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The natural world
is full of extraordinary animals
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with amazing life histories.
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Yet, certain stories
are more intriguing than others.
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The mysteries
of a butterfly's life cycle,
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or the strange biology
of the emperor penguin.
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Some of these creatures were
surrounded by fantastic myths
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and misunderstandings.
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Others have only recently
revealed their secrets.
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These are the creatures
that stand out from the crowd,
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the curiosities that I find
particularly fascinating.
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In this programme,
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I explore the lives of two mothers
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who give birth
to unusually sized young.
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The giant panda,
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which, in relation to its size,
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produces one of the smallest
babies of any mammal.
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And, the kiwi,
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which lays one of the biggest eggs
in the bird world.
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Why do pandas and kiwis have babies
of such extreme sizes?
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Giant pandas are surely one of the
most instantly recognisable
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of all mammals.
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Yet they're also one of the rarest.
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Although they once lived
over large parts of Central China,
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today they're restricted
to just six mountain ranges.
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Once lowland creatures,
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they now live in higher altitudes,
in dense forests.
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Very little was known about the wild
lives of these elusive animals,
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and their reproduction remained
a mystery for centuries.
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The earliest known ancestors
of giant pandas
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were small forest-dwelling creatures
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that existed just over
11 million years ago.
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Larger pandas have been around
for about 3 million years.
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The giant pandas we know today
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evolved when bamboo forests
were widespread.
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With such an easy,
reliable food source,
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they abandoned
their carnivorous ways,
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and took to a plant-based diet.
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Today, pandas are a huge attraction
in our zoos,
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but, persuading them to breed and
care for their young in captivity,
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has been historically
very difficult.
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Zookeepers were shocked to discover
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that a newborn panda baby is one
900th of the parent's body weight.
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The smallest of all
percentile mammal babies.
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But pandas have been a scientific
enigma for a very long time.
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In 1869,
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a French missionary and naturalist
called Abbe Armand David
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set off on an expedition to China.
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He was an expert horticulturist,
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and had been commissioned
by the Museum of Paris
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to bring back plant specimens.
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On the 21st of March,
while collecting,
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he was invited into a local hunter's
house for tea and sweets.
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He came across a strange,
wiry-haired skin,
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rather like this one.
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He thought it must have come
from an unknown species.
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So he asked the hunters to bring him
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a specimen
of this mysterious creature.
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After several days, they brought
back one that Armand David described
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as "a most excellent
black and white bear".
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Excitedly, he prepared the skin,
and then he sent it off to Paris.
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Knowing that it might
take time to arrive,
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he also wrote a letter
to Parisian zoologist Milne-Edwards,
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urging him to publish a brief
description of the animal
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for which David proposed the
scientific name
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of "Ursus Melanoleucus",
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literally meaning
"black and white bear".
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From the very beginning, this new
creature seemed odd for a bear.
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It had the carnivorous appearance
of other bears,
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but it's diet was actually
almost entirely vegetarian.
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It spent up to ten hours a day
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feeding on up to 20kg of bamboo.
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And unlike other bears,
the panda did not hibernate,
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and its babies proved to be
far smaller
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than those of any other bear.
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In fact, the panda was so different
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that some doubted
that it was a bear at all.
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A creature called a "red panda" had
been discovered some time before,
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and it had striking similarities
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to Armand David's new
black and white bear.
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It, too, fed mainly on plant matter,
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about two-thirds
of which was bamboo.
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But this creature was classified
as a relative of weasels,
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skunks and raccoons, not bears.
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Perhaps the giant panda
was not a bear after all.
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This could explain
why its young was so small,
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compared to most other bears.
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Milne-Edwards,
the Parisian biologist
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who received the very first giant
panda skin and bones,
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compared them
to his specimens of red panda.
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He believed that the skull structure
and the teeth were very similar.
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This is the small red panda,
and this is the giant panda.
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He decided it was a new creature,
which deserved a new name,
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so he called it "Ailuropoda",
meaning "panda foot".
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Thus it became known as a panda,
and not a bear.
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Debate and confusion continued over
the panda's identification
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for nearly 100 years.
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Few people had ever seen more than
a fleeting glimpse of one,
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and their wild behaviour
remained a mystery.
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Then, in the 1920s,
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exploration became very popular
amongst the wealthy.
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And the race was on for the first
foreigner to hunt and kill a panda.
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It's said that Theodore
Roosevelt Jr and Kermit Roosevelt
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were the first Westerners
to shoot a panda.
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They persuaded the Field Museum
in Chicago to foot the bill
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for an expedition,
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and were secretive about the "golden
fleece" that they were hunting.
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After six days of tracking in the
same area where Armand David
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had first found his panda,
they saw nothing.
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But after moving further south,
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they had a dramatic encounter with
a panda that they followed
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and shot dead.
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Sadly, then, the driving force
to collect giant pandas
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was money and fame,
not biological revelation.
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The only way to learn anything
more about the giant panda
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was to watch one in the wild,
or to catch one alive.
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In 1936, a baby panda
was captured alive.
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Named Su Lin, she was the first
to be brought into captivity,
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but sadly died soon after.
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A craze for captive pandas followed.
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And in the late 1950s,
one arrived in Britain.
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This particular individual
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would help us to appreciate
the complexities
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of the giant panda's biology.
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Perhaps the most famous and popular
of all giant pandas was Chi-Chi,
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who came to London Zoo
in September 1958.
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She was actually on her way
to the United States,
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but the US Customs
refused to admit her
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on the grounds
that she was a communist,
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or, at any rate, came from
a communist country.
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So, London Zoo was able
to buy her for £12,000,
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and she was very quickly
extremely popular.
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Desmond Morris, who was in charge
of London Zoo's mammals at the time,
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decided, however, that she was alone
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and she really ought to be
allowed to breed.
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Don't you want to go to Moscow?
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PANDA SQUEAKS
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Here, at last, was a chance to learn
more about panda reproduction.
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Desmond Morris travelled
to Russia with Chi-Chi
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to introduce her to a potential
mate, a male panda called An-An.
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But when they were introduced,
all did not go to plan.
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Chi-Chi was in no mood to breed,
and was sent back home.
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Clearly, panda mating
was not a simple affair,
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and it was a rare sight
in the wild, too.
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Now we know that successful mating
needs very precise timing.
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Female pandas live a solitary life,
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and are only ready to mate
for just one or two days a year.
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Even then, there is a window
of 12 to 24 hours.
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It's little wonder
that Chi-Chi did not breed.
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Males are attracted
to the female's scent,
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and will guard them
until they're ready to mate.
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A female in season is a rare thing,
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and competition to mate
is worth fighting for.
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GROWLING, BARKING SOUND
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The panda was gaining a reputation
for having unusual and difficult
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breeding habits, and its peculiar
diet seemed to be responsible.
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In the 1960s, biologists took
a fresh look at the giant panda.
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This time, they studied
the panda's digestive system,
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and discovered that it was exactly
like that of a carnivorous bear.
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So, the giant panda
was reclassified,
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and changed from being a relative of
the red panda, to being a true bear.
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This also revealed that the
giant panda gut was unsuited
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to its plant-based diet,
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and that this oddity might affect
its metabolism and breeding.
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But how?
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Female bears feed on rich food
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to build up fat reserves
for motherhood and hibernation.
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They then give birth
to up to four babies,
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and produce enough milk
to feed all of them.
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The well-grown cubs emerge
from the den in early spring.
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Panda reproduction
has significant differences.
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They don't have enough
fat reserves to hibernate,
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and usually produce
only one small baby at a time.
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Their poor vegetarian diet
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seems to have had an impact
on their breeding.
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Bamboo presents a lot of problems
as a food.
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To start with,
it's very low in energy.
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Secondly,
the panda has to sit upright
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in order to release its front paws,
in order to handle the bamboo.
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On top of that,
the panda's gut is very short,
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like that of a carnivore,
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so that the food, when it's eaten,
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passes through
its body very quickly.
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As a consequence
of all those difficulties,
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the panda only manages to extract
about 20% of the little energy
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that bamboo does contain.
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So, the Panda's ancestors
switched from being meat eaters
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to plant eaters, and this
compromised their digestive systems
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and greatly affected
their metabolism.
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They became slow-moving,
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and their breeding changed
to cope with such a low-energy diet.
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In the late 1960s,
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efforts to understand panda
reproduction became more crucial
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as their numbers
in the wild plummeted.
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The Worldwide Fund for Nature
was formed,
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and their famous logo
was a panda based on Chi-Chi.
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The Chinese built a
state-of-the-art reserve in Wolong,
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leading to a new era of great
progress in panda breeding.
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Small babies weighing
an average of just 100g
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are now regularly born in captivity,
and are fed on milk for many months.
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On a poor diet of bamboo,
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pandas are unable to grow
bigger babies in the womb,
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so they give birth to small young,
and use their limited nutrition
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to produce food for them
after birth.
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As with all mammals,
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milk is essential
to the baby's development,
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and ensures even the tiniest babies
grow up to be giants.
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So, the giant panda
is not a racoon, it's a bear.
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A bear that spends nearly all its
time eating vegetation,
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and that's nearly always bamboo.
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Which, although it can
occasionally produce twins,
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normally gives birth
to just one baby at a time.
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And that a very small one.
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But those are the consequences
if you are a bear
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that has become adapted to living
on a very low-energy diet.
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The panda's tiny baby is an oddity,
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but the only solution
for a bamboo-eating bear.
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In New Zealand,
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there's a very different creature
that has just as curious a story.
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The kiwi is one of
the strangest of birds.
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WARBLING
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It sleeps underground, and usually
only comes out at night.
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It can't fly, and its brown feathers
resemble a thick coat of fur.
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Its small eyes are virtually
useless and it finds its food
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with its sensitive beak.
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It's a peculiar lifestyle, more like
that of a nocturnal mammal.
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But most remarkable of all,
it lays the biggest egg of any bird
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in proportion to its body.
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A kiwi is roughly the size
of a chicken.
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But its egg...
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..is more than seven times
as large as a chicken's egg.
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And it can weigh half a kilo.
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It's hard to imagine
how this huge egg
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could fit into a kiwi's
small body.
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And, yet, it does.
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Just before the egg is laid,
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it takes up so much room
inside the female
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that her belly
almost touches the ground.
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And when she lays it,
it's equivalent, in terms of weight,
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to a human mother giving birth
to a four-year-old child.
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Most birds only take around a day
to produce an egg.
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But because the kiwi's is so large,
it takes almost ten days.
242
00:16:15,920 --> 00:16:20,240
The female's inner organs become
so compressed, she can't feed.
243
00:16:24,080 --> 00:16:27,880
Expelling the monster egg
is also a huge effort.
244
00:16:37,840 --> 00:16:40,760
Why is the kiwi such a curiosity?
245
00:16:40,760 --> 00:16:43,960
And why does it lay
such a gigantic egg?
246
00:16:47,040 --> 00:16:50,280
The kiwi didn't come
to the attention of Europeans
247
00:16:50,280 --> 00:16:54,920
until about 200 years ago, when a
dried specimen, much like this one,
248
00:16:54,920 --> 00:16:58,080
arrived in England
on a merchant vessel.
249
00:16:58,080 --> 00:17:00,080
It puzzled those who saw it.
250
00:17:00,080 --> 00:17:03,320
It was clearly a bird,
but it had no wings.
251
00:17:04,360 --> 00:17:09,360
Its feathers were soft and hairy,
more like mammalian fur.
252
00:17:09,360 --> 00:17:11,720
And it had these strange,
long whiskers
253
00:17:11,720 --> 00:17:13,440
around the base of the beak.
254
00:17:13,440 --> 00:17:16,080
The first specimen was examined
and described by a naturalist
255
00:17:16,080 --> 00:17:19,640
at the British Museum,
a man called George Shaw,
256
00:17:19,640 --> 00:17:24,000
who gave it the scientific name
Apteryx, which, in Greek,
257
00:17:24,000 --> 00:17:26,600
means "wingless creature".
258
00:17:26,600 --> 00:17:30,320
Shaw studied the skin, together
with his colleague John Latham,
259
00:17:30,320 --> 00:17:34,240
but the two men disagreed as to
what kind of bird it could be.
260
00:17:34,240 --> 00:17:36,600
They knew it had come
from New Zealand,
261
00:17:36,600 --> 00:17:40,600
and Shaw thought it was probably
related to the ratites,
262
00:17:40,600 --> 00:17:44,320
a group of primitive flightless
birds that includes the ostrich.
263
00:17:45,520 --> 00:17:47,040
Latham, on the other hand,
264
00:17:47,040 --> 00:17:50,000
was convinced that
it was a kind of penguin.
265
00:17:51,520 --> 00:17:54,320
When Shaw published
his description in 1813,
266
00:17:54,320 --> 00:17:58,280
it was accompanied by an artist's
impression of the living bird.
267
00:17:58,280 --> 00:17:59,480
This is it.
268
00:17:59,480 --> 00:18:03,840
Clearly, the artist must have been
swayed by Latham's argument,
269
00:18:03,840 --> 00:18:05,880
rather than Shaw's.
270
00:18:05,880 --> 00:18:08,920
He shows the kiwi standing
bolt upright and very tall,
271
00:18:08,920 --> 00:18:10,240
much like a penguin.
272
00:18:11,520 --> 00:18:15,000
And so the kiwi was introduced
to the scientific world.
273
00:18:17,800 --> 00:18:22,560
Shaw's kiwi continued to provoke
debate long after his death.
274
00:18:22,560 --> 00:18:26,320
The most eminent zoologists
of the time disagreed
275
00:18:26,320 --> 00:18:28,880
over the nature
of the strange creature
276
00:18:28,880 --> 00:18:31,680
and, indeed,
whether it actually existed.
277
00:18:34,520 --> 00:18:38,200
It's not surprising that many
wondered if the kiwi was a hoax.
278
00:18:38,200 --> 00:18:41,720
It was a time when travellers were
bringing back all kinds of strange
279
00:18:41,720 --> 00:18:45,440
creatures from far-flung places,
and many were frauds,
280
00:18:45,440 --> 00:18:48,880
put together from parts
of different animals.
281
00:18:49,920 --> 00:18:51,720
Almost 20 years later,
282
00:18:51,720 --> 00:18:54,960
and with only one specimen
on which to make a judgment,
283
00:18:54,960 --> 00:19:00,960
the Zoological Society of London
made an appeal for more kiwi skins.
284
00:19:00,960 --> 00:19:04,960
So, other specimens finally
began to arrive in Britain.
285
00:19:07,480 --> 00:19:10,560
European naturalists may have been
mystified by the kiwi,
286
00:19:10,560 --> 00:19:12,680
but the Maori people of New Zealand
287
00:19:12,680 --> 00:19:16,880
had admired and respected
the bird for a very long time.
288
00:19:18,160 --> 00:19:20,160
According to Maori legend,
289
00:19:20,160 --> 00:19:23,240
the kiwi lost its wings at the
request of Tane,
290
00:19:23,240 --> 00:19:24,760
the god of the forest.
291
00:19:24,760 --> 00:19:30,000
Tane asked all birds to go down
to live on the forest floor
292
00:19:30,000 --> 00:19:32,920
and feed on the insects
that were killing the trees.
293
00:19:32,920 --> 00:19:38,400
But only the kiwi agreed, and gave
up his wings and beautiful feathers.
294
00:19:39,760 --> 00:19:43,360
So, the kiwi has always
been sacred to the Maori.
295
00:19:48,760 --> 00:19:52,400
Back in Europe,
others now joined in the debate.
296
00:19:53,640 --> 00:19:55,160
Professor Richard Owen,
297
00:19:55,160 --> 00:19:58,120
the most powerful British
zoologist of the time,
298
00:19:58,120 --> 00:20:00,840
studied the anatomy of the kiwi
in detail.
299
00:20:03,960 --> 00:20:07,120
Comparing its features
to those of other birds,
300
00:20:07,120 --> 00:20:10,440
he concluded that it
was most closely related
301
00:20:10,440 --> 00:20:13,280
to that group of flightless birds
called the ratites.
302
00:20:20,040 --> 00:20:23,720
The ratites include the largest
birds in the world -
303
00:20:23,720 --> 00:20:27,160
the emu, the South American rhea,
304
00:20:27,160 --> 00:20:30,080
the cassowary, and the ostrich.
305
00:20:30,080 --> 00:20:33,720
All of them stand
nearly as tall as a human being.
306
00:20:36,280 --> 00:20:39,920
So, could the kiwi's large egg
have anything to do
307
00:20:39,920 --> 00:20:43,520
with its possible relationship
to these larger birds?
308
00:20:43,520 --> 00:20:47,720
To answer that, we need
to look at its close relatives.
309
00:20:52,920 --> 00:20:55,640
The emu lives nearby in Australia.
310
00:20:57,040 --> 00:21:00,000
It has remnants of wings,
but it can't fly.
311
00:21:01,280 --> 00:21:03,920
And its feathers are similar
to those of the kiwi,
312
00:21:03,920 --> 00:21:05,640
hairy and plume-like.
313
00:21:07,320 --> 00:21:10,480
They simply serve to protect
the bird, and keep it warm.
314
00:21:13,120 --> 00:21:18,040
So, how similar are the emu and the
kiwi when it comes to their eggs?
315
00:21:19,640 --> 00:21:22,040
This is the egg of a kiwi.
316
00:21:22,040 --> 00:21:25,120
And this is the egg of an emu.
317
00:21:25,120 --> 00:21:27,480
More or less the same size.
318
00:21:27,480 --> 00:21:30,320
And, yet, the kiwi is the size
of a chicken,
319
00:21:30,320 --> 00:21:33,480
but an emu is almost
as tall as I am.
320
00:21:33,480 --> 00:21:37,640
Why should such a big egg
come from such a small bird?
321
00:21:37,640 --> 00:21:39,480
Well, for a long time,
322
00:21:39,480 --> 00:21:44,000
it was argued that that was because
the ancestors of the kiwi
323
00:21:44,000 --> 00:21:47,880
were once as big as the emu
and, over time,
324
00:21:47,880 --> 00:21:51,480
they got smaller, but the egg
remained the same size.
325
00:21:51,480 --> 00:21:55,760
And the originator of that theory
was, in fact, Richard Owen himself.
326
00:21:58,960 --> 00:22:05,240
In 1839, Owen acquired the fragment
of a strange bone from New Zealand.
327
00:22:07,000 --> 00:22:11,320
After studying it closely, he
suggested it came from a gigantic,
328
00:22:11,320 --> 00:22:14,720
flightless bird
that was probably extinct.
329
00:22:15,760 --> 00:22:19,920
From this meagre evidence,
he reconstructed the entire animal,
330
00:22:19,920 --> 00:22:23,000
a giant moa.
331
00:22:23,000 --> 00:22:26,560
Owen was ridiculed
by other scientists at the time,
332
00:22:26,560 --> 00:22:30,520
who considered such a deduction
on one bone outrageous.
333
00:22:30,520 --> 00:22:33,720
But in due course,
other moa birds were found,
334
00:22:33,720 --> 00:22:35,720
and he was proved to be correct.
335
00:22:37,320 --> 00:22:40,680
Owen's discoveries
seemed to confirm the idea
336
00:22:40,680 --> 00:22:44,440
that the kiwi could have evolved
from a big bird like the moa,
337
00:22:44,440 --> 00:22:48,560
and that maybe its egg was
a relic from a giant ancestor.
338
00:22:51,960 --> 00:22:54,880
Large, flightless birds
first appeared
339
00:22:54,880 --> 00:22:57,120
when the dinosaurs became extinct.
340
00:22:58,520 --> 00:23:01,440
This is a southern cassowary.
341
00:23:01,440 --> 00:23:05,480
It's a native of northern Australia
and New Guinea.
342
00:23:05,480 --> 00:23:07,520
And the males, like this one,
343
00:23:07,520 --> 00:23:11,000
are extremely territorial
and, therefore, dangerous.
344
00:23:11,000 --> 00:23:14,280
They will attack you,
as I know to my cost.
345
00:23:14,280 --> 00:23:16,480
So, I'm not going to get in there
with him.
346
00:23:16,480 --> 00:23:19,160
Instead, I'll see
if I can tempt him
347
00:23:19,160 --> 00:23:22,440
with a few grapes, which are
one of his favourite foods.
348
00:23:24,280 --> 00:23:27,800
Like the kiwi, the cassowary evolved
349
00:23:27,800 --> 00:23:31,840
in an area where the adult birds
have no ground predators.
350
00:23:31,840 --> 00:23:34,760
As a consequence, they don't fly.
351
00:23:35,880 --> 00:23:38,800
Flying is a very energy-demanding
business.
352
00:23:38,800 --> 00:23:42,600
If birds don't need to fly,
birds don't fly.
353
00:23:46,840 --> 00:23:50,120
Until recently, it was thought
that all the ratites
354
00:23:50,120 --> 00:23:52,320
had one common flightless ancestor.
355
00:23:54,040 --> 00:23:57,880
This seemed possible because
the places where they live today
356
00:23:57,880 --> 00:24:01,440
were once part of a supercontinent
called Gondwanaland.
357
00:24:02,880 --> 00:24:07,200
When this continent split up
around 150 million years ago,
358
00:24:07,200 --> 00:24:08,960
the fragments drifted apart.
359
00:24:10,600 --> 00:24:14,640
Each one might independently have
evolved its own flightless species,
360
00:24:14,640 --> 00:24:16,280
including New Zealand.
361
00:24:20,000 --> 00:24:22,720
When Owen came to examine
the skeleton of a kiwi,
362
00:24:22,720 --> 00:24:26,000
he noticed something very strange
about the skull.
363
00:24:27,080 --> 00:24:30,640
Most bird skulls have two little
tiny holes there
364
00:24:30,640 --> 00:24:33,320
at the base of the beak,
which accommodates the nostrils,
365
00:24:33,320 --> 00:24:34,760
through which they smell.
366
00:24:34,760 --> 00:24:38,440
But there are no such things here
on the kiwi skull.
367
00:24:38,440 --> 00:24:43,960
Instead, the nostrils are right
at the tip of the beak.
368
00:24:45,120 --> 00:24:49,360
Not only that, but these big spaces
on either side the skull,
369
00:24:49,360 --> 00:24:53,200
which in most birds hold
the big eye,
370
00:24:53,200 --> 00:24:58,080
are, in fact, filled by the
olfactory organ, the smelling organ.
371
00:24:59,640 --> 00:25:03,640
And Owen deduced from those
two facts that this, therefore,
372
00:25:03,640 --> 00:25:07,560
must belong to a bird
that was nocturnal.
373
00:25:07,560 --> 00:25:08,960
And he was quite right.
374
00:25:13,040 --> 00:25:15,840
The kiwi is mostly active at night,
375
00:25:15,840 --> 00:25:19,680
and uses both touch and smell
to find its food.
376
00:25:22,320 --> 00:25:26,000
The long whiskers allow it
to feel its way in the dark,
377
00:25:26,000 --> 00:25:28,280
and special sensory cells
in the beak
378
00:25:28,280 --> 00:25:30,480
detect the movement
of prey underground.
379
00:25:32,120 --> 00:25:35,840
But why did the kiwi
choose this unusual lifestyle?
380
00:25:37,760 --> 00:25:41,360
It's possible that the moas
had already taken the role
381
00:25:41,360 --> 00:25:43,440
of giant plant eaters
during the day,
382
00:25:43,440 --> 00:25:47,320
so the kiwi may have shrunk down
to feed on small insects at night.
383
00:25:49,720 --> 00:25:52,760
Owen had shed light on both
the moa and kiwi,
384
00:25:52,760 --> 00:25:55,800
but he was wrong about their
true relationship.
385
00:25:57,360 --> 00:26:01,680
Evidence from DNA has now revealed
that the kiwi is, in fact,
386
00:26:01,680 --> 00:26:05,720
more closely related to flightless
birds of Africa and Australia.
387
00:26:06,720 --> 00:26:10,920
This means that the moa and the kiwi
had different ancestors,
388
00:26:10,920 --> 00:26:14,840
and flightlessness must
have evolved in New Zealand
389
00:26:14,840 --> 00:26:16,720
on two separate occasions.
390
00:26:19,760 --> 00:26:21,960
It's an extraordinary thought.
391
00:26:21,960 --> 00:26:25,120
But another recent finding
supports the idea.
392
00:26:26,680 --> 00:26:30,760
Genetic techniques have shown that
the closest relative of the ratites
393
00:26:30,760 --> 00:26:35,360
is, in fact, a small flying bird,
the tinamou.
394
00:26:37,240 --> 00:26:40,360
Tinamous are partridge-like birds
from South America
395
00:26:40,360 --> 00:26:42,920
that spend much of their time
on the ground,
396
00:26:42,920 --> 00:26:45,000
but they can fly perfectly well.
397
00:26:46,280 --> 00:26:49,880
So, it seems that birds like this
may have flapped their way
398
00:26:49,880 --> 00:26:54,040
between the continents, giving rise
to the different ratites,
399
00:26:54,040 --> 00:26:55,440
including the kiwi.
400
00:27:01,800 --> 00:27:06,080
We've unravelled much of the mystery
around the kiwi's curious lifestyle,
401
00:27:06,080 --> 00:27:08,480
but one question remains.
402
00:27:08,480 --> 00:27:12,080
What could be the reason
for its huge egg?
403
00:27:14,040 --> 00:27:18,240
Some think that the large egg may
give the kiwi a competitive edge,
404
00:27:18,240 --> 00:27:22,480
by allowing it to hatch a chick that
is already very well developed.
405
00:27:23,880 --> 00:27:25,960
It's like a miniature adult,
406
00:27:25,960 --> 00:27:28,840
and the large yolk sac
provides nourishment
407
00:27:28,840 --> 00:27:31,560
until it becomes fully independent.
408
00:27:37,360 --> 00:27:41,560
So, it seems that the kiwi's
gigantic egg may have evolved
409
00:27:41,560 --> 00:27:43,520
to suit its lifestyle and habitat.
410
00:27:43,520 --> 00:27:47,080
Most birds have to lay their eggs
as soon as possible
411
00:27:47,080 --> 00:27:50,040
to avoid being
weighed down when flying.
412
00:27:50,040 --> 00:27:54,640
But the flightless kiwi has no such
problem, and can, therefore,
413
00:27:54,640 --> 00:27:58,680
keep the heavy egg in its body
for longer, and let it grow bigger.
414
00:27:59,800 --> 00:28:04,080
And in an environment with few
predators, it may make sense to,
415
00:28:04,080 --> 00:28:08,640
as it were, put all your eggs in one
basket and raise a single chick
416
00:28:08,640 --> 00:28:10,440
that is big and strong,
417
00:28:10,440 --> 00:28:13,080
and therefore has the better
chance of survival.
418
00:28:14,320 --> 00:28:18,160
The kiwi and the panda both
produce young that stand out
419
00:28:18,160 --> 00:28:19,920
because of their size,
420
00:28:19,920 --> 00:28:25,520
but are a perfect fit for the life
choices of these curious creatures.