Attenborough's Fabulous Frogs Natural World

There are more than 5,000 species of frogs and toads,

and they come in all colours, shapes and sizes.

Over the years, I've filmed many different kinds of them,

from across the world.

This is the largest frog in the world, the goliath frog.

And here in the leaf litter of this Madagascan forest,

is the tiniest of them all.

They can hop and climb.

They can parachute from the tree tops.

And burrow deep into the ground.

Some, seemingly, can even walk on water.

Frogs, like newts and salamanders, are amphibians,

cold blooded animals that need water to survive.

But despite this, they have colonised some of the hottest

and the coldest places on Earth.

Frogs are truly fascinating.

You many not have thought much about them

and they don't necessarily grab the headlines,

but there's more to frogs than you might suppose.

Frogs were the first creatures that I kept when I was a boy,

and I thought they were fascinating and beautiful,

and I still think they are.

They were, of course, the first creatures to move up onto land.

Today's frogs are descended from a group of amphibians that

lived around 300 million years ago,

and they were very like the modern salamander.

That is to say, they had a very, very long spine

with about 30 vertebrae in it, ending in a tail.

But then about 250 million years ago,

an intermediate form appeared,

like this fossil from Madagascar,

and already you can see a difference.

Most importantly, the spine,

instead of being 30 vertebrae long, is only about 15.

The tail has almost been lost altogether.

The hind legs are very much bigger.

Compare that with today's amphibian.

Most significantly, its spine is now, again halved.

But the pelvis has become greatly elongated.

But that's nothing compared with what has happened to the legs.

They are gigantic.

So you can see that this animal is a leaper.

And today, some exploit these spectacular legs very dramatically.

This little frog is an amazing jumper.

It can leap 30 times its own body length,

and there are some that can go even farther.

One can leap 55 times its body length,

equivalent to me jumping the length of a football pitch.

In the 1930s, in the United States,

frog leaping became something of a craze.

People bet on how far a frog could jump.

Even beauty queens took part in frog-jumping contests,

each with her own pet.

In the past, people couldn't understand how a frog could leap

so far, but a little scientific research revealed how it does it.

When a frog is in its sitting position,

its leg muscles are contracted.

This stretches the leg tendons.

Tendons are elastic like rubber bands.

Stretching them stores energy within them.

And then, when the frog jumps, the tendons release that energy,

like firing a catapult.

And the frog is propelled into the air.

When this skittering frog from India jumps,

it simultaneously extends its webbed toes

so that it virtually bounces across the surface of the water.

The webs between the toes, so useful for swimming,

can also help when moving around on land.

The gliding leaf frog has such extensive webbing that

when it jumps, the outstretched toes of its feet act like parachutes

and keep it in the air long enough to travel considerable distances.

When the first amphibians emerged from the water, the only

animal sounds to be heard on land were the whirrs and hums of insects.

CROAKING

But the amphibians also needed to communicate with one another,

and soon they added their own croaks and whistles.

CROAKING AND WHISTLING

Frogs blow air from their lungs, through vocal chords

and so produce a croak.

But the muscles that do that are comparatively weak, so many species

amplify the sound with resonators, cheek pouches or throat pouches.

FROG CROAKS

One purpose for calling is to find a mate.

A female gliding leaf frog in the jungles of South America

is listening to all the males calling around her.

Then she sets off in the direction of the loudest voice,

because the owner is likely to be the strongest male, the best mate.

It's a long haul.

On the way, she has to avoid the weaker males.

It's not all that easy.

She has to fight off several at a time.

Eventually, the strongest male gets his reward.

It's a case of he who shouts loudest.

This is called the splendid leaf frog,

and quite right, too.

Most frogs communicate with their voice,

by croaking or indeed squeaking.

And this one does, too,

but it has rather a quiet voice

and it also communicates by using its legs.

What he'll do is to use them to wave to other frogs.

And its legs are specially adapted for the purpose.

They have flaps on them

so they appear to be specially wide and prominent.

This waving technique is something I once filmed with another

beautiful frog.

We found it several years ago in the rain forests of Panama.

This is a golden Panama male, and he is looking for a mate.

But a rival stands in his way.

Just in case his call can't be heard above the sound of water,

he reinforces his message with a visual signal, a wave.

His rival waves back.

He repeats his signal so there's no misunderstanding.

But now another male arrives.

He too is looking for a female,

and he isn't going to let anyone stand in his way.

This kind of argument has to be settled with a wrestling match.

That should teach him!

The loser submits, lowering his head.

And the winner continues his hunt for a mate.

Finally, a large golden female arrives. Just the ticket!

HE CROAKS

He waves to show he's interested.

She waves back.

It's a success. His waving courtship has worked.

Calling and waving are comparatively subtle ways of attracting a female.

Other frogs use a more macho approach.

Rains, on the African savannah.

The African male bullfrog, one of the biggest of all frogs.

He fights for the right to mate.

The males assemble in a newly-filled pond

and battle with each other to establish who is the strongest.

The winner will mate with most of the females here.

No such luck for the loser.

Courtship techniques vary widely, but for one remarkable little

brown frog in Madagascar, the key to mating rituals is skin colour.

Following a bout of heavy rain, the frogs all gather at a waterhole.

The females are still brown, but the males have turned a bright yellow.

This enables males and females to tell each other

apart in the multiple mating that is about to happen.

They have to judge the moment very precisely.

There must be enough water in which to lay their eggs,

but not so much that the eggs are washed away.

CROAKING

After a few hours, the orgy is over,

and the males turn back to brown again.

It will happen all over again next year,

when the rains return and more eggs are laid.

When speeded up, you can watch

the extraordinary way in which eggs develop.

These eggs were laid by a leaf frog.

And inside the jelly of each one, you can see a little tiny dot.

And if you look closely, you may even see it move.

And over the next five or seven days,

they will continue to develop until they are strong enough

to emerge from the egg and drop into water beneath.

And then over the next four or five weeks,

an enormous transformation takes place.

The gills, which enabled the tadpole to breathe in water,

gradually disappear.

The tadpole's intestines, accustomed to a vegetarian diet,

have to be completely remodelled to allow them to digest animal tissues.

Its skull, which was made of cartilage, turns to bone

and the backbone grows.

The tadpole's legs get larger as the tail shrinks, absorbed by the body.

It's an astonishing

and radical transformation, which takes around six weeks.

A pond in Madagascar.

Not a good place for eggs

because it's full of fish that would eat frogs' eggs given the chance.

So this little frog lays her eggs on the leaves of trees

that overhang the pond.

The tadpoles are maturing quickly, but there is danger here, too.

A predatory wasp has found the clumps of spawn.

It manages to slice its way through the protective jelly.

And now it starts to chew up the tadpoles.

But these tadpoles,

although only five days old, can react to such attacks.

The vibrations, created by the wasp, stimulate them to hatch prematurely.

The jelly liquefies and the tadpoles travel down the leaf

and drop into the water below.

They may be underdeveloped, but they can swim

and they stand a better chance of survival in the pond than

they did with the wasp on their leaf.

These youngsters had to survive without parental care, but other

frog parents go to great lengths to look after their offspring.

This little frog is tiny, hardly bigger than my thumb nail.

It is a strawberry poison-dart frog.

It may be very small,

but when it comes to caring for its young, it's a real champion.

It lives in the wet lowland forests of Central America.

This female is guarding a clump of newly-fertilised eggs.

She and her mate will keep watch,

making sure that their offspring are safe from predators.

But the leaf litter is drying out and the tadpoles need water.

She must move them, and fast.

So she encourages one of them to jump on to her back.

But it's not a pond on the forest floor that she's looking for now.

She wants a bromeliad, a vase plant, and they grow up in the branches.

Climbing a tree as tall as this is an immense journey for such

a tiny creature.

A bromeliad plant has a tiny permanent

pool of water at its centre,

an excellent nursery for a tadpole.

And there she delivers it.

But she has several tadpoles.

So now she must rush back to the others down on the ground.

She collects them one by one and carries each to its own bromeliad.

She continues to make her long, arduous journeys,

while the male guards the remaining eggs on the forest floor.

But the little bromeliad pools don't have any food in them.

So she lays an unfertilised egg in each one for each tadpole to eat.

A single egg won't sustain a developing tadpole for very long.

So she has to return to each pool every few days

and deliver another food parcel.

This continues for the next two weeks,

during which time, she will have travelled over half a mile.

An astonishing distance for such a tiny creature.

Eventually, the tadpole develops into a froglet large enough

to leave the pool and fend for itself.

Mum has done her job well.

But it isn't always the female who takes on the task of rearing

the young.

Sometimes, the male does.

And one of those lives in the mountains of northern Spain.

This little creature is called a toad because its skin is rather dry.

But the names frog and toad are largely interchangeable,

for all amphibians with this shape are very closely related.

This one is known as the midwife toad.

When they mate, the male clasps the female with his arms

and squeezes until she releases her eggs.

They emerge in a long chain of jelly,

and as they do so, he fertilises them.

He then hitches them up around his hind legs

and then the pair will then separate.

She leaves and he carries them around

until the time comes to deposit them in water.

The midwife toad is not the only species in which the male

takes care of the young.

The African bullfrog is quite a character.

It's the biggest frog in Africa and it's very aggressive.

It's got a very powerful bite, for one thing.

But in spite of that, it's a devoted father.

Bullfrogs spawn in little pools around the margins of a larger pond.

And after mating is over, one male stays to watch over them all.

But the water is evaporating and the tadpoles are now crowded

together in a single pool, and that too is now drying up.

The tadpoles will be dead within an hour,

unless the male can do something to save them.

And he starts doing just that.

He begins to dig a channel to connect the tadpoles'

little pool to the main pond.

He must be quick.

It's a major task, but he is determined.

Down they swim.

The tadpoles are saved!

But perhaps the prize for fatherly care should go to a rare

little frog that lives in the forests of Chile.

This is Darwin's frog.

After the female has laid her eggs on the moist ground

and the male has fertilised them, he, apparently, eats them.

But they go, not into his stomach but into his throat pouch.

And there they develop, and wriggle.

And when they're ready...

..one jumps out.

And another.

Giving birth from your mouth is pretty odd,

but what about producing babies from your back?

The Surinam toad is an aquatic species from South America.

The female produces around 100 eggs at a time.

The male collects them and steers them on to the female's back.

And there they stick.

The skin on the female's back then begins to swell around them.

A membrane grows over them and eventually completely encloses them.

After a couple of days, they've virtually disappeared.

A few weeks later, the young hatch as tadpoles.

In some Surinam toads, the young remain within their mothers'

back so long that they emerge not as tadpoles but little froglets.

It's certainly an odd way of producing young, but it works.

All adult amphibians are hunters.

To help them catch their prey, they have a secret weapon -

a special kind of tongue.

The extendable tongue is an amphibian invention.

No fish ever had one.

And the tongue is not attached to the back of the mouth like ours,

but to the front.

Frogs eat worms and insects.

And the larger the frog, the bigger prey it will tackle.

And some species, like these cane toads,

will eat almost anything, including one another.

It's recently been discovered that way back in prehistory,

there were some frogs big enough to catch mammals.

A few years ago, fragments were found in Madagascar

of a really giant frog dating back from about 65 million years ago.

This is part of its skull.

Here is the orbit of the eye.

And this is where its spine...

The spine would have run down here.

And this is the right cheek.

So the animal's head, when complete, would have been about that wide.

So this really was a monster.

And here is a computer reconstruction

of the complete skeleton.

The scientists who worked on it

referred to it among themselves as a devil frog.

And when the time came to give it a scientific name,

they called it Beelzebufo.

65 million years ago was just towards

the end of the reign of the dinosaurs.

So maybe this giant frog actually ate hatchling dinosaurs,

as been shown in this artist's imaginative reconstruction.

Some frogs today also have teeth, but they don't chew with them.

The teeth are used either for defence

or as a way of gripping prey.

This large monkey frog is in the process of swallowing a cricket.

And, strangely perhaps, it uses its eyes to help it do so.

We're waiting for it to burp.

LAUGHTER

As a frog swallows, it pulls its bulging eyes downwards

so that they help to push the food down its throat.

Most frogs have very big eyes.

They have to be big because frogs, since they don't have necks,

can't turn their heads to look to one side.

Instead, their two eyes, between them,

give a frog an almost 360-degree vision.

They also have a kind of see-through third eye-lid,

which protects their eyes underwater without blocking their sight.

The red-eyed tree frog's third eyelid has a distinctive

green pattern, which, when out of water, helps with camouflage.

Frogs have managed to adapt to a surprising range of environments.

The little red-eyed tree frog lives up in the forest canopy,

catching insects.

And to do that, of course, it has to be an expert climber.

So, not surprisingly, they have very special hands and feet.

Its toe-pads are highly complex structures.

Each has a large surface area, which helps it get a good grip.

Between the six-sided skin cells,

there are small channels which fill with a sticky mucus.

This acts as a continuously renewed glue, but one that allows

the frog to peel off its foot and re-attach it as it climbs.

Some frogs have evolved a way of using their hands

and feet in a quite remarkable way.

In the remote rain forests of South America,

there's a small amphibian known as a waterfall toad.

It, like so many frogs, is a favourite meal of snakes.

Many frogs avoid their enemies by hopping,

but this little toad can't hop more than an inch or so. Instead,

when a swift retreat is needed, it has other techniques.

Free-falling, which is easy,

and stopping, which is more difficult.

Above the rain forests, there are mountains so drenched with rain

that the rocks are bare, except for a coat of slimy black algae.

And here you can find the pebble toad.

But there are predators here, too.

This is a toad-eating tarantula, an expert in ambushing its prey.

The pebble toad can't hop very far either,

but it has a different defence.

It clenches its muscles so tightly

that it becomes as bouncy as a rubber ball.

Danger averted and no damage done.

But hunters are everywhere - not only on the ground, but in the sky.

Camouflage is an excellent defence.

Blink and you could easily miss this Darwin's frog.

Most frogs are beautifully camouflaged

so that it's very difficult sometimes to spot them.

But this one,

which is the tiger-striped monkey frog from South America...

..has tiger stripes - orange and black -

on the inside of its legs.

So when it's sitting like that, it looks green.

But if they're threatened by a predator,

they can suddenly open their legs and reveal

that orange and black underbelly,

which, people think, puts off a predator.

The great majority of frogs rely on camouflage.

But a few take the other option - conspicuousness.

Bright colouring can be a warning that an animal is

unpleasant to eat. But some are more than merely unpalatable.

This is the golden poison-dart frog from Colombia.

And its skin contains enough poison to kill ten human beings,

which is why I'm taking no chances and wearing gloves.

Traditionally, the people in Colombia used that poison

to tip their blow-pipe darts.

But of course, for the frog,

the poison serves as a defence against predators.

And many poison-dart frogs are very brightly coloured, just to

warn predators of what would await them if they did take a mouthful.

The toxicity of frog skin has traditionally been exploited

by local people, but modern medicine has also found ways of using it.

One chemical compound from the skin

of the tri-coloured poison-dart frog...

..is being used in the development of a groundbreaking pain-killer...

..several hundred times more powerful than morphine.

A frog doesn't drink,

it absorbs all the water it needs through its skin.

It also gets most of its oxygen in the same way.

But a permeable skin that allows water to flow in also allows

it to flow out, and for some that can be a problem.

If there's a dry spell,

this giant monkey frog from South America

produces a kind of ointment from glands

in its skin, which it uses as sun cream.

At the beginning of the dry season,

it takes steps to make sure that it doesn't get sun-burnt or dry out.

And with their supple joints, frogs can manage to reach all those

odd places that the rest of us find a little tricky.

The dry season can last for weeks.

So it's best to be really thorough.

Some frogs however, never leave water at all.

This is the highest lake in the world - Lake Titicaca

in the Peruvian Andes.

And the frog that lives here has very different problems.

At 4,000 metres above sea level,

there's very little oxygen in the atmosphere,

and therefore in the water.

So the frog has developed bizarre-looking flaps

and folds that increase the skin's surface area,

and therefore its ability to absorb oxygen.

The frog also increases the flow of water across its skin by doing

what looks like press-ups.

Because their skin is so sensitive to their surroundings,

frogs are important biological indicators.

If there are environmental problems,

they're among the first creatures to be affected.

But that permeability has also led,

in recent years, to alarming declines.

This, crouched on a leaf,

is one of the rarest frogs in the world.

It's called the lemur leaf frog

and it lives in Costa Rica.

Once it was widespread there, but today,

it's been reduced to a very small area.

It's nocturnal and lives in the humid rainforest of the lowlands.

Unusually for a leaf frog, it has no webbing between its toes

and its stick-like legs give it a very distinctive walk.

What a lovely little creature.

Here in the Manchester Museum, they're studying the species

and doing their best to conserve it,

both by breeding it in captivity

and partly by going out to Costa Rica and studying it in the wild.

The cause for its loss in numbers is three-fold -

loss of habitat, pesticides

and a particularly lethal kind of fungus called a chytrid.

The fungus causes the cells in a frog's skin

to suddenly multiply,

so that the outer layers thicken.

That blocks the flow of essential salts through the skin.

The muscles then can't function properly...

..and eventually the heart simply stops beating.

Scientists think that chytrid fungus started to spread

back in the 1940s, when African clawed frogs,

which were probably carrying the fungus,

were shipped all over the world

for medical research, including pregnancy testing.

Today, chytrid fungus is spreading uncontrollably,

causing the extinction of some frog species

and the severe decline of many others.

It's the worst infectious disease ever recorded

in terms of the number of species affected.

Almost a third of all amphibians are now threatened with extinction,

including the lemur leaf frog.

The future of this little frog is still hanging in the balance,

but hopefully the work that's being done here in Manchester

will prevent it from becoming extinct.

But other frogs have not been so lucky.

Over the years, I've filmed a number of different species,

some of which are now extinct in the wild.

The waving golden frogs we filmed in Panama

belonged to one of the last remaining populations.

The chytrid fungus was already spreading up from South America.

So when we had finished, scientists collected all they could find

and took them to specially sterilised breeding centres

to keep them in safety until such time, if ever,

the fungus disappears

and they can be reintroduced to their original home.

But despite the decline, the fact that frogs are such adaptable

creatures does offer some hope.

Some species, after all, manage to survive in places that might

seem to spell certain death for creatures with moist skins.

This is part of the Australian desert where several years

can pass without rain.

It's a great relief when at last the drought breaks.

And then, amazingly, little toads emerge from the sand.

Numbers of them appear almost simultaneously.

They have specially large legs to help them dig,

which gives them their name - spade-foots.

Now they must mate, if possible, before the sun rises.

The desert dries very quickly, even after the heaviest of storms.

Temperatures rise to 50 degrees Centigrade.

Now any water on the surface will evaporate instantly.

But the toads are already retreating and will soon be back underground.

It really is a miracle that they're here at all.

The spade-foot toad is not the only frog species to adapt

to extreme environmental conditions.

Of all the frogs in the world, this perhaps is the most extraordinary.

It's called the wood frog and it lives in America,

north of the Arctic Circle.

And it survives some of the coldest

temperatures on Earth,

and it does so by becoming frozen solid.

As the winter frost starts to bite,

ice begins to form on the frog's skin.

The liver goes into overdrive,

producing glucose which is pumped around the body by the heart.

This glucose acts like an anti-freeze within the cells,

preventing them from freezing.

Instead, ice forms around them.

The blood, however, is frozen and all the organs are encased in ice.

And the heart stops.

But then, months later, spring at last returns.

And the ice around the wood frog begins to melt.

The wood frog's ability to survive is truly extraordinary,

and that does give us the hope that maybe, in spite of the threats

that face them today,

frogs as a whole will continue to live on this planet.

It would be truly sad if we lost them.

That's it.