdom with a thermal camera
and its immediately clear why its so precious.
The rocks are very much hotter than the surrounding grassland
and big tall ones catch the sun earlier and retain its heat longer.
So not only does the sun warm him from above
his rocks do from beneath.
The most powerful dominant male has naturally the best pile of rocks
and not surprisingly almost all the females.
But is it the males themselves or their assets
that the females are interested in?
To find out lets move their hot rocks and give them to a subordinate male.
The females quickly recognise that a more desirable residence
has appeared in the neighbourhood
and start to move across.
And the sex-starved wimp
suddenly finds himself amazingly popular.
So the females do indeed go for the males with the hottest rocks.
These lizards on a small islet off the shores
of Minorca in the Mediterranean get their heat
from another and very unusual source.
Ow.
(LAUGHING)
Sorry.
They are very curious.
I'm the new boy on the block the new object in their environment
and that one just gave me a little nip.
They investigate the world around them by tasting it
and they are still trying to work out what I am.
Their island is rocky and not particularly rich in food.
The lizards are primarily insect eaters
but during the flowering season they also take nectar.
They collect it from plants like spurge
which is very common.
And they have a very special relationship with this flower.
Its called the dead-horse arum
and it certainly looks like carrion and...
(COUGHING) Oh dear.
It smells very strongly of carrion.
As a consequence of both its looks and its smell
it attracts carrion flies.
Of course its the flies that the lizards are after.
But as well as providing food for the lizards
this extraordinary flower helps them in another way.
This central part which is called a spadix
is slightly warm as you can see from a thermal camera.
The chemical process that produces the disgusting smell
also creates heat
and raises the temperature of the flower by up to five degrees
above the surroundings
sufficiently high for a lizard to warm itself on it on a cold morning.
And in case you find that hard to believe
here is confirmation from the thermal camera.
The purplish-blue lizard quickly takes on
the same temperature and colour as the arum.
And sitting on arums brings another benefit.
Breakfast.
A fly lured by the smell crawls inside.
The lizard hears the fly buzzing within.
The fly of course can't find anything it wants
but now it can't get out.
The entrance to the flower is blocked by the lizard.
And the lizard gets an easy meal.
Two months later the arum flowers have shrivelled
and produced their fruits.
Until 20 years ago
the lizards ignored these withered bundles.
After all they hardly look like food.
But then a particularly inquisitive individual
sampled a fruit and found the soft flesh around the seed rather good.
The habit spread and now the whole lizard population
uniquely in the Mediterranean
have become arum fruit eaters.
They do take a bit of swallowing but seeds passing through a lizards gut
not only survive but germinate even more easily.
As a result the arums which were rather scarce here 20 years ago
have suddenly become abundant all over the island.
A cold windswept island off the coast of South Africa
is not the first place you would go to if you were looking for reptiles.
But here on Dassen Island among penguins and seagulls
there is one of the greatest concentrations of tortoises
to be found anywhere on Earth.
There are about 5000 of them on this one tiny island.
The penguins and other birds thanks to their warm blood
are active no matter how cold it is
but the tortoises have to wait for the day to warm up
before they can get about their business.
They bask in the sunshine powering up their bodies to the optimum
working temperature of 33 degrees centigrade
and then they go off to feed.
As the day progresses the temperature rises quickly
and even before noon its too hot for comfort.
The tortoises have to head for shade.
In the late afternoon it gets cooler and the tortoises venture out again.
For them this is the best time.
They are thoroughly warmed up they've digested their morning meal
and they've got energy to spare.
The males begin to fight
jousting like medieval knights
using a projection on the front of the shell like a lance.
(EXCLAIMS)
The technique is to get the spike under your opponent
and then flick him over onto his back.
Contests can last for half an hour.
The loser tries to right himself but the winner keeps biting his legs.
At last the victor loses interest and goes off to find the female
who caused the argument in the first place.
As for the loser if he doesn't manage to right himself soon
he may cook in the sun.
Tortoises are able to sunbathe out in the open
because their strong bony shell gives them
almost complete protection from predators.
Less well-armoured reptiles like lizards
are vulnerable of course to hawks and coyotes and foxes and cats.
And in the morning when those warm-blooded animals are already active
the lizards are cold and can't move fast.
So they have a problem.
But they also have a solution
secret sunbathing.
You really can't see them until you are right on top of them.
And there's one there.
I'm in Arizona
and that at my feet is a lizard buried in the sand up to its neck.
Even while its buried it can use the sunshine
to warm its whole body.
It can control the supply of blood to its head
so that it pools in a cavity behind the eye.
Soon the blood there is as much as five degrees
above the temperature of the rest of its body.
Then the animal opens the major blood vessels in its neck
and the hot blood circulates
so that its whole body is thoroughly warmed
even though its still mostly below ground.
This is a horned lizard
and very beautiful too.
This particular species is called the regal horned lizard
because it has this splendid crown of spikes at the back of his neck.
When he is hidden they break up the outline of his head
and so you hardly see him at all.
And now in the warmth of my hand and in the sunshine
I guess he has warmed up quite a lot.
And if I put him down he now at last may be able to run for it.
And indeed he does.
South African armadillo lizards which live on these rocky outcrops
have a different solution to the problem of safe sunbathing.
they've turned it into a social activity.
Whole families of them live together
in the crevices among the rocks and in the morning
they all emerge to warm up in the sun.
Of course there is safety in numbers.
There are lots of eyes to spot danger if it appears.
And when one sunbather takes fright they all dive for safety.
If a predator is quick it is possible to grab one
but even then an armadillo lizard is not going to be an easy meal.
Ow.
(LAUGHING)
They have an additional form of defence.
They bite their tails.
The reason they do that is that it covers up
their vulnerable underside
and exposes only these very sharp spiny scales
which is very good protection against predators like snakes or mongooses.
They stay like this for quite a long time
before they are confident enough to uncurl.
I will put him down and see how he does.
Sunset necessarily brings an end to activity for most reptiles.
But not for all.
A leopard gecko.
It like most geckos is nocturnal
and it manages to get all the heat it needs from the rocks
which retain something of their warmth for several hours after the sun has set.
This male is in search of a mate.
She is less brightly coloured.
They inspect one another.
He collects her scent with his tongue
and discovers that not only is she female
but she's sexually available.
He's interested.
He nibbles her neck and strokes her flanks
all part of his elaborate courtship routine.
Copulation begins.
This is the time in mammals and birds
when the sex of the young is determined
but not in a number of reptiles including geckos.
Once again its temperature that profoundly influences their lives.
The female goes away to lay her eggs.
She has chosen a place where the temperature
is about 31 degrees.
As her body is the same temperature as her environment
she can't heat her eggs by sitting on them
as warm-blooded birds do
so they are exactly the same temperature as the rocks beneath.
After a couple of months both eggs begin to hatch.
The first to emerge is a male.
And the second will be too.
Its the temperature which has determined that.
If it had been a few degrees lower
both eggs would have developed into females.
Crocodiles have their sex determined by temperature in a similar way.
This clutch belongs to the Indian fish-eating crocodile the gharial.
(CALLING)
The female has heard the calls from below ground
made by her hatching young
and is helping them to dig their way out of the sand.
They immediately make their way down to the water.
And mother goes too.
Here of course they are nice and warm.
Water retains its daytime heat
better and longer than rock
so unlike many other reptiles
gharials and other crocodilians
have enough energy to feed actively all night.
(HISSING)
While being nocturnal is unusual among reptiles
its the norm for amphibians.
Their skin is not scaly and watertight like a reptiles.
Its soft moist and permeable.
If they exposed themselves to sunlight for any length of time
they would dry out and die.
So most frogs only leave their shelters at night.
Since they can't absorb sunshine directly
they either get their heat from their surroundings
or draw their energy from the fat reserves
that they built up when the feeding was good.
But even so they seldom hop
unless they have very good reason to do so.
This frog however the South American waxy monkey frog is exceptional.
Its one of the few that can tolerate direct sunshine for any length of time.
And that is because it secretes a wax from glands on its neck.
No human sunbather goes to more trouble than they do
to make quite sure that every part of their skin
is properly anointed.
The sunshine may also bring them an extra benefit.
It probably protects them from the fungal infections
to which many moist-skinned amphibians are prone.
In the rainforests of Central America the air is heavy with moisture.
So the poison arrow frogs can risk basking
in the little patches of sunshine
that dapple the forest floor and if they begin to dry out
they can retreat into the leaf litter.
(CROAKING RAPIDLY)
The sunshine gives them sufficient energy
to permit the extravagance of calling almost continuously
in defence of their territories.
They even have enough spare energy
to indulge in long battles with their neighbours.
These fights can go on for well over half an hour at a time
until both contestants are completely exhausted.
So a moist skin limits not only where amphibians can live
but how energetic they can be.
Out in the sunshine dry-skinned reptiles have more options.
By collecting solar power so efficiently
reptiles need to use very little of the energy they generate themselves
to warm their bodies.
In fact they use around a tenth
compared with a mammal of a similar size.
That means they don't have to eat very often.
A puff adder like this one can wait almost indefinitely for its next meal.
Amongst predators patience really is a virtue.
Whilst waiting for a meal to wander within striking distance
a snake shuts down its body processes
so that it uses the minimum amount of energy.
Only the equivalent of a pilot light is left on
and it can remain like this for weeks.
All around it mammals are expending their energy in a way that
compared with the snake seems extraordinarily extravagant.
But when a snake needs to move fast it can do so with lightning speed.
Once its prey is secured a snake can take its time over its meal.
This gigantic python is feeding on a deer.
A python kills its prey by wrapping its coils around it
and squeezing its victim so tightly and for so long
that it can no longer breathe.
But swallowing its meal takes time.
The deer will go down head first. Its much easier that way.
The ligaments connecting the snakes upper and lower jaw are elastic
so that it can engulf the deers head
even though it is much bigger than its own.
With its mouth stretched tightly around its meal
the snake can't breathe in a normal way.
But its able to push the top of its windpipe right out of its mouth
and so continue to take in air.
After some hours all that can be seen of the deer are its hind legs.
Once the meal has been completely swallowed
the inner workings of the snakes body change greatly.
Its digestive processes switch to full power
and increase their activity 40 times.
There is an explosion of biochemical activity.
The liver the secretions of which power digestion
doubles in size within two days.
The heart grows by some 40%
It will take the python at least a week to completely digest this enormous meal
but then it will not need to feed again for months or even a year.
This ability to switch off helps reptiles and amphibians in another way.
A baby North American painted turtle.
It and the rest of its clutch have only just hatched.
But its late in the year and the chill of winter has already begun.
If the hatchlings clambered out of their hole now
they would find nothing to eat.
So they stay where they are.
The temperature will fall to minus 10 degrees.
Ice crystals grow around the babies and even inside their bodies
but their tissues are protected by a kind of antifreeze.
This would kill any mammal or bird.
They remain in this deep freeze for up to six months.
But spring comes at last.
The ice melts around them and eventually within them.
Slowly they begin to come to life.
It takes quite a time for them to become fully functional
but eventually they are ready to face the outside world.
So by allowing their bodies to cool they have avoided the hard times.
With the arrival of spring
their parents are now preparing to breed again.
The male courts the female
by gently strumming her cheeks with his long claws.
And she responds.
Cold blood is clearly no barrier to affection.
In fact reptiles can conduct
as complex and as sensitive a courtship as many a mammal.
This is the biggest of all living reptiles and one of the most feared.
If one creature were to be labelled a cold-blooded killer
it would be this a saltwater crocodile
a monster that can grow to a length of 20 feet six metres and weigh a tonne.
But male and female when they court blow bubbles at one another.
He is three times her size and could easily crush her
yet he treats her with great gentleness.
He strokes her back.
Slowly he aligns his body with hers.
So union is achieved.
Crocodiles are among the most ancient of reptiles.
Their ancestors appeared at about the same time as the dinosaurs.
But what about them? Were dinosaurs similarly cold-blooded?
The rocks of the North American west are particularly rich in dinosaur fossils.
A hundred million years ago
this was a horizontal mudflat at the edge of a sea.
And across it came an adult dinosaur
with a smaller younger one trotting alongside
leaving their footprints behind to be fossilised.
They were iguanodons a herd of them
together with some bird-footed dinosaurs.
Were these all solar-powered?
Some of the ancient reptiles had specific adaptations
to help them collect heat.
This is a plate from the back of a stegosaurus
and you can still see the lines where the blood vessels ran
which collected the heat and carried it to the rest of the body.
So for the stegosaurus at least the need to collect heat
seems to have been just as important as it is for its relatives alive today.
But there are clues that suggest that ancient reptiles were better
at maintaining their temperature than their modern counterparts.
This is the jaw bone of a very large and very famous dinosaur.
In life its head would have been 18 feet six metres above ground.
This is the jaw of Tyrannosaurus rex.
An animal as big as this
has a very large body mass which retains heat very well.
So perhaps these huge dinosaurs were in fact warm all the time
simply because they were too big to lose all their heat overnight
as a smaller reptile would.
But what about when they were small?
Were adolescent Tyrannosaurs able to maintain a steady body temperature?
Were they in short warm-blooded?
Evidence on that can be found in
the microscopic structure of their bones.
(ROARING)
This is the leg bone of a young Tyrannosaurus
and it has bands in it.
The inner section formed when the animal was young
has an open structure like the bone of a fast-growing warm-blooded mammal.
The outer part is more dense more like that of todays reptiles.
But whether dinosaurs were really truly warm-blooded we may never know.
What we do know however is that dinosaurs
were extraordinarily successful
and dominated the Earth for 150 million years.
But there are some reptiles today that can keep their body temperature
well above that of their surroundings
and these are the tracks of one of them.
These giants haul themselves up out of the sea along beaches like this
in many parts of the tropics but in order not to disturb them
I will turn this light out and well look for them with infrared cameras.
Leatherback turtles.
Like crocodiles turtles are very ancient creatures
having first appeared at about the same time as the early dinosaurs.
Today leatherbacks are the biggest of all reptiles
and the most widely distributed
for they are found all the way from these warm tropical waters
to the freezing seas of the Arctic.
These have come ashore on a beach in Trinidad
where almost certainly they were hatched.
Now they in their turn are laying their eggs here.
Leatherbacks we know can generate heat internally
and there is proof of that if you have a look
at the eggs that she is laying right now on that thermal camera.
They are emerging from her body
and lo and behold they are bright yellow verging on white
proving that they are warmer than their surroundings.
And she generates that heat within her body
from special deposits of fat so that she can maintain her
internal body temperature up to eight degrees centigrade
above that of the water through which she swims.
As she sweeps away the surface sand
you can see that the sand too is yellower
warmer than the outside of her shell
for it still retains the heat it acquired during the day.
So how do leatherbacks retain that precious and expensive
internally generated heat?
Well to start with they have their huge size to help them.
They really are massive animals.
This one is getting on for two metres six feet long
and they can grow to weigh a tonne and a half.
And of course big objects retain their heat
very much more readily than small ones do.
And there's another reason.
Now I am bright yellow going into white
which shows that I am losing a great deal of my heat.
But she on the other hand is very much darker
and that is because she has an internal layer of fat
an insulating layer just beneath the shell which wraps around her body.
The leatherbacks are the only reptiles in the world
to have this kind of insulation.
Her eggs laid she fills in the hole with sand.
And now she's on her way back to the sea.
Life in cold blood has been a great success.
It has after all endured for some 350 million years.
But how did it all begin?
To find the answer to that we have to go back in time and back to the water
to the age when strange fish were hauling themselves up onto the land
fish that were the ancestors of the amphibians.
Amphibians and reptiles are not easy creatures to film.
They certainly do interesting things
but they also spend a great deal of time doing nothing much.
We needed the help of scientists who really understood these creatures.
Some workers have spent over 20 years studying their animals
both in the lab and in the field.
They investigate the lives of their chosen species using all kinds of gear
some sophisticated some perhaps less so.
With their help we had a rare chance to get
under the skin of some of our subjects.
Madagascar was going to be a very important location for us.
Its a huge island 1000 miles long
with a great variety of habitats
and its extraordinarily rich in reptiles.
I first went to Madagascar back in 1960 filming for a series called Zoo Quest.
Back then I was trying to film all kinds of creatures
including the monkey-like lemurs and many rare birds
but I was particularly fascinated by the islands chameleons.
There are in fact more species of chameleons in Madagascar
than in all the rest of the world put together.
There is one the pygmy leaf chameleon
which was said to be only an inch or so long.
I yearned to see it but I've never found it.
Now I was back and this time reptiles were our sole subject.
Although Madagascar is only separated from the east coast of Africa
by 300 miles of sea its people and particularly its animals
are very different indeed from those on the continent
with hundreds of species that are found nowhere else in the world.
Once again I was in search of chameleons.
Then all television was black and white
but now I could film and record chameleons in colour
and what colours they have.
We had come in the rainy season when most creatures including reptiles
tend to breed and are therefore particularly active and interesting.
And this time I had the help of Bertrand Razahamatra
a Malagasy naturalist who has made a particular study of chameleons.
He's worked on them for over 10 years and knows most kinds very well.
I asked him about the pygmy species that had fascinated me for so long.
-So I mean that really is full-grown? -Yes full-grown.
-Then its only that big? -Yeah its very small.
He suggested that although chameleons are mostly active during the day
we should look for them at night
because most of them turn pale in the dark
and are therefore easily picked out in the light of our torches.
Ah.
What is that?
-This is... -What species?
-This is oustaleti. -Oustaleti. And male or female?
-Female. -How do you know?
The colour.
-There's another one. -Oh there's another.
ATTENBOROUGH: This one was far from upset at being woken up.
Ah.
(ATTENBOROUGH LAUGHING)
It fed. That's absolutely extraordinary.
It can't possibly feed normally in the darkness.
It just takes advantage of our light and finds an insect. Bravo.
Lets go and see if we can find more.
Bertrand explained that there was another reason
why night was the best time to look for chameleons.
When they go to sleep they climb to the very far end of branches
where they are out of the way of predators such as snakes.
There's another.
And of course that was where we found them just as he said.
That's a big one.
Beautiful.
BERTRAND: Yes.
ATTENBOROUGH: This one is just a baby.
And how old do you think that is?
-I think just a few days. -A few days.
So even when its newly hatched it knows to come to the end of the branch.
Yes. Yeah. Look. They choose the tip of a branch.
-Yes. Where its very difficult to get. -Yeah.
Of course if it was in the day
-a bird could get it. -Yeah.
-But at night safe. -But at night safe.
Back in 1960
my chameleon-hunting techniques weren't quite so expert.
However I did discover that if you put a stick in front of a chameleon
it would usually obligingly walk onto it.
But now with Bertrand as my guide we could search
for the wonderful species that I had failed to find before.
ATTENBOROUGH: Would they be down here?
It lives on the ground almost invisible among the leaf litter.
-That? -There.
But Bertrand spotted it.
How extraordinary.
(WHISPERING) This is a pygmy leaf chameleon
the smallest chameleon in the world.
-In the world. -Yeah.
And probably the smallest reptile in the world.
-Of any kind. -Mmm.
(WHISPERING) You know I had heard about these
when I was here in Madagascar 47 years ago.
And I read about these and I never saw one.
And I think it was because
I never knew they were as small as this.
That is absolutely extraordinary.
Its about the size of a bluebottle a blowfly.
-And what does it feed on? -Small flies.
Small flies. How absolutely wonderful.
I am astonished. That is the most marvellous thing
I have seen for a very very long time.
Finding the pygmy chameleon would not have been possible without
Bertrands expertise and sharp eyes.
He's just one of the scientists who has helped to reveal to us
the secret lives of reptiles and amphibians.