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ATTENBOROUGH: 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 most.

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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 myths and misunderstandings

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for a very long time.

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And some have only recently
revealed their secrets.

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These are the animals
that stand out from the crowd.

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The curiosities 1 find
most fascinating of all.

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some animals live in conditions so cold

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that they seem to defy
the rules of nature.

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The Emperor Penguin is the only animal

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able to raise its young during
the harsh Antarctic winter.

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And the tiny wood frog
faces freezing conditions

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that would kill any other amphibian.

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How do they do it?

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These eggs were collected
more than a hundred years ago

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during an expedition to the Antarctic.

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The conditions were so cold
that the man who collected them

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never made it back to England alive.

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He perished alongside Captain Scott

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during the ill-fated journey
to reach the South Pole.

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The eggs were laid
by an Emperor Penguin,

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a bird whose life history

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would surprise and confound
those early polar explorers.

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At the end of the 1 9th century,

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the Antarctic was an unfamiliar
and mysterious place.

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Only a handful of explorers
had ventured this far south

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and there was still
a huge blank in the world map.

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But then, in 1 901,

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a British expedition set off
on a purpose-built ship,

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the Discovery,
to explore this most southerly land.

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1n charge was
Commander Robert Falcon scott.

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Scott took on board with him
a young man named Edward Wilson

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who would serve
as the ship's doctor and naturalist.

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Wilson had only just qualified
as a surgeon

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and had no formal training
in scientific research,

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but the young man's passion
for natural history and art

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would prove to be an
invaluable asset to the expedition.

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Wilson's job was to draw and record

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any plants or animals
that they encountered.

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But, from the start,

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there was one creature that
fascinated him more than any other,

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the Emperor Penguin.

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This largest of all penguins had only
been discovered 60 years earlier.

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But, as yet, nothing
was known about its habits

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or where it breeds.

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The expedition was an opportunity
to find out more.

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When the Discovery
reached the southern continent,

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they put up a hut in which
they would spend the long, dark winter.

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Then as the sun started
to appear again in spring,

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the sledge team started to explore

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and one returned
with some tantalising news.

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They had discovered a breeding
colony of Emperor Penguins

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in a place called Cape Crozier.

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1t was the first colony
any human being had ever seen.

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And much to their surprise,

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the birds were breeding on sea ice.

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1t was a truly astonishing discovery.

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No other bird breeds on ice

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and Wilson was keen to find out more
about this remarkable creature.

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Very little was known
about Emperor Penguins,

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but there was another bird

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which could give Wilson
some insights into their lives,

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the King Penguin.

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Adult King Penguins look very much
the same as adult Emperors.

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The main difference is in size.

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These Kings are only
about half as big as an Emperor.

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And they live in
the northern part of Antarctica.

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They breed in the middle
of the Antarctic summer,

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November, December,

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and incubation takes about seven weeks.

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And Wilson thought that Emperors
would do very much the same.

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But he was about to discover otherwise.

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The following spring, with the hope
of collecting some penguin eggs,

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Wilson left for Cape Crozier
as early as he dared.

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When he got there however,
much to his surprise,

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he found only well-grown chicks.

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After repeated calculations,

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he finally concluded that
these penguins must lay their eggs

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in the middle of the Antarctic winter.

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That Emperors should start breeding

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at the coldest and bleakest
time of the year,

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was an astonishing discovery.

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It seemed to defy
all the rules of nature.

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And Wilson was indeed amazed.

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But it seems that this strange lifestyle
does, in fact, make sense.

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Emperor Penguins are big birds

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and their chicks take more than a year
to grow large enough to be independent.

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By laying the eggs earlier in midwinter,

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the Emperors give their chicks
a head start,

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so that they first go to sea
in the summer months

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when food is plentiful.

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But how do Emperor Penguins
protect their eggs and chicks

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from the bitter cold?

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Neither Kings nor Emperors make a nest

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or lay their eggs on the ground.

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If they did,
the eggs would freeze within minutes.

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Instead, they keep their eggs
on the top of their feet

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and cover them with a feathered
fold of skin from the abdomen.

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And inside that pouch,

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the temperature is about
70 degrees warmer than it is outside.

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With temperatures of
minus 60 degrees Celsius

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and winds gusting
at 200 kilometres an hour,

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the birds huddle together for warmth.

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Even under these extremely
difficult conditions,

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Wilson recorded everything he saw.

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Able to work for only
a few minutes at a time,

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he still managed to produce
detailed notes and drawings

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that give us a first insight
into the southern continent.

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This is the expedition's
scientific report

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and it contains most of Wilson's
observations in the Antarctic.

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At a time when illustrations of animals
were often drawn from dead specimens,

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Wilson drew his subjects
live in the field, wherever possible,

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to capture the true nature
of the animal.

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Despite the extreme conditions
under which he had to work,

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he made over 900 detailed
drawings in the Antarctic.

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Wilson was an exceptional artist
and a meticulous scientist.

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And most of his observations
have stood the test of time.

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But some things puzzled him
more than others.

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He noted, for example,
that the brooding of the chick

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was not just carried out by one bird
or even by a single pair.

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1t appeared as if numerous birds

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were taking turns
in looking after the chick.

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Today, of course,
we know that this is not quite correct.

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1t's only the parents
who care for both the egg

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and then the chick.

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We now have a much better understanding
of how Emperor Penguins breed,

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but Wilson's confusion
as to who cares for the chick

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is, in fact, quite understandable.

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He observed numerous occasions

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when a youngster was
accidentally dropped by its parent.

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In his report, he writes,

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''What we actually saw, again and again,

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''was the wild dash
made by a dozen adults,

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''each weighing anything up to 90 pounds,

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''to take possession of any chick

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''that happened to find itself
deserted on the ice.

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''1t can be compared to nothing better
than a football scrimmage. ''

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The birds Wilson had observed
were, in fact, females

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who had lost their own egg or chick

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and were trying to adopt or kidnap
any unattended youngsters.

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What he couldn't know

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was that these adoptions
are never successful.

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The new parent
rarely feeds its foster chick

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and simply broods it for a few days.

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After that, the youngster
is abandoned again

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or dies of starvation.

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1t's likely that the female
eventually recognises

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that the adopted chick is not her own.

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Although Wilson had been the first man
to find an Emperor Penguin colony,

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he had not been able to obtain
any freshly-laid eggs.

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These were particularly sought after
by scientists of the day.

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1t was thought at that time

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that the Emperor Penguin
was one of the most primitive birds

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and possibly a missing
evolutionary link with dinosaurs.

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1f embryos could be obtained
at an early enough stage,

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then maybe one would see
reptilian scales

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or some other dinosaur features.

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so the Emperor Penguin egg

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was regarded as
a great scientific prize.

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A few years later, scott and Wilson

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planned a second expedition
to the Antarctic.

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The main objective
was to reach the south Pole,

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but Wilson was determined

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to bring back newly-laid
Emperor Penguin eggs.

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This time, he made plans to
travel to Cape Crozier even earlier

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so as not to miss the birds on eggs.

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He picked two men to accompany him,

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Bowers and Cherry-Garrard,

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and they set off in
the pitch black of the winter.

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It was a journey of over 70 miles

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and they had to cover it on foot.

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For six painful weeks,

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the three men pulled their heavy sledges

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in complete darkness and howling gales,

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at temperatures of
minus 40 degrees centigrade.

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Never before had anyone
travelled in such bitter cold

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or in such difficult conditions.

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They sometimes barely
covered a mile a day.

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It was what Cherry-Garrard
would later call,

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''The worst journey in the world.''

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Their clothes were iced up

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and their breath and sweat
froze on their bodies.

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Each night, it took them an hour

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to chip into their sleeping bags,
which were frozen solid.

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When they finally
reached the penguin colony,

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they collected five eggs
with great difficulty

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and put them
inside their mittens for safety.

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The men staggered back
to base camp close to death

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and only three eggs
survived the journey.

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These are two of them.

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1t was an extraordinary feat
of determination

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by Wilson and his companions.

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The precious eggs were supposed
to reveal the evolutionary links

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between reptiles and birds.

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But getting them
had nearly killed the collectors.

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A few months later,

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scott led his party on the final push
to reach the south Pole.

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His team consisted of just five men

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and Wilson was amongst them.

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On their return journey,
all five men perished,

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succumbing to the cold and starvation

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just a few kilometres
from their nearest food depot.

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In the end,

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Wilson's eggs didn't contribute
as much to our understanding

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of the development of the penguin chick

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as he had hoped.

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But his beautiful drawings
and meticulous observations

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are quite a different matter.

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They helped to unravel
the biology of a bird

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that is able to rear its young
in the depths of the polar winter.

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The Emperor Penguin amazes us

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by raising its chicks in the most
inhospitable place on earth.

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But a small frog has
a way of coping with the cold

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that seems to be beyond belief.

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This is a North American wood frog

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and it lives as far north
as the Arctic Circle.

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But like all cold-blooded creatures,
it can't generate its own heat.

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And its body temperature rises
and falls with the surroundings.

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So when conditions drop below zero,
the frog risks freezing.

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How does a creature like this
survive the harsh winters?

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The skin of amphibians is thin and moist

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and this makes them particularly
vulnerable to the cold.

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Any contact with ice

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can instantly trigger
freezing inside their bodies.

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And, for most animals,
this means almost certain death.

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When water freezes, it expands

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and the sharp ice crystals
can puncture blood vessels

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and break cell walls
causing irreparable damage.

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The animal's internal organs
may never function properly again.

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so how do frogs avoid freezing?

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Many sit out the winter
by hibernating at the bottom of a pond.

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The surface may freeze
but underneath the ice,

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the temperature
remains just above freezing.

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And most land-living amphibians

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seek out a sheltered spot underground
to avoid the deadly frost.

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But in the 1 8th century,

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Arctic travellers came back
with tales so extraordinary

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they were scarcely believable.

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A British explorer called samuel Hearne

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reported seeing frozen frogs among
the piles of leaves in Arctic Canada.

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He went on to make
an extraordinary claim,

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''Frogs of various colours
are numerous in these parts.

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''I've frequently seen
them dug up with moss,

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''frozen as hard as ice,

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''in which state, the legs are
as easily broken off as a pipe stem

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00:15:15,087 --> 00:15:18,636
''without giving the least sensation
to the animals.

250
00:15:20,007 --> 00:15:22,680
''But by wrapping them up in warm skins

251
00:15:22,807 --> 00:15:25,275
''and exposing them to a slow fire,

252
00:15:25,367 --> 00:15:27,437
''they soon recover life,

253
00:15:27,527 --> 00:15:31,406
''and the mutilated animal
gains its usual activity.''

254
00:15:32,887 --> 00:15:34,639
Seems an unlikely story.

255
00:15:34,727 --> 00:15:37,844
Frozen frogs that,
if gently warmed by a fire,

256
00:15:37,927 --> 00:15:39,076
would come back to life.

257
00:15:39,167 --> 00:15:41,761
What truth could there be
in this account?

258
00:15:42,127 --> 00:15:43,242
Well,

259
00:15:44,047 --> 00:15:47,084
this is a marsh frog,

260
00:15:47,167 --> 00:15:50,762
and it's found in ponds and marshes
throughout Central and Northern Europe.

261
00:15:50,847 --> 00:15:53,600
It's lying completely immobile
in my hand

262
00:15:53,687 --> 00:15:55,723
because it's frozen solid.

263
00:15:57,527 --> 00:16:00,246
From the outside,
it feels much like a rock.

264
00:16:00,607 --> 00:16:03,041
And you might be forgiven
for thinking it was dead.

265
00:16:03,887 --> 00:16:05,479
Well, watch what happens

266
00:16:05,567 --> 00:16:08,639
when I put it into a bowl of warm water.

267
00:16:15,927 --> 00:16:19,522
Although it appears dead
and has in fact stopped breathing,

268
00:16:19,607 --> 00:16:22,121
the frog's heart is still beating.

269
00:16:22,287 --> 00:16:23,959
Only the outer layer has frozen.

270
00:16:24,047 --> 00:16:26,959
The vital organs inside
are still undamaged.

271
00:16:30,567 --> 00:16:33,479
Lab experiments have shown
that in this state,

272
00:16:33,567 --> 00:16:38,880
the marsh frog can survive temperatures
of two degrees below freezing.

273
00:16:41,567 --> 00:16:44,445
Yes, it's lifted itself up. It's moving.

274
00:16:44,807 --> 00:16:45,876
Look at this.

275
00:16:47,767 --> 00:16:49,758
There, it's moving its right leg.

276
00:16:50,847 --> 00:16:52,200
Within a few minutes,

277
00:16:52,287 --> 00:16:55,484
the frog has awakened to life
once again.

278
00:16:57,807 --> 00:17:01,083
This is surely one of the most
extraordinary miracles in nature.

279
00:17:03,647 --> 00:17:04,682
Nonetheless,

280
00:17:04,767 --> 00:17:07,918
the marsh frog can only survive
a few hours of freezing.

281
00:17:09,127 --> 00:17:11,880
Anything more would mean certain death.

282
00:17:13,247 --> 00:17:16,478
Where it lives,
it rarely faces extreme winters

283
00:17:16,567 --> 00:17:20,242
and is protected from the worst
by the insulating water.

284
00:17:22,367 --> 00:17:24,881
so what about samuel Hearne's story?

285
00:17:25,047 --> 00:17:28,164
Could some frogs survive
longer periods of freezing?

286
00:17:28,967 --> 00:17:32,755
Another account from North America
would seem to suggest so.

287
00:17:33,847 --> 00:17:37,635
1n the 1 9th century,
a naturalist called John Burroughs

288
00:17:37,727 --> 00:17:42,243
found a wood frog underneath the leaf
litter at the beginning of the winter.

289
00:17:43,127 --> 00:17:44,845
Burroughs was surprised,

290
00:17:44,927 --> 00:17:48,966
but reasoned that the frog must know
that a mild winter was on the way

291
00:17:49,047 --> 00:17:51,845
and had therefore not bothered
to bury to itself deeper.

292
00:17:53,847 --> 00:17:56,998
1n fact, a very severe winter followed.

293
00:17:59,447 --> 00:18:00,880
Wondering about his frog,

294
00:18:00,967 --> 00:18:03,640
Burroughs went back
to the same spot in spring

295
00:18:03,727 --> 00:18:06,685
and found the animal seemingly unharmed.

296
00:18:08,287 --> 00:18:11,836
The wood frog must have spent
the entire winter above ground

297
00:18:11,927 --> 00:18:14,646
and survived temperatures
that should have killed it.

298
00:18:15,847 --> 00:18:17,997
How did the tiny frog do it?

299
00:18:20,487 --> 00:18:23,126
The wood frog is not strong
and large enough

300
00:18:23,207 --> 00:18:24,959
to dig itself into the ground

301
00:18:25,287 --> 00:18:28,165
so it has to sit out the winter
beneath the leaf litter.

302
00:18:28,927 --> 00:18:32,397
But this doesn't provide
sufficient protection against the cold.

303
00:18:32,927 --> 00:18:35,964
So how does this small frog survive?

304
00:18:36,807 --> 00:18:38,286
Today, we know the truth.

305
00:18:38,687 --> 00:18:42,521
And if Burroughs had done so,
he would have been astounded.

306
00:18:45,007 --> 00:18:48,204
1t's only recently that we've
discovered just how the wood frog

307
00:18:48,287 --> 00:18:51,916
avoids the usually fatal
consequences of freezing.

308
00:18:53,727 --> 00:18:55,240
As winter sets in,

309
00:18:55,327 --> 00:18:58,478
the frog prepares
for an extraordinary change.

310
00:19:06,447 --> 00:19:08,597
First, it draws water out of its cells

311
00:19:08,687 --> 00:19:12,316
into spaces where it would
do less damage if it freezes.

312
00:19:13,087 --> 00:19:14,156
At the same time,

313
00:19:14,247 --> 00:19:19,367
its liver produces large amounts
of sugar that act as antifreeze.

314
00:19:19,447 --> 00:19:23,281
This is pumped through the body
to slow down the freezing.

315
00:19:29,087 --> 00:19:31,237
Now, the entire frog

316
00:19:31,327 --> 00:19:35,115
slowly freezes from the outside inwards.

317
00:19:46,247 --> 00:19:48,715
And, finally, the heart stops.

318
00:19:49,407 --> 00:19:51,079
The frog isn't dead,

319
00:19:51,167 --> 00:19:53,761
but it's probably about
as close as you can get.

320
00:19:54,767 --> 00:19:56,837
seventy percent of its body is frozen

321
00:19:57,967 --> 00:20:02,245
and it can remain like this
for several weeks on end.

322
00:20:10,167 --> 00:20:12,727
Then, as the air warms up again,

323
00:20:12,807 --> 00:20:15,640
a miraculous transformation takes place.

324
00:20:16,967 --> 00:20:20,642
The ice melts and the frogs body thaws

325
00:20:21,287 --> 00:20:24,836
and, suddenly, the heart
sparks back to life.

326
00:20:29,167 --> 00:20:32,398
Unlike the marsh frog,
the deeply-frozen wood frog

327
00:20:32,487 --> 00:20:36,719
needs several hours before
it can resume normal activity.

328
00:20:41,807 --> 00:20:44,924
The wood frog's ability
to survive in a frozen state

329
00:20:45,047 --> 00:20:46,958
has fascinated scientists.

330
00:20:47,047 --> 00:20:51,802
Could this one day help advance
our own medical understanding?

331
00:20:53,767 --> 00:20:55,678
We still don't completely understand

332
00:20:55,767 --> 00:20:59,726
how the wood frog survives something
that would kill most animals.

333
00:21:00,407 --> 00:21:01,522
What we do know

334
00:21:01,607 --> 00:21:05,122
is that, when freezing occurs slowly
and in the right places,

335
00:21:05,207 --> 00:21:07,163
it appears to do less damage.

336
00:21:07,807 --> 00:21:10,685
This little frog seems to have
mastered the problem

337
00:21:10,767 --> 00:21:14,362
by controlling how and where
ice forms in its body.

338
00:21:16,807 --> 00:21:20,561
The Emperor Penguin's ability
to breed during the Antarctic winter

339
00:21:20,647 --> 00:21:23,400
is a remarkable feat of endurance.

340
00:21:23,487 --> 00:21:27,560
But for a small frog to freeze solid
and come back to life,

341
00:21:27,647 --> 00:21:32,482
must surely be one of the most
astonishing curiosities of nature.