Impossible Feats David Attenborough's Natural Curiosities


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The natural world is full of extraordinary animals

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with amazing life histories.

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Yet certain stories are more intriguing than most.

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The mysteries of a butterfly's life cycle or the strange biology

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of the emperor penguin, some of these creatures were surrounded

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by myth and misunderstandings for a very long time.

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And some have only recently revealed their secrets.

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These are the animals that stand out from the crowd,

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the curiosities I find particularly fascinating.

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Some animals can perform amazing physical feats.

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

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a man leaping over St Paul's Cathedral.

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And it is famously quoted that cheetahs can run at speeds

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of 70mph.

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But are these claims really true?

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Quick, look!

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This is a real live flea circus and you can see this one pulling

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along this tiny chariot.

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There are very few circuses like this these days.

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The whole business of performing fleas dates back into

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the 16th century and it was used by watchmakers,

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who used them to demonstrate how they themselves could work on

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a near miniature scale.

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They used thin gold wires to harness fleas and then link the fleas

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to tiny chains.

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Early magnifying devices like this were actually named

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"flea glasses" after these pests.

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The fleas were excellent creatures to demonstrate a newly-visible

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microscopic world. Fleas appear to be extraordinarily strong.

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After all, this little badger flea, here,

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pulling this chariot, what an extraordinary thing.

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

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

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The secret of the flea's strength and ability to move such

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equipment lies in their powerful walking and jumping techniques.

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They have the ability to store and then release energy and that

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enables them to leap upwards with great acceleration.

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Fleas need to be good jumpers.

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

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So they have to be able to quickly leap on board their

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travelling hosts when they get the chance.

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There are more than 2,500 species worldwide,

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62 of which live in Britain.

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Fortunately, only a few feed on us.

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Rat fleas were said to be responsible for

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

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But it wasn't until the invention of the magnifying

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

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

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made one of the first compound microscopes.

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This is a later reproduction of it.

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He then published his discoveries that he made using it in

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a marvellous book called Micrographia.

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It became one of the first scientific bestsellers.

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Samuel Pepys mentioned it in his diary.

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It contained magnificent detailed drawings that revealed

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biological structures that had never been seen before.

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He saw that plant tissue was made up of little units that

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he called cells, the word we still use.

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And he drew this marvellously detailed flea,

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showing its great strikingly long legs.

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He also watched it through the microscope and

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he described how a flea jumped. This is what he says.

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"When the flea intends to leap,

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"he folds up these six legs together,

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"then springs them all out at the same instant and thereby

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"exerting his whole strength at once,

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"carries his little body to a considerable distance."

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Indeed he does.

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

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

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Many researchers have been fascinated by fleas,

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and for one particular family they became an obsession.

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Charles Rothschild, a banker and keen naturalist, amassed

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over 30,000 specimens and identified more than 500 new species.

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He purchased them from specialist traders worldwide.

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One parcel from America had a special surprise,

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the tiny fleas were dressed as Mexicans.

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Miriam, Charles's daughter,

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shared his passion for fleas and catalogued his whole collection.

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

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

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theoretically have been possible.

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But could their reputation for jumping 200 times their body

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length possibly be true?

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Most of the natural world's top jumpers achieve their

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impressive leaps by using straightforward muscle power.

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Kangaroos can make single bounds of almost eight metres.

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

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The jumping spider's leap is even more impressive,

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100 times its own length.

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It achieves this by exploiting hydraulics.

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And scientists had long suspected that fleas and other insects

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

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

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that helped explain how bigger flying insects, like locusts

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and dragonflies, were able to fly and jump so well.

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A rubbery protein was found in the hinges and joints of locusts'

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wings and legs.

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Using ultraviolet light, it is possible to see it,

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as in this picture of the leg joint of a locust, here,

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that blue is this new substance.

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But just like this rubber, it could bend and then release energy.

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But the newly discovered material

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did that with more than 90% efficiency.

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Remarkably, too,

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it repeatedly snapped back into shape without any deformation.

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It was named resilin.

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This stretchy protein allows insects to bend their stiff bodies

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and stretch their tendons without snapping.

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It is so robust it lasts a lifetime and it is believed to be the

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most efficient elastic protein known.

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

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and in 1966, Henry Bennet-Clark,

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an expert in insect biomechanics, had a breakthrough moment.

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

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shot on a newly invented high-speed camera.

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Bennet-Clark studied the new flea footage and built

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a mechanical model 400 times bigger than the flea.

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He calculated that the fleas were somehow generating much more

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power than their muscles could actually provide.

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He noticed that just before leaping,

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

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body and hesitated for about a 10th of a second.

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

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that proved to be resilin.

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

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in this rubberlike tissue and then released it,

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as they pushed off with their shins and feet.

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So the tiny wingless fleas use internal resilin springs, like

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those of other bigger flying and jumping insects.

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

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

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

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

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

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

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which will enable us to see how it jumps.

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The camera is already running, the flea is in that little box there.

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

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

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There!

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Its legs are already cocked in the jumping position and the cuticle,

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which is fused to the resilin,

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is bent and ready to release its energy.

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Then it lifts itself from the ground and it is catapulted into the air.

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Our story about fleas started 350 years ago with Robert Hooke's

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first microscopic study.

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Today, images from electron microscopes reveal even more

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details than Hooke's beautiful drawings.

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

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help it grip before thrusting itself into the air with

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a final push from its toes.

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So can fleas jump 200 times their own body length?

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It would seem not.

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Nonetheless, they can leap a respectable 38 times the length

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of their bodies, which is not bad.

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Fleas are extraordinarily strong, and we now know how they jump.

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The flea's story isn't quite over.

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A new discovery has added a twist to their lives and dispelled

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another myth.

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Recently, bodies of people who died of the Black Death were

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uncovered by workers digging a new railway line.

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Close inspection revealed that the Black Death was an airborne

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disease and had nothing to do with rats or their fleas.

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So the flea's good name can at last be restored and we can

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

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A springy protein propels fleas with great force.

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Next, we investigate another impossible feat,

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the cheetah's legendary top speed of 70mph.

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Is this really possible?

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Cheetahs are beautiful, athletic-looking cats.

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They have got a streamlined body, small head,

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elongated legs and narrow shoulders and a very long spine.

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

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how fast can he run?

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

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The Egyptians were sometimes buried with these cats because they

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believed they could hasten the journey into the afterworld.

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And in more recent times, sports hunters have used cheetahs

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to run down their prey.

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So the cheetah's impressive sprint

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has been known about for some time.

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But where did the magical figure

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of 70mph come from?

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Back in 1957, a cheetah hit the headlines with news of

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a rather unusual experiment.

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A photographer called Kurt Severin filmed and measured the running

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speed of a tame cheetah using an upturned bicycle, rather like this.

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

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

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As the cheetah ran the 80 yard, 73 metre, course,

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the pedals of the bike were hand-cranked as fast as humanly

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possible to drag the bag along just ahead of the cheetah.

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

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Severin wrote that from a deep crouch, the cheetah spurted to the

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end of the course in 2.25 seconds, for an average speed of 71mph.

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So the legend was born.

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This impressive figure was immediately accepted and is still

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often quoted today. But how accurate is it?

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The top speed of any running mammal depends on the power of its

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muscles and the strength of its tendons and bones.

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Human athletes train hard to reach their personal best,

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

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In a 100-metre sprint, a mere two seconds separates

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a good amateur sprinter from a world-class champion.

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The greyhound is similar in size and shape to a cheetah so it is

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a good substitute animal to test out the cheetah's legendary top

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speed of 70mph.

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Their backs flex and extend so greatly that, at times, none of

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their feet touch the ground.

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But when the greyhound's top speed was measured,

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it was found to be 45mph, a whole 25mph slower than the cheetah.

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People argue that the cheetah could nonetheless achieve

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a bigger stride because of extra flexibility in its back.

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But doubts about its top speed were beginning to creep in,

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a new, more accurate, way of testing was needed.

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Here in the Royal Veterinary College,

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

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Using a lurcher as a stand-in,

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they have developed an extraordinary data collecting collar.

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It has a GPS attachment that will register position to within

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a fraction of a metre.

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

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It can be remotely programmed and it has a solar charged battery

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that will last for up to a year.

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The collars were tested and perfected on

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lurchers in Britain, to make sure that they were small and

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light enough not to disturb their wearer.

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Then the collars were put on captive cheetahs to see if they could

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cope with the twisting run of the hunt.

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The results were excellent and the collars were ready

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for the ultimate test in the wild.

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

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to hunting really enabled it to run at 70mph.

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

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because of their lighter bones.

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An advantage in a short, high-speed chase.

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They have big nostrils

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so they can take in large amounts of oxygen, and an enlarged heart

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and lungs that increase circulation.

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Their long tails act like rudders,

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to help them steer and assist their balance as they twist and turn.

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They need to be fast and manoeuvrable because the

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prey they hunt is extremely agile

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and able to change direction very quickly.

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

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

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Data from the collars has revealed fascinating details about

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cheetahs' lives. How they hunt and exactly how fast they can run.

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The GPS measurements collected are accurate to within half

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a metre and can be precisely matched to satellite images

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of the area, so it is possible to see exactly what kind of

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terrain the cheetahs were hunting on.

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

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And there it starts to hunt.

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The cheetah ran in one circular direction, like this.

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The blue represents deceleration, getting slower, here,

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

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And the arrows represent the power of the force on the cheetah's

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body as it swerves. And there, finally, it made the kill.

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367 hunts were studied and the top speed of

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a chase was calculated to be 58mph.

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For more than half a century,

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we have overestimated the cheetah's speed.

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It is nonetheless still the fastest animal on land and its

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greatest feat is its acceleration.

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Four times that of Usain Bolt.

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

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

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

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a really remarkable way.

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But the cheetah's real impossible feat, so-called...

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

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That makes it one of the most manoeuvrable animals alive.

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Aren't you?

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Aren't you?

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We may have overestimated the abilities of the flea and the

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cheetah but both exhibit remarkable feats of acceleration in

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their quest for food.

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The flea, to hop onto a passing host,

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and the cheetah, to outmanoeuvre its prey.

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