0:00:02 > 0:00:06The natural world is full of extraordinary animals
0:00:06 > 0:00:09with amazing life histories.
0:00:09 > 0:00:14Yet certain stories are more intriguing than most...
0:00:16 > 0:00:19..the mysteries of a butterfly's lifecycle,
0:00:19 > 0:00:23or the strange biology of the Emperor Penguin...
0:00:23 > 0:00:25Some of these creatures
0:00:25 > 0:00:30were surrounded by myth and 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 > 0:00:41the curiosities I find...
0:00:41 > 0:00:43most fascinating of all.
0:00:50 > 0:00:53Some of our most familiar animals
0:00:53 > 0:00:58puzzled scientific minds for a surprisingly long time.
0:00:58 > 0:01:01The mysterious comings and goings of Barn Swallows
0:01:01 > 0:01:05led to some far-fetched ideas,
0:01:05 > 0:01:08while the life-cycle of the Painted Lady butterfly
0:01:08 > 0:01:10took centuries to unravel.
0:01:17 > 0:01:19Swallows have successfully nested
0:01:19 > 0:01:23and raised their young in this barn for several years.
0:01:23 > 0:01:25These chicks will soon leave the nest
0:01:25 > 0:01:29and make their first exploratory flights around the farm.
0:01:29 > 0:01:33But in a few weeks' time, they will suddenly vanish.
0:01:33 > 0:01:34Where do they go to?
0:01:34 > 0:01:38In the past, that gave rise to some extraordinary speculations.
0:01:38 > 0:01:40In fact, in the 18th century
0:01:40 > 0:01:43it became a very long-running debate
0:01:43 > 0:01:45headed by some well-known church figures.
0:01:47 > 0:01:49And swallows are not the only birds
0:01:49 > 0:01:53that appear and disappear with the changing seasons.
0:01:53 > 0:01:58For centuries, people speculated about where such birds go.
0:01:58 > 0:02:02One explanation was that some birds changed into others
0:02:02 > 0:02:04by growing different adult plumage.
0:02:04 > 0:02:10Perhaps the Redstart turned into a Robin,
0:02:10 > 0:02:15or the Garden Warbler into a Blackcap.
0:02:15 > 0:02:18Since these species were seldom present at the same time,
0:02:18 > 0:02:22the explanation seemed entirely plausible.
0:02:24 > 0:02:29The Barnacle goose was another mystery.
0:02:29 > 0:02:34Each winter, huge noisy flocks of them appear on European shores,
0:02:34 > 0:02:37apparently from out of nowhere.
0:02:37 > 0:02:40No-one had ever seen them build a nest
0:02:40 > 0:02:43or raise young.
0:02:46 > 0:02:51The Barnacle goose gave rise to some extraordinary folklore,
0:02:51 > 0:02:54as this medieval illustration shows.
0:02:54 > 0:02:58It was thought that the geese grew on underwater trees,
0:02:58 > 0:03:01starting life as small marine creatures
0:03:01 > 0:03:03called goose barnacles.
0:03:03 > 0:03:06Goose barnacles do of course exist.
0:03:06 > 0:03:09They're small-shelled marine organisms
0:03:09 > 0:03:10with what looks like the head,
0:03:10 > 0:03:13which is in fact enclosed by a shell,
0:03:13 > 0:03:15attached by a stalk,
0:03:15 > 0:03:18which was thought to resemble the neck of a bird,
0:03:18 > 0:03:21to a bit of wood or a rock.
0:03:23 > 0:03:29The confusion about the nature of the Barnacle goose was put to good use by some.
0:03:29 > 0:03:33Since it was unclear whether it was a bird, a fish or some other creature,
0:03:33 > 0:03:36you could surely be allowed to eat it
0:03:36 > 0:03:39on days when meat was forbidden by the church.
0:03:40 > 0:03:43But the most commonly held belief
0:03:43 > 0:03:47was that birds disappear in winter because they hibernated.
0:03:47 > 0:03:52Swallows and their close relatives, the swifts and martins,
0:03:52 > 0:03:56were thought to do so in mud at the bottom of ponds and rivers.
0:03:56 > 0:03:59And it's easy to see how this idea originated,
0:03:59 > 0:04:02because the birds spend much of their time near water,
0:04:02 > 0:04:06skimming low over the surface, hunting for insects or taking a drink.
0:04:08 > 0:04:12It wasn't until the Middle Ages that another theory was proposed -
0:04:12 > 0:04:15that some birds may migrate.
0:04:15 > 0:04:21And one of its strongest proponents was an influential religious leader.
0:04:22 > 0:04:25Frederick II of Hohenstaufen
0:04:25 > 0:04:31was a powerful Holy Roman Emperor and known for his unorthodox views.
0:04:31 > 0:04:33He ignored the philosophy of the church
0:04:33 > 0:04:37and based his knowledge of natural history on direct observation,
0:04:37 > 0:04:40rather than what was ordained.
0:04:40 > 0:04:42Frederick was also a keen falconer
0:04:42 > 0:04:46and he wrote this book, The Art of Falconry,
0:04:46 > 0:04:48and in it, surprisingly,
0:04:48 > 0:04:52there are entire chapters on the migration of birds.
0:04:52 > 0:04:54His confidence came from the fact that,
0:04:54 > 0:04:58unlike his contemporaries and those before him,
0:04:58 > 0:05:02he had actually observed birds in the field for himself.
0:05:02 > 0:05:04He had no doubt about the migration,
0:05:04 > 0:05:08and so little patience for the myths surrounding the Barnacle goose.
0:05:08 > 0:05:10He considered the story to be quite ridiculous
0:05:10 > 0:05:15and argued that the birds simply breed in distant lands.
0:05:17 > 0:05:21His views started a debate that split people into two camps -
0:05:21 > 0:05:24those believing in the old hibernation theory
0:05:24 > 0:05:29and those who supported the idea that birds migrate.
0:05:29 > 0:05:31This was the start of a new era,
0:05:31 > 0:05:33which was to sweep away myths
0:05:33 > 0:05:38and focus instead on facts and careful observation.
0:05:38 > 0:05:41Across Europe, the evidence for bird migration
0:05:41 > 0:05:44started to accumulate.
0:05:44 > 0:05:49In Germany, a 12th-century monk is said to have taken a swallow from its nest
0:05:49 > 0:05:53and attached a parchment note to its leg that read,
0:05:53 > 0:05:57"Oh, swallow, where do you live in winter?"
0:05:58 > 0:06:01The following spring, the bird returned with a note saying,
0:06:01 > 0:06:05"In Asia, in the home of Petrus" - that is Israel.
0:06:06 > 0:06:08The story may not have been true,
0:06:08 > 0:06:11but it certainly gave the right hint.
0:06:14 > 0:06:16In the early 16th century,
0:06:16 > 0:06:21a bishop from Sweden called Olaus Magnus
0:06:21 > 0:06:23reignited the debate about swallows
0:06:23 > 0:06:25with this picture...
0:06:25 > 0:06:27He claimed that in winter,
0:06:27 > 0:06:29fishermen often drew up swallows in their nets,
0:06:29 > 0:06:33hanging together in a mass.
0:06:33 > 0:06:37This astonishing assertion provided ample fuel for the anti-migration lobby
0:06:37 > 0:06:39and, unlikely as it was,
0:06:39 > 0:06:42the view that swallows spent their winters underwater
0:06:42 > 0:06:45became increasingly entrenched.
0:06:48 > 0:06:55By the 18th century, the debate about migration versus hibernation had come to a head,
0:06:55 > 0:06:59and across the continent opinions were divided.
0:07:01 > 0:07:06But new evidence was about to come from an unusual source.
0:07:06 > 0:07:09Edward Jenner was an English country doctor
0:07:09 > 0:07:13who also had a deep interest in natural history.
0:07:13 > 0:07:18He noted that although swallows often splash in water as they skim across it,
0:07:18 > 0:07:21they never immerse themselves.
0:07:21 > 0:07:23Were they to do so, he suggested,
0:07:23 > 0:07:28their wings would become so wet that they would be unable to fly.
0:07:28 > 0:07:34To test his idea, Jenner reportedly held a swift underwater for two minutes.
0:07:34 > 0:07:38Not surprisingly, it died.
0:07:38 > 0:07:41Jenner went on to devise another experiment
0:07:41 > 0:07:43to discover where the birds go.
0:07:43 > 0:07:46He took 12 swifts from their nests
0:07:46 > 0:07:49and marked them by taking off two of their claws.
0:07:49 > 0:07:52The following year, some of the birds he'd marked
0:07:52 > 0:07:54were caught again in exactly the same spot.
0:07:54 > 0:07:59Although Jenner could not discover where his swifts had been over the winter,
0:07:59 > 0:08:03he was the first to show that they return to use the same breeding sites
0:08:03 > 0:08:05in the following years.
0:08:05 > 0:08:09And we now know that this is true for swallows, as well.
0:08:10 > 0:08:12About the same time across the Channel,
0:08:12 > 0:08:18a German bird enthusiast had come up with a similar idea.
0:08:18 > 0:08:22Johann Frisch caught several birds near his house
0:08:22 > 0:08:25and attached to their legs woollen threads like this,
0:08:25 > 0:08:28which he'd dipped in red watercolour.
0:08:28 > 0:08:32He predicted that if swallows really did spend the winter at the bottom of lakes,
0:08:32 > 0:08:35the red colour would be washed off.
0:08:35 > 0:08:40The following spring, Frisch's swallows returned and the threads were unchanged.
0:08:40 > 0:08:45It was a very simple but very effective experiment.
0:08:45 > 0:08:49Evidence against the hibernation theory continued to mount
0:08:49 > 0:08:54and eventually, a new technique put the final nail in its coffin -
0:08:54 > 0:08:57systematic bird ringing.
0:08:59 > 0:09:03This bird has just been fitted with its own individual marker,
0:09:03 > 0:09:08a small metal ring on its leg, with a unique code of numbers.
0:09:08 > 0:09:13It's part of a national scheme that's been running for over a 100 years
0:09:13 > 0:09:17and provides scientists with invaluable data on bird movements.
0:09:17 > 0:09:19Early in the 20th century,
0:09:19 > 0:09:22the study of migration really took off.
0:09:22 > 0:09:25Birds were recovered on their breeding and wintering grounds
0:09:25 > 0:09:28and often en route, too.
0:09:28 > 0:09:32600 years after Frederick von Hohenstaufen had first started the debate,
0:09:32 > 0:09:36real evidence was beginning to accumulate.
0:09:37 > 0:09:41In the summer of 1911, a metal ring, just like this one,
0:09:41 > 0:09:44was clipped onto the leg of a young swallow in Staffordshire.
0:09:44 > 0:09:49The number on the ring was B830.
0:09:49 > 0:09:5418 months later, the same bird was caught by a farmer in South Africa.
0:09:54 > 0:09:57Here, at last, was the indisputable proof
0:09:57 > 0:09:59that swallows migrate
0:09:59 > 0:10:04and spend the winter thousands of miles away.
0:10:04 > 0:10:06Off you go. There we are.
0:10:09 > 0:10:13Today, of course, we know that the swallow's migration
0:10:13 > 0:10:17is one of the most impressive in all the animal kingdom.
0:10:17 > 0:10:21It takes it across the largest desert in the world - the Sahara.
0:10:21 > 0:10:23It's a gruelling and dangerous journey,
0:10:23 > 0:10:28and many die on the way from exhaustion or starvation.
0:10:28 > 0:10:30They travel for nearly four months,
0:10:30 > 0:10:34covering nearly 6,000 miles,
0:10:34 > 0:10:37and eventually reach southern Africa.
0:10:43 > 0:10:48And bird ringing also helped to dispel the myth of the Barnacle goose.
0:10:48 > 0:10:52In the 1960s, a Norwegian expedition ringed geese
0:10:52 > 0:10:55nesting on the Arctic island of Spitsbergen.
0:10:55 > 0:11:00That autumn, some of the same birds were sighted on the west coast of Scotland,
0:11:00 > 0:11:03over 1,000 miles away.
0:11:03 > 0:11:10Frederick von Hohenstaufen had been proved to be absolutely correct.
0:11:11 > 0:11:14It took centuries to discover the truth
0:11:14 > 0:11:18behind the swallow's seasonal movements.
0:11:18 > 0:11:22But in that time, they baffled the minds of many great naturalists
0:11:22 > 0:11:27and started one of the longest-running of all scientific debates.
0:11:27 > 0:11:32But in the end, the true story proved to be even more extraordinary
0:11:32 > 0:11:36than the fantastic myths that were invented to explain it.
0:11:38 > 0:11:40Just like the swallow,
0:11:40 > 0:11:44the Painted Lady butterfly seems to appear magically out of nowhere,
0:11:44 > 0:11:49and that started some extraordinary ideas and controversies.
0:11:49 > 0:11:53The Painted Lady is one of our largest butterflies
0:11:53 > 0:11:56and a familiar summer visitor to our gardens,
0:11:56 > 0:12:01and yet its appearance and disappearance each year has puzzled us for centuries.
0:12:01 > 0:12:05It's only now that we are beginning to understand this extraordinary lifecycle
0:12:05 > 0:12:09and discover where it vanishes each year.
0:12:09 > 0:12:13Early naturalists were confused by sudden appearance of Painted Ladies each spring
0:12:13 > 0:12:15because they were unaware of the connection
0:12:15 > 0:12:19between butterflies and caterpillars.
0:12:19 > 0:12:22For a very long time, it was widely believed
0:12:22 > 0:12:25that butterflies arise from rotting material
0:12:25 > 0:12:30by what was called "spontaneous generation".
0:12:30 > 0:12:32In the 1830s,
0:12:32 > 0:12:37a German scientist named Renous was arrested for heresy
0:12:37 > 0:12:41for claiming that he could change caterpillars into butterflies.
0:12:41 > 0:12:46Arresting someone for something now known to be common knowledge may seem rather extreme,
0:12:46 > 0:12:51but many still believed that caterpillars and butterflies were completely different creatures,
0:12:51 > 0:12:54created by the hand of God.
0:12:56 > 0:12:59Needless to say, people had been well aware of the existence
0:12:59 > 0:13:01of both butterflies and caterpillars
0:13:01 > 0:13:05since the earliest times.
0:13:05 > 0:13:08But the thought that any two were related -
0:13:08 > 0:13:12let alone the same species - seemed impossible,
0:13:12 > 0:13:15and it's easy to see why.
0:13:16 > 0:13:19Not only do caterpillars and butterflies
0:13:19 > 0:13:22look like very different types of animals,
0:13:22 > 0:13:25but the colours and patterns of a caterpillar
0:13:25 > 0:13:28don't match up with those of its adult form.
0:13:28 > 0:13:33The only way to know which larva and which butterfly go together
0:13:33 > 0:13:37is to keep caterpillars and watch them turn into butterflies.
0:13:37 > 0:13:39But it wasn't until the 17th century
0:13:39 > 0:13:43that anyone left a record of doing that.
0:13:43 > 0:13:49One of the first was a remarkable woman named Maria Sibylla Merian.
0:13:49 > 0:13:51Merian was born in Germany
0:13:51 > 0:13:54at a time when women still had little formal education
0:13:54 > 0:13:57and no role in the scientific world.
0:13:57 > 0:14:00But she was an accomplished artist
0:14:00 > 0:14:03and painted plants and insects she saw around her.
0:14:03 > 0:14:07To do that, she kept caterpillars, fed them on leaves,
0:14:07 > 0:14:11and watched them turn into butterflies.
0:14:11 > 0:14:17Merian produced hundreds of beautiful paintings of butterflies in their stages of development,
0:14:17 > 0:14:19along with the plants on which they feed.
0:14:19 > 0:14:22Her drawings are so exquisite and detailed
0:14:22 > 0:14:26that they still rank among the best in the world.
0:14:27 > 0:14:32Among the things she observed with great care were things like this -
0:14:32 > 0:14:37a curious, yet strangely beautiful object.
0:14:37 > 0:14:38It's a chrysalis,
0:14:38 > 0:14:44the intermediate stage between a caterpillar and a butterfly.
0:14:45 > 0:14:49She was one of the first to record the remarkable change
0:14:49 > 0:14:52that takes place in the chrysalis.
0:14:53 > 0:14:58It's one of nature's most extraordinary transformations.
0:15:00 > 0:15:06At the age of 52, she sailed from Europe to South America
0:15:06 > 0:15:11on a two-year expedition to study insects in the tropical jungles of Surinam.
0:15:11 > 0:15:15It was an exceptional journey for any naturalist at the time
0:15:15 > 0:15:17and particularly for a woman.
0:15:17 > 0:15:22When she returned, she produced this beautiful book.
0:15:22 > 0:15:24It turned out to be popular
0:15:24 > 0:15:29because it was one of the few to be published not in the scientific language of Latin,
0:15:29 > 0:15:31but in Dutch.
0:15:31 > 0:15:36Because of this, her work was largely dismissed by scientists of the time.
0:15:36 > 0:15:38But Merian was one of the first naturalists
0:15:38 > 0:15:43to correctly connect the caterpillar with its pupa and the adult form.
0:15:45 > 0:15:48Today, Merian's book is widely recognised
0:15:48 > 0:15:51as a pioneering work of scientific observation,
0:15:51 > 0:15:57and it put an end to the idea of "spontaneous generation".
0:15:58 > 0:16:00Around the same time,
0:16:00 > 0:16:05further evidence for the connection between butterflies and caterpillars
0:16:05 > 0:16:08came from a different source.
0:16:09 > 0:16:14In 1669, a Dutch scientist by the name of Jan Swammerdam
0:16:14 > 0:16:17published the results of experiments which would finally prove
0:16:17 > 0:16:21that the caterpillar and butterfly are one and the same animal.
0:16:21 > 0:16:24Swammerdam was a master of the miniature
0:16:24 > 0:16:29and dissected the caterpillars and pupae of butterflies and moths under a microscope.
0:16:29 > 0:16:31With a steady hand and endless patience,
0:16:31 > 0:16:35he carefully cut into the layers of skin with tiny scissors
0:16:35 > 0:16:39and what he discovered was truly astonishing.
0:16:40 > 0:16:44He found some of the body parts of a butterfly.
0:16:44 > 0:16:48The structures were fragile and not complete,
0:16:48 > 0:16:51but Swammerdam had proved that caterpillar and butterfly
0:16:51 > 0:16:55are indeed one and the same animal.
0:16:57 > 0:17:02We now know that without the caterpillar there can be no butterfly.
0:17:02 > 0:17:06Yet for a very long time, the Painted Lady seemed to be an exception.
0:17:06 > 0:17:10Every spring, the adult butterflies would appear across Britain
0:17:10 > 0:17:14without any sightings of their caterpillars.
0:17:14 > 0:17:17While some butterflies hibernate in Britain,
0:17:17 > 0:17:20there was no sign of Painted Ladies doing so.
0:17:20 > 0:17:26Some speculated that they flew to warmer climates, as birds do.
0:17:26 > 0:17:30But how could a tiny insect cross the English Channel?
0:17:30 > 0:17:32In the 20th century,
0:17:32 > 0:17:34swarms of butterflies moving across Europe
0:17:34 > 0:17:36finally provided evidence
0:17:36 > 0:17:40that Painted Ladies do indeed cross the sea.
0:17:40 > 0:17:45They were found to fly all the way from North Africa to Britain.
0:17:45 > 0:17:51But there were almost no records of Painted Ladies making the reverse trip south
0:17:51 > 0:17:55so, for years, it was thought that Britain must be a dead-end
0:17:55 > 0:17:58for the most northerly stragglers.
0:17:58 > 0:18:04And then, in 2009, the public was asked to help solve the mystery.
0:18:04 > 0:18:07Among 12,000 sightings,
0:18:07 > 0:18:12there were reports of Painted Ladies flying out to sea in the autumn.
0:18:12 > 0:18:16And a radar station detected them flying south
0:18:16 > 0:18:18at heights of 500 metres,
0:18:18 > 0:18:21way beyond the sight of human eyes.
0:18:22 > 0:18:25We now know that the Painted Lady's migration
0:18:25 > 0:18:29is a round trip of over 12,000km.
0:18:29 > 0:18:33But it's not made by any one individual.
0:18:33 > 0:18:36Each only flies part of the way,
0:18:36 > 0:18:39passing on the migratory baton to the next generation.
0:18:39 > 0:18:41It's like a relay race
0:18:41 > 0:18:44with up to six generations of butterflies involved.
0:18:45 > 0:18:49The Painted Lady's epic journey from one continent to the next
0:18:49 > 0:18:52would be a truly astonishing feat for any animal,
0:18:52 > 0:18:56but for a tiny creature like this it seems really extraordinary.
0:18:56 > 0:18:58How does it battle the wind and the weather
0:18:58 > 0:19:01and navigate across vast bodies of water?
0:19:01 > 0:19:05And with no single individual ever undertaking the whole migration,
0:19:05 > 0:19:08how do they find the way?
0:19:09 > 0:19:13It seems that Painted Ladies are pre-programmed
0:19:13 > 0:19:16to either fly north or south.
0:19:16 > 0:19:19This is determined whilst they are still caterpillars,
0:19:19 > 0:19:24possibly by temperature, day length, and also by the plants they feed on.
0:19:24 > 0:19:27But how does this information get passed on
0:19:27 > 0:19:30from caterpillar to butterfly?
0:19:30 > 0:19:34The answer may be hidden within the chrysalis.
0:19:34 > 0:19:39Recently, CT scanners have allowed us to look inside a pupa.
0:19:39 > 0:19:43They reveal that some organs remain intact
0:19:43 > 0:19:46during the transformation.
0:19:46 > 0:19:51A one-day-old pupa clearly shows the gut and breathing tubes,
0:19:51 > 0:19:55which only change slightly as the chrysalis develops.
0:19:58 > 0:20:02Could it be that the brain or nerves also remain intact
0:20:02 > 0:20:06and that memories are passed on?
0:20:06 > 0:20:11Recent experiments in the lab appear to support this idea.
0:20:11 > 0:20:15Scientists taught caterpillars to avoid specific smells
0:20:15 > 0:20:19by linking them with an unpleasant reaction.
0:20:19 > 0:20:21Later on, as adults,
0:20:21 > 0:20:23the same individuals remembered these smells
0:20:23 > 0:20:26and chose to keep away from them.
0:20:26 > 0:20:30If the experiences of a caterpillar can be carried over to the adult,
0:20:30 > 0:20:35then maybe cues for migration can also be passed on.
0:20:36 > 0:20:40Although we've unravelled much of the Painted Lady's life cycle,
0:20:40 > 0:20:42many questions remain...
0:20:42 > 0:20:45How far does each individual travel,
0:20:45 > 0:20:49and do offspring follow similar routes to their ancestors?
0:20:49 > 0:20:52One day, we may know the answers
0:20:52 > 0:20:58but, for now, they remain some of the unsolved mysteries of nature.
0:20:59 > 0:21:04The arrival each spring of our Painted Lady butterflies and our swallows
0:21:04 > 0:21:06never ceases to delight us.
0:21:06 > 0:21:11But now we also understand the extraordinary journeys they undertake
0:21:11 > 0:21:15when they disappear again at the end of summer.