0:01:12 > 0:01:14Although all those creatures are different,
0:01:14 > 0:01:19they are in fact closely related to one another. They are all mammals.
0:01:19 > 0:01:22But how have they become so varied?
0:01:22 > 0:01:27And what is the ancestral form, the basic theme, on which they are all variations?
0:01:27 > 0:01:33You can find a close approximation to that theme in the jungles of South-East Asia.
0:01:35 > 0:01:37It's properly called a tupaia,
0:01:37 > 0:01:40and it's certainly a mammal, with a hairy coat and warm blood.
0:01:40 > 0:01:44But what kind? It looks very like a squirrel.
0:01:44 > 0:01:48A close look at its anatomy reveals resemblances to a rabbit,
0:01:48 > 0:01:53but it doesn't gnaw nuts and it doesn't nibble grass, it catches insects.
0:01:55 > 0:01:59Its teeth are small, numerous and spiky, like a shrew's.
0:01:59 > 0:02:01Indeed, its popular name is tree shrew,
0:02:01 > 0:02:04but its large brain and those grasping hands
0:02:04 > 0:02:07have suggested to some that it's related to monkeys.
0:02:07 > 0:02:12It seems in fact to contain hints of many different mammals.
0:02:12 > 0:02:14One thing, though, is clear.
0:02:14 > 0:02:17It's very like the earliest of mammals,
0:02:17 > 0:02:22that were living when the dinosaurs dominated the Earth 100 million years ago.
0:02:22 > 0:02:27The basic pattern on which there's been such a multitude of variations.
0:02:27 > 0:02:31Some of those variations are so extreme that it's difficult to believe
0:02:31 > 0:02:35there's any connection between them and the basic theme,
0:02:35 > 0:02:40were it not for the evidence of fossils and the anatomy of the living animals.
0:02:43 > 0:02:47The tree shrew's continuous activity and swift reactions are typical of a mammal.
0:02:47 > 0:02:51A consequence of its ability to generate heat within its body
0:02:51 > 0:02:56so that its chemistry works fast and provides it with abundant energy.
0:02:56 > 0:03:00This talent probably developed a very long time ago indeed,
0:03:00 > 0:03:02at a time when the dinosaurs dominated the Earth.
0:03:02 > 0:03:06For fossils of a creature remarkably similar to the living tree shrew
0:03:06 > 0:03:11have been found in rocks that are 200 million years old.
0:03:13 > 0:03:17Its numerous spiky teeth suggest that it ate insects,
0:03:17 > 0:03:20and the shape of its limbs that it was a swift runner.
0:03:20 > 0:03:24In fact, its lifestyle was not unlike a tree shrew.
0:03:24 > 0:03:28And creatures like it survived alongside the dinosaurs throughout their reign,
0:03:28 > 0:03:31probably scampering about at night
0:03:31 > 0:03:35when the colder-blooded dinosaurs became torpid in the cold.
0:03:35 > 0:03:40Then, 65 million years ago, the dinosaurs disappeared.
0:03:41 > 0:03:46The forests and swamps of the world were suddenly empty of large creatures.
0:03:46 > 0:03:49Primitive birds flapped through the sky,
0:03:49 > 0:03:53but on the ground there were few creatures other than insects and other invertebrates
0:03:53 > 0:03:58and those small warm-blooded primitive mammals that fed on them.
0:03:58 > 0:04:00And here and there, in odd corners of the world,
0:04:00 > 0:04:03their descendants still survive, little changed.
0:04:03 > 0:04:05The tree shrew of Malaysia is one.
0:04:05 > 0:04:12Here in the streams of the Pyrenees lives another little-known and very engaging one.
0:04:17 > 0:04:20It's called a desman.
0:04:22 > 0:04:27Like most of these primitive mammals, the desman has a stupendous appetite.
0:04:27 > 0:04:30It eats two-thirds of its own body weight every day
0:04:30 > 0:04:33and seems never to stop the hunt for more.
0:04:51 > 0:04:54Its nose does most of the searching.
0:04:54 > 0:04:59It scents the faintest changes in the taste of the water with its nostrils,
0:04:59 > 0:05:02and feels its way around with all those whiskers.
0:05:17 > 0:05:22Its feet are a combination of web and claw, for both swimming and clambering.
0:05:32 > 0:05:37Its eyes are tiny, minute beads hidden in its long fur.
0:05:41 > 0:05:46When at last it does find something good, it doesn't give up easily.
0:06:05 > 0:06:08Its snorkel nose allows it to snatch a breath
0:06:08 > 0:06:11with the minimum of interruption in the struggle.
0:06:57 > 0:07:03Its hard-fought-for worm will now keep it going for another hour or so.
0:07:14 > 0:07:19Another of these primitive survivals lives along the streams of North America.
0:07:21 > 0:07:26It's not only an energetic swimmer, but a burrower as well.
0:07:26 > 0:07:30It's possible the swimming way of life and the body design to go with it
0:07:30 > 0:07:34led to a similar activity not in water, but underground.
0:07:34 > 0:07:37What were paddles have become spades.
0:07:43 > 0:07:46This is the star-nosed mole.
0:07:48 > 0:07:54The odd fleshy flower on its nose is another highly sensitive smelling device.
0:07:54 > 0:07:58It may have yet another way of investigating its surroundings.
0:07:58 > 0:08:01Many of these little insect-eaters, such as shrews,
0:08:01 > 0:08:04make squeaks so high-pitched that we can't hear them,
0:08:04 > 0:08:09and the echo they produce helps the animals to find their way around.
0:08:19 > 0:08:22Moles, like desmans and shrews, have formidable appetites
0:08:22 > 0:08:25and have to eat every few hours.
0:08:25 > 0:08:28Their tunnels are not simply passageways, but traps.
0:08:28 > 0:08:32Worms and insects burrowing through the soil drop into them,
0:08:32 > 0:08:35and the mole collects whatever turns up.
0:08:37 > 0:08:40If its appetite is momentarily sated,
0:08:40 > 0:08:46then it paralyses a surplus worm with sharp bites and stores it away in a special larder
0:08:46 > 0:08:50before setting off again on its never-ending patrols.
0:09:03 > 0:09:06Variations on the theme of the small insect-eater
0:09:06 > 0:09:09began to appear soon after the dinosaurs vanished.
0:09:09 > 0:09:15Creatures developed that specialised in feeding on one kind of insect - ants and termites.
0:09:15 > 0:09:19This is another digger, the aardvark, from Africa.
0:09:25 > 0:09:29And this is its South American equivalent, the giant anteater.
0:09:35 > 0:09:38The essential equipment for a diet of ants and termites, it seems,
0:09:38 > 0:09:42is an elongated snout for poking inside the nests
0:09:42 > 0:09:45and a long sticky tongue for collecting the insects.
0:09:45 > 0:09:50And the giant anteater has the most extreme version of both that exists.
0:09:55 > 0:09:57Termites are easily crushed,
0:09:57 > 0:10:00so the anteater has no need of teeth and has lost them all.
0:10:00 > 0:10:03Termites' nests, however, can be as hard as cement,
0:10:03 > 0:10:08and strong claws and muscular legs are needed to tear them open.
0:10:13 > 0:10:19The anteater is very fussy about its food. In spite of its name it seldom eats ants.
0:10:19 > 0:10:22Termites, like these, are a much more usual meal,
0:10:22 > 0:10:26and even then, it prefers some termites to others.
0:10:37 > 0:10:41There are a dozen or so species of mammal round the world
0:10:41 > 0:10:44that have specialised in living on ants and termites.
0:10:44 > 0:10:47As a lifestyle it doesn't seem to require
0:10:47 > 0:10:51a particularly quick intelligence or vivacious disposition.
0:10:51 > 0:10:55And all these anteaters are relatively slow-moving creatures.
0:10:55 > 0:10:58Because of that and their total lack of teeth,
0:10:58 > 0:11:01they might seem to be easy meat for a hunter.
0:11:01 > 0:11:05But the giant anteater's front legs are so strong that its hug is lethal,
0:11:05 > 0:11:08and few creatures interfere with it.
0:11:13 > 0:11:16The termite-eating specialist of Africa, the pangolin,
0:11:16 > 0:11:20is much smaller and not nearly such a powerful digger.
0:11:20 > 0:11:23It's developed a flexible armour of scales
0:11:23 > 0:11:26and can curl itself up into a ball so that it's virtually impregnable.
0:11:26 > 0:11:29Its muscular tail also acts as a counterbalance
0:11:29 > 0:11:33so that the creature can trundle along with most of its weight on its back legs,
0:11:33 > 0:11:39and its front legs at the ready for digging into termite mounds, like this one.
0:11:51 > 0:11:55It's so confident of its defences that it takes little notice of any other creature around,
0:11:55 > 0:11:57unless they molest it.
0:11:59 > 0:12:05Smallest of all, the pygmy silky-furred anteater of South America.
0:12:05 > 0:12:08It does seem to be defenceless and can't move fast enough
0:12:08 > 0:12:11to escape even the clumsiest hunter.
0:12:11 > 0:12:17But it keeps out of the way up in the branches, living almost entirely on tree ants.
0:12:17 > 0:12:21This one has a baby on its back, and it may be either male or female,
0:12:21 > 0:12:25for both parents take a share in carrying the load.
0:13:06 > 0:13:10There's yet another kind of specialist anteater in South America,
0:13:10 > 0:13:15intermediate between the giant and the pygmy - the tamandua.
0:13:26 > 0:13:28It feeds mostly at night.
0:13:28 > 0:13:32Its thick, bristly fur is supposed to protect the tamandua
0:13:32 > 0:13:37from the bites of infuriated ants, swarming from their shattered nest.
0:13:37 > 0:13:39But when you watch the animal feeding,
0:13:39 > 0:13:44you can't help wondering just how effective that protection really is.
0:13:44 > 0:13:49Ants and termites are among the most numerous insects, particularly in the tropics.
0:13:49 > 0:13:51And the tamandua and its relatives around the world
0:13:51 > 0:13:56have little difficulty in finding more than enough to eat.
0:13:56 > 0:14:02And there are insects not only in water and in the soil and all over plants,
0:14:02 > 0:14:05but in the air, and particularly at night.
0:14:05 > 0:14:08It's difficult to realise just how many there are
0:14:08 > 0:14:11until you put up a mercury vapour lamp in the tropics.
0:14:11 > 0:14:15Here, within a few minutes, you've got all sorts of creatures.
0:14:15 > 0:14:19Small moths, crickets, huge beetles, mantises,
0:14:19 > 0:14:23big moths, insects of all kinds.
0:14:24 > 0:14:29The insects first took to the air about 300 million years ago.
0:14:29 > 0:14:33They had it to themselves for about 100 million years,
0:14:33 > 0:14:35at least until the arrival of the reptiles.
0:14:35 > 0:14:40Whether there were any night-flying, insect-hunting reptiles, we don't know,
0:14:40 > 0:14:44but it seems unlikely because reptiles, being cold-blooded,
0:14:44 > 0:14:46are usually active during the day.
0:14:46 > 0:14:50And then about 150 million years ago, the birds developed.
0:14:50 > 0:14:53But there's no reason to suppose
0:14:53 > 0:14:56there were any more night-flying birds in the past
0:14:56 > 0:14:59than there are today, and that's precious few.
0:14:59 > 0:15:02So this great feast of insects
0:15:02 > 0:15:08awaited any creature that could master the tricky technique of flying at night.
0:15:08 > 0:15:11And one group of the mammals did.
0:15:11 > 0:15:13The bats.
0:15:38 > 0:15:41The majority of them are hunters of flying insects,
0:15:41 > 0:15:44such as moths, mosquitoes or even beetles.
0:15:44 > 0:15:49Caught on the wing and eaten at the roost as the bats hang upside down.
0:16:04 > 0:16:09Bats began to fly a very long time ago.
0:16:09 > 0:16:14These fossil bones of what is undoubtedly a bat are about 50 million years old.
0:16:14 > 0:16:18The bat skeleton is very similar to the tree shrew's.
0:16:18 > 0:16:22Seen here from above, and now side on.
0:16:22 > 0:16:26But how did this flying variation arise?
0:16:26 > 0:16:31It may be that the early insect-eaters sought their food up in the branches of trees,
0:16:31 > 0:16:34as indeed some kinds of tree shrews do today.
0:16:34 > 0:16:39And as they leapt about trying to snatch flying insects from the air,
0:16:39 > 0:16:44some may have developed flaps of skin between their arms and the sides of their body
0:16:44 > 0:16:48so that they could glide, as the living flying squirrels can today.
0:16:48 > 0:16:53They then supported those flaps with their fingers and strengthened the arm muscles
0:16:53 > 0:16:57until, eventually, they were able to flap their newly developed wings
0:16:57 > 0:17:02and fly in search of their insect prey, and so became bats.
0:17:04 > 0:17:08But living on insects has one great disadvantage.
0:17:13 > 0:17:18In many parts of the world insects disappear almost totally during the winter.
0:17:18 > 0:17:21What does an insect-eater do then?
0:17:21 > 0:17:24It hibernates in any sheltered place it can find
0:17:24 > 0:17:28where the temperature might remain a few degrees higher than elsewhere,
0:17:28 > 0:17:32as it is inside this old Canadian mine.
0:17:43 > 0:17:47These tiny lumps, as cold as stone, are living bats.
0:17:47 > 0:17:51They fed voraciously during the summer, building up reserves of fat,
0:17:51 > 0:17:55but now a profound change has taken place in their bodies.
0:17:55 > 0:17:59Their heat has seeped away, and their body processes have slowed down
0:17:59 > 0:18:02to almost, but not quite, a complete halt.
0:18:02 > 0:18:05They must keep their body chemistry ticking over
0:18:05 > 0:18:10just enough to generate sufficient heat to prevent them from freezing solid,
0:18:10 > 0:18:13for that they can't survive.
0:18:14 > 0:18:16Not all of them are successful.
0:18:16 > 0:18:19Sometimes an individual cannot stave off the chill,
0:18:19 > 0:18:23falls and is entombed in the ice.
0:18:30 > 0:18:33You might think they huddle together to keep warm.
0:18:33 > 0:18:37But careful measurements have shown those in groups get just as cold
0:18:37 > 0:18:39as those hanging by themselves.
0:18:39 > 0:18:43It may be that grouping protects them from another hazard,
0:18:43 > 0:18:44the loss of moisture during breathing.
0:18:44 > 0:18:48That does seem to be less for those in clusters.
0:18:49 > 0:18:52Other creatures also take refuge in the mine,
0:18:52 > 0:18:56the very ones which in summer are food for the bats: moths.
0:18:56 > 0:19:03Both hunters and hunted shelter together from that overwhelming killer, cold.
0:19:05 > 0:19:08In other parts of the world, as here in New Mexico,
0:19:08 > 0:19:13bats solve the problem of lack of insect food by migrating.
0:19:13 > 0:19:18From this cave they will fly south some 1,000km for the winter.
0:19:18 > 0:19:20They have to, to find enough food,
0:19:20 > 0:19:23for their populations are measured in millions,
0:19:23 > 0:19:26and tonnes of insects are needed.
0:19:44 > 0:19:48Caves like these contain the densest populations of mammals
0:19:48 > 0:19:51to be found anywhere on Earth.
0:19:53 > 0:19:57How is it that all those bats flying at such a speed
0:19:57 > 0:19:59can find their way around in the dark?
0:19:59 > 0:20:02The answer is echolocation.
0:20:02 > 0:20:06Although I can only hear just the faintest twitter,
0:20:06 > 0:20:11in fact, each bat is emitting a more or less continuous stream
0:20:11 > 0:20:15of high-frequency sound beyond the range of my ears.
0:20:15 > 0:20:19But I can translate those into sounds that I can hear using a machine like this.
0:20:19 > 0:20:23A bat detector. Listen.
0:20:23 > 0:20:28TWITTERING
0:20:39 > 0:20:43The system is based on those high-pitched ultrasounds,
0:20:43 > 0:20:45like those produced today by shrews
0:20:45 > 0:20:49and which the early insect-eaters may have used as well.
0:20:49 > 0:20:51The bats have developed that ability
0:20:51 > 0:20:54into a highly sophisticated technique called sonar.
0:20:54 > 0:20:58Every bat sends out a stream of short squeaks,
0:20:58 > 0:21:02which can be as many as 20 or 30 a second, or even more.
0:21:02 > 0:21:05From the echoes it can gauge its distance from an object,
0:21:05 > 0:21:09whether it's a cave wall or an insect in the air.
0:21:10 > 0:21:15The horseshoe bat produces such ultrasounds from its nostrils,
0:21:15 > 0:21:18and that construction around the nose serves as a megaphone,
0:21:18 > 0:21:21focusing the sound into a beam.
0:21:22 > 0:21:26The easiest way to study these signals is to pick them up with a special microphone
0:21:26 > 0:21:31and relay them to an oscilloscope so that they can be analysed in a visual form.
0:21:35 > 0:21:39The oscilloscope tells us that the bat is producing sounds,
0:21:39 > 0:21:42though they are beyond the range of our hearing.
0:21:45 > 0:21:49But with the right equipment we can translate those ultrasounds
0:21:49 > 0:21:51into sounds that we can hear.
0:21:51 > 0:21:55HIGH-PITCHED PULSE
0:21:59 > 0:22:02With the oscilloscope as well, we can both see and hear
0:22:02 > 0:22:06the variations that the bat can make.
0:22:07 > 0:22:09FASTER HIGH-PITCHED PULSE
0:22:12 > 0:22:14SLOWER PULSE
0:22:14 > 0:22:16FASTER PULSE
0:22:19 > 0:22:22Another way to analyse the bat's signals
0:22:22 > 0:22:25is to slow them down using a special tape recorder.
0:22:25 > 0:22:31These are the horseshoe bat's ultrasounds slowed down 32 times.
0:22:33 > 0:22:35LONG WHISTLING NOTES
0:22:37 > 0:22:40This is a different species also slowed down.
0:22:40 > 0:22:43And it's emitting the ultrasounds through its mouth.
0:22:43 > 0:22:48With these echolocating signals bouncing back off the prey,
0:22:48 > 0:22:53bats can home in very accurately, raising the rate of output as they approach.
0:22:53 > 0:22:56BAT CHIRRUPS
0:22:58 > 0:23:02Both sound and action are slowed down 16 times.
0:23:05 > 0:23:08The bait, a mealworm, is located precisely by sonar,
0:23:08 > 0:23:14and the bat, a pipistrelle, catches it first with its wing membrane,
0:23:14 > 0:23:18then flicks it across to its tail membrane,
0:23:18 > 0:23:23which is then brought up to its head so the mealworm is passed to the mouth.
0:23:23 > 0:23:26The tail membrane is still over the head.
0:23:28 > 0:23:33Now it's pulled back, and the bat continues to eat its prey in flight.
0:23:34 > 0:23:38Since bats evolved to take advantage of the rich insect larder,
0:23:38 > 0:23:42the insects themselves have developed their own countermeasures. Watch.
0:23:48 > 0:23:50The lacewing's escape technique
0:23:50 > 0:23:54is to close its wings and fall out of the path of the bat.
0:24:12 > 0:24:15Lacewings have tiny ears on their wings.
0:24:15 > 0:24:20So in this conflict between predator and prey, the insect has tuned in
0:24:20 > 0:24:25to be able to hear the bat coming, and therefore take avoiding action.
0:24:29 > 0:24:33Some moths, including tiger moths, have an even more elaborate defence.
0:24:33 > 0:24:38Not only can they hear bats coming and then dive or spiral away,
0:24:38 > 0:24:42but, as a last resort, they can emit their own sounds.
0:24:42 > 0:24:47First we will see and hear the sound of the threatening bat,
0:24:47 > 0:24:50and then the reaction of the moth.
0:24:50 > 0:24:54CRACKLING
0:24:54 > 0:24:57The moth has either jammed the bat's signals
0:24:57 > 0:25:00or sent some kind of warning which puts the bat off.
0:25:00 > 0:25:04Anyway, the moth nearly always escapes.
0:25:09 > 0:25:13We may assume the battle of techniques will continue to evolve
0:25:13 > 0:25:16as bats further develop their sonar equipment.
0:25:16 > 0:25:20The apparatus often dominates the faces of bats.
0:25:20 > 0:25:22Huge ears for detecting the echoes,
0:25:22 > 0:25:27and on the nose, leaves, flanges and spears for directing the sound,
0:25:27 > 0:25:33so they look as grotesque as any gargoyle produced by the medieval imagination.
0:25:41 > 0:25:44Some bats tackle insects much bigger than mosquitoes or lacewings.
0:25:44 > 0:25:48This one is quite prepared to alight on the forest floor
0:25:48 > 0:25:50and grapple with a giant cockroach.
0:26:00 > 0:26:04The insect-eating teeth, inherited from the shrew-like ancestor,
0:26:04 > 0:26:09are essential here to break up the tough chitin of the insect's body.
0:26:33 > 0:26:37When it hangs up, the wings form a kind of tent,
0:26:37 > 0:26:42preventing bits of the prey from dropping out. This is a top view.
0:26:47 > 0:26:52And an even tougher adversary for the pallid bat, a scorpion.
0:26:52 > 0:26:56The poisonous sting is to be carefully avoided.
0:27:02 > 0:27:06And some bats are real carnivores.
0:27:11 > 0:27:16This huge silk cotton tree contains a small colony of them.
0:27:21 > 0:27:24They are hanging at the very top of the hollow interior,
0:27:24 > 0:27:27sharing the tree with other species of bats.
0:27:28 > 0:27:33This is strange, because this carnivorous species feeds on other bats,
0:27:33 > 0:27:36but here it leaves its neighbours in peace.
0:27:42 > 0:27:47The also feed on birds, which they catch on their roosts at night.
0:27:49 > 0:27:53This is Vampyrum spectrum, but it doesn't actually suck blood.
0:27:53 > 0:27:56This is not the true vampire.
0:27:56 > 0:27:58This is. Its teeth and mouth
0:27:58 > 0:28:01are very specialised for feeding on blood.
0:28:02 > 0:28:07Vampires may have originally fed on insects that cluster around grazing animals
0:28:07 > 0:28:10and chased them on or near the ground.
0:28:16 > 0:28:19By shaving away the skin with razor teeth
0:28:19 > 0:28:22and having a saliva that prevents oozing blood clotting,
0:28:22 > 0:28:27the vampire shows how extremely specialised a mammal can become.
0:28:27 > 0:28:30And it probably all started with insects.
0:28:33 > 0:28:35And the originally insect-eating bat
0:28:35 > 0:28:40evolved in yet another direction in Arizona and Mexico.
0:28:41 > 0:28:46This is the land of big plants, like cactus, yuccas and agaves.
0:28:46 > 0:28:50The agave flowers, branching from a mast some six metres high,
0:28:50 > 0:28:53attract hummingbirds that feed on the nectar.
0:28:55 > 0:28:58And insects, too.
0:28:58 > 0:29:01It was probably these that attracted bats in the first place.
0:29:01 > 0:29:03Nectar feeding came later.
0:29:17 > 0:29:21The bats, in small parties, move from plant to plant,
0:29:21 > 0:29:26dipping and sipping at the energy-rich nectar.
0:29:26 > 0:29:28Often they get covered in pollen.
0:29:28 > 0:29:33In this way they ferry it from plant to plant, so bringing about cross-fertilisation.
0:29:33 > 0:29:38So both bat and plant have evolved together to become unlikely partners.
0:29:38 > 0:29:43As in other bats, this feeding specialisation involves adaptation.
0:29:43 > 0:29:48Long noses and long tongues enable them to reach deep into the flowers.
0:29:59 > 0:30:01When flying, seen here in slow motion,
0:30:01 > 0:30:07they emit a weak sonar, so they've been called whispering bats.
0:30:07 > 0:30:10FAST IRREGULAR PULSE
0:30:25 > 0:30:28Carrying pollen and dripping nectar,
0:30:28 > 0:30:32this bat will fly on to another agave, where cross-fertilisation will occur.
0:30:41 > 0:30:45When the bat has helped that to happen, the fruit will appear.
0:30:45 > 0:30:49And fruit, too, has become a food for bats.
0:30:49 > 0:30:52This one, lapping at a banana with its tongue,
0:30:52 > 0:30:56was the same kind as the one biting into a cockroach with its teeth.
0:30:56 > 0:31:00For some bats have developed broad tastes.
0:31:05 > 0:31:08Some, however, are exclusively fruit-eaters,
0:31:08 > 0:31:10and they include the biggest of all.
0:31:10 > 0:31:12These hardly ever live in caves,
0:31:12 > 0:31:17but instead hang themselves up in great roosts in trees, called camps.
0:31:25 > 0:31:29Their wings are immense, up to two metres across.
0:31:29 > 0:31:34Just as birds have to groom their feathers with great care to keep themselves airworthy,
0:31:34 > 0:31:40so bats spend a lot of time meticulously cleaning the elastic membrane of skin
0:31:40 > 0:31:42on which they depend.
0:31:54 > 0:32:00Fruit bats are often called flying foxes, and indeed their faces do look rather foxy.
0:32:00 > 0:32:02The fact that they have large eyes
0:32:02 > 0:32:07and no immense ears or grotesque ornaments on their noses is significant.
0:32:07 > 0:32:12They have no sonar and rely instead on vision to find their way around.
0:32:12 > 0:32:15In fact they are so different from insect-eating bats
0:32:15 > 0:32:20that they may well be descended from a different branch of the primitive mammals.
0:32:32 > 0:32:37They're powerful flyers and regularly go off on journeys of 50km
0:32:37 > 0:32:39just to find a tree in fruit.
0:32:39 > 0:32:42These are in slow motion.
0:33:23 > 0:33:27The structure of a bat's wing is very different from that of a bird's.
0:33:27 > 0:33:32The bird's, in effect, is formed from just one finger fringed with feathers.
0:33:32 > 0:33:36All the other fingers have been effectively lost.
0:33:36 > 0:33:40But the bat's ancestors didn't have feathers with long stiff quills.
0:33:40 > 0:33:43They created a broad wing by a different method.
0:33:43 > 0:33:47By retaining all their fingers and greatly elongating them
0:33:47 > 0:33:49to support the wing membrane.
0:33:49 > 0:33:55Their feet also help, for the membrane goes right down to the ankle.
0:33:55 > 0:33:57Only the thumb remains free,
0:33:57 > 0:34:00and that the bat needs for its toilet
0:34:00 > 0:34:03and to hook onto branches as it clambers about.
0:34:08 > 0:34:12When, over 50 million years ago, the first mammals flew,
0:34:12 > 0:34:16they opened up great possibilities for their descendants.
0:34:16 > 0:34:18They had the night sky virtually to themselves,
0:34:18 > 0:34:24and they developed into a multitude of different forms to take full advantage of it.
0:34:24 > 0:34:27Today there are nearly 1,000 different species of them,
0:34:27 > 0:34:30flying through the skies of the world.
0:34:30 > 0:34:36Many of them have remained insect-feeders, like their earth-bound ancestors,
0:34:36 > 0:34:41but fruit, nectar, blood, birds and even other bats
0:34:41 > 0:34:46is by no means the complete list of the diets they've discovered for themselves.
0:34:46 > 0:34:49And one of them has actually become a fisherman.
0:34:51 > 0:34:54It lives in Central America.
0:34:54 > 0:35:00Its closest relatives are all insect-feeders, and it too will take a beetle, like this one,
0:35:00 > 0:35:03though in a unique way.
0:35:04 > 0:35:09It caught that beetle by using its hind legs as grapnels,
0:35:09 > 0:35:13and it goes after fish in the same way. Watch.
0:35:17 > 0:35:21It hooked the fish, but not well enough.
0:35:28 > 0:35:31So back it comes.
0:35:39 > 0:35:44Like other bats, it immediately transfers its capture into its mouth.
0:35:46 > 0:35:52And only eats it when it gets back to its roost, stuffing some of it into cheek pouches.
0:35:58 > 0:36:03The membrane doesn't go down to the ankle, like most bats', so it's kept clear of the water.
0:36:03 > 0:36:06And the claws are as sharp as needles.
0:36:06 > 0:36:11But how does it know where to trawl? The answer's ultrasounds again.
0:36:13 > 0:36:16BAT CHIRRUPS
0:36:20 > 0:36:23It's able to detect the ripple of a fish at the surface
0:36:23 > 0:36:26and home in on it with deadly accuracy.
0:36:42 > 0:36:48But fishing, for the bats, is a rare and very recently acquired talent.
0:36:48 > 0:36:51The first really accomplished fisherman amongst the mammals
0:36:51 > 0:36:54appeared early on in the history of the group.
0:36:54 > 0:36:58When the great ocean-going reptiles, the ichthyosaurs and plesiosaurs,
0:36:58 > 0:37:01disappeared at the end of the age of the dinosaurs,
0:37:01 > 0:37:03the mammals were very quick indeed
0:37:03 > 0:37:08to fill the space that was left in the economy of the sea.
0:37:08 > 0:37:13At first, doubtless, the creature lived partly in the water, partly on land,
0:37:13 > 0:37:15rather as the hippopotamus does today,
0:37:15 > 0:37:19but very soon, within a few million years,
0:37:19 > 0:37:22truly specialised mammalian swimmers appeared.
0:37:22 > 0:37:27Some of them grew to be bigger even than the biggest of the dinosaurs - the whales.
0:37:27 > 0:37:32And here in the blue waters of the Pacific, off the Hawaiian islands,
0:37:32 > 0:37:38every year humpback whales assemble to give birth and to court.
0:37:38 > 0:37:43And if you have a lot of patience and even more luck, you may be able to swim among them.
0:37:59 > 0:38:02I was lucky enough to dive with a group of whale experts
0:38:02 > 0:38:07who knew just how to get close to these magnificent creatures.
0:38:21 > 0:38:27And there, in the distance, a 40-tonne mother and her baby.
0:38:31 > 0:38:36The changes that have taken place during the descent of these vast creatures
0:38:36 > 0:38:40from their little furry ancestors are obviously immense.
0:38:40 > 0:38:43But they're all adaptations to a sea-going life.
0:38:43 > 0:38:46The forelegs have become flippers and the back legs lost.
0:38:46 > 0:38:50But what about their huge increase in size?
0:38:50 > 0:38:54The larger you are, the lower the ratio between your volume and your surface area,
0:38:54 > 0:38:57and the easier it is to retain heat.
0:38:57 > 0:39:00Dinosaurs also had problems about getting chilled
0:39:00 > 0:39:04and solved it in a similar way by getting big.
0:39:04 > 0:39:07Their size, however, was limited by the strength of bone.
0:39:07 > 0:39:10Above a certain weight, leg bones would simply break.
0:39:10 > 0:39:12But whales are less hampered.
0:39:12 > 0:39:16Their bodies are not supported by legs, but by the water.
0:39:16 > 0:39:20So they have grown into the biggest animals the world has seen,
0:39:20 > 0:39:24some of them four times bigger than the largest known dinosaur.
0:40:28 > 0:40:33As far as we can tell, the whales, when in Hawaiian waters, don't feed at all.
0:40:33 > 0:40:37They come here only to court and to give birth to their young.
0:40:41 > 0:40:46Around April they begin to swim north, up to the Arctic.
0:40:48 > 0:40:51Many of them assemble off the coast of Alaska,
0:40:51 > 0:40:54and here they begin to feed.
0:41:05 > 0:41:09As they gather on their feeding grounds in ever-increasing numbers,
0:41:09 > 0:41:11they begin to behave in a most dramatic way.
0:41:16 > 0:41:21The breaching, 40 tonnes of animal right out of the water,
0:41:21 > 0:41:25may be something to do with the establishment of territories.
0:41:46 > 0:41:52The need to breathe air, bequeathed to them by their mammalian ancestors,
0:41:52 > 0:41:54might seem to be a major handicap.
0:41:54 > 0:41:59But the whales have minimised the problem by breathing particularly efficiently.
0:41:59 > 0:42:04Human beings only clear about 15% of the air in their lungs with a normal breath.
0:42:04 > 0:42:11The whale, in great exhalations, gets rid of about 90% of its spent air.
0:42:29 > 0:42:33It also has a well-developed system for storing oxygen in the muscles,
0:42:33 > 0:42:40and some can swim for up to 40 minutes without drawing breath if they want to.
0:42:48 > 0:42:50Humpbacks are one of the group of whales
0:42:50 > 0:42:54that feed on shoals of shrimp-like creatures, krill.
0:42:54 > 0:42:58Sometimes they concentrate the krill with a ring of bubbles from the blowhole,
0:42:58 > 0:43:04and the mouthful is filtered through plates of whalebone hanging from the upper jaw.
0:43:04 > 0:43:06In a way they parallel the anteaters.
0:43:06 > 0:43:10Both creatures have modified their jaws and lost their teeth
0:43:10 > 0:43:14in order to collect swarms of tiny invertebrates.
0:43:16 > 0:43:19Another group of whales tackle much bigger prey.
0:43:19 > 0:43:21These whales have kept their teeth
0:43:21 > 0:43:24and become among the fiercest creatures in the sea.
0:43:24 > 0:43:28These are killer whales, and they're hunting seals.
0:43:35 > 0:43:40That dot is the head of a seal, desperately searching for safety,
0:43:40 > 0:43:42but it has no chance.
0:43:54 > 0:44:00That most dramatic and elusive creature, the narwhal, is another of the toothed whales.
0:44:00 > 0:44:04And one of its teeth has grown enormous.
0:44:08 > 0:44:11Only the males have this impressive tusk,
0:44:11 > 0:44:15but no-one yet has discovered just what it's for.
0:44:21 > 0:44:25The most familiar toothed whales of all are dolphins and porpoises.
0:44:25 > 0:44:27They're the friendliest and also the smallest.
0:44:27 > 0:44:31They were among the first whales to be kept in tanks.
0:44:31 > 0:44:34As a result, we've been able to watch the moment
0:44:34 > 0:44:38that must be among the trickiest of a sea mammal's life, the moment of birth.
0:44:38 > 0:44:44This is the mother-to-be. Her belly is swollen, and birth is imminent.
0:44:44 > 0:44:46The baby's tail is just showing.
0:44:48 > 0:44:50Now it's half out.
0:44:53 > 0:44:55And there is the puff of red blood,
0:44:55 > 0:44:58as the umbilical cord breaks and the youngster swims free.
0:44:58 > 0:45:02Here is that remarkable moment again.
0:45:08 > 0:45:10The baby can swim immediately,
0:45:10 > 0:45:14but the mother helps it to the surface for its first breath of air.
0:45:14 > 0:45:18Now it swims alongside her, gliding just as fast as she does,
0:45:18 > 0:45:21seemingly without any difficulty.
0:45:21 > 0:45:25Soon, as it swims, it will suckle at that other mammalian device,
0:45:25 > 0:45:30the nipple on its mother's underside, to take its first meal of milk.
0:45:46 > 0:45:50The dolphins' gymnastic skills, their ability to copy from one another
0:45:50 > 0:45:54and their apparent eagerness to learn new tricks from their trainers
0:45:54 > 0:45:58have made them the most accomplished and popular performers in oceanaria.
0:45:58 > 0:46:01But how intelligent are they?
0:46:01 > 0:46:04SQUEAKING
0:46:07 > 0:46:11Speculations about dolphin intelligence have been stimulated in particular
0:46:11 > 0:46:13by these calls.
0:46:13 > 0:46:18Some people have even suggested that dolphins have a true language,
0:46:18 > 0:46:22and that if only we were clever enough, we would not only be able to understand,
0:46:22 > 0:46:27but might be able to speak it and convey quite complex messages to dolphins.
0:46:27 > 0:46:32It's true dolphins not only make sounds when they have their heads above water,
0:46:32 > 0:46:35but do so almost continuously below water.
0:46:35 > 0:46:39And we can listen to them do it with an underwater microphone.
0:46:41 > 0:46:46CLICKING
0:46:46 > 0:46:49Over 20 different kinds of calls have been identified.
0:46:49 > 0:46:53Some serve to keep a school together when they're travelling at top speed,
0:46:53 > 0:46:57and they can swim at 20mph, and they go on long migrations.
0:46:57 > 0:47:01Some sounds are warning cries, some call signs
0:47:01 > 0:47:06that enable one animal to be recognised at a distance by another.
0:47:06 > 0:47:08Complex though these calls are,
0:47:08 > 0:47:12no-one has yet demonstrated that dolphins ever put calls together
0:47:12 > 0:47:15to form the equivalent of a two-word sentence.
0:47:15 > 0:47:19That can be regarded as the beginning of a true language.
0:47:22 > 0:47:24But those aren't the only sounds they make.
0:47:24 > 0:47:30They also use sound for echolocation in rather the same way that bats do.
0:47:30 > 0:47:35That's to say they emit a series of very high-pitched clicks and squeaks,
0:47:35 > 0:47:37and by sensing the echoes,
0:47:37 > 0:47:41they can detect the presence of objects in the water around them.
0:47:41 > 0:47:46The frequencies they use are around 200,000 vibrations per second,
0:47:46 > 0:47:49which is about the same as that used by bats
0:47:49 > 0:47:52and way, way above the range of the human ear.
0:47:52 > 0:47:55But by once again using the bat detector,
0:47:55 > 0:47:58this time connected to the underwater microphone,
0:47:58 > 0:48:03we can translate those clicks into sounds that we can hear.
0:48:03 > 0:48:09Normally, of course, the dolphins use their eyesight in conjunction with echolocation,
0:48:09 > 0:48:13but just to show how accurate that echolocation can be,
0:48:13 > 0:48:16we're going to blindfold the dolphins.
0:48:22 > 0:48:26The dolphin has been trained to retrieve this hoop.
0:48:26 > 0:48:28What's more, it can find it in the water
0:48:28 > 0:48:34and distinguish it from these two shapes blindfold. Watch.
0:48:42 > 0:48:45CLICKING
0:48:50 > 0:48:55And just to show that that's no fluke, let's try it again.
0:49:00 > 0:49:04The waters around Hawaii are also filled with strange sounds,
0:49:04 > 0:49:07but these we know far less about.
0:49:07 > 0:49:11DEEP GROANS
0:49:14 > 0:49:18A moment ago we made this recording with an underwater microphone
0:49:18 > 0:49:23here in the Pacific near Hawaii. Just listen to this.
0:49:23 > 0:49:28DEEP GROANS
0:49:31 > 0:49:36LOW WAIL
0:49:43 > 0:49:46This is the sound of a humpback whale
0:49:46 > 0:49:50that's lying in the water about 100 feet below us in the sea.
0:49:52 > 0:49:54There are many extraordinary things about its song.
0:49:54 > 0:49:57To start with, they're so long.
0:49:57 > 0:50:01They may last anything from a quarter of an hour to half an hour.
0:50:01 > 0:50:07Although the various themes within the song may be repeated a varying number of times,
0:50:07 > 0:50:12the actual themes themselves and the order in which they appear in the song is unvarying.
0:50:13 > 0:50:17And even more remarkable, all the singing whales within this area
0:50:17 > 0:50:20sing the same song.
0:50:20 > 0:50:24WHALES SING
0:50:24 > 0:50:28After the breeding season they disperse. Next year they'll be back,
0:50:28 > 0:50:31but next year they'll have a slightly different song
0:50:31 > 0:50:35which contains themes that have never been heard before.
0:50:35 > 0:50:38And all of them will be singing the same song.
0:50:39 > 0:50:43And that song can be heard echoing throughout these waters
0:50:43 > 0:50:47for miles and miles and miles.
0:50:48 > 0:50:52WHALES SINGING
0:50:52 > 0:50:55It seems extraordinary that a creature like this
0:50:55 > 0:51:01could have given rise to whales, as well as to moles and bats and anteaters.
0:51:01 > 0:51:03Those swimming, burrowing, flying specialists
0:51:03 > 0:51:07appeared a few million years after the dinosaurs disappeared.
0:51:07 > 0:51:10The only mammals around from which they could have sprung
0:51:10 > 0:51:14were these small furry insect-eaters.
0:51:14 > 0:51:19So this tiny theme has proved to be one of the most fruitful in the animal kingdom.
0:51:19 > 0:51:23There are still some variations we haven't looked at yet -
0:51:23 > 0:51:25the vegetarians, the leaf-and-grass-eaters,
0:51:25 > 0:51:28and the carnivores that developed to prey on them.
0:51:28 > 0:51:31They will have to have a programme of their own.
0:51:55 > 0:51:59Subtitles by Red Bee Media Ltd