David Attenborough's Natural Curiosities (2013) s02e07 Episode Script

ATTENBOROUGH: The natural world is full of extraordinary animals with amazing life histories.
Yet, certain stories are more intriguing than most.
The mysteries of a butterfly's life-cycle or the strange biology of the emperor penguin.
Some of these creatures were surrounded by myths and misunderstandings for a very long time.
And some have only recently revealed their secrets.
These are the animals that stand out from the crowd.
The curiosities I find most fascinating of all.
Some animals live in conditions so cold that they seem to defy the rules of nature.
The Emperor Penguin is the only animal able to raise its young during the harsh Antarctic winter.
And the tiny wood frog faces freezing conditions that would kill any other amphibian.
How do they do it? These eggs were collected more than a hundred years ago during an expedition to the Antarctic.
The conditions were so cold that the man who collected them never made it back to England alive.
He perished alongside Captain Scott during the ill-fated journey to reach the South Pole.
The eggs were laid by an Emperor Penguin, a bird whose life history would surprise and confound those early polar explorers.
At the end of the 19th century, the Antarctic was an unfamiliar and mysterious place.
Only a handful of explorers had ventured this far south and there was still a huge blank in the world map.
But then, in 1901, a British expedition set off on a purpose-built ship, the Discovery, to explore this most southerly land.
In charge was Commander Robert Falcon Scott.
Scott took on board with him a young man named Edward Wilson who would serve as the ship's doctor and naturalist.
Wilson had only just qualified as a surgeon and had no formal training in scientific research, but the young man's passion for natural history and art would prove to be an invaluable asset to the expedition.
Wilson's job was to draw and record any plants or animals that they encountered.
But, from the start, there was one creature that fascinated him more than any other, the Emperor Penguin.
This largest of all penguins had only been discovered 60 years earlier.
But, as yet, nothing was known about its habits or where it breeds.
The expedition was an opportunity to find out more.
When the Discovery reached the southern continent, they put up a hut in which they would spend the long, dark winter.
Then as the sun started to appear again in spring, the sledge team started to explore and one returned with some tantalising news.
They had discovered a breeding colony of Emperor Penguins in a place called Cape Crozier.
It was the first colony any human being had ever seen.
And much to their surprise, the birds were breeding on sea ice.
It was a truly astonishing discovery.
No other bird breeds on ice and Wilson was keen to find out more about this remarkable creature.
Very little was known about Emperor Penguins, but there was another bird which could give Wilson some insights into their lives, the King Penguin.
Adult King Penguins look very much the same as adult Emperors.
The main difference is in size.
These Kings are only about half as big as an Emperor.
And they live in the northern part of Antarctica.
They breed in the middle of the Antarctic summer, November, December, and incubation takes about seven weeks.
And Wilson thought that Emperors would do very much the same.
But he was about to discover otherwise.
The following spring, with the hope of collecting some penguin eggs, Wilson left for Cape Crozier as early as he dared.
When he got there however, much to his surprise, he found only well-grown chicks.
After repeated calculations, he finally concluded that these penguins must lay their eggs in the middle of the Antarctic winter.
That Emperors should start breeding at the coldest and bleakest time of the year, was an astonishing discovery.
It seemed to defy all the rules of nature.
And Wilson was indeed amazed.
But it seems that this strange lifestyle does, in fact, make sense.
Emperor Penguins are big birds and their chicks take more than a year to grow large enough to be independent.
By laying the eggs earlier in midwinter, the Emperors give their chicks a head start, so that they first go to sea in the summer months when food is plentiful.
But how do Emperor Penguins protect their eggs and chicks from the bitter cold? Neither Kings nor Emperors make a nest or lay their eggs on the ground.
If they did, the eggs would freeze within minutes.
Instead, they keep their eggs on the top of their feet and cover them with a feathered fold of skin from the abdomen.
And inside that pouch, the temperature is about 70 degrees warmer than it is outside.
With temperatures of minus 60 degrees Celsius and winds gusting at 200 kilometres an hour, the birds huddle together for warmth.
Even under these extremely difficult conditions, Wilson recorded everything he saw.
Able to work for only a few minutes at a time, he still managed to produce detailed notes and drawings that give us a first insight into the southern continent.
This is the expedition's scientific report and it contains most of Wilson's observations in the Antarctic.
At a time when illustrations of animals were often drawn from dead specimens, Wilson drew his subjects live in the field, wherever possible, to capture the true nature of the animal.
Despite the extreme conditions under which he had to work, he made over 900 detailed drawings in the Antarctic.
Wilson was an exceptional artist and a meticulous scientist.
And most of his observations have stood the test of time.
But some things puzzled him more than others.
He noted, for example, that the brooding of the chick was not just carried out by one bird or even by a single pair.
It appeared as if numerous birds were taking turns in looking after the chick.
Today, of course, we know that this is not quite correct.
It's only the parents who care for both the egg and then the chick.
We now have a much better understanding of how Emperor Penguins breed, but Wilson's confusion as to who cares for the chick is, in fact, quite understandable.
He observed numerous occasions when a youngster was accidentally dropped by its parent.
In his report, he writes, "What we actually saw, again and again, "was the wild dash made by a dozen adults, "each weighing anything up to 90 pounds, "to take possession of any chick "that happened to find itself deserted on the ice.
"It can be compared to nothing better than a football scrimmage.
" The birds Wilson had observed were, in fact, females who had lost their own egg or chick and were trying to adopt or kidnap any unattended youngsters.
What he couldn't know was that these adoptions are never successful.
The new parent rarely feeds its foster chick and simply broods it for a few days.
After that, the youngster is abandoned again or dies of starvation.
It's likely that the female eventually recognises that the adopted chick is not her own.
Although Wilson had been the first man to find an Emperor Penguin colony, he had not been able to obtain any freshly-laid eggs.
These were particularly sought after by scientists of the day.
It was thought at that time that the Emperor Penguin was one of the most primitive birds and possibly a missing evolutionary link with dinosaurs.
If embryos could be obtained at an early enough stage, then maybe one would see reptilian scales or some other dinosaur features.
So the Emperor Penguin egg was regarded as a great scientific prize.
A few years later, Scott and Wilson planned a second expedition to the Antarctic.
The main objective was to reach the South Pole, but Wilson was determined to bring back newly-laid Emperor Penguin eggs.
This time, he made plans to travel to Cape Crozier even earlier so as not to miss the birds on eggs.
He picked two men to accompany him, Bowers and Cherry-Garrard, and they set off in the pitch black of the winter.
It was a journey of over 70 miles and they had to cover it on foot.
For six painful weeks, the three men pulled their heavy sledges in complete darkness and howling gales, at temperatures of minus 40 degrees centigrade.
Never before had anyone travelled in such bitter cold or in such difficult conditions.
They sometimes barely covered a mile a day.
It was what Cherry-Garrard would later call, "The worst journey in the world.
" Their clothes were iced up and their breath and sweat froze on their bodies.
Each night, it took them an hour to chip into their sleeping bags, which were frozen solid.
When they finally reached the penguin colony, they collected five eggs with great difficulty and put them inside their mittens for safety.
The men staggered back to base camp close to death and only three eggs survived the journey.
These are two of them.
It was an extraordinary feat of determination by Wilson and his companions.
The precious eggs were supposed to reveal the evolutionary links between reptiles and birds.
But getting them had nearly killed the collectors.
A few months later, Scott led his party on the final push to reach the South Pole.
His team consisted of just five men and Wilson was amongst them.
On their return journey, all five men perished, succumbing to the cold and starvation just a few kilometres from their nearest food depot.
In the end, Wilson's eggs didn't contribute as much to our understanding of the development of the penguin chick as he had hoped.
But his beautiful drawings and meticulous observations are quite a different matter.
They helped to unravel the biology of a bird that is able to rear its young in the depths of the polar winter.
The Emperor Penguin amazes us by raising its chicks in the most inhospitable place on earth.
But a small frog has a way of coping with the cold that seems to be beyond belief.
This is a North American wood frog and it lives as far north as the Arctic Circle.
But like all cold-blooded creatures, it can't generate its own heat.
And its body temperature rises and falls with the surroundings.
So when conditions drop below zero, the frog risks freezing.
How does a creature like this survive the harsh winters? The skin of amphibians is thin and moist and this makes them particularly vulnerable to the cold.
Any contact with ice can instantly trigger freezing inside their bodies.
And, for most animals, this means almost certain death.
When water freezes, it expands and the sharp ice crystals can puncture blood vessels and break cell walls causing irreparable damage.
The animal's internal organs may never function properly again.
So how do frogs avoid freezing? Many sit out the winter by hibernating at the bottom of a pond.
The surface may freeze but underneath the ice, the temperature remains just above freezing.
And most land-living amphibians seek out a sheltered spot underground to avoid the deadly frost.
But in the 18th century, Arctic travellers came back with tales so extraordinary they were scarcely believable.
A British explorer called Samuel Hearne reported seeing frozen frogs among the piles of leaves in Arctic Canada.
He went on to make an extraordinary claim, "Frogs of various colours are numerous in these parts.
"I've frequently seen them dug up with moss, "frozen as hard as ice, "in which state, the legs are as easily broken off as a pipe stem "without giving the least sensation to the animals.
"But by wrapping them up in warm skins "and exposing them to a slow fire, "they soon recover life, "and the mutilated animal gains its usual activity.
" Seems an unlikely story.
Frozen frogs that, if gently warmed by a fire, would come back to life.
What truth could there be in this account? Well, this is a marsh frog, and it's found in ponds and marshes throughout Central and Northern Europe.
It's lying completely immobile in my hand because it's frozen solid.
From the outside, it feels much like a rock.
And you might be forgiven for thinking it was dead.
Well, watch what happens when I put it into a bowl of warm water.
Although it appears dead and has in fact stopped breathing, the frog's heart is still beating.
Only the outer layer has frozen.
The vital organs inside are still undamaged.
Lab experiments have shown that in this state, the marsh frog can survive temperatures of two degrees below freezing.
Yes, it's lifted itself up.
It's moving.
Look at this.
There, it's moving its right leg.
Within a few minutes, the frog has awakened to life once again.
This is surely one of the most extraordinary miracles in nature.
Nonetheless, the marsh frog can only survive a few hours of freezing.
Anything more would mean certain death.
Where it lives, it rarely faces extreme winters and is protected from the worst by the insulating water.
So what about Samuel Hearne's story? Could some frogs survive longer periods of freezing? Another account from North America would seem to suggest so.
In the 19th century, a naturalist called John Burroughs found a wood frog underneath the leaf litter at the beginning of the winter.
Burroughs was surprised, but reasoned that the frog must know that a mild winter was on the way and had therefore not bothered to bury to itself deeper.
In fact, a very severe winter followed.
Wondering about his frog, Burroughs went back to the same spot in spring and found the animal seemingly unharmed.
The wood frog must have spent the entire winter above ground and survived temperatures that should have killed it.
How did the tiny frog do it? The wood frog is not strong and large enough to dig itself into the ground so it has to sit out the winter beneath the leaf litter.
But this doesn't provide sufficient protection against the cold.
So how does this small frog survive? Today, we know the truth.
And if Burroughs had done so, he would have been astounded.
It's only recently that we've discovered just how the wood frog avoids the usually fatal consequences of freezing.
As winter sets in, the frog prepares for an extraordinary change.
First, it draws water out of its cells into spaces where it would do less damage if it freezes.
At the same time, its liver produces large amounts of sugar that act as antifreeze.
This is pumped through the body to slow down the freezing.
Now, the entire frog slowly freezes from the outside inwards.
And, finally, the heart stops.
The frog isn't dead, but it's probably about as close as you can get.
Seventy percent of its body is frozen and it can remain like this for several weeks on end.
Then, as the air warms up again, a miraculous transformation takes place.
The ice melts and the frogs body thaws and, suddenly, the heart sparks back to life.
Unlike the marsh frog, the deeply-frozen wood frog needs several hours before it can resume normal activity.
The wood frog's ability to survive in a frozen state has fascinated scientists.
Could this one day help advance our own medical understanding? We still don't completely understand how the wood frog survives something that would kill most animals.
What we do know is that, when freezing occurs slowly and in the right places, it appears to do less damage.
This little frog seems to have mastered the problem by controlling how and where ice forms in its body.
The Emperor Penguin's ability to breed during the Antarctic winter is a remarkable feat of endurance.
But for a small frog to freeze solid and come back to life, must surely be one of the most astonishing curiosities of nature.