Original subtitles

There was a time when myths and science were entwined,

when mermaids and unicorns could mysteriously appear...

..and devilfish flew the oceans.

Nature was weird.

When science revealed the truth behind these imaginary creatures,

it found REAL animals lay behind the legends.

Today, science still makes astonishing discoveries.

But nature seems just as weird.

It's just that fact has broken free from fiction.

In Weird Nature, real animal behaviour is set against human backdrops.

They give astonishing insights.

The spiral tusk of the unicorn has been traced to a white whale, just as wonderful as the legend.

The narwhal uses its twisted horns in jousts, like a medieval knight.

The mermaid's forked tail belongs to the dugong.

Half-seen, its body and face can appear surprisingly human.

The devilfish is a manta ray.

They leap to shed parasites and then briefly glide, like phantom craft.

Weird nature takes you into a world where imaginary human settings

showcase animal behaviour that is absolutely real.

What is weird is best defined when compared to our own lives.

Our first weird journey shows the wonderful ways that animals move.

Life began in the oceans.

This imaginary wreck brings together some early forms of motion.

Jellyfish are the only animal to move by wafting water through a pulsating skirt,

but such graceful jet propulsion is no match for the tides.

A strange ancient mollusc improved the concept.

The nautilus jets water through a siphon that can move to control direction.

It controls depth, by regulating gas in a series of buoyancy chambers in its shell.

Flame scallops jet-propel by clapping their shells like castanets.

They jet water from either side of their hinge.

They dance to escape predators or to find new places.

The Spanish dancer's technique is more elegant.

It flamencos, by rippling the ribbons along its body.

The frills of its costume are actually gills,

and, despite its romantic name, it's really a sea slug.

The sea horse can't move its armoured body in sinuous waves, like other swimming fish.

Instead, a fin that quivers 20 times a second whirrs it around.

Shimmering side fins act as steering propellers.

Jointed legs were an exciting new movement in evolution.

Spiny lobsters used them to conga.

Their procession provides safety in numbers, as they move to deeper water to avoid winter storms.

The slipstream from the leader cuts drag for those behind.

Legs helped animals make the next evolutionary step.

Today, we prefer faster options.

But legs have been in vogue

since the first amphibians crawled from the sea.

They dragged their bodies along, using four legs, splayed to the side.

The Mount Lyell salamander uses its tail as a fifth leg

to negotiate the Sierra Nevada mountainside.

They are also special in more human terms.

The wheel was hailed as one of our greatest inventions.

But, as these creatures prove,

we were simply reinventing it!

Rolling is the quickest way down a hill,

as this salamander has discovered.

It's designed to flex like a rubber tyre, so it doesn't feel the bumps.

The pearl moth caterpillar is common,

but its talent for doing "wheelies" is a new discovery.

It rolls with its caterpillar track on the inside.

Salamanders and caterpillars were born to rock'n'roll,

so this behaviour is second nature.

The salamander's more normal motion

can cause problems for heavier creatures that move in the same way.

For the early reptiles, crawling along the ground was literally a drag.

Crocodiles had an odd solution.

Walking on stilts cuts friction on rough ground.

But the splayed feet have to rotate forward to take a step.

It may be slow, but it saves energy,

and most crocs use this stiff-legged walk whenever the going gets rough.

The Australian fresh-water croc shows an even stranger gait,

when provoked by predators, such as the salt-water croc.

It gallops...

but not like any other animal.

Its front feet work together in opposite motion to the back.

As the front feet hit the ground, the back swing forward.

When the back push away, the front reach out.

Galloping horses were once painted like this.

In truth, only fresh-water crocs run in this seesaw way.

It can reach 15mph and easily leap to safety.

Evolution has taken many weird twists and turns.

Each year, 20 million leapers of a more playful kind

arrive in the world's toy shops, from a tiny part of Mexico.

The jumping bean is really the seed of a desert shrub.

Only a few show this odd leaping.

The seeds, imported as novelty toys,

seem to have a mind of their own.

There really IS a mind behind the jumping.

A moth caterpillar lives and feeds inside the seed.

The caterpillars flip their home to escape.

They not only feel the heat,

light makes them jumpy.

They fuss and fidget into the shade.

This behaviour is a life-saver in the hot Mexican desert.

The caterpillar repairs the damage by weaving a silken wall.

It grips onto the silk wall when it leaps.

The shape of the bean helps it roll.

For weirdness, the Mexican jumping bean is hard to beat.

But Sifaka lemurs from Madagascar

turn leaping into a surreal ballet.

The secret of their graceful pogo-ing stems from a life in the trees.

They can leap 30m with ease.

These acrobatic skills have to be modified for the challenge of moving over the ground.

The legs act as springs...

..and feet curled for gripping become landing pads.

With no branches to grab, the arms are free to act as stabilisers.

Every move of the legs is complemented by a matching move of the arms.

The balletic poses maintain perfect balance.

Sifakas only show such bizarre and beautiful motion because they evolved for a life in the trees.

The same is true of the bushbaby.

This time-slice sequence

shows the various poses a bushbaby adopts as it jumps.

It leaps two-and-a-quarter metres in height -

equivalent to us clearing two stacked double-decker buses.

To achieve this, the legs and feet act like springs,

converting the energy of impact back into propulsion.

It really DOES have a spring in its step.

It waits until the peak of its jump before reaching out.

The tail acts as a counterbalance.

It's like a rubber ball with a brain -

almost impossible for a predator to catch.

This sequence freezes a bushbaby as it becomes airborne.

But gliding animals specialise in prolonging their time in the air.

The golden tree frog of Malaysia is a treetop acrobat.

Usually, it hops just a few metres.

But if it meets a golden tree snake,

it happily makes a leap into the unknown.

As it plummets, spread limbs slow its descent, and its webbed feet double up as a parachute.

The Javan flying frog goes one better.

Its webbed feet have evolved into miniature wings.

Instead of parachuting, it paraglides at an angle.

But it's the Wallace frog that achieves aeronautical perfection.

Its huge webbed feet become aerofoils that slow and control its descent.

It glides as far forward as the distance it falls.

As well as winged feet, its whole body is aerodynamically shaped.

This is classic evolution.

One feature progressively improved until perfection is achieved.

Lizards lack webbed feet,

so they expand other body features to get their wings.

The flying gecko's impressive glide angle is due to wing-like fringes on its body.

Every available edge has an aerodynamic extension.

But it's the draco lizard whose design really flies.

A huge aerofoil turns the draco into a living Frisbee,

while its tail steers like a rudder.

Foldable ribs act as support struts to create the perfect wing.

The golden tree snake uses other aeronautical tricks for its leap of faith.

It loops its body for the ultimate take-off,

and projects forward to gain a head start.

It then flattens into a ribbon and swims through the air using S-shaped waves of its body.

The star of this jungle air show is the owner of the most extravagant wings.

From 80m up, the Wallace frog glides 80m forward.

The gecko soars 100m.

But nothing beats the flying Frisbee.

The draco reaches a full 200m.

Even a flying snake makes 150, complete with controlled landing!

A lack of legs has made snakes devise other weird ways of moving.

SIREN WAILS

In the deserts of the American South-West, off-road travelling is notoriously difficult.

Shifting sand is one of the most challenging surfaces to negotiate.

The horned rattlesnake's solution is to touch the sand with as little of its body as possible.

Appropriately, its nickname is the sidewinder.

Like tyre tread, a snake's scales usually grip the ground as it moves.

But sand simply gives way.

So the snake makes an S-shape with its body and lifts the loops in a rolling corkscrew.

This continually shifts the points of contact to stop that sinking feeling.

As waves of grip pass down the body, the snake rapidly picks up speed.

Its hidden prey can also make a surprise move.

Sidewinders avoid being buried by sand.

Others welcome its smothering embrace.

This predator spends much of its life lurking just beneath the surface.

It can swim through shifting sand, like an eel up a river...

..because the grains act like liquid rock.

The sand swimmer's wedge-shaped head parts the grains like the prow of a boat.

Its over-slung upper jaw stops it swallowing sand,

and it can close its nostrils to avoid suffocating.

As the snake submerges, its polished scales slip through the grains as if immersing in water.

Nature shows many wonderful forms of travelling.

Those that seem weird are usually the least familiar.

But although we think we're normal, in nature, it is WE who are peculiar.

Our two legs place us among the world's oddest animals.

We are the only mammal to regularly walk like this.

Sometimes, other primates hint at the origins of our strange bipedal walk.

Proboscis monkeys use it to cross mangroves.

A few scientists think we were once semi-aquatic.

Walking like this kept our heads above water.

Others believe that freeing the hands for gripping or carrying

allowed a land ape to bring back food to a family.

Whatever the reason, animals that walk like us seem strange.

We find it weird to see our actions mirrored in other animals.

In the age of the dinosaurs, we might have felt more at home. Many were also bipedal.

Today, a few unrelated lizards continue in their footsteps.

Oww!

Like a miniature tyrannosaur, the collared lizard hunts on two legs.

But it is more agile than any dinosaur,

and, size for size, much faster.

Being smaller gives speed and manoeuvrability.

Most bipedal lizards live in deserts.

This kind of running needs space.

When hunting other lizards, two legs give it the edge.

The tyrannosaur's modern equivalent.

But while this lizard uses two legs for speed, we now prefer alternatives.

The dinosaur's REAL descendants are birds.

Because they fly, we rarely notice that they walk on two legs like we do.

But the roadrunner is an exception.

Its comical, human-like gait made it a cartoon character.

To save energy for its sprint, the roadrunner exposes a solar panel.

This dark skin patch raises its body temperature seven degrees.

It's primed for a super-heated performance.

To the roadrunner, our open roads are racetracks, good for chasing insects and lizards.

Its tiny legs take it to 26mph.

If our legs moved this fast, we would overtake any speeding bike.

Because two-legged running limits our own speed,

we use artificial means of travel, such as flying.

But even though it CAN fly, the strange roadrunner chooses to run on two legs for speed.

Our machines take us ever-faster...

and we sometimes pay the price.

But when we smile at the roadrunner's bipedal running,

are we recognising our OWN weird nature?

Our next weird journey looks at

the strange ways animals defend themselves.