Impossible Feats 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 particularly fascinating.

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 is famously quoted that cheetahs can run at speeds

of 70mph.

But are these claims really true?

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 link the fleas

to tiny chains.

Early magnifying devices like this were actually named

"flea glasses" after these pests.

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 of me trying to pull a jumbo jet single-handed.

This tiny merry-go-round, that too is completely powered by fleas.

The secret of the flea's 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 on board 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.

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.

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."

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.

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 is 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 is so robust it lasts a lifetime and it is 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 10th 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 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.

Then it lifts itself from the ground and it is 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

a 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.

The flea's 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 flea's 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.

Is this really possible?

Cheetahs are beautiful, athletic-looking cats.

They have got a streamlined body, small head,

elongated legs and narrow shoulders and a very long spine.

This looks like an animal that is built for speed but exactly

how fast can he run?

They have been admired for their grace and speed since antiquity.

The Egyptians were sometimes buried with these cats because they

believed they could hasten the journey into the afterworld.

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, 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.

So the legend was born.

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 is still a limit to how fast they can run.

In a 100-metre 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 is

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 argue 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 have 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.

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.

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 movement 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 is 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, 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.

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.

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...

..is the ability to change speed so extremely quickly.

That makes it one of the most manoeuvrable animals alive.

Aren't you?

Aren't you?

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.