Episode 9 David Attenborough's Natural Curiosities

The natural world is full of extraordinary animals with

amazing life histories.

Yet certain stories are more intriguing than most.

The mysteries of a butterfly's lifecycle,

or the strange biology of the Emperor penguin,

some of these creatures were surrounded by myth

and misunderstandings for a very long time.

And some have only recently revealed their secrets.

These are the animals that stand out from the crowd.

The curiosities I find most fascinating of all.

The bodies of some animals stretch and shrink in extraordinary ways.

Constrictor snakes can swallow prey twice their own size.

While the camel's hump can almost double in weight,

giving it the energy to travel huge distances across deserts.

What is the secret behind such expandable bodies?

Also in this programme, we meet two animals whose extraordinary

body shapes are determined by their diet.

The blue whale grows enormous

by feeding on tiny shrimp-like creatures,

while flamingos spend their lives eating with their heads upside down.

And yet, both ways are curiously similar.

We've long been fascinated by the camel's ability to live in the

harshest of deserts, places where during summer temperatures

can soar up to 50 degrees Celsius.

While in winter, they can drop to 30 degrees below freezing.

With little in the way of food or water,

camels can sometimes go without eating or drinking for over a week.

Most other animals couldn't survive conditions like this.

How does the camel do it?

The camel's secret was thought to lie in its hump.

In a healthy camel, it can be big and firm, like this one, and

weigh as much as 30 kilos, which is the weight of a ten-year-old child.

But if the camel goes without food, and particularly water,

for any length of time, then the hump can get floppy

and even droop over on one side, as that one has done.

So, people used to think that the camel stored water in its hump.

In fact, there are two different kinds of camel - the one hump,

or dromedary, and the two-humped, or the bactrian.

Nearly all camels alive today are the domesticated

descendants of one or the other.

The wild dromedary almost certainly doesn't exist.

And only a few bactrian camels remain,

roaming the deserts of central Asia.

The camel is a very tough animal, but in the wild today,

it's rarer than the giant panda.

It's hard to say where the idea of a water storing hump came from.

The Ancient Romans were the first to suggest that the

camel may have in a built-in water reservoir.

And then, later on, people got the idea that it had two stomachs -

one for food and one for water.

In the 18th century, an eminent anatomist, John Hunter, decided to

investigate the truth behind these assertions,

and he dissected a camel.

He found that the stomach consisted of three or four compartments,

similar to those of a cow or a sheep.

But inside one of those compartments, he discovered these

pocket-like structures, which are not found in any other large mammal.

Hunter didn't know what the pockets were for, but others after him

proposed that they were special water storage cells.

And then, despite any kind of evidence to prove that this

was true, for another 250 years, books on natural history,

like this one, featured illustrations of water

storage cells in the camel's stomach.

We now know that that's not true, even though

we don't know exactly what the strange pockets are for.

But the camel's hump is certainly not filled with water,

it's made entirely of fatty tissue.

It is, in fact, an energy reserve for times when food is scarce

and it can expand to such a degree that it makes

up 80% of the camel's body fat.

This enables a camel to go for two weeks without feeding, if necessary.

But there's a twist to the story.

When fat is broken down in the body, it produces not just energy,

but also water.

In fact, each gram of fat broken down during metabolism

produces one gram of water.

So could the camel's hump provide it with extra water after all?

A fatty hump that contains both food and water would seem to be

just what a desert animal needs, but it's not as simple as that.

To consume its fat, an animal needs more oxygen,

so it has to breathe more, so when living on the fat in its hump,

the camel actually loses more water through its airways than it gains.

So the camel doesn't have a secret store of water.

How then can it survive in a waterless desert?

Camels can go without drinking for more than a week

because they have an extraordinary ability to retain the body moisture.

We ourselves lose over a litre of water a day

through our moisture-laden breath.

But the camel has nostrils which it can shut tight.

And that not only keeps out the sand,

but retains the breath within the nose, and there,

the moisture can be reabsorbed by the linings of the nostrils.

Most mammals also lose a lot of water

when they cool their bodies by sweating.

But camels can endure a rise in body temperature that would kill

most other mammals without sweating.

If our temperature goes up by as little as one degree, it's a

sign of illness.

While three degrees causes vital organ damage and eventually, death.

The camel can cope with as much a six degree rise,

with no ill effect.

This means that camels don't have to sweat

until conditions get very hot indeed.

And if necessary,

they tolerate losing more of their body water than other mammals.

When animals become dehydrated, their blood becomes thicker

and more difficult to pump through the body.

If we lose 10% of our body water, we start to go dizzy and blind.

At 15%, our internal organs start to fail.

Camels however can lose a third of their body water with no ill

effect, something that would kill most other animals.

How do they do it?

Well, some of the answers may lie in the shape of their blood cells.

These are the red blood cells from a human being,

which are disc-shaped, like that of most mammals.

These, on the other hand, are from a camel

and are slimmer and more oval in shape.

It may be that the oval, streamlined shape makes it

easier for the blood to flow when the animal is dehydrated.

Certainly, a camel's blood is less thick and sticky than ours.

The cells also have particularly strong walls.

This prevents them from rupturing

when the animal suddenly drinks large amounts of water, and when

they do find water, camels have the ability to drink it very quickly.

A single camel can take the contents of all these bottles,

that's 100 litres, in a mere 10 minutes.

For any other animal to do that, it would be extremely dangerous,

but the camel has the ability to hold the water in the stomach

and only release it into the bloodstream very slowly,

in a way that does no damage.

We now understand how camels can survive harsh desert conditions.

And yet, surprisingly, new research suggests that they first have

evolved to live in the cold Arctic.

Scientists have recently discovered the fossil bones of giant shaggy

camels that roamed the forests of the Canadian Arctic

some 3.5 million years ago.

The Arctic camel was a third larger than the modern bactrian,

but otherwise looked very similar.

And that may be no coincidence.

The wide, flat feet that stop the camel from sinking into desert

sand could also have helped its ancestors walk in deep snow.

And a fatty hump provided the food reserve a camel would need to

survive long cold winters.

We may never fully understand the mysteries of the camel's hump,

whether it evolved first as a way of keeping warm or staying cool.

But we have unravelled many other mysteries of the animal's

body that enable it to endure conditions that few other

animals would be able to withstand.

The camel's expandable hump was a mystery to us for centuries.

Our second curiosity can stretch its body in even more

extraordinary ways and devour prey many times its own size.

This is a green anaconda, one of the largest snakes in the world.

It's about four metres long and weighs 70 kilos,

and it's only half grown.

They can grow to a length of six metres

and weigh twice as much as this one.

But it's their ability to be able to swallow enormous prey that's

really grabbed our imagination.

Could one of these really bite a man

and swallow him whole and alive?

In the 16th century, European explorers venturing in to the

Amazon jungle were fascinated by tales of a huge river monster.

It was said to devour cattle and deer and to spit out

water like shot from a cannon, knocking animals out of trees.

These fantastic stories led people to go in search of this

marvellous beast.

In 1907, a British explorer, Colonel Percy Fawcett,

claimed to have encountered an enormous snake on the Amazon River.

A huge head, he said, rose up from the water,

dangerously close to his canoe, and a colossal anaconda emerged.

Greatly alarmed, he shot the snake dead.

He claimed that when measured, it proved to be nearly 19 metres,

over 60ft, long.

But Fawcett's account was met with disbelief and he never provided

convincing proof because soon after that, he

vanished into the Brazilian jungle and was never seen again.

The creature that Fawcett encountered was almost

certainly a green anaconda.

Despite their massive proportions,

these huge snakes are seldom seen because they spend

most of their time in water, waiting in ambush for their prey.

In this murky world, they're certainly well camouflaged

and so some people believed that somewhere,

another real monster might still be lurking unseen.

In the 1960s, a snake was brought to the

Museum Of Zoology at the University College London.

This is it.

It had lived in London Zoo for some years before it died

and it was five metres long.

A lot of work went into preparing the skeleton.

It had to be carried out on to the flat roof of the museum

and it was finally displayed in this rather unusual way -

wrapped around the branch of a tree.

For years, the museum displayed it as an anaconda,

but in 2012,

a member of the public saw an old photo of the snake

on the museum's website and pointed out that it

looked like an African rock python and not an anaconda.

It's unclear how the mistake came about.

The markings on the two snakes are quite different.

But both are giants and there's much controversy as to which

species is the largest snake of all.

Anacondas, pythons, and boas, like this one, don't kill with venom.

They're constrictors. They squeeze their prey to death.

And their coils can exert a very strong pressure indeed,

as I can feel with this one on my arm.

But a big anaconda can squeeze with the force of around 4,000 kilos,

that's like having a bus on your chest.

And that can certainly crush the spine of a deer or a capybara.

And yet, constrictor snakes don't usually crush their prey.

In most cases, they simply squeeze it

so hard that the animal can't breathe.

Every time its prey tries to inhale,

the snake's powerful muscles squeeze harder.

The unfortunate victim then either dies

because its blood can no longer circulate, or suffocates.

An anaconda, or a python, can kill prey that is not only

twice its own body size, but many times bigger than its head.

So how does it manage to swallow its victim whole?

Popular folklore has it that anacondas

and pythons unhinge or dislocate their jaws to swallow large prey.

That is not true.

They do, however, have the ability to open their mouths wider than

most animals.

Pythons and anacondas have this additional bone

attached to the back of their jaws.

This provides a double hinge at the joint and allows them

to open their jaws extremely wide, both downwards and sideways.

In addition, the two sides of the lower jaw are not fused

together, but joined by an elastic ligament.

This gives the jaws a lot of stretch and they can even move apart

when the snake is swallowing large prey.

It also allows each side of the jaw to move independently of the other.

When eating a meal,

particularly one that is much larger than itself,

the snake can alternately move its jaws on either side of its head

and walk its prey into its mouth,

even while its victim is still alive.

As the jaws open wide, the snake's elastic skin stretches.

But the mobility of the skull comes with a price.

Many of the joints that in other snakes are solid have been

replaced by mobile ones.

So the skull has less crushing power.

As a consequence,

the snake has to use its entire body to overpower its prey.

Getting large prey into the mouth is one problem, but how does the snake

push it all the way down the length of its body, into its stomach?

This is a Burmese python and it hasn't fed for a long time.

So I'm hoping to give it a little breakfast.

With a dead rat.

What about that?

Saliva from the salivary glands in the mouth has moistened

the prey, so it's easier to swallow.

And now, it's moving its jaws,

drawing the rat farther down its throat,

until eventually the muscles of the flanks take over,

squeezing the prey and pushing against the ribs, so that it

looks as though the snake is, as it were, crawling around the rat.

And that will continue for some time,

as the prey is worked down, in to the snake's body, until

eventually it reaches the stomach, which is around the middle here.

Equally remarkable is what happens inside the snake.

After months of fasting,

it has to restart its digestive system quickly.

Within a day, some of the internal organs double in size.

The heart expands,

pumping greater volumes of blood around the body

and special cells in the lining of the stomach produce powerful

enzymes that break down flesh and bones.

And when the prey is entirely digested,

the python's organs return to normal again.

Anacondas and pythons are able to take in enormous

meals in a single mouthful.

But how do they then survive fasting for months on end?

Like all coldblooded animals,

snakes get much of their heat from the sun,

so they need less food to fuel their bodies

and most of what they eat is converted directly into body mass.

Snakes continue to grow throughout their lives and anacondas get

bigger than any other species because they live mostly in water.

Their massive body is supported by its buoyancy.

So it's certainly possible that an anaconda could grow to

an enormous size.

But how large can a snake really get?

In 2009, further light was shed on this question with

the discovery of the fossils of a super snake.

It was given the name titanoboa

and it suggests that snakes can get very large indeed.

Titanoboa was nearly 13 metres long, the length of a bus,

and must have weighed over a tonne.

It lived around 60 million years ago,

shortly after the extinction of the dinosaurs.

We don't know for sure,

but it may be that the warmer climate of the Earth

at the time allowed coldblooded snakes to grow much larger in size.

What is certain is that for at least 10 million years,

titanoboa was the largest predator on the planet.

Both the camel

and the anaconda can withstand extreme periods of fasting,

but it's only by looking inside the camel's hump

and the anaconda's stomach that we've discovered

the truth behind their amazing expandable bodies.

The blue whale weighs almost 200 tonnes.

It's the largest animal on Earth and it's rarely seen.

I didn't glimpse one until I had been filming animals for almost

50 years and when I did, it was one of the greatest thrills of my life.

I can see its tail, just under my boat here.

And it's coming up... It's coming up...

There!

The blue whale is 100ft long.

30 metres.

Nothing like that can grow on land

because no bone is solid enough to support such bulk.

Only in the sea can you get such

huge size as that magnificent creature.

The blue whale was a mystery to science for a long time.

Living out in the deep oceans,

people rarely caught sight of more than the spout of this giant.

The first published description comes from a physician, Robert

Sibbald, who found a whale stranded off the coast of Scotland in 1692.

It was first named after Sibbald,

but later given the scientific name Balaenoptera musculus.

the Latin "musculus" means both muscle and little mouse,

an ironic double meaning for the largest animal on Earth.

When the first blue whale specimens were washed up on our shores,

they must have caused quite a stir and excitement.

Here was a colossal animal, weighing over 150 tonnes,

nothing as big had even been seen before.

A giant of this scale must be a predator,

at the top of the food chain.

But what kind of creature was it?

And what was it feeding on to make it so big?

The first blue whale specimens were found at a time

when scientists were just starting to classify animals, not

only by their external appearance, but by their internal structures.

And few animals proved as problematic as the whales.

From the outside, they looked and behaved like fish,

but their internal organs were like those of a large mammal.

The bones of the whale's front fins are very similar to

those in our own arms.

The five digits on the hand are clearly visible.

But they've been modified in to paddles for swimming.

What kind of creatures were these truly extraordinary animals?

The controversy as to whether whales were fish or mammals came to

a head in a New York courtroom in 1818.

A jury was asked to pass

judgement on the question for the purpose of the New York state law.

The issue had come up because a shrewd merchant who owned three

barrels of whale oil had refused to pay tax levied on fish oil.

He pointed out that, according to the latest scientific opinion,

whales weren't in fact fish.

The inspector collecting the tax had scorned the idea. "What?!

"Whales not fish?!" he said.

And slapped handcuffs on the merchant.

The lead witness was a respected scientist called Samuel Mitchell.

Mitchell entered the courtroom expecting to explain to

everybody why whales were mammals, not fish,

but instead, found himself being attacked by the most gifted

lawyer in the country, William Sampson.

Sampson argued that scientists didn't have the right to

rename God's creatures and force them in to absurd groupings.

The idea that humans

and whales should be in the same category seemed to him grotesque.

Mitchell and science never stood a chance.

After deliberating for 15 minutes, the jury announced

the verdict in favour of Sampson and the fish oil inspector.

According to New York state law, whales were deemed to be fish,

not mammals.

Although the general public still considered whales to be fish,

scientists were by now largely agreed that they were indeed

mammals that had taken to living in the sea.

But what was the blue whale feeding on to allow it to grow to

such an extraordinary size?

The answer can be found by looking inside the mouth,

which contains some very bizarre looking structures.

This is the skeleton of a right whale

and its mouth parts are very similar to those of the blue whale.

Instead of teeth, it has these strange plate-like structures

hanging from the upper jaw.

The plates are aligned alongside each other and the inner

edges fray because the large tongue continually rubs up against them.

And then, the frayed edges entangle to form a thick mat that

acts like a gigantic sieve.

And when early naturalists opened up the gigantic gut of these whales,

they found not fish or other large prey,

but tiny shrimp-like creatures called krill.

To everyone's astonishment,

it turned out that these whales feed on some of the smallest

prey in the sea and these strange plates serve to filter

the krill out of the water.

The rows of plates are called baleen and we now know that they

form a highly specialised filter feeding system.

The giant animal dives deep beneath the surface,

in search of swarms of krill.

The pleated skin on the throat

and belly expand and the mouth balloons outward to four

times the size, taking in an enormous mouthful of water.

The tongue then forces the water out through the baleen

and thousands of tiny krill are left behind.

Today, we know a lot more about this unusual feeding structure.

This is baleen.

It's often referred to as whale bone, but it's not bone at all.

It's keratin, the same substance as our hair and fingernails.

And it's both strong and slightly elastic.

The plates emerge from the whale's jaws instead of teeth

and continue to grow throughout the whale's lifetime.

These bands in it are much like the rings of a tree.

Several may be laid down in the course of a year,

so the baleen can give us an indication of the age of a whale.

We also know from other evidence that blue whales can live to

be over 100 years old.

Recently discovered fossil whales have both teeth and simple filters,

which suggest that early filter feeding whales may have

sucked small animals from the sea floor.

There is a whale alive today that feeds in just that way,

the grey whale.

It stirs up the sediment and scoops it in to its mouth

and then filters out small food particles with its baleen.

Krill is abundant in the oceans

and blue whales can eat enormous quantities of it with each mouthful,

soon swallowing 90 times more than they immediately need.

The surplus is then stored in the form of blubber

and this helps them cope with periods when food is scarce.

The blue whale was a mystery to us for a long time.

But we now know that its enormous body is fuelled with vast

quantities of the tiniest of prey. Over the course of its lifetime,

a blue whale will consume around 50,000 tonnes of krill

and unlike teeth, which fall out with old age,

the baleen never stops growing and is constantly replaced.

Maybe this unusual body design not only helps the blue whale

grow to this enormous size, but also to such a formidable old age.

The blue whale has become a giant by filtering tiny creatures

out of the ocean.

Our second curiosity, the flamingo,

also has an unusual body that has been shaped by its diet.

For a long time, the flamingos were birds of myth and mystery.

Travellers in Africa saw them shrouded by the hazy mists,

rising from volcanic soda lakes and believed that they were firebirds.

In Egyptian mythology, the firebird, or phoenix,

was a sacred creature with beautiful red plumage that was

consumed by magical fire and then rose again from its own ashes.

The flamingo's scientific name, Phoenicopterus,

reflects some of its legendary past.

It means phoenix wing.

These beautiful

and elegant creatures are some of the most curious looking of birds.

No other bird has a beak shaped quite like this.

Or indeed such glorious pink colours.

And yet, we're so familiar with them that we

rarely think about their strange appearance.

Why is it that the flamingo is so different from all other birds?

In that classic children's book,

Alice In Wonderland, Lewis Carroll has fun with the flamingo's oddity.

Alice plays croquet with the Red Queen, using them as mallets,

holding their heads and necks upside down,

in much the same posture as the birds take when feeding.

When you look at the skeleton of a flamingo, the thing that strikes

you most is the extraordinary length of the legs and the neck.

The neck has 17 bones in it,

which is no more than in other birds, but each is greatly

elongated, giving the flamingo its extra long neck and flexibility.

But the flamingo's most curious feature is surely its beak.

And the reason it looks

so strange is that it is the only beak adapted for use upside down.

In most birds, the upper part of the bill is larger than the lower

one, but in the flamingo's, it's the other way round.

The lower bill is much bigger

and has a deep central groove in it that holds the flamingo's tongue.

The upper jaw is thin and moveable, so when the bird's head is

upside down, the flamingo's jaws work, as it were, normally.

When feeding, the flamingo gently sweeps its bill back and forth,

sucking water in at the front and squirting it out from the sides.

The water that goes in is murky, while that which flows out is

clear and that gives us a clue to what it's feeding on.

The beak has tiny bristles all along its edges,

much like the whale's baleen.

And the tongue has two rows of horny spikes along its length.

When feeding, the bristles and spikes form a sieve,

trapping any particles inside.

And the large tongue acts as a pump, pushing water in and out.

It's a unique design for a beak. No other bird has one like it.

Although at first sight, they may look the same,

flamingo beaks in fact come in two different shapes.

This is because they eat slightly different food.

This is the beak of a greater flamingo,

which feeds on crustaceans,

which are usually found near the bottom of a lake.

It's long and shallow,

so the birds can feed in water only a few millimetres deep.

This beak, on the other hand, is from a lesser flamingo.

Its bill is shorter, but more bulbous and deep-keeled.

The lesser flamingo feeds on microscopic algae,

which usually float just below the surface of the water,

and the deep keel acts as a buoy, bobbing along just at the

right depth, as the bird moves through the water.

These different bills allow two species of flamingo to live

side by side.

In Africa's Rift Valley, greater and lesser flamingos are found on

the soda lakes, having specialised on food that others can't reach.

The waters are so hot and toxic that they would strip

the flesh off any other animal, but flamingos thrive here.

Their long spindly legs have tough scales

and their webbed feet prevent them from sinking in to the soft mud.

The birds can even drink the water, which is

two or three times saltier than the ocean.

But it's not just the mud and water which are poisonous.

The blue green algae, which many of them feed on,

actually contain nasty toxic chemicals.

If that were to accumulate in the internal organs of the bird,

they could be lethal.

But the flamingo deals with that by directing these

chemicals into the feathers and the skin, where they do no damage.

The feathers of flamingos contain very high concentrations

of toxins, but they also contain another chemical, carotene.

Carotene is the reddish pigment that gives

flamingos their distinctive pink colour.

And it also comes from their diet. But carotene is not harmful.

On the contrary, it's a source of vitamin

and boosts the immune system, protecting against illness,

so a pink bird is also a healthy bird.

This glorious pink colour was probably an incidental

by-product of their diet.

Nonetheless over time,

it's evolved to play an important role in the flamingo's social life.

The flashes of colour are an integral part of their

courtship display and recent research has shown that the pinkest

flamingos are the most popular when it comes to finding a mate.

When flamingos breed, much of the carotene in their diet gets

channelled into the developing young.

Even the eggs receive pigments.

So much, in fact, that the yolk can be virtually blood red in colour.

These eggs are from captive flamingos and are infertile.

Let's have a look.

There.

Well, it's nothing like the colour or any other bird yolk that

I've ever seen.

Flamingos are so efficient at collecting their specialised

food that the yolk is actually packed full of protein and fat.

And this allows the chick to grow particularly quickly

and gives it a good start in life.

Despite the colour of the yolk,

the chicks hatch with fluffy grey feathers.

They're fed on special milk from their parents' crop.

This is not regurgitated food,

but a secretion produced by the lining of the digestive tract.

And it's deep red in colour.

The flamingo chick relies on this for the first few weeks of its life.

And it will eventually enable it to grow its glorious pink plumes.

We now know that much of the flamingo's bizarre

appearance has been shaped by its diet.

But one question continues to baffle scientists -

to which group of birds do the flamingos actually belong?

Some thought that they must be related to ducks and geese

because of their webbed feet and short duck-like beaks.

But others were convinced that with their long legs,

they're more like waders, such as storks.

Recent DNA studies contradict both these suggestions.

They reveal that the flamingo's closest relative may in fact

be a small diving bird that looks nothing like a flamingo.

The grebe.

Further studies found other similarities in the structure

of the eye and the number of feathers on the wing.

So, it seems that flamingos

and grebes are indeed each other's closest relatives.

But over time, diet and lifestyle has shaped the flamingo into a very

different looking bird, far removed from its grebe-like ancestor.

It's fair to say there's nothing else quite like a flamingo.

The flamingo and the blue whale are two very different creatures,

one living on land and one in the deep oceans.

And yet their bodies have been shaped in a similar way,

by their diet,

making each of them a curiosity within its own group.