0:00:02 > 0:00:05The natural world is full of extraordinary animals
0:00:05 > 0:00:07with amazing life histories.
0:00:07 > 0:00:12Yet, certain stories are more intriguing than others.
0:00:13 > 0:00:17The mysteries of a butterfly's life cycle,
0:00:17 > 0:00:20or the strange biology of the emperor penguin.
0:00:20 > 0:00:25Some of these creatures were surrounded by fantastic myths
0:00:25 > 0:00:27and misunderstandings.
0:00:27 > 0:00:32Others have only recently revealed their secrets.
0:00:32 > 0:00:37These are the creatures that stand out from the crowd,
0:00:37 > 0:00:41the curiosities that I find particularly fascinating.
0:00:51 > 0:00:52In this programme,
0:00:52 > 0:00:55I explore the lives of two mothers
0:00:55 > 0:00:59who give birth to unusually sized young.
0:00:59 > 0:01:01The giant panda,
0:01:01 > 0:01:03which, in relation to its size,
0:01:03 > 0:01:07produces one of the smallest babies of any mammal.
0:01:07 > 0:01:08And, the kiwi,
0:01:08 > 0:01:12which lays one of the biggest eggs in the bird world.
0:01:13 > 0:01:19Why do pandas and kiwis have babies of such extreme sizes?
0:01:26 > 0:01:30Giant pandas are surely one of the most instantly recognisable
0:01:30 > 0:01:31of all mammals.
0:01:31 > 0:01:33Yet they're also one of the rarest.
0:01:33 > 0:01:37Although they once lived over large parts of Central China,
0:01:37 > 0:01:41today they're restricted to just six mountain ranges.
0:01:51 > 0:01:52Once lowland creatures,
0:01:52 > 0:01:56they now live in higher altitudes, in dense forests.
0:02:01 > 0:02:05Very little was known about the wild lives of these elusive animals,
0:02:05 > 0:02:09and their reproduction remained a mystery for centuries.
0:02:12 > 0:02:16The earliest known ancestors of giant pandas
0:02:16 > 0:02:18were small forest-dwelling creatures
0:02:18 > 0:02:21that existed just over 11 million years ago.
0:02:21 > 0:02:26Larger pandas have been around for about 3 million years.
0:02:28 > 0:02:29The giant pandas we know today
0:02:29 > 0:02:33evolved when bamboo forests were widespread.
0:02:33 > 0:02:36With such an easy, reliable food source,
0:02:36 > 0:02:39they abandoned their carnivorous ways,
0:02:39 > 0:02:41and took to a plant-based diet.
0:02:43 > 0:02:46Today, pandas are a huge attraction in our zoos,
0:02:46 > 0:02:50but, persuading them to breed and care for their young in captivity,
0:02:50 > 0:02:53has been historically very difficult.
0:02:53 > 0:02:56Zookeepers were shocked to discover
0:02:56 > 0:03:01that a newborn panda baby is one 900th of the parent's body weight.
0:03:01 > 0:03:05The smallest of all percentile mammal babies.
0:03:06 > 0:03:10But pandas have been a scientific enigma for a very long time.
0:03:12 > 0:03:14In 1869,
0:03:14 > 0:03:19a French missionary and naturalist called Abbe Armand David
0:03:19 > 0:03:21set off on an expedition to China.
0:03:22 > 0:03:24He was an expert horticulturist,
0:03:24 > 0:03:27and had been commissioned by the Museum of Paris
0:03:27 > 0:03:29to bring back plant specimens.
0:03:30 > 0:03:32On the 21st of March, while collecting,
0:03:32 > 0:03:36he was invited into a local hunter's house for tea and sweets.
0:03:36 > 0:03:39He came across a strange, wiry-haired skin,
0:03:39 > 0:03:41rather like this one.
0:03:43 > 0:03:46He thought it must have come from an unknown species.
0:03:46 > 0:03:48So he asked the hunters to bring him
0:03:48 > 0:03:51a specimen of this mysterious creature.
0:03:51 > 0:03:56After several days, they brought back one that Armand David described
0:03:56 > 0:03:59as "a most excellent black and white bear".
0:03:59 > 0:04:04Excitedly, he prepared the skin, and then he sent it off to Paris.
0:04:06 > 0:04:08Knowing that it might take time to arrive,
0:04:08 > 0:04:12he also wrote a letter to Parisian zoologist Milne-Edwards,
0:04:12 > 0:04:15urging him to publish a brief description of the animal
0:04:15 > 0:04:19for which David proposed the scientific name
0:04:19 > 0:04:21of "Ursus Melanoleucus",
0:04:21 > 0:04:24literally meaning "black and white bear".
0:04:27 > 0:04:31From the very beginning, this new creature seemed odd for a bear.
0:04:31 > 0:04:34It had the carnivorous appearance of other bears,
0:04:34 > 0:04:38but it's diet was actually almost entirely vegetarian.
0:04:39 > 0:04:41It spent up to ten hours a day
0:04:41 > 0:04:45feeding on up to 20kg of bamboo.
0:04:53 > 0:04:57And unlike other bears, the panda did not hibernate,
0:04:57 > 0:04:59and its babies proved to be far smaller
0:04:59 > 0:05:01than those of any other bear.
0:05:03 > 0:05:05In fact, the panda was so different
0:05:05 > 0:05:09that some doubted that it was a bear at all.
0:05:12 > 0:05:16A creature called a "red panda" had been discovered some time before,
0:05:16 > 0:05:18and it had striking similarities
0:05:18 > 0:05:21to Armand David's new black and white bear.
0:05:24 > 0:05:27It, too, fed mainly on plant matter,
0:05:27 > 0:05:29about two-thirds of which was bamboo.
0:05:31 > 0:05:35But this creature was classified as a relative of weasels,
0:05:35 > 0:05:38skunks and raccoons, not bears.
0:05:38 > 0:05:43Perhaps the giant panda was not a bear after all.
0:05:43 > 0:05:46This could explain why its young was so small,
0:05:46 > 0:05:48compared to most other bears.
0:05:51 > 0:05:53Milne-Edwards, the Parisian biologist
0:05:53 > 0:05:57who received the very first giant panda skin and bones,
0:05:57 > 0:06:00compared them to his specimens of red panda.
0:06:01 > 0:06:05He believed that the skull structure and the teeth were very similar.
0:06:05 > 0:06:09This is the small red panda, and this is the giant panda.
0:06:10 > 0:06:15He decided it was a new creature, which deserved a new name,
0:06:15 > 0:06:19so he called it "Ailuropoda", meaning "panda foot".
0:06:19 > 0:06:23Thus it became known as a panda, and not a bear.
0:06:25 > 0:06:29Debate and confusion continued over the panda's identification
0:06:29 > 0:06:31for nearly 100 years.
0:06:32 > 0:06:36Few people had ever seen more than a fleeting glimpse of one,
0:06:36 > 0:06:38and their wild behaviour remained a mystery.
0:06:40 > 0:06:41Then, in the 1920s,
0:06:41 > 0:06:45exploration became very popular amongst the wealthy.
0:06:45 > 0:06:50And the race was on for the first foreigner to hunt and kill a panda.
0:06:52 > 0:06:57It's said that Theodore Roosevelt Jr and Kermit Roosevelt
0:06:57 > 0:07:00were the first Westerners to shoot a panda.
0:07:00 > 0:07:04They persuaded the Field Museum in Chicago to foot the bill
0:07:04 > 0:07:06for an expedition,
0:07:06 > 0:07:10and were secretive about the "golden fleece" that they were hunting.
0:07:10 > 0:07:15After six days of tracking in the same area where Armand David
0:07:15 > 0:07:18had first found his panda, they saw nothing.
0:07:18 > 0:07:20But after moving further south,
0:07:20 > 0:07:23they had a dramatic encounter with a panda that they followed
0:07:23 > 0:07:25and shot dead.
0:07:27 > 0:07:31Sadly, then, the driving force to collect giant pandas
0:07:31 > 0:07:35was money and fame, not biological revelation.
0:07:36 > 0:07:40The only way to learn anything more about the giant panda
0:07:40 > 0:07:43was to watch one in the wild, or to catch one alive.
0:07:45 > 0:07:49In 1936, a baby panda was captured alive.
0:07:49 > 0:07:53Named Su Lin, she was the first to be brought into captivity,
0:07:53 > 0:07:55but sadly died soon after.
0:07:56 > 0:07:59A craze for captive pandas followed.
0:08:00 > 0:08:03And in the late 1950s, one arrived in Britain.
0:08:03 > 0:08:05This particular individual
0:08:05 > 0:08:08would help us to appreciate the complexities
0:08:08 > 0:08:10of the giant panda's biology.
0:08:12 > 0:08:17Perhaps the most famous and popular of all giant pandas was Chi-Chi,
0:08:17 > 0:08:21who came to London Zoo in September 1958.
0:08:22 > 0:08:25She was actually on her way to the United States,
0:08:25 > 0:08:27but the US Customs refused to admit her
0:08:27 > 0:08:30on the grounds that she was a communist,
0:08:30 > 0:08:33or, at any rate, came from a communist country.
0:08:33 > 0:08:36So, London Zoo was able to buy her for £12,000,
0:08:36 > 0:08:40and she was very quickly extremely popular.
0:08:41 > 0:08:45Desmond Morris, who was in charge of London Zoo's mammals at the time,
0:08:45 > 0:08:47decided, however, that she was alone
0:08:47 > 0:08:51and she really ought to be allowed to breed.
0:08:51 > 0:08:52Don't you want to go to Moscow?
0:08:52 > 0:08:55PANDA SQUEAKS
0:08:58 > 0:09:02Here, at last, was a chance to learn more about panda reproduction.
0:09:02 > 0:09:05Desmond Morris travelled to Russia with Chi-Chi
0:09:05 > 0:09:10to introduce her to a potential mate, a male panda called An-An.
0:09:10 > 0:09:14But when they were introduced, all did not go to plan.
0:09:14 > 0:09:18Chi-Chi was in no mood to breed, and was sent back home.
0:09:23 > 0:09:26Clearly, panda mating was not a simple affair,
0:09:26 > 0:09:29and it was a rare sight in the wild, too.
0:09:29 > 0:09:34Now we know that successful mating needs very precise timing.
0:09:34 > 0:09:37Female pandas live a solitary life,
0:09:37 > 0:09:41and are only ready to mate for just one or two days a year.
0:09:41 > 0:09:44Even then, there is a window of 12 to 24 hours.
0:09:44 > 0:09:48It's little wonder that Chi-Chi did not breed.
0:09:49 > 0:09:52Males are attracted to the female's scent,
0:09:52 > 0:09:55and will guard them until they're ready to mate.
0:09:56 > 0:09:59A female in season is a rare thing,
0:09:59 > 0:10:02and competition to mate is worth fighting for.
0:10:02 > 0:10:06GROWLING, BARKING SOUND
0:10:21 > 0:10:25The panda was gaining a reputation for having unusual and difficult
0:10:25 > 0:10:30breeding habits, and its peculiar diet seemed to be responsible.
0:10:36 > 0:10:41In the 1960s, biologists took a fresh look at the giant panda.
0:10:43 > 0:10:47This time, they studied the panda's digestive system,
0:10:47 > 0:10:51and discovered that it was exactly like that of a carnivorous bear.
0:10:52 > 0:10:55So, the giant panda was reclassified,
0:10:55 > 0:11:00and changed from being a relative of the red panda, to being a true bear.
0:11:02 > 0:11:06This also revealed that the giant panda gut was unsuited
0:11:06 > 0:11:07to its plant-based diet,
0:11:07 > 0:11:11and that this oddity might affect its metabolism and breeding.
0:11:11 > 0:11:13But how?
0:11:15 > 0:11:17Female bears feed on rich food
0:11:17 > 0:11:21to build up fat reserves for motherhood and hibernation.
0:11:21 > 0:11:25They then give birth to up to four babies,
0:11:25 > 0:11:28and produce enough milk to feed all of them.
0:11:28 > 0:11:33The well-grown cubs emerge from the den in early spring.
0:11:33 > 0:11:36Panda reproduction has significant differences.
0:11:36 > 0:11:39They don't have enough fat reserves to hibernate,
0:11:39 > 0:11:43and usually produce only one small baby at a time.
0:11:43 > 0:11:45Their poor vegetarian diet
0:11:45 > 0:11:48seems to have had an impact on their breeding.
0:11:49 > 0:11:53Bamboo presents a lot of problems as a food.
0:11:53 > 0:11:56To start with, it's very low in energy.
0:11:56 > 0:11:59Secondly, the panda has to sit upright
0:11:59 > 0:12:03in order to release its front paws, in order to handle the bamboo.
0:12:03 > 0:12:07On top of that, the panda's gut is very short,
0:12:07 > 0:12:09like that of a carnivore,
0:12:09 > 0:12:12so that the food, when it's eaten,
0:12:12 > 0:12:15passes through its body very quickly.
0:12:15 > 0:12:17As a consequence of all those difficulties,
0:12:17 > 0:12:23the panda only manages to extract about 20% of the little energy
0:12:23 > 0:12:24that bamboo does contain.
0:12:26 > 0:12:30So, the Panda's ancestors switched from being meat eaters
0:12:30 > 0:12:33to plant eaters, and this compromised their digestive systems
0:12:33 > 0:12:37and greatly affected their metabolism.
0:12:37 > 0:12:39They became slow-moving,
0:12:39 > 0:12:43and their breeding changed to cope with such a low-energy diet.
0:12:46 > 0:12:48In the late 1960s,
0:12:48 > 0:12:52efforts to understand panda reproduction became more crucial
0:12:52 > 0:12:54as their numbers in the wild plummeted.
0:12:54 > 0:12:58The Worldwide Fund for Nature was formed,
0:12:58 > 0:13:02and their famous logo was a panda based on Chi-Chi.
0:13:05 > 0:13:09The Chinese built a state-of-the-art reserve in Wolong,
0:13:09 > 0:13:13leading to a new era of great progress in panda breeding.
0:13:16 > 0:13:20Small babies weighing an average of just 100g
0:13:20 > 0:13:24are now regularly born in captivity, and are fed on milk for many months.
0:13:27 > 0:13:29On a poor diet of bamboo,
0:13:29 > 0:13:32pandas are unable to grow bigger babies in the womb,
0:13:32 > 0:13:37so they give birth to small young, and use their limited nutrition
0:13:37 > 0:13:39to produce food for them after birth.
0:13:41 > 0:13:42As with all mammals,
0:13:42 > 0:13:45milk is essential to the baby's development,
0:13:45 > 0:13:49and ensures even the tiniest babies grow up to be giants.
0:13:52 > 0:13:56So, the giant panda is not a racoon, it's a bear.
0:13:56 > 0:14:01A bear that spends nearly all its time eating vegetation,
0:14:01 > 0:14:03and that's nearly always bamboo.
0:14:03 > 0:14:07Which, although it can occasionally produce twins,
0:14:07 > 0:14:11normally gives birth to just one baby at a time.
0:14:11 > 0:14:12And that a very small one.
0:14:14 > 0:14:17But those are the consequences if you are a bear
0:14:17 > 0:14:21that has become adapted to living on a very low-energy diet.
0:14:23 > 0:14:26The panda's tiny baby is an oddity,
0:14:26 > 0:14:30but the only solution for a bamboo-eating bear.
0:14:32 > 0:14:33In New Zealand,
0:14:33 > 0:14:38there's a very different creature that has just as curious a story.
0:14:45 > 0:14:48The kiwi is one of the strangest of birds.
0:14:48 > 0:14:51WARBLING
0:14:51 > 0:14:55It sleeps underground, and usually only comes out at night.
0:14:57 > 0:15:02It can't fly, and its brown feathers resemble a thick coat of fur.
0:15:04 > 0:15:08Its small eyes are virtually useless and it finds its food
0:15:08 > 0:15:10with its sensitive beak.
0:15:10 > 0:15:15It's a peculiar lifestyle, more like that of a nocturnal mammal.
0:15:16 > 0:15:21But most remarkable of all, it lays the biggest egg of any bird
0:15:21 > 0:15:23in proportion to its body.
0:15:25 > 0:15:28A kiwi is roughly the size of a chicken.
0:15:28 > 0:15:30But its egg...
0:15:30 > 0:15:33..is more than seven times as large as a chicken's egg.
0:15:33 > 0:15:36And it can weigh half a kilo.
0:15:36 > 0:15:39It's hard to imagine how this huge egg
0:15:39 > 0:15:42could fit into a kiwi's small body.
0:15:42 > 0:15:43And, yet, it does.
0:15:44 > 0:15:46Just before the egg is laid,
0:15:46 > 0:15:48it takes up so much room inside the female
0:15:48 > 0:15:50that her belly almost touches the ground.
0:15:50 > 0:15:54And when she lays it, it's equivalent, in terms of weight,
0:15:54 > 0:15:58to a human mother giving birth to a four-year-old child.
0:16:02 > 0:16:06Most birds only take around a day to produce an egg.
0:16:06 > 0:16:11But because the kiwi's is so large, it takes almost ten days.
0:16:15 > 0:16:20The female's inner organs become so compressed, she can't feed.
0:16:24 > 0:16:27Expelling the monster egg is also a huge effort.
0:16:37 > 0:16:40Why is the kiwi such a curiosity?
0:16:40 > 0:16:43And why does it lay such a gigantic egg?
0:16:47 > 0:16:50The kiwi didn't come to the attention of Europeans
0:16:50 > 0:16:54until about 200 years ago, when a dried specimen, much like this one,
0:16:54 > 0:16:58arrived in England on a merchant vessel.
0:16:58 > 0:17:00It puzzled those who saw it.
0:17:00 > 0:17:03It was clearly a bird, but it had no wings.
0:17:04 > 0:17:09Its feathers were soft and hairy, more like mammalian fur.
0:17:09 > 0:17:11And it had these strange, long whiskers
0:17:11 > 0:17:13around the base of the beak.
0:17:13 > 0:17:16The first specimen was examined and described by a naturalist
0:17:16 > 0:17:19at the British Museum, a man called George Shaw,
0:17:19 > 0:17:24who gave it the scientific name Apteryx, which, in Greek,
0:17:24 > 0:17:26means "wingless creature".
0:17:26 > 0:17:30Shaw studied the skin, together with his colleague John Latham,
0:17:30 > 0:17:34but the two men disagreed as to what kind of bird it could be.
0:17:34 > 0:17:36They knew it had come from New Zealand,
0:17:36 > 0:17:40and Shaw thought it was probably related to the ratites,
0:17:40 > 0:17:44a group of primitive flightless birds that includes the ostrich.
0:17:45 > 0:17:47Latham, on the other hand,
0:17:47 > 0:17:50was convinced that it was a kind of penguin.
0:17:51 > 0:17:54When Shaw published his description in 1813,
0:17:54 > 0:17:58it was accompanied by an artist's impression of the living bird.
0:17:58 > 0:17:59This is it.
0:17:59 > 0:18:03Clearly, the artist must have been swayed by Latham's argument,
0:18:03 > 0:18:05rather than Shaw's.
0:18:05 > 0:18:08He shows the kiwi standing bolt upright and very tall,
0:18:08 > 0:18:10much like a penguin.
0:18:11 > 0:18:15And so the kiwi was introduced to the scientific world.
0:18:17 > 0:18:22Shaw's kiwi continued to provoke debate long after his death.
0:18:22 > 0:18:26The most eminent zoologists of the time disagreed
0:18:26 > 0:18:28over the nature of the strange creature
0:18:28 > 0:18:31and, indeed, whether it actually existed.
0:18:34 > 0:18:38It's not surprising that many wondered if the kiwi was a hoax.
0:18:38 > 0:18:41It was a time when travellers were bringing back all kinds of strange
0:18:41 > 0:18:45creatures from far-flung places, and many were frauds,
0:18:45 > 0:18:48put together from parts of different animals.
0:18:49 > 0:18:51Almost 20 years later,
0:18:51 > 0:18:54and with only one specimen on which to make a judgment,
0:18:54 > 0:19:00the Zoological Society of London made an appeal for more kiwi skins.
0:19:00 > 0:19:04So, other specimens finally began to arrive in Britain.
0:19:07 > 0:19:10European naturalists may have been mystified by the kiwi,
0:19:10 > 0:19:12but the Maori people of New Zealand
0:19:12 > 0:19:16had admired and respected the bird for a very long time.
0:19:18 > 0:19:20According to Maori legend,
0:19:20 > 0:19:23the kiwi lost its wings at the request of Tane,
0:19:23 > 0:19:24the god of the forest.
0:19:24 > 0:19:30Tane asked all birds to go down to live on the forest floor
0:19:30 > 0:19:32and feed on the insects that were killing the trees.
0:19:32 > 0:19:38But only the kiwi agreed, and gave up his wings and beautiful feathers.
0:19:39 > 0:19:43So, the kiwi has always been sacred to the Maori.
0:19:48 > 0:19:52Back in Europe, others now joined in the debate.
0:19:53 > 0:19:55Professor Richard Owen,
0:19:55 > 0:19:58the most powerful British zoologist of the time,
0:19:58 > 0:20:00studied the anatomy of the kiwi in detail.
0:20:03 > 0:20:07Comparing its features to those of other birds,
0:20:07 > 0:20:10he concluded that it was most closely related
0:20:10 > 0:20:13to that group of flightless birds called the ratites.
0:20:20 > 0:20:23The ratites include the largest birds in the world -
0:20:23 > 0:20:27the emu, the South American rhea,
0:20:27 > 0:20:30the cassowary, and the ostrich.
0:20:30 > 0:20:33All of them stand nearly as tall as a human being.
0:20:36 > 0:20:39So, could the kiwi's large egg have anything to do
0:20:39 > 0:20:43with its possible relationship to these larger birds?
0:20:43 > 0:20:47To answer that, we need to look at its close relatives.
0:20:52 > 0:20:55The emu lives nearby in Australia.
0:20:57 > 0:21:00It has remnants of wings, but it can't fly.
0:21:01 > 0:21:03And its feathers are similar to those of the kiwi,
0:21:03 > 0:21:05hairy and plume-like.
0:21:07 > 0:21:10They simply serve to protect the bird, and keep it warm.
0:21:13 > 0:21:18So, how similar are the emu and the kiwi when it comes to their eggs?
0:21:19 > 0:21:22This is the egg of a kiwi.
0:21:22 > 0:21:25And this is the egg of an emu.
0:21:25 > 0:21:27More or less the same size.
0:21:27 > 0:21:30And, yet, the kiwi is the size of a chicken,
0:21:30 > 0:21:33but an emu is almost as tall as I am.
0:21:33 > 0:21:37Why should such a big egg come from such a small bird?
0:21:37 > 0:21:39Well, for a long time,
0:21:39 > 0:21:44it was argued that that was because the ancestors of the kiwi
0:21:44 > 0:21:47were once as big as the emu and, over time,
0:21:47 > 0:21:51they got smaller, but the egg remained the same size.
0:21:51 > 0:21:55And the originator of that theory was, in fact, Richard Owen himself.
0:21:58 > 0:22:05In 1839, Owen acquired the fragment of a strange bone from New Zealand.
0:22:07 > 0:22:11After studying it closely, he suggested it came from a gigantic,
0:22:11 > 0:22:14flightless bird that was probably extinct.
0:22:15 > 0:22:19From this meagre evidence, he reconstructed the entire animal,
0:22:19 > 0:22:23a giant moa.
0:22:23 > 0:22:26Owen was ridiculed by other scientists at the time,
0:22:26 > 0:22:30who considered such a deduction on one bone outrageous.
0:22:30 > 0:22:33But in due course, other moa birds were found,
0:22:33 > 0:22:35and he was proved to be correct.
0:22:37 > 0:22:40Owen's discoveries seemed to confirm the idea
0:22:40 > 0:22:44that the kiwi could have evolved from a big bird like the moa,
0:22:44 > 0:22:48and that maybe its egg was a relic from a giant ancestor.
0:22:51 > 0:22:54Large, flightless birds first appeared
0:22:54 > 0:22:57when the dinosaurs became extinct.
0:22:58 > 0:23:01This is a southern cassowary.
0:23:01 > 0:23:05It's a native of northern Australia and New Guinea.
0:23:05 > 0:23:07And the males, like this one,
0:23:07 > 0:23:11are extremely territorial and, therefore, dangerous.
0:23:11 > 0:23:14They will attack you, as I know to my cost.
0:23:14 > 0:23:16So, I'm not going to get in there with him.
0:23:16 > 0:23:19Instead, I'll see if I can tempt him
0:23:19 > 0:23:22with a few grapes, which are one of his favourite foods.
0:23:24 > 0:23:27Like the kiwi, the cassowary evolved
0:23:27 > 0:23:31in an area where the adult birds have no ground predators.
0:23:31 > 0:23:34As a consequence, they don't fly.
0:23:35 > 0:23:38Flying is a very energy-demanding business.
0:23:38 > 0:23:42If birds don't need to fly, birds don't fly.
0:23:46 > 0:23:50Until recently, it was thought that all the ratites
0:23:50 > 0:23:52had one common flightless ancestor.
0:23:54 > 0:23:57This seemed possible because the places where they live today
0:23:57 > 0:24:01were once part of a supercontinent called Gondwanaland.
0:24:02 > 0:24:07When this continent split up around 150 million years ago,
0:24:07 > 0:24:08the fragments drifted apart.
0:24:10 > 0:24:14Each one might independently have evolved its own flightless species,
0:24:14 > 0:24:16including New Zealand.
0:24:20 > 0:24:22When Owen came to examine the skeleton of a kiwi,
0:24:22 > 0:24:26he noticed something very strange about the skull.
0:24:27 > 0:24:30Most bird skulls have two little tiny holes there
0:24:30 > 0:24:33at the base of the beak, which accommodates the nostrils,
0:24:33 > 0:24:34through which they smell.
0:24:34 > 0:24:38But there are no such things here on the kiwi skull.
0:24:38 > 0:24:43Instead, the nostrils are right at the tip of the beak.
0:24:45 > 0:24:49Not only that, but these big spaces on either side the skull,
0:24:49 > 0:24:53which in most birds hold the big eye,
0:24:53 > 0:24:58are, in fact, filled by the olfactory organ, the smelling organ.
0:24:59 > 0:25:03And Owen deduced from those two facts that this, therefore,
0:25:03 > 0:25:07must belong to a bird that was nocturnal.
0:25:07 > 0:25:08And he was quite right.
0:25:13 > 0:25:15The kiwi is mostly active at night,
0:25:15 > 0:25:19and uses both touch and smell to find its food.
0:25:22 > 0:25:26The long whiskers allow it to feel its way in the dark,
0:25:26 > 0:25:28and special sensory cells in the beak
0:25:28 > 0:25:30detect the movement of prey underground.
0:25:32 > 0:25:35But why did the kiwi choose this unusual lifestyle?
0:25:37 > 0:25:41It's possible that the moas had already taken the role
0:25:41 > 0:25:43of giant plant eaters during the day,
0:25:43 > 0:25:47so the kiwi may have shrunk down to feed on small insects at night.
0:25:49 > 0:25:52Owen had shed light on both the moa and kiwi,
0:25:52 > 0:25:55but he was wrong about their true relationship.
0:25:57 > 0:26:01Evidence from DNA has now revealed that the kiwi is, in fact,
0:26:01 > 0:26:05more closely related to flightless birds of Africa and Australia.
0:26:06 > 0:26:10This means that the moa and the kiwi had different ancestors,
0:26:10 > 0:26:14and flightlessness must have evolved in New Zealand
0:26:14 > 0:26:16on two separate occasions.
0:26:19 > 0:26:21It's an extraordinary thought.
0:26:21 > 0:26:25But another recent finding supports the idea.
0:26:26 > 0:26:30Genetic techniques have shown that the closest relative of the ratites
0:26:30 > 0:26:35is, in fact, a small flying bird, the tinamou.
0:26:37 > 0:26:40Tinamous are partridge-like birds from South America
0:26:40 > 0:26:42that spend much of their time on the ground,
0:26:42 > 0:26:45but they can fly perfectly well.
0:26:46 > 0:26:49So, it seems that birds like this may have flapped their way
0:26:49 > 0:26:54between the continents, giving rise to the different ratites,
0:26:54 > 0:26:55including the kiwi.
0:27:01 > 0:27:06We've unravelled much of the mystery around the kiwi's curious lifestyle,
0:27:06 > 0:27:08but one question remains.
0:27:08 > 0:27:12What could be the reason for its huge egg?
0:27:14 > 0:27:18Some think that the large egg may give the kiwi a competitive edge,
0:27:18 > 0:27:22by allowing it to hatch a chick that is already very well developed.
0:27:23 > 0:27:25It's like a miniature adult,
0:27:25 > 0:27:28and the large yolk sac provides nourishment
0:27:28 > 0:27:31until it becomes fully independent.
0:27:37 > 0:27:41So, it seems that the kiwi's gigantic egg may have evolved
0:27:41 > 0:27:43to suit its lifestyle and habitat.
0:27:43 > 0:27:47Most birds have to lay their eggs as soon as possible
0:27:47 > 0:27:50to avoid being weighed down when flying.
0:27:50 > 0:27:54But the flightless kiwi has no such problem, and can, therefore,
0:27:54 > 0:27:58keep the heavy egg in its body for longer, and let it grow bigger.
0:27:59 > 0:28:04And in an environment with few predators, it may make sense to,
0:28:04 > 0:28:08as it were, put all your eggs in one basket and raise a single chick
0:28:08 > 0:28:10that is big and strong,
0:28:10 > 0:28:13and therefore has the better chance of survival.
0:28:14 > 0:28:18The kiwi and the panda both produce young that stand out
0:28:18 > 0:28:19because of their size,
0:28:19 > 0:28:25but are a perfect fit for the life choices of these curious creatures.