Episode 10 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.

Orang-utans have an extraordinary ability to use tools.

But the full extent of their skills remained undiscovered for centuries.

Surprisingly, crows also make tools.

How and why have these two very different animals

become so inventive?

And also, in this programme,

salamanders can regenerate entire legs and tails

to replace ones that they lose.

And moose can regrow their enormous antlers every year.

How do these animals regenerate entire body parts,

and why isn't it possible for all animals to do the same?

When I first saw orang-utans that have been raised in captivity

using tools, I was truly astonished.

They were extraordinarily skilful at imitating the things we do.

But, at the time, some skills had never been observed

among wild orang-utans.

So, are these apes just clever mimics?

Or do they ever make and use tools in the wild?

We didn't know the answers to such questions until quite recently.

This dramatic sculpture, by the French artist

Emmanuel Fremiet,

entitled 'An Orang-utan Strangling A Borneo Native',

represents the image people have of this formidable giant ape.

It's pretty accurate, as Fremiet studied live orangs

at the Jardin des Plantes in Paris,

and you can see why orangs are so-called.

The name, in Malay, means all 'orang' - people,

and 'hutan' - of the forest.

At first, orang-utans were feared and misunderstood.

Early explorers thought that these long-armed, tree-living apes

were degenerate human beings,

and for centuries their true nature

and behaviour in the wild was largely unknown.

Orang-utans are only found in the rainforests of Indonesia.

One population in Borneo,

and another slightly different one

in the island of Sumatra, to the west.

They have strong, dextrous hands and feet,

and a very mobile mouth, that enable them to break open

and eat the fruits on which they depend.

But although they're clearly very intelligent,

the only tools they seemed to use were sticks,

which they wielded in a very simple way.

Yet, in Africa, chimpanzees had been seen using tools

in a rather more complex fashion.

Back in 1871, Darwin had reported

wild chimpanzees cracking open

walnut-like fruits with stones.

And in the 1960s, they were even seen the modifying sticks

with which they fished for termites.

It seemed strange that,

while wild chimps used tools in a quite complicated way,

orang-utans apparently did not.

Orangs, unlike chimps, are not very sociable.

Individuals are largely solitary.

The males have large, individual territories,

within which several females have their own home ranges.

This more solitary way of life affects the way orangs

share their knowledge and develop their skills.

The most social time of an orang-utan's life

is when it's a baby.

And in the wild,

youngsters stay with their mothers

for the first six years of their lives.

During this time, they learn the skills needed to

survive in the forest alone.

The need to know how to climb, build nests,

and how to solve problems such as breaking into tough food.

And their large brains certainly help them to master these tasks.

So, a young orang behaves like its mother,

and copies the way she searches for food and prepares it to eat.

In captivity, they readily make tools to reach food,

or to escape from their enclosures.

They're clearly very inventive

and good at developing ways to solve particular problems.

So, it was a puzzle as to why such bright and capable apes

were apparently not behaving in a similar way in the wild.

Orangs are clever and physically dextrous.

They've very strong jaws and mobile hands and feet,

and in the wild they can reach and prise open most food.

It was assumed for many years that, even though they used

tools in captivity, they didn't perhaps need to do so in the wild.

It seems that, strangely, these great apes have more skills

than they normally need for their lives in the wild.

It wasn't until 1964 that orangs were studied in detail.

A Lithuanian scientist from Canada called Birute Galdikas

settled in Borneo to live alongside these great apes.

For over 30 years, she watched both tame orangs

and wholly wild ones in the forests.

In her camp, she found that the tame ones quickly discovered how

to use tools in a relatively sophisticated way.

But in the wild she only saw them build nests

and use sticks in a simple fashion.

That picture of the character

and abilities of orangs remained unchanged for long time.

Then, in 1994, our understanding of orangs changed radically.

A group of Swiss scientists observed some orangs that were

behaving very differently.

They lived several hundred miles away from their Borneo cousins,

in swampy rainforests on the island of Sumatra.

The orangs' diet is about 90% fruit.

And this is one of their favourites.

It's a durian and it's well known...

for its pungent smell.

As you can see, it's got a very spiky case.

But orangs are able to break it open and reach the soft,

pulpy flesh inside.

But it's when they tackle another similar spiky fruit called neesia,

which is more difficult to open,

that scientists got their first glimpse of orangs making tools.

Neesia presents an extra challenge because inside,

it contains rich, nutritious seeds

which are embedded in a mass of sharp, needlelike hairs.

To avoid touching these irritating hairs,

the swamp-living orangs slid sticks into cracks in the food husks.

Then they push them up and down to flick out the hairs

and free the seeds.

They also modified sticks

so that they fitted different sized cracks in the fruits.

The particular fruit that grew in these wet forests had stimulated

the Sumatran orangs to make and use special tools.

Unusually, for such solitary creatures,

they gathered at these rich feeding areas in a group,

and feeding close to one another, they shared their skills.

So now it was realised that orangs were not just mimics.

They were able to invent their own ways of making

and using tools, just like chimps.

We have long known that captive orangs can quickly work out

ways to solve problems.

And now, it was clear that wild orangs are no different.

In recent years, they've been seen

using sticks to fish for termites and honey

in much the same way as individuals do in captivity.

In the flooded forests,

many insects are forced above ground to live in tree holes.

So the orangs use sticks to extract them.

It seems incredible that tool use in wild orangs

took hundreds of years to discover.

In fact, it had been happening all the time,

just hidden away from view.

These red men and women of the forest

have very dextrous hands and feet,

strong jaws and a large brain.

In the wild, they have little need for complex tools,

and being solitary means that tool use

is not usually shared or spread.

But even as loners, they are inventive

and can work out how to solve problems.

Here is a creature that could be one of the greatest tool users

in the animal kingdom.

Orang-utan tool use was not discovered for many years.

Next, meet the clever crow that also makes tools.

How have crows' curious minds helped them become so inventive?

The most famous members of the crow family in Britain

are the ravens that live here in the Tower of London.

By tradition, they protect the Crown.

And they are recruited

and indeed dismissed from the British Army, just like soldiers.

In 1986, one of them, called George,

had to be exiled to Wales for persistent bad behaviour

in destroying the television aerials around here.

And more recently, another one,

noticing that one of its fellows had died

and was attracting a great deal of attention,

also lay down on the ground feigning death.

And when the raven master came over to see what the matter was,

he got a sharp peck.

Well, stories like those suggest that members of the crow family

have minds rather different from other birds.

Ravens are cheeky, self-aware and socially intelligent.

They're part of the big crow family that, in Britain, includes

hooded and carrion crows, jackdaws, jays, chuffs and magpies.

Their brains are twice as large as other birds'

and, relative to body size, comparable to a chimpanzee's.

This extra brain capacity has helped them

become very good at solving problems.

Here is Bran the raven,

and I've put a screen in front of his cage,

so he can't see what is going on.

And this is Bran's stone.

He's had it since he was a chick,

and he can recognise it amongst a whole pile of other pebbles.

Now, I've put a few of a similar size on this grid,

and I'll put his stone just there.

And now, we'll see whether he can find it.

Bran, where's your stone?

Immediately. Well done!

The only explanation of this

is that he has an extremely acute visual memory.

Indeed he has.

You could say that by putting stones on a gridded square like that,

that makes each one very obvious. All right.

Well, let's make things a little more difficult.

This is his stone and I'll put it in this pile of stones

so that he can only see just a little tip of it.

Now, Bran. Where's your stone?

Oh, come on.

HE LAUGHS

Fantastic. Thank you very much.

And this ability to recognise a little small detail

is used by these birds when they cache food.

In the good times, they will hide hundreds of different

pieces of food and conceal them, and remember every one.

And come back to it in the hard times to pick up that piece of food.

Extraordinary. You're an amazing bird, Bran.

Another species of crow, Clark's Nutcracker,

is a champion at caching food.

It collects and hides up to 33,000 seeds every season,

and remembers where each one is put for up to nine months.

It can even find them under snow.

Crows also remember the kind of food that they have hidden.

Freshly buried grubs perish quickly

so need to be recovered sooner than seeds.

The ability to think ahead

and anticipate future events can also help in other situations.

Other birds will steal buried food if they can find it,

but some kinds of crows are able to recognise these thieves

and outwit them.

Recent research at Cambridge has revealed that scrub jays

take great care in how they hide their food.

One jay is given the choice of two locations in which to cache food.

Under stones which make a noise if they are moved,

or soil which can be cleared away quietly.

In the cage next door, another scrub jay watches.

He is a potential thief.

When the caching jay knows that its neighbour can see,

it buries its food under stones.

If the jay next door attempts to steal that buried food,

the noisy stones will act like a burglar alarm.

But when the screen is added,

so that the neighbouring jay can only hear what's happening,

the caching jay changes its plan.

This time it decides to bury its food under soil,

which makes hardly any noise,

so its location remains unknown to the jay next door.

For centuries, members of the crow family

have been recognised to be unusual birds.

Their noisy gatherings gave them a sinister reputation.

But their intelligence was legendary.

In one of Aesop's Fables, a clever crow

drops pebbles into a jug of water

to raise the level high enough so that it can drink.

This is perhaps one of the first recorded examples

of a crow using a tool.

Here, once again, is Bran the raven.

And like the crow in Aesop's fable, he is extremely intelligent

and clever at collecting food.

I'm going to set him a problem, which he has seen before,

and for which he produced his own solution.

I'm going to take a little bit of meat,

put it in this plastic bottle and then just to make it

difficult for him, I'm going to crush the bottle.

So that it won't come out just by shaking it.

Now, then, Bran.

How are you going to get that out?

HE LAUGHS

What he did was to take this bottle,

put it in the water,

and use the water to swill it out and collect the bit.

And he did that in about 10 seconds flat.

Bran, in effect, used the water as a tool.

And he is very quick to understand the potential of any object

and work out how it might help solve one of his problems.

All crows, it seems, have extraordinary memories,

acute vision and great ingenuity in devising tools.

In New Caledonia, a tropical island east of Australia,

wild crows use tools just as expertly and inventively as apes.

They fashion sticks to tease grubs out from places

they would otherwise find impossible to reach.

More recently, scientists discovered

and filmed crows that had taken their tool making a stage further.

They were creating hooks,

by carefully modifying the thick ends of twigs.

This seemed extraordinary.

But there were more surprises.

On the nearby island of Grand Terre,

the crows were making even more sophisticated implements.

These are the actual tools made by New Caledonian crows.

They are constructed from the leaves of the pandanus tree,

which have lines of sharp spikes along their margins.

And the crows use them to winkle insects out of crevices.

But each population of these crows makes the tool in their own way.

This one is a broad strip,

this one a very thin strip,

and these two, which come from the north of the island,

are used by two different populations.

One makes a two-step tool, thin at the end.

And this one makes a one, two, three-step tool.

In this rare footage,

the crow strips off the serrated edge of a leaf.

The series of small spines are better than just a single hook,

because they can snag an insect along all its length.

Each population of the crows have their own design,

which they pass on to the next generation.

So just like us, these New Caledonian crows

have their own cultures, their own inquisitive, curious minds.

Which is pretty unusual for a bird.

Orang-utans, in the wild, make very simple tools.

But surprisingly, it's the smart crows that take the prize

for making the most sophisticated tools used by any animal.

Very clever.

Are we finished now?

Where's my lunch?

When I was a boy, my father gave me one of these for my eighth birthday.

It's a fire salamander.

They may look like lizards but in fact they're not reptiles,

they're amphibians with moist skins.

For centuries, mythical stories surrounded these creatures.

It was believed that they were icy cold animals that could

dwell within fires, unharmed by the heat.

Although their fire-surviving powers may be untrue,

the salamander nonetheless possesses a real natural ability,

that is just as extraordinary.

They're able to regrow damaged tails, legs

and other parts of the body through a process called regeneration.

There are more than 600 different species of salamander.

They range in size from just a couple of centimetres,

up to the world's largest amphibian, the Chinese giant salamander,

that can grow to over a metre and a half in length

Salamanders are predators and many hunt for small invertebrates

such as slugs and worms.

But sometimes, they hunt each other with dramatic consequences.

This tiny North American red-backed salamander

is on the menu of the much bigger seal salamander.

Time to make a retreat.

This may look shocking, but the red-back isn't badly injured.

A weak point in its skin allows its tail to break off easily.

Incredibly, it will regrow a new tale in just a matter of weeks.

This ability to replace an entire body part

is unusual among adult vertebrates, and seems almost magical.

Regeneration is a subject that fascinates us.

Modern medicine has spent a lot of money and time

studying the ways our own bodies can regenerate tissue.

All living creatures, including humans,

have the ability to repair damaged parts of the body

but the extent of that repair varies considerably.

As small infants, we have the ability to

regrow the tips of our fingers if they're severed,

but we lose this ability as we age.

So animals, like salamanders,

with their super-regenerative powers,

seem intriguing to us.

Regeneration had been known about since ancient times.

But for a long time, no-one understood how it happened.

In the 17th and 18th century,

there was a new wave of scientific discovery.

A brilliant Italian scientist named Lazzaro Spallanzani

made meticulous observations into regeneration

across many different species,

and shared his ideas in detailed letters.

In November, 1765, he wrote to the eminent scientist Charles Bonnet,

whom he regularly corresponded with,

to announce that he had discovered tail regeneration in salamanders.

Throughout the following year, he followed up his initial observations

with numerous experiments to try to understand

how the salamander could regrow a tail just like the original.

He found that all species of salamander that he tested

could regrow their tails when injured,

and that they did so more rapidly in summer than in winter.

And retained this incredible ability throughout their lives.

Spallanzani advocated a radical theory.

He thought that salamanders already possessed

a number of miniature spare parts at the base of each limb,

that could grow in size to replace a lost or damaged one.

He was unable to prove this theory but he didn't give up.

He studied salamander tadpoles,

and came up with another, even more interesting idea.

A year after his initial letter,

Spallanzani once again wrote to Charles Bonnet.

This time with detailed descriptions of further

experiments into tail regeneration.

Most notably, in this description, he wrote,

'I am almost led to believe that the tail regenerates in tadpoles

'are more of an elongation of the old parts

'than a development from the germ.'

This suggests that Spallanzani was on the right track.

But the idea that a salamander could regrow a new tail

from seemingly nothing was not well supported,

and Spallanzani was therefore never willing to pursue the idea further.

However, there's no doubt that his research helped

to lead other scientists closer

towards proving what really happens when a salamander regrows its tail.

In fact, Spallanzani's rough sketches did make sense.

And they were the first to describe some of the vital processes in

the remarkable growth of new limbs that we understand better today.

When a limb is lost, the exposed blood vessels

and tissue contract to quickly stop any bleeding.

Then, skin from the edges begins to grow across the damaged area

to protect the body from infection.

Now, cells that were once dormant begin dividing

and multiplying to create new ones.

Each cell retains a kind of memory of the type of tissue it used to be,

so a new cell that regrows from damaged muscle will

always become muscle.

Within weeks, the salamander has a full-grown leg

almost identical to the original.

Although we now know the steps

that take place during the regeneration of the body parts,

we still don't fully understand what triggers this kind of response.

But it seems the answer may lie

in how the salamander's body responds to injury.

In humans, if an arm is severed, the cells die,

alerting the immune system to the problem.

In response, the area becomes swollen and is covered over

with scar tissue, preventing any new growth occurring.

But in salamanders, the immune system responds differently.

And instead of forming a scar, it triggers regeneration.

Another rather unusual-looking salamander

that lives in the fresh waters of Mexico,

sheds new light on how this happens.

Axolotls among the best regenerators in the natural world.

And scientists wondered if their blood played a role in the process.

Like us, they have special white blood cells that consume

invading bacteria and damaged tissue around injuries and wounds.

Researchers removed them and the results were surprising.

The axolotl was unable to regrow new limbs.

So white blood cells were part of the secret of their powers

of regeneration.

Understanding the role of the salamander's blood cells

in regrowing limbs could be a step towards discovering why

they can regenerate body parts and we can't.

All amphibians have tadpoles which develop limbs

and enable them to move onto land.

But salamanders are able to re-trigger that remarkable process.

We, too, undergo extraordinary development in the womb.

Maybe, like the salamander, there is a way of us

retaining this ability into our adult lives as well.

The salamander has a truly amazing ability

to regrow complex body parts

to enhance its chances of survival.

While we don't yet know all the answers,

it's likely that this incredible creature

could revolutionise modern medicine,

and the way we treat injuries.

Next, we uncover the secret behind how moose

and other deer regrow their enormous new antlers every year.

And discover what happens when regeneration goes wrong.

This impressive skeleton belonged to one of the biggest deer

to ever live on the planet.

It's an Irish elk.

Its antlers are enormous. They're almost 4 metres, 12 feet, across.

And they weigh 40 kilos.

An Irishman named Dr Molyneux

first scientifically described the elk in 1697,

from specimens taken out of an Irish peat bog.

Some believed that this elk was a large moose, and were convinced

living specimens could be found elsewhere across Europe and Russia.

But not everyone agreed.

And a debate about the life of this creature would continue

for more than 100 years.

The skeleton of an Irish elk looks very similar to that of a moose.

So it's easy to see why many believed them to be the same animal.

Both have very impressive antlers.

Antlers are only found in the deer family and are made of bone.

Unlike horns, which are permanent structures,

they are shed and replaced every year.

But how can deer regrow huge chunks of bone?

Something no other mammal can do.

Moose, like this young bull behind me, start growing their new antlers

immediately after they shed their old ones.

The antlers first appear on little bumps on either side of the head,

known as pedicles.

And they have a soft, furry covering, called velvet.

This is vital to their amazing powers of regeneration.

Blood vessels at the base start the growth.

But as the antler gets longer, this blood supply is cut off.

Then, blood vessels within the velvet take over

and transport nutrients and growth hormones to the growing tips.

In older males, the antlers can grow at a rate of two centimetres a day.

Making it the fastest-growing bone of any animal.

Once at full size, the velvet is shed.

The animal rubs its head against the tree

to encourage the thin velvet to fall off.

It may look gruesome,

but it's a natural part of the animal's cycle

and does the animal no harm.

But why should a huge set of antlers be regrown every year?

It's a question that baffled early naturalists.

Until Charles Darwin suggested it may be to do with

attracting the opposite sex.

In the first few years of adulthood, the anglers are small,

and as a result, young males remain subordinate to the larger bulls.

But as they get older, and their body size increases,

so the antlers will also increase.

Eventually becoming impressive ornaments with which to

compete for females.

Those with the biggest answers are certainly more

attractive to the females.

Maybe they are an indicator of fitness and strength.

And it's no coincidence that antlers are at their full size

during the breeding season.

This is a time when a bull must protect his harem,

and see off competitors.

Competing males tilt their heads to show off their antlers

to their best advantage.

But if the bulls are equally matched, then the competitors fight.

The winner then gains access to the females.

The benefits of such a victory are huge.

But to get to that point,

every young bull must, for many years, grow and regrow antlers.

It's a big investment, draining the body of vital resources.

And no investment was bigger than that of the Irish elk.

The sheer size of these antlers have led some to argue that they

were unlikely to have been used in physical combat.

Unlike other deer, the antlers of the Irish elk grew with a large

flat palm-like plain facing forwards.

So that if a bull looked straight ahead,

it would be at its biggest and most impressive.

In this way, they may been able to intimidate rivals

and attract females without actually fighting.

So although the Irish elk was armed with what appeared to be

enormous weapons, it seems they were mostly for show.

But this strategy might have been an advantage for the large elk.

Fighting is always a risky business

and will often result in serious injuries.

After the breeding season, the antlers are discarded.

Moose shed theirs in the winter,

whereas smaller deer keep theirs until the next spring.

This may be because the moose antlers are such a heavy load

to carry throughout the winter.

But why are antlers shed at all?

Antlers are made of dead bone and can't be repaired.

If a moose damages an antler during a fight,

it will lose its chance of mating for that season.

By shedding and regrowing their antlers each year,

bulls ensure that they stay in the mating game.

Just before antlers are shed,

minerals within them are reabsorbed from the base,

weakening the structure so that they eventually fall off.

The flesh underneath is exposed, but not for long,

as new skin soon covers the wound.

Experiments have shown that the skin lesion that forms over

the open wound creates a connection with the underlying tissue,

that is crucial to regeneration.

If this connection isn't made, the production of velvet will be

interrupted and the antlers will either not grow at all,

or develop into strange shapes.

So, what about the Irish elk?

Could the problems of regenerating such gigantic antlers

have determined its fate?

The French scientist George Cuvier was keen to demonstrate

that the Irish elk was a unique species that had become extinct.

To prove this point,

Cuvier undertook a detailed examination of Irish elk fossils.

He was able to show that it was indeed a distinct type of deer,

that could no longer be found alive.

And so the Irish elk was one of the first animals to be

recognised as being extinct.

George Cuvier had solved the question of whether or not

the Irish elk and moose were one and the same creature.

But why did the Irish elk die out?

Cuvier suggested that evolution has set it

on a course of ever-increasing growth.

And that eventually, the antlers became

so large that the poor animal could not even lift its neck.

He may not have been that far from the truth.

It's now thought that the annual growth of the Irish elk antlers

put a strain on their bodies.

A significant proportion of minerals within their bones

were extracted and moved into their growing antlers.

This led to a seasonal osteoporosis, with their bones weakening.

They were, in effect, robbing one part of their body to boost another.

It was a gamble that worked for thousands of years.

But around 10,000 years ago, the climate began to warm.

The nutrient-rich grasses that the elk relied upon began to disappear.

Growing massive antlers may now have been too much of a drain,

and permanently weakened the skeleton.

The change in diet may also have affected their ability to breed,

with females no longer able to produce young every year.

Whatever the reason, the Irish elk, with its magnificent antlers,

finally vanished from the landscape.

And in its place,

the moose has become the largest deer on earth today.

So, while regeneration can give the salamander

a second chance to a full life,

the yearly regeneration of antlers

in male moose is a risky strategy.

But one with huge rewards for those with the best antlers.