Episode 8 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 life cycle.

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.

Some animals have intriguing ways of protecting their skin.

The hippopotamus lives in Africa under the hot tropical sun,

yet doesn't get sunburnt.

And capuchin monkeys live in insect-infested jungles,

but hardly ever get bitten.

How do these animals beat the elements

and protect themselves from sun, parasites, and disease?

And also in this programme,

some animals can perform amazing physical feats.

A flea's jump is said to be the equivalent of a man leaping

over St Paul's cathedral.

And it's famously quoted that cheetahs can run at speeds of 70mph.

But are these claims really true?

Hippos are large land mammals that can weigh up to three tonnes.

And they need to keep their huge bodies cool

and protected from the sun.

To avoid the heat, they spend much of the day swimming,

as they are doing now in the waters behind me.

But when they're on land, strangely they don't appear to get sunburnt.

The secret of their sun tolerance lies within their skin

that can sometimes appear shiny and greasy.

It has unique properties that shocked the early explorers

and now excites modern scientists.

Hippos live in Africa, south of the Sahara,

where temperatures can reach 40 degrees centigrade.

But they spend much of the day submerged in rivers,

lakes and swamps, and so avoid the worst of the sun's rays.

They possess formidable teeth, but they are in fact herbivores

and eat mostly grass, great quantities of it.

And they graze mostly at night.

Even so, continually moving in and out of water, together with being

roasted by the rays of the sun, could be very damaging to their skin.

But curiously, hippos remain healthy.

Throughout history,

the hippopotamus has been the subject of many strange tales.

The Greeks claimed they sweated blood, and the Romans said

they deliberately pierced their skin on sharp rushes to release blood.

It seemed bizarre that an animal would make itself bleed on purpose.

In the 19th century, one special hippopotamus allowed people

to get a closer look at these strange skin secretions.

In 1849, the British consul for Egypt, Charles Augustus Murray,

formally requested that the Pasha of Egypt helped capture

a hippo for the Zoological Society of London.

Hunters searched the reeds on a remote island called Obaysch.

2,000km up the Nile from Cairo,

they discovered a male hippo that was only a few days old.

When they tried to grab it, a strange thing happened.

Murray describes how, "A slimy exudation lavishly poured forth

"from the innumerable pores in the skin,

"rendering it so slippery that the animal was impossible to hold."

The hunters dropped the baby hippo back into the waters of the Nile,

but they managed to retrieve it again, using the hook of a spear.

The prized hippo was named Obaysch after the island of its capture,

and here he is.

Before his capture, young Obaysch lived with his mother.

She had moved away from the herd to give birth alone,

and she protected him from lions and crocodiles.

Whether Obaysch became accidentally separated from his mother,

we'll never know,

but we do know that secretions from his skin made him

so slippery that he very nearly escaped capture.

At this time, very little was known about hippos,

and many people believed that they were some kind of horse

that had taken to living in rivers.

In the early 20th century,

naturalists decided that they were closely related to pigs.

DNA evidence, however, now shows that, in fact, their ancestors

were cetaceans - the group that contains whales and dolphins -

so hippos still retain many adaptations for a life in water.

Hippos are very heavy animals

but, for most of their time, their bodies are supported by water.

They're not really very good swimmers.

In the water, they move by bounding across the bottom.

They're well adapted to a semi-aquatic life

because their ears, their eyes, and their nostrils are all towards

the top of the head, which enables them to lie almost totally submerged

and yet still keep notice of what's going on on land,

but their skin is almost entirely hairless,

so, on land, it has to be kept moist.

In order to prevent young Obaysch from sunburn and drying out,

the Egyptian Pasha had a boat built with a bathing pool,

to transport Obaysch in comfort all the way down the River Nile.

Accompanied by several cows to supply him with milk,

he arrived safely in Cairo four months later.

On receiving Obaysch,

the British Consul wrote excitedly to the Zoological Society of London,

confirming that the hippo was alive, and as tame and playful as a puppy.

But his travels were not yet over.

In the spring of 1850, Obaysch was taken to Alexandria,

to board a P&O steamship called the Ripon.

A special hippo house with a water tank was built on the deck

and, in May, Obaysch arrived safely in Southampton.

With the help of a block and tackle,

he was loaded onto a train bound for London,

and at 10 o'clock at night,

the tired hippo and his keeper reached London Zoo.

His home was a newly constructed enclosure,

complete with a heated swimming pool.

After many hours of travelling,

the hippo gratefully plunged into the water.

Obaysch, the hippo sensation, had arrived.

A journey of over 5,000 miles, by sailboat, steamboat and a train,

brought a hippo to England -

the first one since Roman times.

Now, Europeans had a chance to get close to this unusual creature

and perhaps learn more about its strange skin secretions.

Later, more hippos arrived at other zoos,

and the blood-red sweat was seen again.

In the cooler climate of Europe,

hippos don't sweat very much

but, zookeepers have reported that, sometimes, in the morning,

they see red trickles forming on the flanks of these animals.

It comes from particularly large pores,

which form streaks on the animal's side,

which does look a little like blood.

We've known for some time that this is a...

a moisturiser, but why it's red has only just been discovered.

A little more.

Come on.

There we go.

Recently, Japanese scientists were intrigued to see

photos of a wild baby hippo with light pink skin

that still didn't burn under the harsh African sun.

They wondered if the red secretion played

a role in protecting its pale skin,

so they collected hippo secretion from captive hippos

to look at its composition.

They discovered two pigments -

a red one, that they named hipposudoric acid,

and an orange one, that they called norhipposudoric acid.

The red pigment was found to absorb harmful wavelengths of light

and both pigments were antibacterial.

Here was the answer to why hippos never got sunburnt

and why the wounds of battling males rarely became infected.

HIPPOS GRUNT

The mysterious slime is neither blood nor sweat,

but a specialised secretion that turns red in sunlight

and protects the hippos' skin.

HIPPOS GRUNT

So, what became of Obaysch, the first ever hippo in captivity

that gave us a close-up view of these curious creatures?

For several years, he was a sensation at the London Zoo.

He even inspired the Hippo Polka, a popular dance of its time,

but visitors grew weary of him.

Some were disappointed not to see a giant river-horse

and others expected a ferocious beast, not a gentle giant.

Obaysch died in 1878 at the age of 28,

and he and others that followed

taught us some intriguing things about hippos,

including the reason for the blood-red droplets

found on their skin. HIPPOS GRUNT

So, hippos can produce their very own natural sun cream

that is waterproof, moisturising and antibacterial.

Next, we meet another animal that has its own natural cure.

Capuchin monkeys have a surprising way of protecting their skin

from stings and bites.

MONKEYS SCREECH

When early explorers reached the Americas in the 15th century,

they encountered small monkeys

with patches of dark brown fur on their heads that resembled hoods,

so they named them after a group of Franciscan friars

called Capuchin monks.

Capuchin monkeys quickly charmed their way into our hearts.

With dextrous hands and inquisitive personalities,

they seemed very humanlike.

They were also adept at learning tricks

and soon became popular performers on our streets.

MONKEY SQUEAKS

In the past, we used to teach monkeys how to do things -

how to perform tricks -

but things are different today.

Today, monkeys are teaching us things.

Watch what happens when I give them a few spring onions

and some chilli peppers.

MONKEYS SQUEAK

MONKEY SQUEAKS

They're clearly not eating what I offered them.

They're rubbing themselves with the peppers and the onions.

You might think that that's because they're captive monkeys,

and they are just doing that to entertain themselves,

but not so.

I've seen capuchins do just that in the wild.

MONKEYS SQUEAK

These white-faced capuchins in Costa Rica

reacted in much the same way

when they came across a particular rainforest plant - the piper plant.

These leaves have a distinctive liquorice scent

and they are hard to come by, so when they do find them,

the monkeys passed the leaves around the troop

so that everyone can have a share.

MONKEYS CHATTER

Both in the wild and in captivity,

capuchin monkeys become similarly excited

at the sight of lemons or limes,

and, again, the same frenzied activity and fur-rubbing follows.

What is it about these plants that gets the monkeys so excited?

We know they all give off a pungent smell,

so could this be what the capuchins are after?

LEMURS SQUEAL

Smell plays an important part in the lives of many primates,

but none more so than in the lives

of these lovely ring-tailed lemurs. LEMURS CHATTER

They use it both to establish their position within the troop

and also the boundaries - the frontiers - of their territory.

If you look at the inside of their forearms,

there's a black patch without fur, and there,

the skin is loaded with glands that produce a very strong smell,

and when these boys go into battle... Whoops!

When they go into battle,

they draw their furry tail through their forearms,

loading it with scent from those glands,

and then they wave it over their backs

in the direction of their enemies, in a kind of stink fight.

You understand that, don't you?

LEMURS SQUEAK Oh!

LEMURS CHIRP The pungent scent is also used

by males during the mating season.

This male has rubbed his own distinctive smell onto his tail

and he now wafts over towards a female to signal his intentions...

LEMUR SQUEALS ..but she is not entirely convinced.

Unlike lemurs, capuchins don't have scent glands,

so some thought that they could be

using the smell of certain plants

for communication... MONKEYS CHATTER

..but it turns out that they have a different perfume for that job -

urine, which they apply lavishly to their fur.

So, why, then, do they also anoint themselves with other smells?

The answer may be found in our own history.

The early Romans noticed some 2,000 years ago that the fruits

and leaves of the lemon plant have an exceptionally strong scent

that could be used to ward off insects.

A further clue as to why capuchins might cover themselves

in such pungent smells comes from this plant -

the piper plant.

Throughout the Amazon,

Indian tribes apply it as an antiseptic on wounds,

and in Costa Rica, it's used as an insect repellent.

Could it be that capuchin monkeys protect themselves

against the onslaught of mosquitoes in much the same way

as humans do by rubbing themselves with mosquito repellent?

In 1993, scientists at Oxford University

decided to put the question to the test.

They collected some feather lice

and put them into petri dishes overnight.

Into one dish,

they also placed a slice of lime.

The next day, the lice without the lime were mostly alive,

whilst, in the other dish, two thirds had died

and the remainder were paralysed.

Clearly, the lime contains a lethal insecticide.

Today, we know that citrus-fruit peel

does indeed contain insecticides,

which disrupt the nervous system of many small insects,

causing them to become uncoordinated and paralysed.

The leaves of the piper plant are antiseptic

and contain substances that protect against fungal

and bacterial infection,

and chilli pepper extract is commonly used in households

and gardens to deter small mammals and insect pests.

So, it seems that the clever monkeys know exactly how to make

the best use of nature's remedies. MONKEYS SQUEAK

Recent research has also revealed

that capuchins anoint themselves far more during the wet season,

when mosquitoes are more abundant and the risk of infection is higher.

Troops use different plants, possibly, simply,

because they have to use what's locally available.

But there's one substance with insect-repellent qualities

that appeals to primates, including capuchins,

that comes not from a plant but from an animal -

an animal like this -

a giant millipede.

When attacked or in danger,

tropical millipedes often produce a powerful defensive secretion...

MONKEYS SCREECH ..and black lemurs have worked out

how to use this to their advantage.

When they find a millipede,

they give it a gentle bite to the head

to make it release its secretion,

and then rub this through their fur.

The toxic fluid has a strong smell

and is highly irritating... LEMURS SCREECH

..but it protects the lemurs against mosquitoes.

This pungent secretion has apparently another strange effect -

it seems to act as a narcotic,

sending the lemur into a kind of trance.

Like other drugs,

it has powerful side effects.

We still don't understand how capuchins and lemurs

select the plants that they use for medicinal purposes.

These capuchins behind me were born and raised in captivity,

so they never encountered the plants that their parents

and ancestors would have used.

So, how do the monkeys know

which plants to choose? MONKEYS CHATTER

Can they detect particular substances in them

or is it something they learn from others?

We don't yet know the answers,

but it could be that babies learn by watching the adults

and that it's passed down the family line.

It's clearly a great social event,

with everyone joining in

and, afterwards, the entire group appears to be more tightly bonded.

MONKEYS SQUEAK

When Europeans first saw monkeys in the wild,

they thought that they were imitating what people did

in some of their behaviours, but quite the reverse.

It now turns out that many of the local people did things

that the monkeys had taught them -

using plants as medicines -

so it seems that clever monkeys have taught us a trick or two.

Quick! Look!

This is a real live flea circus,

and you can see this one pulling along this tiny chariot.

There are very few circuses like this these days.

The whole business of performing fleas dates back

into the 16th century,

and it was used by watchmakers,

who used them to demonstrate how they themselves could

work on a near-miniature scale.

They used thin gold wires to harness fleas

and then linked the fleas to tiny chains.

Early magnifying devices like this

were actually named fleaglasses after these pests,

and the fleas were excellent creatures to

demonstrate a newly-visible microscopic world.

Fleas appear to be extraordinarily strong.

After all, this little badger flea here, pulling this chariot -

what an extraordinary thing.

That's the equivalent to me trying to pull a jumbo jet single-handed.

And this tiny merry-go-round -

that, too, is completely powered by fleas.

The secret of the fleas' strength and ability to move such equipment

lies in their powerful walking and jumping techniques.

They have the ability to store and then release energy,

and that enables them to leap upwards with great acceleration.

Fleas need to be good jumpers.

They live on the skin of mammals and birds, sucking their blood,

so they have to be able to quickly leap onboard their travelling hosts

when they get the chance.

There are more than 2,500 species worldwide,

62 of which live in Britain.

Fortunately, only a few feed on us.

Rat fleas were said to be responsible

for the spread of the Black Death in 1665, which killed millions,

but it wasn't until the invention of the magnifying glass

that we were able to see these tiny creatures face-to-face.

In 1665, Robert Hooke, an inventor and natural philosopher,

made one of the first compound microscopes.

This is a later reproduction of it.

And he then published his discoveries that he made using it

in a marvellous book called Micrographia.

It became one of the first scientific bestsellers.

Samuel Pepys mentioned it in his diary,

and it contained magnificent, detailed drawings

that revealed biological structures that had never been seen before.

He saw that plant tissue was made up of little units

that he called cells - the word we still use -

and he drew this marvellously detailed flea,

showing its great, strikingly long legs.

He also watched it through the microscope

and he described how a flea jumped.

This is what he says...

"When the flea intends to leap, he folds up these six legs together,

"then springs them all out at the same instant,

"and thereby exerting his whole strength at once,

"carries his little body to a considerable distance."

And indeed he does.

A flea's jump takes just one thousandth of a second,

so Hooke must have had very sharp eyesight to see it.

Many researchers have been fascinated by fleas,

and for one particular family, they became an obsession.

Charles Rothschild, a banker and keen naturalist,

amassed over 30,000 specimens

and identified more than 500 new species.

He purchased them from specialist traders worldwide,

and one parcel from America had a special surprise -

the tiny fleas were dressed as Mexicans.

Miriam, Charles's daughter, shared his passion for fleas

and catalogued his whole collection.

She looked closely at the flea's body and the way they jumped,

and was puzzled to find that they could leap far higher than

should theoretically have been possible,

but could their reputation for jumping 200 times their body length

possibly be true?

Most of the natural world's top jumpers

achieve their impressive leaps by using straightforward muscle power.

Kangaroos can make single bounds of almost eight metres

and frogs are able to jump more than 20 times their body length.

The jumping spider's leap is even more impressive -

100 times its own length.

It achieves this by exploiting hydraulics,

and scientists had long suspected that fleas and other insects

also needed something other than muscle to make their huge jumps.

In the 1960s, an exciting discovery was made in the insect world

that helped explain how bigger flying insects,

like locusts and dragonflies,

were able to fly and jump so well.

A rubbery protein was found in the hinges and joints

of locusts' wings and legs.

Using ultraviolet light, it's possible to see it,

as in this picture of the leg joint of a locust.

Here, that blue is this new substance.

But, just like this rubber,

it could bend and then release energy,

but the newly discovered material did that

with more than 90% efficiency.

Remarkably, too, it repeatedly snapped back into shape

without any deformation.

It was named resilin.

This stretchy protein allows insects to bend their stiff bodies

and stretch their tendons without snapping.

It's so robust, it lasts a lifetime,

and it's believed to be the most efficient elastic protein known.

The discovery of resilin opened up a whole new area of study,

and in 1966, Henry Bennet-Clark,

an expert in insect biomechanics,

had a breakthrough moment.

He had the chance to see some exciting new footage of fleas,

shot on a newly invented

high-speed camera.

Bennet-Clark studied the new flea footage

and built a mechanical model 400 times bigger than the flea.

He calculated that the fleas were somehow generating

much more power than their muscles could actually provide.

He noticed that, just before leaping,

the flea bent the closest segment of its hindmost legs towards the body

and hesitated for about a tenth of a second.

Carefully, he dissected fleas and found a pad of material,

and that proved to be resilin.

He proposed that fleas stored some of the energy for their jumps

in this rubberlike tissue,

and then released it as they pushed off with their shins and feet.

So, the tiny wingless fleas use internal resilin springs

like those of other, bigger, flying and jumping insects,

and the secret of their huge leaps lies in the efficient way they

combine muscle, tendons and joints to harness the resilin's energy.

Only today do we know how a flea jumps and how high it can jump,

just as, in Hooke's time, a modern technology - a microscope -

enabled him to see the anatomy of the flea for the very first time,

so we have a camera now which is recording 5,000 images a second,

which will enable us to see how it jumps.

The camera is already running.

The flea is in that little box there

and we can see the image from the camera on this computer.

I will stop it as soon as I see that the flea has jumped.

There.

Its legs are already cocked in the jumping position,

and the cuticle, which is fused to the resilin,

is bent and ready to release its energy,

and then it lifts itself from the ground

and it's catapulted into the air.

Our story about fleas started 350 years ago

with Robert Hooke's first microscopic study.

Today, images from electron microscopes reveal even more details

than Hooke's beautiful drawings.

They show the rough hairs on the flea's shins and toes

that help it grip before thrusting itself into the air

with the final push from its toes.

So, can fleas jump 200 times their own body length?

It would seem not.

Nonetheless, they can leap

a respectable 38 times

the length of their bodies, which is not bad.

Fleas are extraordinarily strong

and we now know how they jump,

but the fleas' story isn't quite over.

A new discovery has added a twist to their lives

and dispelled another myth.

Recently, bodies of people who died of the Black Death

were uncovered by workers digging a new railway line.

Close inspection revealed that the Black Death was an airborne disease

and had nothing to do with rats or their fleas,

so the fleas' good name can at last be restored, and we can

celebrate them as one of the natural world's most spectacular jumpers.

A springy protein propels fleas with great force.

Next, we investigate another impossible feat -

the cheetah's legendary top speed of 70mph.

AEROPLANE ENGINE ROARS

Is this really possible?

CHEETAH PURRS

Cheetahs are beautiful, athletic-looking cats.

They've got the streamlined body, the small head,

elongated legs and narrow shoulders,

and a very long spine.

This looks like an animal that's built for speed,

but exactly how fast can he run? CHEETAH PURRS

They've been admired for their

grace and speed since antiquity.

The Egyptians were sometimes

buried with these cats because

they believed that they could hasten

the journey to the after-world

and, in more recent times,

sports hunters have used cheetahs to run down their prey.

So, the cheetah's impressive sprint has been known about for some time,

but where did the magical figure of 70mph come from?

Back in 1957, a cheetah hit the headlines,

with news of a rather unusual experiment.

A photographer called Kurt Severin

filmed and measured the running speed of a tame cheetah

using an upturned bicycle rather like this.

The back wheel was modified so that a strong fishing line could be

wound through the rim and pull along a meat-scented bag.

As the cheetah ran the 80-yard or 73-metre course

the pedals of the bike were hand-cranked

as fast as humanly possible

to drag the bag along just ahead of the cheetah.

The measurements were made manually using a stopwatch and a pistol.

Severin wrote that,

"From a deep crouch, the cheetah spurted to

"the end of the course in 2.25 seconds,

"for an average speed of 71mph."

And so, the legend was born.

BIRDS SCREECH

This impressive figure was immediately accepted

and is still often quoted today,

but how accurate is it?

The top speed of any running mammal depends on the power

of its muscles and the strength of its tendons and bones.

Human athletes train hard to reach their personal best

but there's still a limit to how fast they can run.

In a 100m sprint, a mere two seconds separates

a good amateur sprinter from a world-class champion.

The greyhound is similar in size and shape to a cheetah

so it's a good substitute animal to test out the cheetah's

legendary top speed of 70mph.

Their backs flex and extend so greatly that,

at times, none of their feet touch the ground...

..but when the greyhound's top speed was measured,

it was found to be 45mph -

a whole 25mph slower than the cheetah.

People argued that the cheetah could nonetheless achieve

a bigger stride because of extra flexibility in its back...

..but doubts about its top speed were beginning to creep in.

A new, more accurate way of testing was needed.

Here in the Royal Veterinary College,

they use dogs to help them in their studies of cheetahs.

Using a lurcher as a stand-in,

they've developed an extraordinary data-collecting collar.

It has a GPS attachment that will register position

to within a fraction of a metre.

It has movement sensors to show how the animal is, in fact, moving.

It can be remotely programmed

and it has a solar-charged battery that will last for up to a year.

The collars were tested and perfected on lurchers in Britain

to make sure that they were small and light enough

not to disturb their wearer.

Then, the collars were put on captive cheetahs,

to see if they could cope with the twisting run of the hunt.

The results were excellent,

and the collars were ready for the ultimate test...

in the wild. CHEETAH PANTS

FLIES BUZZ

Here was a chance to see if a wild cheetah's special adaptations

to hunting really enabled it to run at 70mph.

Wild cheetahs are faster than other, larger cats, like lions,

because of their lighter bones -

an advantage in a short, high-speed chase.

They have big nostrils, so they can take in large amounts of oxygen,

and an enlarged heart and lungs that increase circulation.

Their long tails act like rudders to help them steer

and assist their balance as they twist and turn.

BIRDS SCREECH

They need to be fast and manoeuvrable

because the prey they hunt is extremely agile

and able to change direction very quickly.

A cheetah can mirror such changes of movements in an instant.

But what would the GPS collars tell us about their speed?

Data from the collars has revealed fascinating details

about cheetahs' lives,

how they hunt and exactly how fast they can run.

The GPS measurements collected are accurate to within half a metre

and can be precisely matched to satellite images of the area,

so it's possible to see exactly what kind of terrain the cheetahs

were hunting on.

Here, we can see an 11-hour day in the life of a cheetah,

and there it starts to hunt.

The cheetah ran in one circular direction,

like this.

The blue represents deceleration,

getting slower here,

and there, at the red, where it gets faster and accelerates,

and the arrows represent the power of the force on the cheetah's body

as it swerves, and there, finally,

it made the kill.

367 hunts were studied

and the top speed of a chase was calculated to be 58mph.

BIRDS SCREECH

For more than half a century,

we have overestimated the cheetah's speed.

It is, nonetheless, still the fastest animal on land,

and its greatest feat is its acceleration -

four times that of Usain Bolt.

CHEETAH GROWLS

BIRDS SCREECH

CHEETAH SNARLS

The cheetah's legendary 70mph speed record is just a myth

but their true top speed of 58mph is still extraordinary.

A body that is fine-tuned for hunting helps them run in a really

remarkable way, but the cheetah's real impossible feat, so-called...

CHEETAH PURRS

..is the ability to change speeds so extremely quickly,

and that makes it one of the most manoeuvrable animals alive.

Aren't you? Aren't you?

CHEETAH PURRS

We may have overestimated the abilities of the flea

and the cheetah, but both exhibit remarkable feats of acceleration

in their quest for food -

the flea, to hop onto a passing host,

and the cheetah, to outmanoeuvre its prey.

BIRDS SCREECH