0:00:22 > 0:00:27There are more than 5,000 species of frogs and toads,
0:00:27 > 0:00:30and they come in all colours, shapes and sizes.
0:00:31 > 0:00:35Over the years, I've filmed many different kinds of them,
0:00:35 > 0:00:36from across the world.
0:00:37 > 0:00:42This is the largest frog in the world, the goliath frog.
0:00:42 > 0:00:46And here in the leaf litter of this Madagascan forest,
0:00:46 > 0:00:49is the tiniest of them all.
0:00:54 > 0:00:56They can hop and climb.
0:01:00 > 0:01:02They can parachute from the tree tops.
0:01:03 > 0:01:06And burrow deep into the ground.
0:01:06 > 0:01:11Some, seemingly, can even walk on water.
0:01:14 > 0:01:18Frogs, like newts and salamanders, are amphibians,
0:01:18 > 0:01:21cold blooded animals that need water to survive.
0:01:21 > 0:01:25But despite this, they have colonised some of the hottest
0:01:25 > 0:01:27and the coldest places on Earth.
0:01:29 > 0:01:33Frogs are truly fascinating.
0:01:33 > 0:01:35You many not have thought much about them
0:01:35 > 0:01:37and they don't necessarily grab the headlines,
0:01:37 > 0:01:41but there's more to frogs than you might suppose.
0:01:57 > 0:02:02Frogs were the first creatures that I kept when I was a boy,
0:02:02 > 0:02:07and I thought they were fascinating and beautiful,
0:02:07 > 0:02:09and I still think they are.
0:02:09 > 0:02:15They were, of course, the first creatures to move up onto land.
0:02:35 > 0:02:39Today's frogs are descended from a group of amphibians that
0:02:39 > 0:02:42lived around 300 million years ago,
0:02:42 > 0:02:45and they were very like the modern salamander.
0:02:45 > 0:02:49That is to say, they had a very, very long spine
0:02:49 > 0:02:55with about 30 vertebrae in it, ending in a tail.
0:02:55 > 0:02:59But then about 250 million years ago,
0:02:59 > 0:03:01an intermediate form appeared,
0:03:01 > 0:03:04like this fossil from Madagascar,
0:03:04 > 0:03:07and already you can see a difference.
0:03:07 > 0:03:09Most importantly, the spine,
0:03:09 > 0:03:14instead of being 30 vertebrae long, is only about 15.
0:03:14 > 0:03:18The tail has almost been lost altogether.
0:03:18 > 0:03:21The hind legs are very much bigger.
0:03:21 > 0:03:24Compare that with today's amphibian.
0:03:24 > 0:03:31Most significantly, its spine is now, again halved.
0:03:31 > 0:03:34But the pelvis has become greatly elongated.
0:03:35 > 0:03:39But that's nothing compared with what has happened to the legs.
0:03:39 > 0:03:42They are gigantic.
0:03:42 > 0:03:46So you can see that this animal is a leaper.
0:03:49 > 0:03:55And today, some exploit these spectacular legs very dramatically.
0:04:01 > 0:04:05This little frog is an amazing jumper.
0:04:05 > 0:04:10It can leap 30 times its own body length,
0:04:10 > 0:04:12and there are some that can go even farther.
0:04:12 > 0:04:17One can leap 55 times its body length,
0:04:17 > 0:04:21equivalent to me jumping the length of a football pitch.
0:04:30 > 0:04:33In the 1930s, in the United States,
0:04:33 > 0:04:37frog leaping became something of a craze.
0:04:37 > 0:04:40People bet on how far a frog could jump.
0:04:51 > 0:04:54Even beauty queens took part in frog-jumping contests,
0:04:54 > 0:04:56each with her own pet.
0:05:15 > 0:05:19In the past, people couldn't understand how a frog could leap
0:05:19 > 0:05:25so far, but a little scientific research revealed how it does it.
0:05:38 > 0:05:41When a frog is in its sitting position,
0:05:41 > 0:05:44its leg muscles are contracted.
0:05:44 > 0:05:47This stretches the leg tendons.
0:05:52 > 0:05:55Tendons are elastic like rubber bands.
0:05:59 > 0:06:03Stretching them stores energy within them.
0:06:03 > 0:06:08And then, when the frog jumps, the tendons release that energy,
0:06:08 > 0:06:10like firing a catapult.
0:06:13 > 0:06:16And the frog is propelled into the air.
0:06:31 > 0:06:35When this skittering frog from India jumps,
0:06:35 > 0:06:38it simultaneously extends its webbed toes
0:06:38 > 0:06:42so that it virtually bounces across the surface of the water.
0:06:57 > 0:07:01The webs between the toes, so useful for swimming,
0:07:01 > 0:07:04can also help when moving around on land.
0:07:05 > 0:07:09The gliding leaf frog has such extensive webbing that
0:07:09 > 0:07:14when it jumps, the outstretched toes of its feet act like parachutes
0:07:14 > 0:07:18and keep it in the air long enough to travel considerable distances.
0:07:43 > 0:07:47When the first amphibians emerged from the water, the only
0:07:47 > 0:07:51animal sounds to be heard on land were the whirrs and hums of insects.
0:07:51 > 0:07:55CROAKING
0:07:55 > 0:07:58But the amphibians also needed to communicate with one another,
0:07:58 > 0:08:02and soon they added their own croaks and whistles.
0:08:02 > 0:08:08CROAKING AND WHISTLING
0:08:10 > 0:08:15Frogs blow air from their lungs, through vocal chords
0:08:15 > 0:08:16and so produce a croak.
0:08:16 > 0:08:22But the muscles that do that are comparatively weak, so many species
0:08:22 > 0:08:28amplify the sound with resonators, cheek pouches or throat pouches.
0:08:28 > 0:08:33FROG CROAKS
0:08:58 > 0:09:01One purpose for calling is to find a mate.
0:09:04 > 0:09:08A female gliding leaf frog in the jungles of South America
0:09:08 > 0:09:11is listening to all the males calling around her.
0:09:16 > 0:09:20Then she sets off in the direction of the loudest voice,
0:09:20 > 0:09:25because the owner is likely to be the strongest male, the best mate.
0:09:30 > 0:09:33It's a long haul.
0:09:41 > 0:09:45On the way, she has to avoid the weaker males.
0:09:49 > 0:09:51It's not all that easy.
0:09:51 > 0:09:53She has to fight off several at a time.
0:10:12 > 0:10:16Eventually, the strongest male gets his reward.
0:10:16 > 0:10:20It's a case of he who shouts loudest.
0:10:34 > 0:10:39This is called the splendid leaf frog,
0:10:39 > 0:10:41and quite right, too.
0:10:41 > 0:10:43Most frogs communicate with their voice,
0:10:43 > 0:10:46by croaking or indeed squeaking.
0:10:46 > 0:10:48And this one does, too,
0:10:48 > 0:10:51but it has rather a quiet voice
0:10:51 > 0:10:55and it also communicates by using its legs.
0:10:57 > 0:11:01What he'll do is to use them to wave to other frogs.
0:11:01 > 0:11:06And its legs are specially adapted for the purpose.
0:11:06 > 0:11:08They have flaps on them
0:11:08 > 0:11:13so they appear to be specially wide and prominent.
0:11:15 > 0:11:19This waving technique is something I once filmed with another
0:11:19 > 0:11:21beautiful frog.
0:11:21 > 0:11:27We found it several years ago in the rain forests of Panama.
0:11:36 > 0:11:42This is a golden Panama male, and he is looking for a mate.
0:11:43 > 0:11:45But a rival stands in his way.
0:11:48 > 0:11:52Just in case his call can't be heard above the sound of water,
0:11:52 > 0:11:57he reinforces his message with a visual signal, a wave.
0:12:00 > 0:12:02His rival waves back.
0:12:04 > 0:12:07He repeats his signal so there's no misunderstanding.
0:12:21 > 0:12:24But now another male arrives.
0:12:24 > 0:12:25He too is looking for a female,
0:12:25 > 0:12:28and he isn't going to let anyone stand in his way.
0:12:31 > 0:12:35This kind of argument has to be settled with a wrestling match.
0:12:37 > 0:12:38That should teach him!
0:12:43 > 0:12:46The loser submits, lowering his head.
0:12:58 > 0:13:01And the winner continues his hunt for a mate.
0:13:06 > 0:13:12Finally, a large golden female arrives. Just the ticket!
0:13:12 > 0:13:18HE CROAKS
0:13:25 > 0:13:28He waves to show he's interested.
0:13:29 > 0:13:31She waves back.
0:13:49 > 0:13:52It's a success. His waving courtship has worked.
0:13:58 > 0:14:03Calling and waving are comparatively subtle ways of attracting a female.
0:14:03 > 0:14:06Other frogs use a more macho approach.
0:14:12 > 0:14:15Rains, on the African savannah.
0:14:27 > 0:14:31The African male bullfrog, one of the biggest of all frogs.
0:14:31 > 0:14:34He fights for the right to mate.
0:14:47 > 0:14:51The males assemble in a newly-filled pond
0:14:51 > 0:14:54and battle with each other to establish who is the strongest.
0:15:10 > 0:15:13The winner will mate with most of the females here.
0:15:16 > 0:15:19No such luck for the loser.
0:15:28 > 0:15:33Courtship techniques vary widely, but for one remarkable little
0:15:33 > 0:15:39brown frog in Madagascar, the key to mating rituals is skin colour.
0:15:43 > 0:15:49Following a bout of heavy rain, the frogs all gather at a waterhole.
0:15:49 > 0:15:54The females are still brown, but the males have turned a bright yellow.
0:16:01 > 0:16:04This enables males and females to tell each other
0:16:04 > 0:16:08apart in the multiple mating that is about to happen.
0:16:19 > 0:16:22They have to judge the moment very precisely.
0:16:22 > 0:16:26There must be enough water in which to lay their eggs,
0:16:26 > 0:16:29but not so much that the eggs are washed away.
0:16:31 > 0:16:35CROAKING
0:17:16 > 0:17:19After a few hours, the orgy is over,
0:17:19 > 0:17:23and the males turn back to brown again.
0:17:23 > 0:17:26It will happen all over again next year,
0:17:26 > 0:17:30when the rains return and more eggs are laid.
0:17:35 > 0:17:37When speeded up, you can watch
0:17:37 > 0:17:40the extraordinary way in which eggs develop.
0:18:06 > 0:18:09These eggs were laid by a leaf frog.
0:18:09 > 0:18:15And inside the jelly of each one, you can see a little tiny dot.
0:18:15 > 0:18:19And if you look closely, you may even see it move.
0:18:19 > 0:18:22And over the next five or seven days,
0:18:22 > 0:18:25they will continue to develop until they are strong enough
0:18:25 > 0:18:29to emerge from the egg and drop into water beneath.
0:18:49 > 0:18:52And then over the next four or five weeks,
0:18:52 > 0:18:55an enormous transformation takes place.
0:18:59 > 0:19:02The gills, which enabled the tadpole to breathe in water,
0:19:02 > 0:19:04gradually disappear.
0:19:07 > 0:19:11The tadpole's intestines, accustomed to a vegetarian diet,
0:19:11 > 0:19:16have to be completely remodelled to allow them to digest animal tissues.
0:19:17 > 0:19:21Its skull, which was made of cartilage, turns to bone
0:19:21 > 0:19:23and the backbone grows.
0:19:25 > 0:19:30The tadpole's legs get larger as the tail shrinks, absorbed by the body.
0:19:31 > 0:19:33It's an astonishing
0:19:33 > 0:19:37and radical transformation, which takes around six weeks.
0:19:46 > 0:19:48A pond in Madagascar.
0:19:48 > 0:19:50Not a good place for eggs
0:19:50 > 0:19:54because it's full of fish that would eat frogs' eggs given the chance.
0:19:56 > 0:20:01So this little frog lays her eggs on the leaves of trees
0:20:01 > 0:20:03that overhang the pond.
0:20:03 > 0:20:08The tadpoles are maturing quickly, but there is danger here, too.
0:20:11 > 0:20:15A predatory wasp has found the clumps of spawn.
0:20:22 > 0:20:26It manages to slice its way through the protective jelly.
0:20:32 > 0:20:37And now it starts to chew up the tadpoles.
0:20:47 > 0:20:48But these tadpoles,
0:20:48 > 0:20:52although only five days old, can react to such attacks.
0:20:52 > 0:20:58The vibrations, created by the wasp, stimulate them to hatch prematurely.
0:20:59 > 0:21:03The jelly liquefies and the tadpoles travel down the leaf
0:21:03 > 0:21:05and drop into the water below.
0:21:13 > 0:21:16They may be underdeveloped, but they can swim
0:21:16 > 0:21:20and they stand a better chance of survival in the pond than
0:21:20 > 0:21:22they did with the wasp on their leaf.
0:21:26 > 0:21:30These youngsters had to survive without parental care, but other
0:21:30 > 0:21:34frog parents go to great lengths to look after their offspring.
0:21:38 > 0:21:44This little frog is tiny, hardly bigger than my thumb nail.
0:21:47 > 0:21:49It is a strawberry poison-dart frog.
0:21:49 > 0:21:51It may be very small,
0:21:51 > 0:21:55but when it comes to caring for its young, it's a real champion.
0:22:06 > 0:22:10It lives in the wet lowland forests of Central America.
0:22:27 > 0:22:32This female is guarding a clump of newly-fertilised eggs.
0:22:35 > 0:22:38She and her mate will keep watch,
0:22:38 > 0:22:42making sure that their offspring are safe from predators.
0:22:43 > 0:22:47But the leaf litter is drying out and the tadpoles need water.
0:22:47 > 0:22:50She must move them, and fast.
0:22:50 > 0:22:54So she encourages one of them to jump on to her back.
0:22:55 > 0:23:00But it's not a pond on the forest floor that she's looking for now.
0:23:00 > 0:23:06She wants a bromeliad, a vase plant, and they grow up in the branches.
0:23:13 > 0:23:18Climbing a tree as tall as this is an immense journey for such
0:23:18 > 0:23:19a tiny creature.
0:23:30 > 0:23:33A bromeliad plant has a tiny permanent
0:23:33 > 0:23:35pool of water at its centre,
0:23:35 > 0:23:39an excellent nursery for a tadpole.
0:23:39 > 0:23:42And there she delivers it.
0:23:53 > 0:23:57But she has several tadpoles.
0:23:57 > 0:24:01So now she must rush back to the others down on the ground.
0:24:03 > 0:24:09She collects them one by one and carries each to its own bromeliad.
0:24:17 > 0:24:21She continues to make her long, arduous journeys,
0:24:21 > 0:24:24while the male guards the remaining eggs on the forest floor.
0:24:31 > 0:24:35But the little bromeliad pools don't have any food in them.
0:24:35 > 0:24:41So she lays an unfertilised egg in each one for each tadpole to eat.
0:24:45 > 0:24:50A single egg won't sustain a developing tadpole for very long.
0:24:50 > 0:24:53So she has to return to each pool every few days
0:24:53 > 0:24:56and deliver another food parcel.
0:24:56 > 0:25:00This continues for the next two weeks,
0:25:00 > 0:25:03during which time, she will have travelled over half a mile.
0:25:05 > 0:25:08An astonishing distance for such a tiny creature.
0:25:11 > 0:25:15Eventually, the tadpole develops into a froglet large enough
0:25:15 > 0:25:18to leave the pool and fend for itself.
0:25:21 > 0:25:23Mum has done her job well.
0:25:25 > 0:25:29But it isn't always the female who takes on the task of rearing
0:25:29 > 0:25:30the young.
0:25:32 > 0:25:34Sometimes, the male does.
0:25:38 > 0:25:41And one of those lives in the mountains of northern Spain.
0:25:44 > 0:25:49This little creature is called a toad because its skin is rather dry.
0:25:49 > 0:25:53But the names frog and toad are largely interchangeable,
0:25:53 > 0:25:56for all amphibians with this shape are very closely related.
0:25:57 > 0:26:00This one is known as the midwife toad.
0:26:02 > 0:26:07When they mate, the male clasps the female with his arms
0:26:07 > 0:26:10and squeezes until she releases her eggs.
0:26:14 > 0:26:17They emerge in a long chain of jelly,
0:26:17 > 0:26:20and as they do so, he fertilises them.
0:26:27 > 0:26:30He then hitches them up around his hind legs
0:26:30 > 0:26:32and then the pair will then separate.
0:26:40 > 0:26:43She leaves and he carries them around
0:26:43 > 0:26:47until the time comes to deposit them in water.
0:26:52 > 0:26:56The midwife toad is not the only species in which the male
0:26:56 > 0:26:57takes care of the young.
0:27:06 > 0:27:09The African bullfrog is quite a character.
0:27:09 > 0:27:14It's the biggest frog in Africa and it's very aggressive.
0:27:14 > 0:27:17It's got a very powerful bite, for one thing.
0:27:17 > 0:27:20But in spite of that, it's a devoted father.
0:27:26 > 0:27:32Bullfrogs spawn in little pools around the margins of a larger pond.
0:27:32 > 0:27:36And after mating is over, one male stays to watch over them all.
0:27:37 > 0:27:41But the water is evaporating and the tadpoles are now crowded
0:27:41 > 0:27:47together in a single pool, and that too is now drying up.
0:27:50 > 0:27:54The tadpoles will be dead within an hour,
0:27:54 > 0:27:57unless the male can do something to save them.
0:28:00 > 0:28:03And he starts doing just that.
0:28:03 > 0:28:06He begins to dig a channel to connect the tadpoles'
0:28:06 > 0:28:09little pool to the main pond.
0:28:11 > 0:28:12He must be quick.
0:28:28 > 0:28:32It's a major task, but he is determined.
0:28:41 > 0:28:43Down they swim.
0:29:08 > 0:29:10The tadpoles are saved!
0:29:31 > 0:29:36But perhaps the prize for fatherly care should go to a rare
0:29:36 > 0:29:39little frog that lives in the forests of Chile.
0:29:42 > 0:29:45This is Darwin's frog.
0:29:47 > 0:29:50After the female has laid her eggs on the moist ground
0:29:50 > 0:29:54and the male has fertilised them, he, apparently, eats them.
0:29:54 > 0:29:59But they go, not into his stomach but into his throat pouch.
0:30:01 > 0:30:04And there they develop, and wriggle.
0:30:08 > 0:30:10And when they're ready...
0:30:12 > 0:30:14..one jumps out.
0:30:19 > 0:30:21And another.
0:30:31 > 0:30:34Giving birth from your mouth is pretty odd,
0:30:34 > 0:30:38but what about producing babies from your back?
0:30:39 > 0:30:44The Surinam toad is an aquatic species from South America.
0:30:44 > 0:30:48The female produces around 100 eggs at a time.
0:30:51 > 0:30:55The male collects them and steers them on to the female's back.
0:31:01 > 0:31:03And there they stick.
0:31:15 > 0:31:19The skin on the female's back then begins to swell around them.
0:31:21 > 0:31:26A membrane grows over them and eventually completely encloses them.
0:31:29 > 0:31:33After a couple of days, they've virtually disappeared.
0:31:37 > 0:31:41A few weeks later, the young hatch as tadpoles.
0:31:51 > 0:31:56In some Surinam toads, the young remain within their mothers'
0:31:56 > 0:32:02back so long that they emerge not as tadpoles but little froglets.
0:32:30 > 0:32:35It's certainly an odd way of producing young, but it works.
0:32:51 > 0:32:55All adult amphibians are hunters.
0:32:55 > 0:32:59To help them catch their prey, they have a secret weapon -
0:32:59 > 0:33:02a special kind of tongue.
0:33:16 > 0:33:20The extendable tongue is an amphibian invention.
0:33:20 > 0:33:22No fish ever had one.
0:33:25 > 0:33:29And the tongue is not attached to the back of the mouth like ours,
0:33:29 > 0:33:30but to the front.
0:33:42 > 0:33:45Frogs eat worms and insects.
0:33:45 > 0:33:48And the larger the frog, the bigger prey it will tackle.
0:33:50 > 0:33:53And some species, like these cane toads,
0:33:53 > 0:33:58will eat almost anything, including one another.
0:34:11 > 0:34:15It's recently been discovered that way back in prehistory,
0:34:15 > 0:34:20there were some frogs big enough to catch mammals.
0:34:24 > 0:34:27A few years ago, fragments were found in Madagascar
0:34:27 > 0:34:34of a really giant frog dating back from about 65 million years ago.
0:34:34 > 0:34:37This is part of its skull.
0:34:37 > 0:34:40Here is the orbit of the eye.
0:34:40 > 0:34:43And this is where its spine...
0:34:43 > 0:34:46The spine would have run down here.
0:34:46 > 0:34:49And this is the right cheek.
0:34:49 > 0:34:55So the animal's head, when complete, would have been about that wide.
0:34:55 > 0:34:57So this really was a monster.
0:34:58 > 0:35:00And here is a computer reconstruction
0:35:00 > 0:35:02of the complete skeleton.
0:35:05 > 0:35:07The scientists who worked on it
0:35:07 > 0:35:12referred to it among themselves as a devil frog.
0:35:12 > 0:35:14And when the time came to give it a scientific name,
0:35:14 > 0:35:17they called it Beelzebufo.
0:35:17 > 0:35:2065 million years ago was just towards
0:35:20 > 0:35:22the end of the reign of the dinosaurs.
0:35:22 > 0:35:29So maybe this giant frog actually ate hatchling dinosaurs,
0:35:29 > 0:35:33as been shown in this artist's imaginative reconstruction.
0:35:36 > 0:35:40Some frogs today also have teeth, but they don't chew with them.
0:35:40 > 0:35:43The teeth are used either for defence
0:35:43 > 0:35:46or as a way of gripping prey.
0:35:50 > 0:35:54This large monkey frog is in the process of swallowing a cricket.
0:35:57 > 0:36:03And, strangely perhaps, it uses its eyes to help it do so.
0:36:09 > 0:36:10We're waiting for it to burp.
0:36:10 > 0:36:12LAUGHTER
0:36:25 > 0:36:30As a frog swallows, it pulls its bulging eyes downwards
0:36:30 > 0:36:34so that they help to push the food down its throat.
0:36:46 > 0:36:49Most frogs have very big eyes.
0:36:49 > 0:36:52They have to be big because frogs, since they don't have necks,
0:36:52 > 0:36:56can't turn their heads to look to one side.
0:36:59 > 0:37:02Instead, their two eyes, between them,
0:37:02 > 0:37:06give a frog an almost 360-degree vision.
0:37:11 > 0:37:15They also have a kind of see-through third eye-lid,
0:37:15 > 0:37:19which protects their eyes underwater without blocking their sight.
0:37:19 > 0:37:23The red-eyed tree frog's third eyelid has a distinctive
0:37:23 > 0:37:27green pattern, which, when out of water, helps with camouflage.
0:37:29 > 0:37:35Frogs have managed to adapt to a surprising range of environments.
0:37:41 > 0:37:46The little red-eyed tree frog lives up in the forest canopy,
0:37:46 > 0:37:47catching insects.
0:37:47 > 0:37:52And to do that, of course, it has to be an expert climber.
0:37:53 > 0:37:58So, not surprisingly, they have very special hands and feet.
0:38:16 > 0:38:20Its toe-pads are highly complex structures.
0:38:22 > 0:38:27Each has a large surface area, which helps it get a good grip.
0:38:30 > 0:38:33Between the six-sided skin cells,
0:38:33 > 0:38:37there are small channels which fill with a sticky mucus.
0:38:37 > 0:38:42This acts as a continuously renewed glue, but one that allows
0:38:42 > 0:38:46the frog to peel off its foot and re-attach it as it climbs.
0:38:46 > 0:38:50Some frogs have evolved a way of using their hands
0:38:50 > 0:38:53and feet in a quite remarkable way.
0:39:01 > 0:39:03In the remote rain forests of South America,
0:39:03 > 0:39:06there's a small amphibian known as a waterfall toad.
0:39:16 > 0:39:21It, like so many frogs, is a favourite meal of snakes.
0:39:35 > 0:39:38Many frogs avoid their enemies by hopping,
0:39:38 > 0:39:42but this little toad can't hop more than an inch or so. Instead,
0:39:42 > 0:39:46when a swift retreat is needed, it has other techniques.
0:39:50 > 0:39:53Free-falling, which is easy,
0:39:53 > 0:39:56and stopping, which is more difficult.
0:40:18 > 0:40:23Above the rain forests, there are mountains so drenched with rain
0:40:23 > 0:40:28that the rocks are bare, except for a coat of slimy black algae.
0:40:30 > 0:40:33And here you can find the pebble toad.
0:40:36 > 0:40:40But there are predators here, too.
0:40:52 > 0:40:58This is a toad-eating tarantula, an expert in ambushing its prey.
0:41:01 > 0:41:04The pebble toad can't hop very far either,
0:41:04 > 0:41:06but it has a different defence.
0:41:17 > 0:41:20It clenches its muscles so tightly
0:41:20 > 0:41:22that it becomes as bouncy as a rubber ball.
0:42:01 > 0:42:05Danger averted and no damage done.
0:42:08 > 0:42:13But hunters are everywhere - not only on the ground, but in the sky.
0:42:22 > 0:42:25Camouflage is an excellent defence.
0:42:25 > 0:42:28Blink and you could easily miss this Darwin's frog.
0:42:45 > 0:42:48Most frogs are beautifully camouflaged
0:42:48 > 0:42:52so that it's very difficult sometimes to spot them.
0:42:52 > 0:42:53But this one,
0:42:53 > 0:42:57which is the tiger-striped monkey frog from South America...
0:42:58 > 0:43:03..has tiger stripes - orange and black -
0:43:03 > 0:43:05on the inside of its legs.
0:43:05 > 0:43:09So when it's sitting like that, it looks green.
0:43:09 > 0:43:11But if they're threatened by a predator,
0:43:11 > 0:43:15they can suddenly open their legs and reveal
0:43:15 > 0:43:18that orange and black underbelly,
0:43:18 > 0:43:21which, people think, puts off a predator.
0:43:24 > 0:43:28The great majority of frogs rely on camouflage.
0:43:30 > 0:43:36But a few take the other option - conspicuousness.
0:43:36 > 0:43:39Bright colouring can be a warning that an animal is
0:43:39 > 0:43:43unpleasant to eat. But some are more than merely unpalatable.
0:43:44 > 0:43:49This is the golden poison-dart frog from Colombia.
0:43:49 > 0:43:54And its skin contains enough poison to kill ten human beings,
0:43:54 > 0:43:57which is why I'm taking no chances and wearing gloves.
0:43:57 > 0:44:02Traditionally, the people in Colombia used that poison
0:44:02 > 0:44:04to tip their blow-pipe darts.
0:44:04 > 0:44:06But of course, for the frog,
0:44:06 > 0:44:09the poison serves as a defence against predators.
0:44:09 > 0:44:14And many poison-dart frogs are very brightly coloured, just to
0:44:14 > 0:44:17warn predators of what would await them if they did take a mouthful.
0:44:22 > 0:44:26The toxicity of frog skin has traditionally been exploited
0:44:26 > 0:44:31by local people, but modern medicine has also found ways of using it.
0:44:37 > 0:44:39One chemical compound from the skin
0:44:39 > 0:44:42of the tri-coloured poison-dart frog...
0:44:43 > 0:44:47..is being used in the development of a groundbreaking pain-killer...
0:44:49 > 0:44:53..several hundred times more powerful than morphine.
0:44:58 > 0:45:00A frog doesn't drink,
0:45:00 > 0:45:04it absorbs all the water it needs through its skin.
0:45:04 > 0:45:07It also gets most of its oxygen in the same way.
0:45:11 > 0:45:15But a permeable skin that allows water to flow in also allows
0:45:15 > 0:45:19it to flow out, and for some that can be a problem.
0:45:20 > 0:45:22If there's a dry spell,
0:45:22 > 0:45:26this giant monkey frog from South America
0:45:26 > 0:45:29produces a kind of ointment from glands
0:45:29 > 0:45:33in its skin, which it uses as sun cream.
0:45:37 > 0:45:40At the beginning of the dry season,
0:45:40 > 0:45:44it takes steps to make sure that it doesn't get sun-burnt or dry out.
0:45:46 > 0:45:51And with their supple joints, frogs can manage to reach all those
0:45:51 > 0:45:55odd places that the rest of us find a little tricky.
0:46:05 > 0:46:07The dry season can last for weeks.
0:46:07 > 0:46:10So it's best to be really thorough.
0:46:26 > 0:46:29Some frogs however, never leave water at all.
0:46:32 > 0:46:35This is the highest lake in the world - Lake Titicaca
0:46:35 > 0:46:37in the Peruvian Andes.
0:46:42 > 0:46:45And the frog that lives here has very different problems.
0:46:47 > 0:46:50At 4,000 metres above sea level,
0:46:50 > 0:46:52there's very little oxygen in the atmosphere,
0:46:52 > 0:46:54and therefore in the water.
0:46:55 > 0:46:58So the frog has developed bizarre-looking flaps
0:46:58 > 0:47:02and folds that increase the skin's surface area,
0:47:02 > 0:47:05and therefore its ability to absorb oxygen.
0:47:11 > 0:47:16The frog also increases the flow of water across its skin by doing
0:47:16 > 0:47:18what looks like press-ups.
0:47:35 > 0:47:39Because their skin is so sensitive to their surroundings,
0:47:39 > 0:47:43frogs are important biological indicators.
0:47:43 > 0:47:45If there are environmental problems,
0:47:45 > 0:47:48they're among the first creatures to be affected.
0:47:48 > 0:47:51But that permeability has also led,
0:47:51 > 0:47:54in recent years, to alarming declines.
0:47:56 > 0:48:00This, crouched on a leaf,
0:48:00 > 0:48:03is one of the rarest frogs in the world.
0:48:03 > 0:48:06It's called the lemur leaf frog
0:48:06 > 0:48:08and it lives in Costa Rica.
0:48:08 > 0:48:12Once it was widespread there, but today,
0:48:12 > 0:48:14it's been reduced to a very small area.
0:48:20 > 0:48:26It's nocturnal and lives in the humid rainforest of the lowlands.
0:48:26 > 0:48:31Unusually for a leaf frog, it has no webbing between its toes
0:48:31 > 0:48:34and its stick-like legs give it a very distinctive walk.
0:48:46 > 0:48:48What a lovely little creature.
0:48:50 > 0:48:54Here in the Manchester Museum, they're studying the species
0:48:54 > 0:48:56and doing their best to conserve it,
0:48:56 > 0:48:58both by breeding it in captivity
0:48:58 > 0:49:02and partly by going out to Costa Rica and studying it in the wild.
0:49:02 > 0:49:06The cause for its loss in numbers is three-fold -
0:49:06 > 0:49:09loss of habitat, pesticides
0:49:09 > 0:49:12and a particularly lethal kind of fungus called a chytrid.
0:49:19 > 0:49:22The fungus causes the cells in a frog's skin
0:49:22 > 0:49:24to suddenly multiply,
0:49:24 > 0:49:27so that the outer layers thicken.
0:49:29 > 0:49:33That blocks the flow of essential salts through the skin.
0:49:35 > 0:49:37The muscles then can't function properly...
0:49:40 > 0:49:44..and eventually the heart simply stops beating.
0:49:56 > 0:50:00Scientists think that chytrid fungus started to spread
0:50:00 > 0:50:04back in the 1940s, when African clawed frogs,
0:50:04 > 0:50:07which were probably carrying the fungus,
0:50:07 > 0:50:08were shipped all over the world
0:50:08 > 0:50:13for medical research, including pregnancy testing.
0:50:13 > 0:50:17Today, chytrid fungus is spreading uncontrollably,
0:50:17 > 0:50:20causing the extinction of some frog species
0:50:20 > 0:50:24and the severe decline of many others.
0:50:24 > 0:50:27It's the worst infectious disease ever recorded
0:50:27 > 0:50:30in terms of the number of species affected.
0:50:32 > 0:50:36Almost a third of all amphibians are now threatened with extinction,
0:50:36 > 0:50:39including the lemur leaf frog.
0:50:41 > 0:50:45The future of this little frog is still hanging in the balance,
0:50:45 > 0:50:48but hopefully the work that's being done here in Manchester
0:50:48 > 0:50:51will prevent it from becoming extinct.
0:50:51 > 0:50:54But other frogs have not been so lucky.
0:50:57 > 0:51:01Over the years, I've filmed a number of different species,
0:51:01 > 0:51:04some of which are now extinct in the wild.
0:51:09 > 0:51:13The waving golden frogs we filmed in Panama
0:51:13 > 0:51:16belonged to one of the last remaining populations.
0:51:16 > 0:51:20The chytrid fungus was already spreading up from South America.
0:51:20 > 0:51:25So when we had finished, scientists collected all they could find
0:51:25 > 0:51:28and took them to specially sterilised breeding centres
0:51:28 > 0:51:32to keep them in safety until such time, if ever,
0:51:32 > 0:51:34the fungus disappears
0:51:34 > 0:51:38and they can be reintroduced to their original home.
0:51:54 > 0:51:59But despite the decline, the fact that frogs are such adaptable
0:51:59 > 0:52:02creatures does offer some hope.
0:52:04 > 0:52:08Some species, after all, manage to survive in places that might
0:52:08 > 0:52:13seem to spell certain death for creatures with moist skins.
0:52:14 > 0:52:18This is part of the Australian desert where several years
0:52:18 > 0:52:19can pass without rain.
0:52:27 > 0:52:31It's a great relief when at last the drought breaks.
0:52:35 > 0:52:39And then, amazingly, little toads emerge from the sand.
0:52:49 > 0:52:52Numbers of them appear almost simultaneously.
0:52:52 > 0:52:55They have specially large legs to help them dig,
0:52:55 > 0:52:58which gives them their name - spade-foots.
0:53:22 > 0:53:26Now they must mate, if possible, before the sun rises.
0:53:37 > 0:53:42The desert dries very quickly, even after the heaviest of storms.
0:53:45 > 0:53:49Temperatures rise to 50 degrees Centigrade.
0:53:49 > 0:53:53Now any water on the surface will evaporate instantly.
0:53:53 > 0:53:58But the toads are already retreating and will soon be back underground.
0:54:00 > 0:54:03It really is a miracle that they're here at all.
0:54:10 > 0:54:14The spade-foot toad is not the only frog species to adapt
0:54:14 > 0:54:17to extreme environmental conditions.
0:54:20 > 0:54:26Of all the frogs in the world, this perhaps is the most extraordinary.
0:54:26 > 0:54:29It's called the wood frog and it lives in America,
0:54:29 > 0:54:32north of the Arctic Circle.
0:54:32 > 0:54:35And it survives some of the coldest
0:54:35 > 0:54:37temperatures on Earth,
0:54:37 > 0:54:41and it does so by becoming frozen solid.
0:55:00 > 0:55:03As the winter frost starts to bite,
0:55:03 > 0:55:06ice begins to form on the frog's skin.
0:55:20 > 0:55:22The liver goes into overdrive,
0:55:22 > 0:55:27producing glucose which is pumped around the body by the heart.
0:55:34 > 0:55:40This glucose acts like an anti-freeze within the cells,
0:55:40 > 0:55:42preventing them from freezing.
0:55:44 > 0:55:47Instead, ice forms around them.
0:55:47 > 0:55:52The blood, however, is frozen and all the organs are encased in ice.
0:55:54 > 0:55:56And the heart stops.
0:56:09 > 0:56:14But then, months later, spring at last returns.
0:56:20 > 0:56:24And the ice around the wood frog begins to melt.
0:57:11 > 0:57:16The wood frog's ability to survive is truly extraordinary,
0:57:16 > 0:57:20and that does give us the hope that maybe, in spite of the threats
0:57:20 > 0:57:21that face them today,
0:57:21 > 0:57:25frogs as a whole will continue to live on this planet.
0:57:25 > 0:57:28It would be truly sad if we lost them.
0:57:43 > 0:57:44That's it.