0:00:02 > 0:00:06'The natural world is full of extraordinary animals
0:00:06 > 0:00:08'with amazing life histories.
0:00:09 > 0:00:13'Yet certain stories are more intriguing than most.'
0:00:15 > 0:00:19The mysteries of a butterfly's life cycle.
0:00:19 > 0:00:23Or the strange biology of the Emperor penguin.
0:00:23 > 0:00:26Some of these creatures were surrounded by myth
0:00:26 > 0:00:30and misunderstandings for a very long time.
0:00:30 > 0:00:34And some have only recently revealed their secrets.
0:00:34 > 0:00:38These are the animals that stand out from the crowd,
0:00:38 > 0:00:44the curiosities I find most fascinating of all.
0:00:51 > 0:00:52'In this programme,
0:00:52 > 0:00:55'I examine the remarkable lives of two animals
0:00:55 > 0:00:58'that have mastered the problems of life in the dark.'
0:01:01 > 0:01:06'The giant squid, which lives in the deepest oceans...'
0:01:07 > 0:01:09..and owls.
0:01:09 > 0:01:13Highly specialised hunters that seek their prey at night.
0:01:21 > 0:01:26When we think of animals of the night, owls tend to come to mind.
0:01:26 > 0:01:29In fact, not all owls are nocturnal,
0:01:29 > 0:01:33but those that are have a very similar-shaped face,
0:01:33 > 0:01:35round and flat.
0:01:36 > 0:01:39And their most prominent facial features
0:01:39 > 0:01:42are the large, forward-facing eyes.
0:01:42 > 0:01:46These give them a seemingly wise look and in fact,
0:01:46 > 0:01:50owls have often been revered for their wisdom.
0:01:52 > 0:01:56But they have also been linked with legends of death and evil.
0:01:58 > 0:02:00They are birds of the night.
0:02:00 > 0:02:04To many, they seem eerie and mysterious.
0:02:06 > 0:02:09'But how good is an owl's eyesight?
0:02:09 > 0:02:13'Can they really see what we can't?'
0:02:13 > 0:02:16The colour picture that forms at the back of our eyes
0:02:16 > 0:02:20is very much like that that forms in the eyes of a bird.
0:02:20 > 0:02:24We have roughly the same number of colour receptors.
0:02:24 > 0:02:28But when day changes to night, the picture changes.
0:02:28 > 0:02:32Then, different receptors come into play, called rods.
0:02:32 > 0:02:35And owls have a much higher proportion of rods
0:02:35 > 0:02:37in their eyes than we do.
0:02:37 > 0:02:41So they're extremely good at seeing at low light levels.
0:02:41 > 0:02:43Aren't you?
0:02:45 > 0:02:49The barn owl sets off to hunt shortly after dusk.
0:02:50 > 0:02:53As the light fades, we struggle to see.
0:02:53 > 0:02:56But the owl has no such problem.
0:02:57 > 0:03:00Flying low, it keeps its eyes trained on the ground,
0:03:00 > 0:03:03looking for any movement in the grass.
0:03:05 > 0:03:08Its eyes now give it the edge over its prey,
0:03:08 > 0:03:12and it can hunt at a time when few other birds can.
0:03:17 > 0:03:19And there's another important difference
0:03:19 > 0:03:21between an owl's eye and ours.
0:03:21 > 0:03:24The pupil in the front of the eye, the hole,
0:03:24 > 0:03:26is very much bigger in an owl's.
0:03:26 > 0:03:29Ours measures around eight millimetres across.
0:03:29 > 0:03:33An owl's, like this tawny owl, is around 13.
0:03:33 > 0:03:36That means very much more light can get into the eye,
0:03:36 > 0:03:40so the picture formed on the retina is very much brighter.
0:03:40 > 0:03:42In fact, it's about three times as bright.
0:03:42 > 0:03:44OWL SQUEAKS Aw...
0:03:46 > 0:03:48OWL SQUEAKS Aw...
0:03:49 > 0:03:53So, unlike other birds, which cannot see so well in the dark,
0:03:53 > 0:03:57the owl can remain active throughout the night.
0:04:00 > 0:04:03But specialist eyes create problems.
0:04:03 > 0:04:05Squeezing a large eyeball
0:04:05 > 0:04:10into a relatively small skull requires changes.
0:04:10 > 0:04:15The shape of the owl eye is more tubular than round.
0:04:15 > 0:04:19This may help to increase the size of the image on the retina
0:04:19 > 0:04:20at the back.
0:04:20 > 0:04:24But the owl's eye shape and size presents certain problems.
0:04:24 > 0:04:27It doesn't fit snugly into the skull
0:04:27 > 0:04:30and there's no room in the socket for muscles to move it.
0:04:31 > 0:04:33And there's another problem.
0:04:33 > 0:04:36A closer look at an owl's skull
0:04:36 > 0:04:40shows that its ear openings are very big.
0:04:40 > 0:04:44So the only way for the tubular eyes to fit into the skull is for them
0:04:44 > 0:04:48to be placed in the middle of the face in a forward-looking position.
0:04:48 > 0:04:51This limits the owl's field of view.
0:04:54 > 0:04:57But owls have a trick that allows them
0:04:57 > 0:05:01to dramatically increase their field of view.
0:05:01 > 0:05:05They can rotate their heads nearly all the way round.
0:05:05 > 0:05:08Folklore has it that you can kill an owl
0:05:08 > 0:05:12by walking in circles round a tree in which one is perched
0:05:12 > 0:05:14and so make it twist its head off.
0:05:14 > 0:05:16That, of course, is not true.
0:05:16 > 0:05:18But owls can certainly turn their heads
0:05:18 > 0:05:22through 270 degrees in either direction.
0:05:22 > 0:05:27If we tried to do that, we'd tear our arteries and break our necks.
0:05:27 > 0:05:30So, how do owls do it?
0:05:31 > 0:05:34Recently, scientists have discovered that it's due
0:05:34 > 0:05:38to a remarkable adaptation of their bones.
0:05:39 > 0:05:43Owls' necks, as you can see in this skeleton of an eagle owl,
0:05:43 > 0:05:47have 14 vertebrae. That's twice the number that we have.
0:05:47 > 0:05:50This gives them greater flexibility.
0:05:50 > 0:05:53But only recently, CT scans have shown researchers
0:05:53 > 0:05:57how the owl can rotate its head without passing out.
0:05:58 > 0:06:01Cavities within the neck bones are ten times larger
0:06:01 > 0:06:04in an owl's neck than in ours,
0:06:04 > 0:06:06giving more room for vital blood vessels
0:06:06 > 0:06:09that run up to the owl's head.
0:06:09 > 0:06:12What's more, the carotid arteries enter the head
0:06:12 > 0:06:16much higher up the neck and are centrally positioned,
0:06:16 > 0:06:19and this may help avoid damage during twisting.
0:06:19 > 0:06:23And the owl's arteries seem to widen below the brain,
0:06:23 > 0:06:26allowing blood to pool.
0:06:26 > 0:06:30This may create a vital blood reservoir that guarantees blood flow
0:06:30 > 0:06:33to the brain, should the vessels below be squeezed
0:06:33 > 0:06:35while the head is turning.
0:06:35 > 0:06:38So the owl can turn its head almost all the way round
0:06:38 > 0:06:40without risk of injury.
0:06:42 > 0:06:45So, owls have successfully dealt with the problems
0:06:45 > 0:06:47created by having large eyes.
0:06:47 > 0:06:49OWL HOOTS
0:06:49 > 0:06:52But are these eyes really all they seem?
0:06:52 > 0:06:55It was long thought that owls can see perfectly,
0:06:55 > 0:06:58even on the darkest of nights.
0:06:58 > 0:07:00But that is not the case.
0:07:01 > 0:07:05On cloudy nights and beneath trees with dense canopies,
0:07:05 > 0:07:09they can only discern the faintest silhouettes.
0:07:09 > 0:07:12It's nowhere near detailed enough to hunt for prey.
0:07:14 > 0:07:17But the owl has another sense to help it...
0:07:17 > 0:07:19acute hearing.
0:07:21 > 0:07:22In the 18th century,
0:07:22 > 0:07:25the great French naturalist Count de Buffon wrote,
0:07:25 > 0:07:28"Their sense of hearing seems to be superior
0:07:28 > 0:07:32"to that of other birds and perhaps to that of every other animal,
0:07:32 > 0:07:34"for the drum of the ear
0:07:34 > 0:07:37"is proportionately larger than in quadrupeds
0:07:37 > 0:07:41"and besides, they can open and shut this organ at pleasure,
0:07:41 > 0:07:44"a power possessed by no other animal."
0:07:44 > 0:07:47Well, we know today that that's true of some owls,
0:07:47 > 0:07:50though not all, but Buffon was quite right
0:07:50 > 0:07:54to draw our attention to the remarkable hearing of owls.
0:07:55 > 0:07:57OWL HOOTS
0:07:57 > 0:08:00The owl's large ear openings are not visible
0:08:00 > 0:08:03because they're hidden beneath the face feathers.
0:08:03 > 0:08:09And unlike other birds, they have fleshy outer ears like our own.
0:08:09 > 0:08:13In many owls, they're positioned at slightly different levels
0:08:13 > 0:08:14on either side of the head.
0:08:16 > 0:08:18And it's these features that help them
0:08:18 > 0:08:20to accurately pinpoint their prey.
0:08:22 > 0:08:26Most owls have very similar shaped faces, flat and round.
0:08:26 > 0:08:28It's called a facial ruff.
0:08:28 > 0:08:33It's formed from feathers that are particularly dense and bristly,
0:08:33 > 0:08:36and they lie flat on either side of the face,
0:08:36 > 0:08:39just behind the opening to the ears.
0:08:39 > 0:08:43It's thought that they deflect the sound into the ears.
0:08:43 > 0:08:47In fact, the facial ruff seems to be a kind of sound amplifier.
0:08:50 > 0:08:55The barn owl has a distinctive, heart-shaped ruff and its face
0:08:55 > 0:09:01acts like a satellite dish, focusing the sounds from below into the ears.
0:09:03 > 0:09:07Its soft flight feathers enable it to move through the air
0:09:07 > 0:09:10in almost complete silence so that it can hear
0:09:10 > 0:09:15the slightest rustle and approach its prey undetected.
0:09:21 > 0:09:25But few have as large a facial ruff as the great grey owl.
0:09:28 > 0:09:31Although it hunts during the day, its prey is hidden under
0:09:31 > 0:09:36a cover of snow, so it has to rely entirely on its ears.
0:09:40 > 0:09:44Studies have shown that owls' hearing is particularly
0:09:44 > 0:09:47acute for very quiet sounds.
0:09:47 > 0:09:52In fact, part of an owl's brain that detects sound has three times
0:09:52 > 0:09:57as many neurones as its equivalent in, say, a crow's brain.
0:09:57 > 0:10:02The hairs of the inner ear which detect the vibrations
0:10:02 > 0:10:06of sound are particularly abundant in an owl.
0:10:06 > 0:10:10Not only that, whereas the equivalent hairs in my ear
0:10:10 > 0:10:15degrade with age, in an owl's they are regrown.
0:10:15 > 0:10:19So whereas my hearing gets worse as I get older,
0:10:19 > 0:10:22an owl's always remains very acute.
0:10:23 > 0:10:27The owl's ears may in fact be more crucial to its nocturnal
0:10:27 > 0:10:30lifestyle than its eyes.
0:10:30 > 0:10:33But by combining all its senses,
0:10:33 > 0:10:36it has solved the problems of living in the dark.
0:10:37 > 0:10:43So it seems that the shape of the face helps both the owl's sight
0:10:43 > 0:10:44and its hearing.
0:10:44 > 0:10:47So whether or not you think the owl is wise,
0:10:47 > 0:10:52it certainly has a head for life in the dark.
0:10:55 > 0:10:59Next we journey into the darkest of places to try and unravel
0:10:59 > 0:11:03the life of a creature that has long captured our imagination.
0:11:07 > 0:11:11Here in the Natural History Museum is a specimen of an animal
0:11:11 > 0:11:14that has fascinated humanity for thousands of years.
0:11:14 > 0:11:17It's a giant squid.
0:11:17 > 0:11:20This particular one was netted off the Falkland Islands,
0:11:20 > 0:11:22immediately put on ice,
0:11:22 > 0:11:25and then brought here to the museum in London.
0:11:25 > 0:11:29Few museums have complete or as perfectly preserved
0:11:29 > 0:11:31specimens as this one.
0:11:31 > 0:11:37This one measures about eight metres, the length of a London bus.
0:11:37 > 0:11:39But others have been caught even bigger,
0:11:39 > 0:11:42one about twice the length that weighed around a tonne.
0:11:44 > 0:11:48Very few people have ever seen one of these creatures alive.
0:11:48 > 0:11:52That's because they live at depths of around 1,000 metres
0:11:52 > 0:11:54and down there, it's pitch-black.
0:11:55 > 0:11:59So how do these animals manage to hunt in such conditions?
0:12:00 > 0:12:05That's a question that has proved exceedingly difficult to answer.
0:12:07 > 0:12:12Sailors a long time ago told stories of having seen a gigantic,
0:12:12 > 0:12:16squid-like creature known as the Kraken.
0:12:16 > 0:12:20It was said to have huge tentacles strong enough to grip
0:12:20 > 0:12:22and sink a ship.
0:12:22 > 0:12:26The tales seemed unlikely and far-fetched, but could the giant
0:12:26 > 0:12:30squid perhaps have been the source of these extraordinary reports?
0:12:31 > 0:12:35The first clues that this creature may in fact be real came from
0:12:35 > 0:12:38the tales of sailors on whaling ships
0:12:38 > 0:12:40in the 18th and 19th centuries.
0:12:40 > 0:12:44Some of them reported in their ships' logs that they often noticed
0:12:44 > 0:12:49strange, circular scars on the heads and jaws of captured sperm whales.
0:12:49 > 0:12:52The scars suggested a fierce wrestling match with
0:12:52 > 0:12:54some enormous beast.
0:12:54 > 0:12:57But what creature could take on a 70-tonne whale?
0:12:57 > 0:13:01Inside the stomachs of the whales were clues.
0:13:01 > 0:13:06A number of hard, indigestible objects like this one.
0:13:07 > 0:13:10It looks a bit like the beak of a parrot.
0:13:10 > 0:13:13But in fact, it belongs to an entirely different
0:13:13 > 0:13:15kind of animal - to a cephalopod.
0:13:15 > 0:13:20Cephalopods are marine animals that include the octopus,
0:13:20 > 0:13:22the squid and the cuttlefish.
0:13:22 > 0:13:25This beak is the mouth part of one such creature
0:13:25 > 0:13:29and is used to tear its prey into small pieces.
0:13:29 > 0:13:33The sailors on the whaling ships immediately recognised the beak
0:13:33 > 0:13:35as being from a cephalopod.
0:13:35 > 0:13:37But its size suggested a creature
0:13:37 > 0:13:40many times bigger than any known species.
0:13:42 > 0:13:47Cephalopods have a ring of eight or ten arms, or tentacles, which they
0:13:47 > 0:13:50use to push food into their mouth in the centre of the ring.
0:13:51 > 0:13:55The arms are equipped with round suckers to help
0:13:55 > 0:13:57hold on to their prey.
0:13:57 > 0:14:01It is the marks from these that were found by sailors on the bodies
0:14:01 > 0:14:03of sperm whales.
0:14:03 > 0:14:07Could a gigantic squid have caused such injuries,
0:14:07 > 0:14:11and how massive must it be to tackle a sperm whale,
0:14:11 > 0:14:13one of the biggest animals on the planet?
0:14:15 > 0:14:19And then in 1873, fishermen caught what
0:14:19 > 0:14:24they called a sea monster off the coast of Newfoundland in Canada.
0:14:24 > 0:14:28After killing it with their knives, they lost the body,
0:14:28 > 0:14:32but they brought the head and tentacles to the local clergyman.
0:14:32 > 0:14:35The clergyman bought it off the fishermen for 10
0:14:35 > 0:14:38and displayed it in his living room by carefully draping it over
0:14:38 > 0:14:40a bath stand, to show off
0:14:40 > 0:14:42its many arms and tentacles.
0:14:42 > 0:14:45The photograph clearly proved that
0:14:45 > 0:14:47here was a gigantic squid with
0:14:47 > 0:14:51its beak at the top and over seven metre-long tentacles.
0:14:51 > 0:14:56Here last was the evidence that the monster of the deep,
0:14:56 > 0:14:58the Kraken, really does exist.
0:15:00 > 0:15:04But the giant squid itself continued to evade scientists,
0:15:04 > 0:15:06even after its discovery.
0:15:06 > 0:15:09It's only since the invention of submersibles that we have
0:15:09 > 0:15:13been able to follow it down into its deep sea home.
0:15:13 > 0:15:15Even so, we seem to have had little
0:15:15 > 0:15:18success in finding the elusive giant.
0:15:18 > 0:15:21So scientists are now trying to piece together its biology
0:15:21 > 0:15:25by looking at other closely-related animals.
0:15:27 > 0:15:29This is an octopus.
0:15:29 > 0:15:34It uses both its eyes and tentacles to explore its surroundings.
0:15:34 > 0:15:37The octopus's brain is distributed throughout its body
0:15:37 > 0:15:41so that its arms can control much of their own movement.
0:15:41 > 0:15:46It also has a highly complex eyes and sees in much the same way
0:15:46 > 0:15:51as we do, with the lens projecting an image onto the retina behind.
0:15:51 > 0:15:54But while our eyes focus by squeezing the lens to
0:15:54 > 0:15:56change its shape, the octopus's eyes
0:15:56 > 0:16:00focus like a camera, with the lens moving in and out.
0:16:03 > 0:16:06The giant squid's eyes have much the same
0:16:06 > 0:16:11structure as those of an octopus, but when it comes to size, it has
0:16:11 > 0:16:15the biggest eye in the animal kingdom, as large as a football.
0:16:17 > 0:16:21For seeing in dim light, a large eye is better than the small one.
0:16:21 > 0:16:25So many animals of the deep have exceptionally big eyes.
0:16:30 > 0:16:33But in order to see at all, there has to be some light,
0:16:33 > 0:16:37and the giant squid lives at depths of 1,000 metres.
0:16:40 > 0:16:43Although very little sunlight reaches the deeper parts
0:16:43 > 0:16:47of the ocean, there is another kind of light there.
0:16:47 > 0:16:49It's produced by the deep sea animals
0:16:49 > 0:16:52and it's called bioluminescence.
0:16:52 > 0:16:55The light is produced by a chemical reaction in the same
0:16:55 > 0:16:57way as that in a glow stick does.
0:16:57 > 0:16:59When I shake and snap the stick,
0:16:59 > 0:17:04two chemicals called luciferin and luciferase react together to produce
0:17:04 > 0:17:07a bioluminescent glow like this...
0:17:09 > 0:17:11There.
0:17:11 > 0:17:15Some deep sea animals use their own luciferins to produce light, while
0:17:15 > 0:17:19in others it's produced by bacteria living within special light organs.
0:17:21 > 0:17:26A flashing light can act as a lure or confuse a predator.
0:17:26 > 0:17:31It's thought about 90% of deep sea creatures produce
0:17:31 > 0:17:35bioluminescence and they use it in a number of different ways.
0:17:38 > 0:17:42All these fish come from the deep sea.
0:17:42 > 0:17:45They all produce light in one way or another.
0:17:45 > 0:17:50This is the football angler fish and it has a modified
0:17:50 > 0:17:54ray from its dorsal fin which has lots of little tentacles on top.
0:17:54 > 0:17:58The tip of each tentacle produces a little green light
0:17:58 > 0:18:01so it looks as though there is a little shoal of small creatures,
0:18:01 > 0:18:05maybe shrimps, hovering above it in the blackness.
0:18:05 > 0:18:08When another shrimp thinks it might join some friends
0:18:08 > 0:18:12and come along that way, the angler fish simply tilts up,
0:18:12 > 0:18:15opens its immense jaw and has its breakfast.
0:18:16 > 0:18:19This, on the other hand,
0:18:19 > 0:18:23is a stoplight loosejaw, which operates in a different way.
0:18:26 > 0:18:31It produces red light from two little organs at the front.
0:18:31 > 0:18:35Hardly any other species of fish in the sea can see red light,
0:18:35 > 0:18:38so it can hunt that way and find its prey.
0:18:38 > 0:18:43When it does, it opens this immense loose jaw and engulfs it.
0:18:43 > 0:18:46There you are. Back you go.
0:18:49 > 0:18:51But what about the giant squid?
0:18:51 > 0:18:55Could it also be producing bioluminescence?
0:18:55 > 0:18:58Some of its close relatives apparently can.
0:19:00 > 0:19:02This is the vampire squid.
0:19:02 > 0:19:06It has eight arms lined with tooth-like projections.
0:19:09 > 0:19:12When threatened, it turns itself inside out,
0:19:12 > 0:19:14wrapping its body in a dark cloak.
0:19:19 > 0:19:21If that doesn't work, the squid has another trick.
0:19:23 > 0:19:26Small lights at the end of its arms
0:19:26 > 0:19:29flash like eyes to distract the predator.
0:19:35 > 0:19:38With so many creatures of the deep producing light, you might think
0:19:38 > 0:19:41that the giant squid would do so as well.
0:19:43 > 0:19:46But scientists studying their carcasses have not been
0:19:46 > 0:19:49able to find any evidence of light-producing bacteria or
0:19:49 > 0:19:51pigments in their bodies.
0:19:53 > 0:19:59So it seems that the ocean's elusive giant truly hides in the dark.
0:20:04 > 0:20:08Although it may not produce its own light, the giant squid can surely
0:20:08 > 0:20:10see the bioluminescence of others
0:20:10 > 0:20:13and this may help it to locate its prey.
0:20:18 > 0:20:21With no sightings of a living giant squid since it was
0:20:21 > 0:20:25first discovered, we seem to be no closer to discovering the truth.
0:20:26 > 0:20:31But in 2004, Japanese scientists finally made a breakthrough.
0:20:32 > 0:20:35Using small squid as bait,
0:20:35 > 0:20:39they were able to attract a live giant squid.
0:20:42 > 0:20:44These first images are tantalising,
0:20:44 > 0:20:48but they still reveal little of the animal's true behaviour.
0:20:48 > 0:20:51Where does it live and how does it feed?
0:20:51 > 0:20:54Questions such as these remain unanswered.
0:20:56 > 0:20:58In spite of its great size,
0:20:58 > 0:21:02the giant squid has proved remarkably difficult to find.
0:21:02 > 0:21:05No doubt scientists will continue to search for it
0:21:05 > 0:21:07and discover more about it.
0:21:07 > 0:21:12But my guess is that the giant squid is likely to remain ahead of
0:21:12 > 0:21:15the game, that this natural curiosity
0:21:15 > 0:21:18is likely to see us before we see it.
0:21:23 > 0:21:28Both the owl and the giant squid live in a world with little light
0:21:28 > 0:21:31and both have evolved large eyes, the better to
0:21:31 > 0:21:33see the world around them.
0:21:34 > 0:21:38But while we've unravelled the owl's ways of surviving in the dark,
0:21:38 > 0:21:43much about giant squid still remains a mystery.