0:00:44 > 0:00:49100 million years ago, forests like these were just developing,
0:00:49 > 0:00:51and were dominated by dinosaurs.
0:00:55 > 0:00:58But as the giant reptiles slept,
0:00:58 > 0:01:01tiny creatures were stirring.
0:01:01 > 0:01:04They were the early mammals.
0:01:04 > 0:01:10Despite this humble beginning, their descendants would ultimately take over the whole world.
0:01:10 > 0:01:16Yet the rise of this great dynasty was founded on the most surprising diet.
0:01:22 > 0:01:27Creatures very like those first mammals are still around today - shrews.
0:01:27 > 0:01:30They hunted insects at night,
0:01:30 > 0:01:33when most dinosaurs were sleeping.
0:01:38 > 0:01:42They were able to generate heat in their tiny bodies
0:01:42 > 0:01:47so that they could stay active in the cold night air.
0:01:47 > 0:01:53But doing this burns a lot of food, so they had to eat almost continuously - as shrews still do.
0:01:54 > 0:01:58There's never enough food for a shrew.
0:01:58 > 0:02:03Rivals fight over hunting rights with extraordinary ferocity.
0:02:03 > 0:02:06HISSING
0:02:38 > 0:02:46This little insect-eater has now staked his claim to the food in this part of the woodland.
0:02:47 > 0:02:54When he meets a female, he is almost as aggressive towards her as he is towards a rival male.
0:03:04 > 0:03:11After testing one another's strength, the female accepts the male as a contestant and as a mate.
0:03:16 > 0:03:19Two weeks later, the young are born.
0:03:19 > 0:03:25Their mother has nourished them inside her womb, so they arrive comparatively well-developed.
0:03:28 > 0:03:33Caring for the young is a crucial part of a mammals' winning design -
0:03:33 > 0:03:35something few reptiles do.
0:03:35 > 0:03:42A mother shrew will even quench her babies' thirst with her own saliva if necessary.
0:03:45 > 0:03:48Most important of all,
0:03:48 > 0:03:53she provides them with that uniquely mammalian food - milk.
0:03:53 > 0:03:59This milk is so rich that it takes just two weeks for the young to approach their mother in size.
0:04:01 > 0:04:07By this time, they are quite a handful and need to be weaned from the nipple, despite their protests.
0:04:11 > 0:04:16Their mum doesn't abandon them. She leads them into the world outside.
0:04:24 > 0:04:30And the young have their own particular way of ensuring that they don't get lost.
0:05:25 > 0:05:30The first mammals lived alongside the dinosaurs for a very long time,
0:05:30 > 0:05:37but then, about 65 million years ago, when the dinosaurs so suddenly and dramatically disappeared,
0:05:37 > 0:05:41they had their chance to colonise new environments.
0:05:41 > 0:05:46At first, they remained much the same - small, scurrying creatures.
0:05:46 > 0:05:53But that is a versatile body pattern, and one of them, without much change, took to the water.
0:05:53 > 0:06:00It hunts as frenetically as its cousins do on land, but it has a different way of catching insects.
0:06:10 > 0:06:15The water shrew's fur is oily and sheds water with a slight flick.
0:06:18 > 0:06:24Its splendid whiskers are long to help it feel for prey underwater.
0:06:24 > 0:06:28Its ankles are hairy, so its feet serve as excellent paddles.
0:06:34 > 0:06:40It shines like silver, glistening from the bubbles trapped within its fur as it searches for prey.
0:06:46 > 0:06:50Clinging to a root, a dragonfly larva -
0:06:50 > 0:06:54but the shrew's whiskers don't touch it, and it's missed.
0:07:00 > 0:07:02But not this time!
0:07:14 > 0:07:18In Africa's Namib Desert, another insect-hunter swims after prey -
0:07:18 > 0:07:22but without a drop of water in sight.
0:07:27 > 0:07:30It's a sand swimmer -
0:07:30 > 0:07:32a golden mole.
0:07:34 > 0:07:39Sand, unlike water, scratches and it isn't transparent either.
0:07:39 > 0:07:47The mole's eyes are covered with skin, its head a wedge with which it forces its way through sand.
0:07:49 > 0:07:51As it digs,
0:07:51 > 0:07:57sand collapses behind it, making it impossible for a tunnel to form,
0:07:57 > 0:08:02so it doesn't dig through the sand - it really does swim.
0:08:08 > 0:08:16Sound travels well in sand. Unlike shrews, which are adapted to hear high-pitched sound,
0:08:16 > 0:08:19this mole detects very low ones -
0:08:19 > 0:08:23like the faint vibrations made by foraging termites.
0:08:29 > 0:08:34Propelled by its flippers and guided by sound, the mole homes in
0:08:34 > 0:08:37on its prey.
0:09:07 > 0:09:13In North America, another mole has paws that look like flippers.
0:09:17 > 0:09:19These help it to swim under ice
0:09:19 > 0:09:24to collect insects - but this is not their primary purpose.
0:09:25 > 0:09:30This creature is a digger - a star-nosed mole.
0:09:32 > 0:09:36Its paws are spades for pushing aside soil,
0:09:36 > 0:09:41while it tries to locate its prey with its astonishing nose.
0:09:43 > 0:09:47This has 22 fleshy arms.
0:09:47 > 0:09:50Each is so packed with nerve endings,
0:09:50 > 0:09:55that the mole could touch a pinhead with its nose in 600 places at once,
0:09:55 > 0:09:59allowing it to locate the tiniest of prey.
0:10:00 > 0:10:02Living in soil rather than sand,
0:10:02 > 0:10:05this mole can dig proper tunnels.
0:10:05 > 0:10:09It constructs a labyrinth of passages
0:10:09 > 0:10:13and patrols them to collect any prey that drops into them.
0:10:27 > 0:10:32The star-nose, underground, is largely beyond the reach of predators.
0:10:36 > 0:10:39Other insect-hunters, however,
0:10:39 > 0:10:44run along trails above ground and they are not so lucky.
0:10:44 > 0:10:50And one of these trail runners lives here in the scrublands of East Africa.
0:10:55 > 0:10:59This tiny pathway through the withered grass
0:10:59 > 0:11:04shows the insect-hunting rights for this area have been taken.
0:11:04 > 0:11:10To advertise the fact, the owner has left a little pile of its dung.
0:11:10 > 0:11:12But what could have made it?
0:11:12 > 0:11:17Well, to find out, I can use this tiny surveillance camera.
0:11:17 > 0:11:19If I put that there
0:11:19 > 0:11:24and then, just in front of it, put some twigs across the path...
0:11:26 > 0:11:30The creator of these runways is fastidious and with any luck,
0:11:30 > 0:11:33it will stop to clear the twigs
0:11:33 > 0:11:37and then give us a chance to have a good look at it.
0:11:38 > 0:11:42This is the picture from the camera I've just placed,
0:11:42 > 0:11:47and this is from another camera farther up the same trail.
0:11:47 > 0:11:50And now all I have to do is to wait.
0:12:01 > 0:12:04It's an elephant shrew!
0:12:07 > 0:12:10He's not going to like that!
0:12:10 > 0:12:15There you go. He's clearing his trail.
0:12:21 > 0:12:24Oh!
0:12:24 > 0:12:26Oh, dear!
0:12:26 > 0:12:29I'm afraid I have put in too much!
0:12:30 > 0:12:36The elephant shrew or sengi keeps its trails immaculate for a very good reason.
0:12:36 > 0:12:39It sprints to evade its enemies.
0:12:40 > 0:12:44Even the smallest twig could cause a stumble that could be disastrous.
0:12:55 > 0:13:00The goshawk has such keen eyesight that spotting a sengi is no problem.
0:13:03 > 0:13:06Catching one is another matter.
0:13:08 > 0:13:12The sengi holds a map of its trails in its mind
0:13:12 > 0:13:16so that in emergencies it can cut corners to dive for cover.
0:13:24 > 0:13:29Even a brush with death doesn't put a sengi off its food.
0:13:29 > 0:13:34Like all small insect-hunters, it needs to constantly fuel its internal fires.
0:13:37 > 0:13:42That is especially important when there are young to feed.
0:13:45 > 0:13:49Incredibly, this sengi is only a few hours old.
0:13:52 > 0:13:56Few mammals are born as well-developed as a baby sengi.
0:13:56 > 0:13:59This gives them a survival edge.
0:13:59 > 0:14:05Daytime in the African bush is no place for the helpless. Sengis are born to run.
0:14:05 > 0:14:08Its appetite for milk is unquenchable -
0:14:08 > 0:14:12growing at this speed gives it constant hunger.
0:14:13 > 0:14:20Its mother has nipples near her shoulders, which makes them easier to reach and helps a quick get-away.
0:14:27 > 0:14:33The baby will take solid food from its mother on its very first day if it gets a chance.
0:14:41 > 0:14:46SCREECHING
0:14:50 > 0:14:57With continued help from its mother, the youngster will be almost fully grown within a week
0:14:57 > 0:15:01and be able to run as fast as her along their racetracks.
0:15:21 > 0:15:27Catching insects one by one takes a lot of time and a lot of energy,
0:15:27 > 0:15:33and very few creatures that feed that way can get enough to build and sustain big bodies.
0:15:33 > 0:15:38But some insect-eaters, about 40 million years ago,
0:15:38 > 0:15:42solved that problem by broadening their diet.
0:15:42 > 0:15:47And one of their descendants lives right here in my garden in London.
0:15:47 > 0:15:52And I can tempt it out with a wide variety of food, including, for example, minced meat.
0:16:09 > 0:16:15The hedgehog is a creature of the night, but it's too big to hide in the leaves.
0:16:15 > 0:16:20That makes it vulnerable to attack from animals like foxes.
0:16:20 > 0:16:24To make up for this, its hairs have become a cloak of prickles.
0:16:27 > 0:16:33And if it thinks it is in real danger, it's got a special trick.
0:16:39 > 0:16:43The hedgehog will stay an impregnable spiny ball like this
0:16:43 > 0:16:47until it decides that danger is passed.
0:16:58 > 0:17:02But one thing is guaranteed to make a male hedgehog drop his guard -
0:17:02 > 0:17:05an amorous liaison.
0:17:06 > 0:17:10If you are outside on a spring evening,
0:17:10 > 0:17:14you may be lucky enough to witness an extraordinary sight.
0:17:30 > 0:17:34You might think that having a coat of spines on your back
0:17:34 > 0:17:40would be something of a handicap when it comes to the intimacies of courtship.
0:17:40 > 0:17:45Classical naturalists thought that hedgehogs actually mated
0:17:45 > 0:17:48belly to belly.
0:17:48 > 0:17:53The male noses the female's spines, which seems to excite her.
0:17:55 > 0:17:57Although, as far as he is concerned,
0:17:57 > 0:18:00it does look rather painful.
0:18:06 > 0:18:11Whether the female flattens her prickles to help the male is unclear,
0:18:11 > 0:18:17but it does seem that the old joke that asks, "How do hedgehogs mate?" is true.
0:18:17 > 0:18:21The answer is, of course, with great care.
0:18:37 > 0:18:41The early American insect-eaters also needed to protect themselves,
0:18:41 > 0:18:46but they did so, not with spines, but with armour plating.
0:18:49 > 0:18:54Armadillos, like hedgehogs, grew large by broadening their diet.
0:18:54 > 0:18:57Their tastes change with the seasons.
0:18:59 > 0:19:05Fruit is easy to collect, but the nine-banded armadillo is not fussy
0:19:05 > 0:19:09and will pick up anything that looks edible.
0:19:23 > 0:19:26It still eats insects,
0:19:26 > 0:19:29but ants present it with a problem.
0:19:29 > 0:19:35Its armour protects it from large predators, but it isn't good defence against small prey.
0:19:44 > 0:19:50One extraordinary African insect-hunter has no such trouble.
0:19:51 > 0:19:58It's a pangolin. Its horny scales, like the hedgehog's prickles, are made from modified hair.
0:20:04 > 0:20:07Its big front claws are useless for walking.
0:20:07 > 0:20:10It trundles along on its hind legs,
0:20:10 > 0:20:13balancing its torso with its tail.
0:20:17 > 0:20:22Its front claws are reserved for digging up ants.
0:20:22 > 0:20:25As it does so, it swallows stones.
0:20:25 > 0:20:30They accumulate in its stomach and help to grind up the ants.
0:20:46 > 0:20:49But these small underground ant colonies
0:20:49 > 0:20:52are mere snacks to a pangolin.
0:20:57 > 0:21:01This is a real meal - a full-size ants' nest.
0:21:01 > 0:21:05There are a million or so of them in here.
0:21:05 > 0:21:10The pangolin smashes through the nest wall with formidable power.
0:21:10 > 0:21:13Only an adult has the strength to do this.
0:21:13 > 0:21:20Young ones stay with their mother, feeding in her wake until they are big enough to dig for themselves.
0:21:31 > 0:21:35The angry ants swarm all over their attacker,
0:21:35 > 0:21:40but the pangolin's armour is a very effective defence.
0:21:40 > 0:21:43Its eyes are protected by thick lids,
0:21:43 > 0:21:49and its nostrils and ears have special valves to keep the biting insects out.
0:21:53 > 0:21:58For its size, the pangolin has the longest tongue of any mammal -
0:21:58 > 0:22:01and the stickiest saliva.
0:22:11 > 0:22:15But mammals didn't always have ant colonies to feed on.
0:22:15 > 0:22:22The rise of social insects, 60 million years after mammals arrived, was a landmark in evolution.
0:22:23 > 0:22:26It was then that termites and ants
0:22:26 > 0:22:32started to build huge nests, each containing millions of individuals.
0:22:32 > 0:22:37Here was so much food that insect-eaters could grow big.
0:22:42 > 0:22:45There are termites in the Americas
0:22:45 > 0:22:47just as there are in Africa,
0:22:47 > 0:22:51so of course, there are termite-eaters, too.
0:22:51 > 0:22:56And here in Brazil is the biggest of them all - the giant anteater.
0:23:09 > 0:23:11Its eyesight is very poor
0:23:11 > 0:23:16and it relies mostly on its sense of smell, which is very acute.
0:23:18 > 0:23:20But if I keep downwind of it,
0:23:20 > 0:23:23I may not disturb it too much.
0:23:24 > 0:23:29The truth is that ants and termites aren't very nutritious,
0:23:29 > 0:23:34so the giant anteater has to do all it can to conserve energy,
0:23:34 > 0:23:40and one way of doing that is to sleep for 15 out of 24 hours.
0:23:40 > 0:23:45It covers itself, too, with that big bushy tail
0:23:45 > 0:23:48to reduce heat loss to a minimum.
0:23:49 > 0:23:55And it also keeps its body at as low a temperature as any mammal - 32 degrees.
0:23:55 > 0:24:00That means, of course, that its brain does not work very fast.
0:24:00 > 0:24:05It's not an animal with lightning reactions or dazzling intelligence,
0:24:05 > 0:24:11but then you don't really need that if you are an anteater. And now I think I will get out of its way.
0:24:19 > 0:24:24Termite mounds are more numerous here than anywhere,
0:24:24 > 0:24:30but the challenges facing a termite-eater are considerable.
0:24:30 > 0:24:34Anteaters and pangolins have different ancestors
0:24:34 > 0:24:39but the demands of their diet has shaped them in similar ways.
0:24:39 > 0:24:44Both have big claws - the giant's are the largest of any mammal -
0:24:44 > 0:24:51and both have an immensely long tongue that slips through the tube formed by the toothless jaws -
0:24:51 > 0:24:55so that both can virtually drink termites.
0:25:26 > 0:25:30He may lack teeth, but I am going to treat him with caution,
0:25:30 > 0:25:38because, in fact, those huge claws and those powerful front legs can be very dangerous.
0:25:40 > 0:25:43He can rip apart this termite hill,
0:25:43 > 0:25:46and if he wants to defend himself,
0:25:46 > 0:25:51he will use those big bowed legs and their claws and grip you.
0:25:51 > 0:25:59It has even been said that the carcass of a jaguar was found in the embrace of one of these.
0:26:03 > 0:26:07It only collected a few hundred termites on that brief visit.
0:26:07 > 0:26:13As soon as it breaks into a mound, the inhabitants attack it so ferociously that they drive it away.
0:26:13 > 0:26:18But quick sampling like this does have an advantage.
0:26:18 > 0:26:24The termites will soon replace the ones they have lost, so, in effect, the anteater is harvesting
0:26:24 > 0:26:28the termite hills in its territory
0:26:28 > 0:26:30to ensure a continuous supply.
0:26:30 > 0:26:34It may not have a dazzling intelligence,
0:26:34 > 0:26:39but nothing exploits termites more effectively than the giant anteater.
0:26:54 > 0:26:59If you want to explore the origins of this extraordinary animal,
0:26:59 > 0:27:04you would have to go to a very surprising place.
0:27:08 > 0:27:10I'm near Messel in Germany.
0:27:10 > 0:27:17Behind me is a quarry rich in the fossilised remains of animals that died 50 million years ago,
0:27:17 > 0:27:21and that was a pivotal time in the history of the mammals.
0:27:27 > 0:27:34Even though these animals lived a very long time ago, some of them look remarkably familiar.
0:27:34 > 0:27:41This is a tree anteater, very like the tamandua anteater that lives in South America today.
0:27:41 > 0:27:45All the insect-collecting equipment is there -
0:27:45 > 0:27:48huge claws on the front legs,
0:27:48 > 0:27:55no teeth, and jaws fused into a tube, through which a long tongue would have flicked.
0:27:55 > 0:28:00And alongside the anteater, the first known pangolin.
0:28:00 > 0:28:05Once more it has huge claws - no teeth.
0:28:05 > 0:28:09And again it looks identical to its living equivalent,
0:28:09 > 0:28:12the African pangolin of today.
0:28:18 > 0:28:23Why have these animals remained unchanged for 50 million years?
0:28:23 > 0:28:27The rocks of Messel provide an answer to that.
0:28:27 > 0:28:33From them has come a termite - more importantly, the queen of a termite colony.
0:28:33 > 0:28:38It's the same in every important respect as its living relatives,
0:28:38 > 0:28:41and this is the key.
0:28:41 > 0:28:48If termites haven't changed for 50 million years, why change the design of the termite-eater?
0:28:50 > 0:28:57Even back then, the majority of insects were airborne and out of reach of ground-dwelling mammals.
0:28:57 > 0:29:01But one mammal followed the insects into the air,
0:29:01 > 0:29:05and fossils of it have also been found in the Messel deposits.
0:29:08 > 0:29:10It's a bat.
0:29:10 > 0:29:17The ability to catch insects on the wing is an extraordinary achievement. How do the bats do it?
0:29:22 > 0:29:27This is a great place for bats. There are many insects flying around.
0:29:27 > 0:29:32Just now, birds are feeding on them and bats are asleep in their roosts.
0:29:32 > 0:29:34But soon, it will get dark
0:29:34 > 0:29:40and then the birds will go to roost and the bats will come out to claim their share.
0:29:52 > 0:29:58At night, there are even more flying insects than there were during the day
0:29:58 > 0:30:05and by the mill stream is a colony of Daubenton's bats that are already stirring.
0:30:15 > 0:30:18Their faces are so like a shrew's
0:30:18 > 0:30:25that it's easy to imagine shrew-like ancestors in the trees, jumping from branch to branch,
0:30:25 > 0:30:27chasing insects.
0:30:27 > 0:30:32Ever larger flaps of skin between their fingers extended those jumps
0:30:32 > 0:30:36until, eventually, they could fly.
0:30:37 > 0:30:40And how they can fly!
0:30:40 > 0:30:45The change from a scurrying animal like a shrew to a fluttering bat
0:30:45 > 0:30:51is surely the most magical in the whole history of the mammals.
0:31:09 > 0:31:13The bats' mastery of flight is so complete
0:31:13 > 0:31:18that few insects can outmanoeuvre them in the air.
0:31:18 > 0:31:23The bat scoops up the moth with the membrane around its tail
0:31:23 > 0:31:25and passes it forward to the mouth.
0:31:34 > 0:31:38Their ground-living ancestors probably used sound
0:31:38 > 0:31:42to find their way in the night, as shrews still do,
0:31:42 > 0:31:48but bats perfected that technique, using sound frequencies beyond our hearing.
0:31:48 > 0:31:52A bat detector makes those calls audible to us.
0:31:52 > 0:31:59Bats emit high-intensity pulses of sound and then listen to the echoes that bounce back.
0:31:59 > 0:32:03Their brains process these reflections
0:32:03 > 0:32:07to give them a 3-D image of their surroundings
0:32:07 > 0:32:10and their prey.
0:32:15 > 0:32:20Moths, with their laborious flight, are relatively easy to catch.
0:32:26 > 0:32:29But then some evolved a defence -
0:32:29 > 0:32:36a simple ear, so that when they hear the sonar of a bat approaching, they can swerve out of the way.
0:32:36 > 0:32:39So, one bat changed tactics.
0:32:41 > 0:32:45The long-eared doesn't hunt with sonar.
0:32:45 > 0:32:49It uses its enormous ears to listen for prey.
0:32:50 > 0:32:54It can filter the sound of a moth's wing beats
0:32:54 > 0:32:58through the noise of the rushing water.
0:33:05 > 0:33:09Its sonar guides it through the branches,
0:33:09 > 0:33:15but as it nears the moth, it turns that off and enters "stealth mode".
0:33:20 > 0:33:27Now it's guided solely by the noise of the moth's wing beats. But the system isn't perfect.
0:33:27 > 0:33:31The bat can hear the moth through the leaf
0:33:31 > 0:33:34and is approaching it from the wrong side.
0:33:43 > 0:33:47A lucky escape for the moth.
0:33:47 > 0:33:54But now the bat has come round to the other side. If the moth stays still,
0:33:54 > 0:33:58it makes no noise, so the bat can't locate it.
0:34:07 > 0:34:11But, sooner or later, the moth will have to move.
0:34:15 > 0:34:18And that is its undoing.
0:34:23 > 0:34:30But how could a bat catch prey that is silent in a place like this, so cluttered with vegetation
0:34:30 > 0:34:33that echolocation shouldn't work?
0:34:34 > 0:34:38These places are tricky to navigate, but full of food.
0:34:38 > 0:34:44Spiders are more nutritious than moths, but they're silent, venomous,
0:34:44 > 0:34:50and construct webs so strong that a bat could easily become entangled in the sticky silk.
0:34:52 > 0:34:54Here comes Natterer's bat.
0:34:54 > 0:34:59It seems well aware of the almost microscopically thin silken threads
0:34:59 > 0:35:04and, with surgical precision, removes the spider from its web.
0:35:24 > 0:35:29It even reverses away from the web to avoid getting entangled.
0:35:29 > 0:35:34To detect the threads and recognise on which side the spider is sitting
0:35:34 > 0:35:37must be the ultimate refinement of sonar.
0:35:59 > 0:36:02Mexican free-tailed bats.
0:36:02 > 0:36:09They form some of the biggest and the densest assemblages of mammals to be found anywhere on the planet.
0:36:09 > 0:36:12There are 12 million in this cave.
0:36:12 > 0:36:19But where do such a vast number of individuals find food within flying distance of where they roost?
0:36:19 > 0:36:23That puzzle baffled people for a long time.
0:36:23 > 0:36:31But now we're beginning to discover what they feed on and where they find it - and it's very surprising.
0:36:59 > 0:37:07A few years ago, pilots flying above Texas reported seeing bats at high altitude.
0:37:07 > 0:37:12Scientists investigated and made an extraordinary discovery.
0:37:36 > 0:37:41As I climb into the evening sky, the weather conditions seem good.
0:37:43 > 0:37:50But the local weather radar shows a storm nearby, growing with alarming speed.
0:37:50 > 0:37:52However, I needn't worry.
0:37:52 > 0:37:58This is not a storm. It's the bats we just left, leaving their roost.
0:37:58 > 0:38:03They start from a number of points, each the mouth of a different cave.
0:38:03 > 0:38:08The swarms are vast, with up to 20 million bats leaving one entrance.
0:38:08 > 0:38:11Some fly low over Texas,
0:38:11 > 0:38:14but, curiously, most start to climb.
0:38:16 > 0:38:20At 10,000 feet up, bats are so widely dispersed
0:38:20 > 0:38:24that it is very difficult to see them,
0:38:24 > 0:38:27but I've got my bat detector.
0:38:27 > 0:38:34- HIGH-PITCHED CLICKING - And there's one. And, what is more, that is a feeding buzz.
0:38:34 > 0:38:38So, they're eating something. The question is - what?
0:38:46 > 0:38:51They're a kilometre above the ground and most are still climbing.
0:38:51 > 0:38:56But now the radar picks up another front blowing in from New Mexico
0:38:56 > 0:38:59and the bats are flying towards it.
0:38:59 > 0:39:03What could attract them to these great heights?
0:39:03 > 0:39:10Scientists find out what's flying high in the sky at night with a device like this.
0:39:14 > 0:39:17And in it...
0:39:17 > 0:39:19moths.
0:39:19 > 0:39:24Vast numbers of these insects use the prevailing winds at altitude
0:39:24 > 0:39:27to travel from the tropics to feed.
0:39:27 > 0:39:32Bats climb up to three kilometres into the night sky to catch them.
0:39:39 > 0:39:46Bats are so numerous and so voracious that the individuals in this one cave below me
0:39:46 > 0:39:50eat 120 tons of insects every night.
0:40:00 > 0:40:04So, if bats have such ravenous appetites,
0:40:04 > 0:40:09how do they survive in the winter, when there are no flying insects?
0:40:09 > 0:40:12In Texas, they migrate.
0:40:12 > 0:40:16Here, in Canada, they have a truly radical solution.
0:40:37 > 0:40:41Outside, it is 20 degrees below freezing.
0:40:41 > 0:40:44Inside, icicles hang from the ceiling.
0:40:44 > 0:40:48And yet these little brown bats can survive
0:40:48 > 0:40:53throughout the winter without a single meal.
0:40:54 > 0:40:57How do they do it?
0:40:59 > 0:41:03The thermal-imaging camera is showing my face
0:41:03 > 0:41:06as red and orange.
0:41:06 > 0:41:09That's because it's warm. I'm a mammal.
0:41:09 > 0:41:14Putting it more precisely, I am losing energy as heat.
0:41:14 > 0:41:20But these little bats are blue, because they are cold -
0:41:20 > 0:41:24as cold as the rock to which they are clinging.
0:41:24 > 0:41:29As the bats are no longer losing any heat to their surroundings,
0:41:29 > 0:41:32they are using hardly any energy
0:41:32 > 0:41:37and their metabolism has slowed down almost to a stop.
0:41:37 > 0:41:40Although in the deepest hibernation,
0:41:40 > 0:41:44they have to wake up now and then to have a drink.
0:41:44 > 0:41:47As they fire up their body chemistry,
0:41:47 > 0:41:52so their image on the thermal camera glows like a furnace.
0:42:17 > 0:42:21Once awake, a male seeks out the slumbering females.
0:42:21 > 0:42:25He won't get a warm reception to his advances,
0:42:25 > 0:42:29but he won't meet with much resistance either.
0:42:40 > 0:42:43He will mate with several more
0:42:43 > 0:42:48and then, after a drink, he will return to sleep until the spring.
0:42:59 > 0:43:04Flight not only enabled bats to catch insects in the air -
0:43:04 > 0:43:07it also allowed them to extend their range
0:43:07 > 0:43:10far beyond that of any other mammal.
0:43:26 > 0:43:33Bats were the first mammals to find their way to some fragments of land isolated in the South Pacific -
0:43:33 > 0:43:35New Zealand.
0:43:35 > 0:43:40Here, there were no cats, no rats, but lots of insects -
0:43:40 > 0:43:43paradise for any insect-hunter.
0:43:43 > 0:43:49So, the bats flourished and their descendants are still here...somewhere.
0:43:57 > 0:44:00To see them, I must wait for darkness.
0:44:15 > 0:44:19And this is the species I have been waiting for.
0:44:19 > 0:44:22These bats look normal enough,
0:44:22 > 0:44:29but bats are aerial predators and much of the uneaten prey in New Zealand is on the ground.
0:44:30 > 0:44:33They can fly all right,
0:44:33 > 0:44:36but our infrared camera reveals
0:44:36 > 0:44:41that they also have a very un-bat-like way of hunting.
0:44:41 > 0:44:45They land on the ground and forage through the leaf litter,
0:44:45 > 0:44:47just like shrews.
0:44:56 > 0:44:58They are walking on their wrists,
0:44:58 > 0:45:05with the bones of their fingers pointing up and slotted into a groove along the upper arm.
0:45:05 > 0:45:08Now they seem to be hunting as a pack.
0:45:08 > 0:45:13Insects, or other small creatures fleeing from the jaws of one,
0:45:13 > 0:45:16run straight into those of another.
0:45:22 > 0:45:26Worms are a great favourite -
0:45:26 > 0:45:30so much more satisfying than several hundred mosquitoes -
0:45:30 > 0:45:34and they don't want to share them with one another either.
0:45:51 > 0:45:58They finish off with nectar from the Hades plant, that blooms on the ground.
0:45:58 > 0:46:01They are this plant's pollinators.
0:46:01 > 0:46:06Relationships between a plant and its pollinator are slow to evolve,
0:46:06 > 0:46:13so these bats must have been scuttling over the New Zealand forest floor for millions of years.
0:46:16 > 0:46:20Worms and nectar are easy prey, but what about this?
0:46:20 > 0:46:23It's a weta,
0:46:23 > 0:46:27a giant flightless cricket with spiny legs and ferocious jaws.
0:46:27 > 0:46:33How could bats whose ancestors ate mosquitoes tackle this?
0:46:41 > 0:46:46The weta can flick its back legs forward with surprising force.
0:46:46 > 0:46:51Even if you dodge that, you have to contend with its powerful jaws.
0:47:06 > 0:47:09The insect gains the upper hand...
0:47:14 > 0:47:18..but it's soon overwhelmed by numbers
0:47:18 > 0:47:24and the bats fight one another over its remains with equal ferocity.
0:47:32 > 0:47:37Evolution doesn't often go into reverse, but it seems to have here.
0:47:37 > 0:47:41After several million years of aerial combat,
0:47:41 > 0:47:47these bats are reverting to the techniques of their ancestors.
0:47:59 > 0:48:04Mammals have pursued insects to the far corners of the earth.
0:48:04 > 0:48:09They've chased them into the skies and back down to the ground.
0:48:09 > 0:48:16The insect-eaters were there right at the beginning of the rise of mammals, and they are still here.
0:48:16 > 0:48:21They are one of the great success stories in the life of mammals.
0:48:26 > 0:48:30Bats are surely one of the most magical of mammals,
0:48:30 > 0:48:34but they're also one of the most mysterious,
0:48:34 > 0:48:39as they see the world in a way that is utterly different from our way.
0:48:39 > 0:48:46It's SO different that we didn't even know what it was until about 60 years ago.
0:48:46 > 0:48:54The action of Natterer's bats plucking spiders from their webs has never been filmed before.
0:48:54 > 0:48:59The shots show the precision of their flight and their echolocation.
0:48:59 > 0:49:06How did we come to understand the bat's extraordinary use of sound? That's what we'll discover now.
0:49:13 > 0:49:16The story starts in 1941,
0:49:16 > 0:49:23when an American biologist called Don Griffin was working with physicists at Harvard,
0:49:23 > 0:49:26using a revolutionary ultrasound detector.
0:49:26 > 0:49:32When a bat flew at him, he became the first human to detect the sounds it was making.
0:49:32 > 0:49:36They were very loud and very high-pitched.
0:49:36 > 0:49:42This discovery launched a series of experiments to prove that the bats have a sort of airborne radar,
0:49:42 > 0:49:46an invention then being used in aeroplanes.
0:49:46 > 0:49:49Yet bats could detect tiny targets,
0:49:49 > 0:49:53processing their echoes in a brain weighing half a gram.
0:49:53 > 0:49:57When echolocation was discovered, in the 1940s,
0:49:57 > 0:50:01Don Griffin and Robert Galambos
0:50:01 > 0:50:04presented the findings at a meeting.
0:50:04 > 0:50:09There was such disbelief with the suggestion that bats use echolocation
0:50:09 > 0:50:13that one of the scientists came up to Galambos,
0:50:13 > 0:50:18took him by the lapels forcefully, and said, "This cannot be correct."
0:50:18 > 0:50:23But Griffin continued testing the bats' ability to avoid fine wires
0:50:23 > 0:50:26in the flight cages at Harvard.
0:50:26 > 0:50:34By 1960, it was clear that echolocation provided the bats with a detailed sense of their world.
0:50:42 > 0:50:46New technology helped to explore that world.
0:50:46 > 0:50:50Using high-speed tape recorders to slow down calls
0:50:50 > 0:50:55showed different species used sound differently, to suit their habitat.
0:50:58 > 0:51:04The intensity of bat echolocation calls really varies tremendously.
0:51:04 > 0:51:07At one extreme are "whispering bats",
0:51:07 > 0:51:11that we can barely detect on some of our equipment.
0:51:11 > 0:51:18At the other extreme, there are bats that can make calls as loud as 130 decibels.
0:51:18 > 0:51:25To put this into context, the threshold of pain in human hearing is round about 126 decibels,
0:51:25 > 0:51:29so these calls would be painful to us, if we could hear them.
0:51:30 > 0:51:36The calls are loud in order to produce clear echoes for the bat
0:51:36 > 0:51:40and, to cope, the bat goes temporarily deaf on each call,
0:51:40 > 0:51:47by synchronising the nerve impulse of the call with a muscle in the ear, which disconnects the eardrum.
0:51:53 > 0:51:56This may happen 120 times a second,
0:51:56 > 0:52:01one of the highest rates of muscle contraction of any mammal.
0:52:02 > 0:52:09And, of course, it's what the bats hear that creates their view of the world.
0:52:09 > 0:52:13Understanding that was a more complex problem.
0:52:13 > 0:52:17In the '80s, Trachops, the fringe-lipped bat,
0:52:17 > 0:52:21was studied by American scientists Merlin Tuttle and Mike Ryan.
0:52:25 > 0:52:31Using ultrasound, the bats navigate effortlessly through the Panamanian rainforest,
0:52:31 > 0:52:35but their hunting strategy was extraordinary.
0:52:36 > 0:52:41These bats go for a large prey - the mud puddle frog.
0:52:41 > 0:52:46Collecting them in the forest and testing them in a jungle laboratory
0:52:46 > 0:52:53showed that they could distinguish different kinds of frog calls played through a loudspeaker.
0:52:53 > 0:52:59As soon as we turned on the set, the bat just took off from its perch,
0:52:59 > 0:53:06made a beeline to the speaker... It was obvious that this bat thought there was a frog inside that box.
0:53:06 > 0:53:09By playing different tapes,
0:53:09 > 0:53:14they established just what the bats were able to hear in the frog calls.
0:53:14 > 0:53:18Then they tested their findings back in the forest.
0:53:18 > 0:53:22Studying bats in the wild is notoriously difficult,
0:53:22 > 0:53:27but it's a vital step to understanding any animal.
0:53:30 > 0:53:35Whispering bats, like Trachops and the British long-eared bats,
0:53:35 > 0:53:38rely only on hearing to catch prey.
0:53:38 > 0:53:41They can hear the rustling of moth wings
0:53:41 > 0:53:44and pluck them from bushes.
0:53:48 > 0:53:52But most bats intercept insects by patrolling the air,
0:53:52 > 0:54:00listening to the echoes of their own calls and attacking the ones returned by their prey.
0:54:02 > 0:54:09We know that the wavelength of the call is designed to produce the best echo from moth-sized objects,
0:54:09 > 0:54:16and that the bat increases the rate of calls as it homes in on the target, for greater accuracy.
0:54:20 > 0:54:23This is the "feeding buzz".
0:54:37 > 0:54:41It's extraordinary how fast the action happens.
0:54:41 > 0:54:48We use bat detectors to hear the calls and high-speed filming to slow the flight,
0:54:48 > 0:54:51simply to appreciate the behaviour.
0:54:54 > 0:55:00These bats can fly six metres in a second and may catch 25 moths in a night.
0:55:03 > 0:55:10The studies in the wild have also identified a wide range of different call signatures.
0:55:10 > 0:55:14Each is suited to a different habitat.
0:55:14 > 0:55:19The calls of woodland-edge bats are distinct from those of forest bats,
0:55:19 > 0:55:22and from ones that hunt over water.
0:55:27 > 0:55:32By using different frequencies and duration of call,
0:55:32 > 0:55:38different species of bats have adapted to different habitats and hunting techniques.
0:55:38 > 0:55:42Their ecology is based on sound.
0:55:42 > 0:55:48Although research during the last 60 years has revealed extraordinary details
0:55:48 > 0:55:53about the way in which bats find their way around and hunt,
0:55:53 > 0:55:56there's still a great deal to learn.
0:55:57 > 0:56:02How does the bat's brain process the information?
0:56:02 > 0:56:09We know that the strongest echoes will be right in front of the bat, so they have a narrow field of view,
0:56:09 > 0:56:13and by using a wide spectrum of call frequencies,
0:56:13 > 0:56:18the bat's brain may convert the echoes into an equivalent of colour.
0:56:18 > 0:56:25But can their sound perception system be as accurate as our colour vision?
0:56:25 > 0:56:29One of the challenges is trying to work out
0:56:29 > 0:56:33how the nervous systems of these animals cope.
0:56:33 > 0:56:37In terms of time, we know from laboratory studies
0:56:37 > 0:56:42that bats can make discriminations in the order of ten nanoseconds.
0:56:42 > 0:56:46A nanosecond is a billionth of a second.
0:56:46 > 0:56:53In terms of distance, this corresponds to a difference in range in the order of two micrometres.
0:56:53 > 0:56:59Some scientists argue that animals just cannot make these sorts of discriminations,
0:56:59 > 0:57:06given what we know about their nervous systems, so the challenge is trying to work out how bats do it.
0:57:10 > 0:57:15And our sequence of the Natterer's bats may help to solve that mystery.
0:57:15 > 0:57:22To detect a thread of spider's web from its echo is truly extraordinary.
0:57:25 > 0:57:29Next week, in The Life Of Mammals,
0:57:29 > 0:57:32we meet predators that prey on plants.
0:57:32 > 0:57:37They are forced to fight battles with their highly-defended prey,
0:57:37 > 0:57:40with one another,
0:57:40 > 0:57:44and with the meat-eaters that would eat THEM.