0:00:02 > 0:00:06The natural world is full of extraordinary animals
0:00:06 > 0:00:08with amazing life histories.
0:00:09 > 0:00:12Yet certain stories are more intriguing than most.
0:00:16 > 0:00:19The mysteries of a butterfly's life cycle,
0:00:19 > 0:00:22or the strange biology of the emperor penguin.
0:00:23 > 0:00:26Some of these creatures were surrounded by myth
0:00:26 > 0:00:30and misunderstandings for a very long time.
0:00:30 > 0:00:33And some have only recently revealed their secrets.
0:00:35 > 0:00:39These are the animals that stand out from the crowd.
0:00:39 > 0:00:43The curiosities I find most fascinating of all.
0:00:51 > 0:00:55Some animals live in conditions so cold
0:00:55 > 0:00:58that they seem to defy the rules of nature.
0:01:00 > 0:01:02The emperor penguin is the only animal able
0:01:02 > 0:01:05to raise its young in the harsh Antarctic winter.
0:01:06 > 0:01:10And the tiny wood frog faces freezing conditions
0:01:10 > 0:01:13that would kill any other amphibian.
0:01:13 > 0:01:14How do they do it?
0:01:22 > 0:01:24These eggs were collected more than 100 years ago
0:01:24 > 0:01:28during an expedition to the Antarctic.
0:01:28 > 0:01:31The conditions were so cold that the man that collected them
0:01:31 > 0:01:34never made it back to England alive.
0:01:34 > 0:01:38He perished alongside Captain Scott during the ill-fated journey
0:01:38 > 0:01:40to reach the South Pole.
0:01:40 > 0:01:44The eggs were laid by an emperor penguin, a bird whose life history
0:01:44 > 0:01:48would surprise and confound those early polar explorers.
0:01:50 > 0:01:53At the end of the 19th century, the Antarctic was an unfamiliar
0:01:53 > 0:01:55and mysterious place.
0:01:55 > 0:01:58Only a handful of explorers had ventured this far south
0:01:58 > 0:02:01and there was still a huge blank in the world map.
0:02:02 > 0:02:04But then, in 1901,
0:02:04 > 0:02:09a British expedition set off on a purpose-built ship, the Discovery,
0:02:09 > 0:02:11to explore this most southerly land.
0:02:11 > 0:02:15In charge was Commander Robert Falcon Scott.
0:02:17 > 0:02:22Scott took on board with him a young man named Edward Wilson,
0:02:22 > 0:02:25who would serve as the ship's doctor and naturalist.
0:02:26 > 0:02:29Wilson had only just qualified as a surgeon
0:02:29 > 0:02:32and had no formal training in scientific research.
0:02:32 > 0:02:35But the young man's passion for natural history and art
0:02:35 > 0:02:39would prove to be an invaluable asset to the expedition.
0:02:39 > 0:02:41Wilson's job was to draw and record
0:02:41 > 0:02:43any plants and animals that they encountered.
0:02:43 > 0:02:46But from the start there was one creature that fascinated him
0:02:46 > 0:02:49more than any other - the emperor penguin.
0:02:51 > 0:02:53This largest of all penguins
0:02:53 > 0:02:56had only been discovered 60 years earlier.
0:02:56 > 0:03:01But, as yet, nothing was known about its habits or where it breeds.
0:03:01 > 0:03:04The expedition was an opportunity to find out more.
0:03:06 > 0:03:09When the Discovery reached the southern continent,
0:03:09 > 0:03:13they put up a hut in which they would spend the long, dark winter.
0:03:13 > 0:03:16Then, as the sun started to appear again in spring,
0:03:16 > 0:03:19the sledge teams started to explore,
0:03:19 > 0:03:23and one returned with some tantalising news.
0:03:23 > 0:03:26They had discovered a breeding colony of emperor penguins
0:03:26 > 0:03:29in a place called Cape Crozier.
0:03:29 > 0:03:32It was the first colony any human being had ever seen
0:03:32 > 0:03:37and, much to their surprise, the birds were breeding on sea ice.
0:03:39 > 0:03:41It was a truly astonishing discovery.
0:03:41 > 0:03:43No other bird breeds on ice,
0:03:43 > 0:03:47and Wilson was keen to find out more about this remarkable creature.
0:03:50 > 0:03:54Very little was known about emperor penguins but there was another bird
0:03:54 > 0:03:59which could give Wilson some insights into their lives - the king penguin.
0:04:01 > 0:04:06Adult king penguins look very much the same as adult emperors.
0:04:06 > 0:04:09The main difference is in size.
0:04:09 > 0:04:13These kings are only about half as big as an emperor,
0:04:13 > 0:04:16and they live in the northern part of Antarctica.
0:04:17 > 0:04:20They breed in the middle of the Antarctic summer -
0:04:20 > 0:04:25November, December - and incubation takes about seven weeks.
0:04:25 > 0:04:29Wilson thought that emperors would do very much the same.
0:04:30 > 0:04:33But he was about to discover otherwise.
0:04:33 > 0:04:37The following spring, with the hope of collecting some penguin eggs,
0:04:37 > 0:04:41Wilson left for Cape Crozier as early as he dared.
0:04:43 > 0:04:46When he got there, however, much to his surprise,
0:04:46 > 0:04:49he found only well-grown chicks.
0:04:50 > 0:04:55After repeated calculations, he finally concluded that these
0:04:55 > 0:04:59penguins must lay their eggs in the middle of the Antarctic winter.
0:05:03 > 0:05:06That emperors should start breeding at the coldest
0:05:06 > 0:05:09and bleakest time of the year was an astonishing discovery.
0:05:09 > 0:05:12It seemed to defy all the rules of nature,
0:05:12 > 0:05:15and Wilson was indeed amazed.
0:05:17 > 0:05:22But it seems that this strange lifestyle does, in fact, make sense.
0:05:22 > 0:05:25Emperor penguins are big birds and the chicks take more than
0:05:25 > 0:05:28a year to grow large enough to be independent.
0:05:28 > 0:05:31By laying the eggs earlier in winter,
0:05:31 > 0:05:33emperors give their chicks a head start
0:05:33 > 0:05:36so that they first go to sea in the summer months
0:05:36 > 0:05:37when food is plentiful.
0:05:40 > 0:05:42But how do emperor penguins protect their eggs
0:05:42 > 0:05:44and chicks from the bitter cold?
0:05:47 > 0:05:50Neither kings nor emperors make a nest
0:05:50 > 0:05:52or lay their eggs on the ground.
0:05:52 > 0:05:55If they did, the eggs would freeze within minutes.
0:05:55 > 0:05:58Instead, they keep their eggs on the top of their feet
0:05:58 > 0:06:02and cover them with a feathered fold of skin from the abdomen,
0:06:02 > 0:06:03and inside that pouch
0:06:03 > 0:06:07the temperature is about 70 degrees warmer than it is outside.
0:06:11 > 0:06:14With temperatures of minus-60 degrees Celsius,
0:06:14 > 0:06:20and winds gusting at 200km/h, the birds huddle together for warmth.
0:06:25 > 0:06:28Even under these extremely difficult conditions,
0:06:28 > 0:06:31Wilson recorded everything he saw.
0:06:31 > 0:06:32WIND ROARS
0:06:32 > 0:06:35Able to work for only a few minutes at a time,
0:06:35 > 0:06:40he still managed to produce detailed notes and drawings that give us
0:06:40 > 0:06:42a first insight into the southern continent.
0:06:47 > 0:06:51This is the expedition's scientific report.
0:06:51 > 0:06:55And it contains most of Wilson's observations on the Antarctic.
0:06:55 > 0:06:58At a time when illustrations of animals were often
0:06:58 > 0:07:00drawn from dead specimens,
0:07:00 > 0:07:04Wilson drew his subjects live in the field wherever possible,
0:07:04 > 0:07:07to capture the true nature of the animal.
0:07:07 > 0:07:10Despite the extreme conditions under which he had to work,
0:07:10 > 0:07:14he made over 900 detailed drawings in the Antarctic.
0:07:21 > 0:07:25Wilson was an exceptional artist and a meticulous scientist
0:07:25 > 0:07:29and most of his observations have stood the test of time.
0:07:29 > 0:07:32But some things puzzled him more than others.
0:07:32 > 0:07:37He noted, for example, that the brooding of the chick was not
0:07:37 > 0:07:40just carried out by one bird or even by a single pair.
0:07:40 > 0:07:45It appeared as if numerous birds were taking turns in looking after
0:07:45 > 0:07:51the chick. Today, of course, we know that this is not quite correct.
0:07:51 > 0:07:55It's only the parents who care for both the egg and then the chick.
0:07:55 > 0:07:57RAPID STACCATO CAWING
0:07:57 > 0:08:00We now have a much better understanding of how
0:08:00 > 0:08:03emperor penguins breed, but Wilson's confusion as to
0:08:03 > 0:08:07who cares for the chicks is in fact quite understandable.
0:08:07 > 0:08:08He observed numerous occasions
0:08:08 > 0:08:12when a youngster was accidentally dropped by its parent.
0:08:12 > 0:08:14In his report, he writes,
0:08:14 > 0:08:19"what we actually saw again and again was the wild dash made by adults,
0:08:19 > 0:08:23"each weighing anything up to 90 pounds, to take possession
0:08:23 > 0:08:27"of any chick that happened to find itself deserted on the ice.
0:08:27 > 0:08:31"It can be compared to nothing better than a football scrimmage."
0:08:33 > 0:08:35The birds Wilson had observed
0:08:35 > 0:08:39were in fact females who had lost their own egg or chick
0:08:39 > 0:08:43and were trying to adopt or kidnap any unattended youngsters.
0:08:45 > 0:08:50What he couldn't know was that these adoptions are never successful.
0:08:50 > 0:08:53A new parent rarely feeds its foster chick
0:08:53 > 0:08:55and simply broods it for a few days.
0:08:55 > 0:08:59After that, the youngster is abandoned again
0:08:59 > 0:09:00or dies of starvation.
0:09:09 > 0:09:12It's likely that the female eventually recognises that
0:09:12 > 0:09:14the adopted chick is not her own.
0:09:24 > 0:09:29Although Wilson had been the first man to find an emperor penguin colony,
0:09:29 > 0:09:33he had not been able to obtain any freshly laid eggs.
0:09:33 > 0:09:37These were particularly sought-after by scientists of the day.
0:09:39 > 0:09:42It was thought at that time that the emperor penguin was
0:09:42 > 0:09:44one of the most primitive birds
0:09:44 > 0:09:47and possibly a missing evolutionary link with dinosaurs.
0:09:49 > 0:09:53If embryos could be obtained at an early enough stage then maybe
0:09:53 > 0:09:57one would see reptilian scales or some other dinosaur features.
0:09:58 > 0:10:03So the emperor penguin egg was regarded as a great scientific prize.
0:10:08 > 0:10:10A few years later, Scott and Wilson
0:10:10 > 0:10:14planned a second expedition to the Antarctic.
0:10:14 > 0:10:17The main objective was to reach the South Pole,
0:10:17 > 0:10:19but Wilson was determined to bring back
0:10:19 > 0:10:21newly laid emperor penguin eggs.
0:10:23 > 0:10:27This time, he made plans to travel to Cape Crozier even earlier,
0:10:27 > 0:10:29so as not to miss the birds on eggs.
0:10:29 > 0:10:31BIRD CAWS
0:10:31 > 0:10:36He picked two men to accompany him, Bowers and Cherry-Garrard,
0:10:36 > 0:10:39and they set off in the pitch black of the winter.
0:10:40 > 0:10:46It was a journey of over 70 miles and they had to cover it on foot.
0:10:46 > 0:10:48For six painful weeks,
0:10:48 > 0:10:51the three men pulled their heavy sledges in complete darkness
0:10:51 > 0:10:56and howling gales at temperatures of minus-40 degrees centigrade.
0:10:56 > 0:11:00Never before had anyone travelled in such bitter cold
0:11:00 > 0:11:02or in such difficult conditions.
0:11:02 > 0:11:05They sometimes barely covered a mile a day.
0:11:05 > 0:11:08It was what Cherry-Garrard would later call
0:11:08 > 0:11:10"the worst journey in the world".
0:11:12 > 0:11:14Their clothes were iced up and their breath
0:11:14 > 0:11:16and sweat froze on their bodies.
0:11:19 > 0:11:23Each night, it took them an hour to chip into their sleeping bags,
0:11:23 > 0:11:25which were frozen solid.
0:11:29 > 0:11:33When they finally reached the penguin colony, they collected five eggs,
0:11:33 > 0:11:38with great difficulty, and put them inside their mittens for safety.
0:11:38 > 0:11:41The men staggered back to base camp close to death
0:11:41 > 0:11:44and only three eggs survived the journey.
0:11:44 > 0:11:46These are two of them.
0:11:49 > 0:11:52It was an extraordinary feat of determination
0:11:52 > 0:11:54by Wilson and his companions.
0:11:54 > 0:11:58The precious eggs were supposed to reveal the evolutionary links
0:11:58 > 0:12:00between reptiles and birds,
0:12:00 > 0:12:03but getting them had nearly killed the collectors.
0:12:05 > 0:12:07A few months later,
0:12:07 > 0:12:12Scott led his party on the final push to reach the South Pole.
0:12:12 > 0:12:15His team consisted of just five men,
0:12:15 > 0:12:17and Wilson was amongst them.
0:12:19 > 0:12:24On their return journey, all five men perished, succumbing to the cold
0:12:24 > 0:12:29and starvation just a few kilometres from their nearest food depot.
0:12:31 > 0:12:33In the end, Wilson's eggs didn't contribute as much
0:12:33 > 0:12:36to our understanding of the development of the penguin chick
0:12:36 > 0:12:40as he had hoped, but his beautiful drawings
0:12:40 > 0:12:44and meticulous observations are quite a different matter.
0:12:44 > 0:12:48They helped to unravel the biology of a bird that is able
0:12:48 > 0:12:52to rear its young in the depths of the polar winter.
0:12:56 > 0:12:58The emperor penguin amazes us
0:12:58 > 0:13:02by raising its chicks in the most inhospitable place on earth.
0:13:02 > 0:13:06But a small frog has a way of coping with the cold
0:13:06 > 0:13:08that seems to be beyond belief.
0:13:10 > 0:13:13This is a North American wood frog,
0:13:13 > 0:13:16and it lives as far north as the Arctic Circle,
0:13:16 > 0:13:18but, like all cold-blooded creatures,
0:13:18 > 0:13:22it can't generate its own heat and its body temperature rises
0:13:22 > 0:13:24and falls with the surroundings.
0:13:24 > 0:13:28So when conditions drop below zero the frog risks freezing.
0:13:28 > 0:13:32How does a creature like this survive the harsh winters?
0:13:35 > 0:13:40The skin of amphibians is thin and moist and this makes them
0:13:40 > 0:13:43particularly vulnerable to the cold.
0:13:43 > 0:13:47Any contact with ice can instantly trigger freezing within
0:13:47 > 0:13:52their bodies and, for most animals, this means almost certain death.
0:13:54 > 0:13:56When water freezes, it expands,
0:13:56 > 0:13:59and the sharp ice crystals can puncture blood vessels
0:13:59 > 0:14:03and break cell walls, causing irreparable damage.
0:14:03 > 0:14:07The animal's internal organs may never function properly again.
0:14:09 > 0:14:12So, how do frogs avoid freezing?
0:14:13 > 0:14:18Many sit out the winter by hibernating at the bottom of a pond.
0:14:18 > 0:14:20The surface may freeze but underneath the ice
0:14:20 > 0:14:24the temperature remains just above freezing.
0:14:25 > 0:14:28And most land-living amphibians seek out a sheltered spot
0:14:28 > 0:14:31on the ground to avoid the deadly frost.
0:14:36 > 0:14:40But, in the 18th century, Arctic travellers came back with tales
0:14:40 > 0:14:43so extraordinary they were scarcely believable.
0:14:45 > 0:14:50A British explorer called Samuel Hearne reported seeing
0:14:50 > 0:14:53frozen frogs among the piles of leaves in Arctic Canada.
0:14:55 > 0:14:59He went on to make an extraordinary claim.
0:14:59 > 0:15:03"Frogs of various colours are numerous in these parts.
0:15:03 > 0:15:06"I have frequently seen them dug up with moss,
0:15:06 > 0:15:08"frozen as hard as ice,
0:15:08 > 0:15:13"in which state the legs are as easily broken off as a pipe stem,
0:15:13 > 0:15:17"without giving the least sensation to the animals.
0:15:18 > 0:15:22"But, by wrapping them up in warm skins and exposing them
0:15:22 > 0:15:26"to a slow fire, they soon recover life
0:15:26 > 0:15:29"and the mutilated animal gains its usual activity."
0:15:33 > 0:15:37Frozen frogs that, if gently warmed by a fire, would come back to life.
0:15:37 > 0:15:40What truth could there be in this account?
0:15:40 > 0:15:41Well...
0:15:42 > 0:15:44..this is a marsh frog
0:15:44 > 0:15:47and it's found in ponds and marshes throughout
0:15:47 > 0:15:49central and northern Europe.
0:15:49 > 0:15:54It's lying completely immobile on my hand because it's frozen solid.
0:15:56 > 0:15:58From the outside, it feels much like a rock.
0:15:58 > 0:16:02And you might be forgiven for thinking it was dead.
0:16:02 > 0:16:06Well, watch what happens when I put it into a bowl of warm water.
0:16:14 > 0:16:18Although it appears dead and has in fact stopped breathing,
0:16:18 > 0:16:20the frog's heart is still beating.
0:16:20 > 0:16:22Only the outer layer has frozen.
0:16:22 > 0:16:25The vital organs inside are still undamaged.
0:16:29 > 0:16:33Lab experiments have shown that, in this state, the marsh frog
0:16:33 > 0:16:37can survive temperatures of two degrees below freezing.
0:16:40 > 0:16:43Yes! It's lifted itself up, it's moving.
0:16:43 > 0:16:44Look at this.
0:16:45 > 0:16:49There, it's moving its right leg.
0:16:49 > 0:16:53Within a few minutes the frog has awakened to life once again.
0:16:56 > 0:16:59This is surely one of the most extraordinary miracles of nature.
0:17:02 > 0:17:07Nonetheless, the marsh frog can only survive a few hours of freezing.
0:17:07 > 0:17:10Anything more would mean certain death.
0:17:11 > 0:17:15Where it lives, it rarely faces extreme winters
0:17:15 > 0:17:18and is protected from the worst by the insulating water.
0:17:20 > 0:17:23So what about Samuel Hearne's story?
0:17:23 > 0:17:27Could some frogs survive longer periods of freezing?
0:17:27 > 0:17:31Another account from North America would seem to suggest so.
0:17:32 > 0:17:36In the 19th century, a naturalist called John Burroughs
0:17:36 > 0:17:39found a wood frog underneath the leaf litter
0:17:39 > 0:17:41at the beginning of the winter.
0:17:41 > 0:17:43Burroughs was surprised,
0:17:43 > 0:17:47but reasoned that the frog must know that a mild winter was on the way
0:17:47 > 0:17:50and had therefore not bothered to bury itself deeper.
0:17:52 > 0:17:55In fact, a very severe winter followed.
0:17:57 > 0:18:01Wondering about his frog, Burroughs went back to the same spot
0:18:01 > 0:18:05in spring and found the animal seemingly unharmed.
0:18:06 > 0:18:09The wood frog must have spent the entire winter above ground
0:18:09 > 0:18:13and survived temperatures that should have killed it.
0:18:14 > 0:18:16How did the tiny frog do it?
0:18:19 > 0:18:23The wood frog is not strong and large enough to dig itself into the ground,
0:18:23 > 0:18:27so it has to sit out the winter beneath the leaf litter.
0:18:27 > 0:18:31But this doesn't provide sufficient protection against the cold.
0:18:31 > 0:18:34So, how does this small frog survive?
0:18:35 > 0:18:36Today, we know the truth,
0:18:36 > 0:18:40and if Burroughs had done so he would have been astounded.
0:18:43 > 0:18:46It's only recently that we've discovered just how the wood frog
0:18:46 > 0:18:50avoids the usually fatal consequences of freezing.
0:18:52 > 0:18:57As winter sets in, the frog prepares for an extraordinary change.
0:19:05 > 0:19:08First, it draws water out of its cells into spaces where it
0:19:08 > 0:19:10will do less damage if it freezes.
0:19:11 > 0:19:15At the same time, its liver produces large amounts of sugar
0:19:15 > 0:19:17that act as antifreeze.
0:19:17 > 0:19:21This is pumped through the body to slow down the freezing.
0:19:27 > 0:19:33Now the entire frog slowly freezes from the outside inwards.
0:19:44 > 0:19:47And finally, the heart stops.
0:19:47 > 0:19:49The frog isn't dead,
0:19:49 > 0:19:52but it's probably about as close as you can get.
0:19:53 > 0:19:5670% of its body is frozen.
0:19:56 > 0:20:00And it can remain like this for several weeks on end.
0:20:08 > 0:20:11Then, as the air warms up again,
0:20:11 > 0:20:13a miraculous transformation takes place.
0:20:15 > 0:20:20The ice melts and the frog's body thaws and suddenly
0:20:20 > 0:20:23the heart sprouts back to life.
0:20:27 > 0:20:31Unlike the marsh frog, the deeply frozen wood frog needs
0:20:31 > 0:20:35several hours before it can resume normal activity.
0:20:40 > 0:20:43The wood frog's ability to survive in a frozen state
0:20:43 > 0:20:46has fascinated scientists.
0:20:46 > 0:20:50Could this one day help enhance our own medical understanding?
0:20:52 > 0:20:55We still don't understand completely how the wood frogs survive
0:20:55 > 0:20:58something that would kill most animals.
0:20:58 > 0:21:02What we do know is that, when freezing occurs slowly
0:21:02 > 0:21:06and in the right places, it appears to do less damage.
0:21:06 > 0:21:09This little frog seems to have mastered the problem
0:21:09 > 0:21:12by controlling how and where ice forms in its body.
0:21:15 > 0:21:18The emperor penguin's ability to breed during the Antarctic winter
0:21:18 > 0:21:21is a remarkable feat of endurance,
0:21:21 > 0:21:26but for a small frog to freeze solid and come back to life
0:21:26 > 0:21:30must surely be one of the most astonishing curiosities of nature.