BBC Natural World - Attenborough's Fabulous Frogs

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

from a group of amphibians.

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 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.

The life circle of the frog involved a truly remarkable process

Let's see when it all begin though

The frog's life start here.

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.

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.