Natural World (1983) s30e07 Episode Script
Panda Makers
Million dollar bears adored, unique and, quite literally, iconic.
Man and giant panda have shared an eventful century.
We have pushed the symbol of conservation to the brink of extinction.
And now few remain in the wild.
But an international rescue is underway.
It's an attempt to correct our mistakes.
This is the most costly and controversial conservation effort ever mounted.
It's full of risk and reward.
It will use pioneering science .
.
to create a population of giant pandas in captivity and then set them free.
They once roamed from Beijing to Vietnam.
Now, in the craggy mountain ranges of western China, only around 2,000 giant pandas remain.
This most famous of endangered animals is rarely seen, and little understood.
Until recently no-one was even sure that it was a bear.
But it is an enigmatic and peculiar one .
.
a carnivore that exists on a diet of a kind of grass bamboo.
A slow reproducer that often has twins, but nearly always abandons one cub and lets it die.
The panda doesn't seem designed for long-term survival.
Yet, incredibly, it has survived and for millions of years.
Their greatest threat is modern man.
Below the mountains which are their home, the city of Chengdu.
Ten million people live here but little else.
In a busy suburb, however, there are pandas.
This is Chengdu Research Base of Giant Panda Breeding.
It was founded just over 20 years ago with 6 rescued pandas.
Now it's the world's leading panda breeding centre.
For tourists it's a place for a good day out.
And it offers an extraordinary opportunity to see a very rare mammal.
But the years of work here have not been to create a zoo.
This is a man-made solution to a man-made problem an insurance policy against extinction.
A place where captive pandas are held safe because the fate of wild pandas is so uncertain.
50 years ago, no-one had bred a giant panda in captivity.
It seemed an unachievable dream.
By the end of last year, the team at Chengdu had produced 136.
68 pandas live at the base, including these, last year's cubs, being brought in for the night.
They'll grow up here, on the edge of the city, as China's other cities spread relentlessly into the wild.
Can the giant panda continue to compete? Half its habitat has been destroyed in two decades.
Humans, after all, have needs as well.
Forests have been cleared for farmland.
The wood cut for fuel.
What remains of the panda population has been pushed higher and higher into the mountains .
.
and divided by development into isolated groups, some too small to survive.
Efforts are now being made to protect the habitat that's left.
But, with so much damage done, there's no guarantee the slow-breeding panda will be able to rebuild its population without help.
So, here, at the Panda Base, they're making more.
The ultimate goal is to release them into the wild.
It's a risky and controversial plan.
It's been tried only once before, and it failed.
No-one knows if these pandas have the skills to survive in the wild.
So it's vital that there's a stable breeding population before they try to release any.
Experts put that number at 300.
When they reach it, re-introduction can start.
These pandas, however, are completely dependent on their keepers for survival.
The dream is that one day they could be free.
For now, the staff are busy with the day-to-day care and ongoing research.
And with none of the right kind of bamboo growing near Chengdu, the pandas can't even feed themselves here.
And they need vast amounts.
Finding the shoots and, after winter, the roots, involves a 100-mile round trip to small areas of forest on the edge of mountain farms.
The villagers climb high into the mountains to find the best patches.
Wild pandas spend at least ten hours a day selecting bamboo and the villagers put in the same amount of time.
Now begins the long descent.
Each bundle weighs around 60 kilos.
And the pandas, which are very fussy, will reject two-thirds of it.
More cutters carry bundles from the forest to the waiting truck where they're weighed.
THE BAMBOO CUTTERS TALK AMONGST THEMSELVES It's a good income for the farmers, and a regular one.
The quantity needed is huge.
This truckload will last the Chengdu pandas for just one day.
Spring, and last year's cubs are getting to grips with climbing.
It's the breeding season, the busiest time of Chengdu's year.
13 female pandas have been brought to the nursery for observation.
They hope that as many as possible will mate, but breeding pandas is far from easy.
Part of the problem is timing.
Pandas are on heat for only 72 hours a year.
Within that time, there is only a 12 to 24-hour window in which mating could produce a pregnancy.
Several show signs that they might be coming into heat, among them a young female, Ya Shuan.
Meanwhile, over in the males' enclosure a top spectacle for visitors - the dancing bears.
Tough work, and perhaps, for some of us, uncomfortable viewing.
But there's a serious purpose behind it.
These males, whose lives are more sedentary than those in the wild, have a daily sexercise to strengthen the leg muscles in preparation for the rigours of mating.
In the wild, they'll mate with as many females as they can, but the conditions in captivity simply turn them off.
Food, though, is something they always find interesting.
Mating is all they're required to do here at the research base, but most captive males have never succeeded in siring young.
In trying to persuade them to do so, the scientists have tried some imaginative solutions, from panda porn to Viagra.
But the most useful ideas have come from watching pandas in the wild.
By nature, pandas are solitary.
But during the breeding season they sniff out mates and discover who is around from communal scent-mark stations.
Scent plays a pivotal role in courtship.
Males go to great lengths to leave their urine as high above the ground as possible.
A clear, if perhaps deceptive, message about their size and virility.
Female scent carries information about their fertility.
For both sexes, the smells are clearly aphrodisiacs.
So keepers simply collect urine from the enclosure floor with a syringe and use science to interpret the messages it contains.
A sample provided by the young female, Ya Shuan, is being taken to the lab.
At four and a half years old, this panda is only just sexually mature.
They'll be able to tell from the hormones in her urine whether she's close to peak fertility.
This is one of the many breakthroughs that have come from collaborations with western zoos and has brought an end to guesswork.
The analyses are called up on-screen.
Ya Shuan is ready.
The team has only a few hours to match her with the right mate.
The best candidate is Pin Pin.
He's brought to the nursery and placed in an adjoining pen.
To help things along, one of the vets uses a stem of bamboo to touch the glands under Ya Shuan's tail.
Then it's held for Pin Pin to sniff, in the hope he'll find her scent arousing.
But he is more interested in the bamboo itself.
It's going to be a long session.
If the pandas are not attracted sexually to one another they will fight.
So the vets wait until interest picks up before opening the dividing gate.
For young Ya Shuan, this isn't just her first opportunity to mate, it's the first time she has even been close to another adult panda.
Neither of them seem to have any idea of how to go about things.
Most captive-born pandas seem to have lost the knowledge of how to get in the right position.
And position is crucial, because of the male's disproportionately short penis.
Even when things are going well, mating can take many attempts.
And things aren't going well.
They take time out.
Pin Pin's frustration is beginning to show.
After a bite to eat, they try again.
This time, both pandas seem more excited.
Pin Pin hangs onto Ya Shuan's neck in an effort to hold her in place.
A bit of aggression is normal, but after repeated attempts they are both tired and there is a risk of a serious fight.
Frustration and confusion are not a winning combination.
Mating is called off.
In the wild, with perfect conditions and a little foreplay, things are a lot easier.
It's a myth that pandas aren't interested in sex.
They're just picky about their partners.
There's no time to try Ya Shuan with another male.
So they're ready with an alternative.
Pin Pin, genetically, is a suitable mate, so they will collect his sperm and use it to artificially inseminate her.
Under sedation, the male panda's deficiencies are starkly exposed.
They rush to check that they have healthy sperm before they let him go.
The anaesthetist now prepares to dart Ya Shuan.
They have to act fast.
Miss this one opportunity, and they will have to wait a year for the next.
If the timing is spot on, there's a good chance she will conceive.
To increase the chances of conception, they'll often inseminate a female with sperm from a number of different pandas.
A team of 15 vets work with rehearsed precision.
They insert a catheter .
.
and use a syringe to inject the sperm into her womb.
The operation has gone well .
.
and it's all over in just five minutes.
Ya Shuan is returned to her pen to sleep off the effects .
.
and a couple of hours later, she is sitting outside, her appetite unaffected by events.
They won't know if she is pregnant until just before she gives birth.
And, remarkably, that can happen after about 11 weeks, or after nearly 11 months.
So, with a delivery date impossible to predict, all the staff can do is wait.
Meanwhile, over in the lab, the scientists are busy with a new problem - inbreeding.
A staggering 60% of today's total captive population is descended from just four male pandas.
As a result, there's a real risk of pandas being mated with their close relatives.
So Chengdu helps coordinate breeding programmes around the world.
One solution is sharing pandas.
A better one is sharing their sperm.
The scientists perfected a way of freezing panda sperm, and have created a sperm bank.
Now, they're able to pick and choose the best genetic match for female pandas, here and at foreign zoos.
And they're carrying out paternity testing for pandas, so each sample can be stored with its family history attached.
Their sperm bank is a priceless resource, protecting today's genetic diversity against a disaster that could wipe out a generation.
The remaining sperm taken from Pin Pin this morning will be frozen in liquid nitrogen, ready for use in years to come.
That may be long beyond his lifetime and on a far continent.
This advance could end the long history of taking pandas out of China.
The first person to bring a panda alive to the western world was a New York fashion designer, Ruth Harkness.
When asked how she did it, she said, "It behaved as a baby "and was treated as any human child would have been".
Su Lin arrived in 1937.
A second one came in the following year.
The cubs were taken to cocktail parties and press receptions, and slept in hotels before ending up at Brookfield Zoo, Chicago.
No-one in the western world had ever seen a living giant panda and they created a sensation.
Pandamania spread and with big money on offer, hunters travelled to Chengdu and went on up into the mountains in a great panda free-for-all.
Soon pandas were being shipped and flown to zoos across the west, despite attempts by the Chinese authorities to prevent it.
The plunder was forcibly banned by the newly founded People's Republic of China in 1949.
Under communism, pandas became the acceptable face of China - entertaining ambassadors from a secretive regime.
The giant panda had become a political animal.
Starting in 1953, the Chinese Government sent over 20 giant pandas overseas as gifts, initially to the Soviet Union and Korea, to reward alliances, and then to the West, in order to forge them.
Nixon's surprise visit to China in 1972 won America two pandas - Hsing-Hsing and Ling-Ling, from Chairman Mao.
Two years later, Edward Heath went to China, and received Chia-Chia and Ching-Ching for London Zoo.
Pandas were bringing hordes of paying visitors to foreign zoos.
Meanwhile in China, they were becoming increasingly scarce.
So the Chinese stopped handing out pandas as gifts and from the early 1990s adopted a new policy.
Pairs of pandas were now loaned to zoos for a million dollars a year, and the zoos' collaboration in research.
This influx of tens of millions of dollars and international expertise marked a turning point in the panda's survival.
When Zoo Atlanta received two pandas from Chengdu, it was on these terms.
And east-west teamwork led to the birth of a cub - Mei Lan.
Mei Lan! Mei Lan! Under the terms of the loan, all cubs born in foreign zoos have Chinese citizenship.
Mei Lan belongs to China.
And now she's nearly four, they want her back.
SIREN She is priceless cargo.
She travels in presidential style and has a private plane.
This VIP is returning to China to do her bit for her species.
Her arrival in China is greeted in quintessential Chinese style.
CHEERING A crowd is waiting for her at the research base.
She ends her journey at the quarantine house.
MEI LAN YAPS The transfer is inevitably traumatic for Mei Lan.
And for Heather, the American keeper who raised her from a cub.
After this inevitable upheaval, she will receive exceptional care.
And she has a new keeper of her own.
The following morning, Mei Lan's depression is only too clear.
MEI LAN BARKS Her food remains untouched.
Mei Lan.
For her keepers, old and new, it's a distressing sight.
They can only hope that she will soon adjust to her new life.
Six months later - late summer .
.
And Mei Lan is now settled and content.
Next year she will join the breeding programme.
Over at the panda nursery meanwhile, everyone is waiting for this season's births to begin.
It seems that Ya Shuan, the panda that was inseminated, isn't pregnant.
But hopes are high that as many as eight of the others are.
The nursery boss, Wang Cheng-Dong makes a twice daily inspection.
But even he finds it hard to draw any conclusions.
Because of a biological quirk, pandas that come into heat but haven't actually conceived show all the same signs as those females who are actually pregnant, right down to the profiles of their hormones.
So all pandas are given the benefit of the doubt and extra rations.
It's two o'clock in the morning and the vets are woken to take a look at one of the pregnant females who seems a little agitated.
Li Li, a 17-year old, has in the past only given birth to stillborns or young that have died within days.
It seems she may be about to produce the first cub of the season.
PANDA CUB SQUEAKS There is enormous relief when she gives birth to a healthy baby.
Some panda mothers are frightened by all the fuss and panic or refuse to accept their newborn cubs.
But Li Li cradles hers.
With her first baby cub already suckling, she produces a second.
She can't deal with them both, so the second cub is taken to a warm incubator.
Newborns weigh little over a hundred grams, so the next ten days will be critical.
The vets hope that mothers will raise their cubs with little human intervention.
But if a mother abandons her newborn cub, or if the cub is weak, they step in.
These cubs receive intensive care in the incubators for the first five to six weeks.
But all newborns spend some time here so they can be monitored, and if necessary, given a supplementary feed.
The temperature is set to match the warmth of the mother's body deep within her fur.
They are weighed throughout the day and night to check that they're taking in enough of their mother's milk.
And over the course of two weeks, they begin to look a little bit more like pandas.
It has been 18 days since Li Li gave birth.
For her to produce twins is not unusual - half of all panda births result in them.
But for both twins to survive, certainly is.
Pandas almost always abandon one cub.
It's thought that they don't have sufficient milk or energy to care for two.
But the team at Chengdu have hit upon a cunning plan.
By removing one cub at birth and then switching them throughout the day and night, keepers are able to encourage panda mothers to feed both siblings, while being under the impression that they have only one.
Li Li is distracted with a bowl of honey water, but is reluctant to give up her cub.
Doing this successfully requires enormous patience from the keeper and great trust from the panda.
One twin is taken to the incubator where it will have a top-up of formula milk, and switched with the other, which will now get his share of his mother's milk.
The keeper will swap the twins up to ten times a day.
And Li Li will almost always have one cub with her.
Chengdu's technique of twin-swapping at last opens the way to a possible 100% survival rate in newborn captive cubs.
It's winter.
Li Li's cubs are four and a half months old.
They are as inquisitive about people as people are about them.
They spend part of the day supervised in a playpen together.
And with a third cub.
At two and a half months, he's crawling, but he prefers to sleep.
His sight, like his hearing, is still developing.
After 13 births last year, this year the breeding centre had only four.
The youngest is six weeks old.
Still helpless, but fat and healthy.
Her legs, however, aren't yet strong enough to support her weight.
So she will remain in the incubator for at least another week.
The cubs will stay here in the incubator room until they get their own pen at six months.
But they spend much of the day and night with their mothers.
The twins arriving in alternate deliveries.
Li Li's bond with her cubs is strong.
She's very maternal and restless when they're away.
In the wild, she would give birth every two or three years and keep her cub beside her for 18 months or more.
Her twins will soon be weaned, so she can build her strength for breeding next year.
It's a milestone day.
The twins are about to take their first steps into the outside world.
They are, understandably, somewhat wide-eyed.
Their very existence is a triumph for science and skill .
.
Combined with love.
But unless captive-born pandas like these can be released, the extraordinary achievements of the Chengdu team will do little to help the plight of pandas in the wild.
And that continues to be their goal.
The first requirement was to build the worldwide population of captive pandas and produce that critical number of 300.
And, counting these twins, they've made it.
Now is the time for an even greater challenge - to wean the pandas off the human life-support and release them to the wild.
The road to freedom will be a long one.
What will the sociable, trusting pandas from the base make of a solitary life in the wild? They will need to establish and defend a territory, choose their mates, and the females raise their cubs alone.
Is that possible? The truth is no-one knows.
Almost all reintroduction programmes of any rare animal start with failure and death.
But the alternative is to abandon all hope and risk the total loss of a species.
But a new generation in China is waking up to the importance of panda conservation.
Chengdu's teachers visit schools to talk about wildlife.
Efforts are being made to protect panda habitat.
67 panda reserves, amounting to one and a half million hectares, have now been established.
Spending on conservation has doubled in ten years.
There are bans on logging and hunting.
And farmers who turn fields back to the wild are being properly rewarded.
China's first giant panda reintroduction centre is to be built above farmland inside the Sichuan Giant Panda Sanctuaries, a World Heritage site.
The site will have three different zones, each wilder, bigger and higher than the one before.
The pandas will be introduced gradually to the great outdoors.
Only the best-adapted will be freed.
The entire process will take at least 15 years.
There are signs that some wild pandas are still living high in the mountains.
One day those born at the base may find mates from among them.
It is perhaps fitting that the millions of dollars invested in returning the giant panda to the wild have come largely from the fees paid by zoos around the world, to exhibit them in captivity.
And the sanctuary into which the first panda will be released is within the very forest from which the western hunters first took one.
This is the first generation of captive-born giant panda cubs to have a real chance of life in the wild.
It's a bold and controversial move.
And it may not work.
There are those who argue that panda conservation is possibly one of the biggest wastes of conservation money in the last half century.
But we are, in a way, repaying man's debt, simply repairing what we shouldn't have broken, returning what we shouldn't have taken.
And we are using the knowledge and proceeds from pandas in captivity with which to do it.
It's a test case.
After all, if we cannot protect the long-term survival of the giant panda, the icon of global conservation, what chance do we have of protecting those species which do not intrigue us, entertain us and command such passionate adoration the world over?
Man and giant panda have shared an eventful century.
We have pushed the symbol of conservation to the brink of extinction.
And now few remain in the wild.
But an international rescue is underway.
It's an attempt to correct our mistakes.
This is the most costly and controversial conservation effort ever mounted.
It's full of risk and reward.
It will use pioneering science .
.
to create a population of giant pandas in captivity and then set them free.
They once roamed from Beijing to Vietnam.
Now, in the craggy mountain ranges of western China, only around 2,000 giant pandas remain.
This most famous of endangered animals is rarely seen, and little understood.
Until recently no-one was even sure that it was a bear.
But it is an enigmatic and peculiar one .
.
a carnivore that exists on a diet of a kind of grass bamboo.
A slow reproducer that often has twins, but nearly always abandons one cub and lets it die.
The panda doesn't seem designed for long-term survival.
Yet, incredibly, it has survived and for millions of years.
Their greatest threat is modern man.
Below the mountains which are their home, the city of Chengdu.
Ten million people live here but little else.
In a busy suburb, however, there are pandas.
This is Chengdu Research Base of Giant Panda Breeding.
It was founded just over 20 years ago with 6 rescued pandas.
Now it's the world's leading panda breeding centre.
For tourists it's a place for a good day out.
And it offers an extraordinary opportunity to see a very rare mammal.
But the years of work here have not been to create a zoo.
This is a man-made solution to a man-made problem an insurance policy against extinction.
A place where captive pandas are held safe because the fate of wild pandas is so uncertain.
50 years ago, no-one had bred a giant panda in captivity.
It seemed an unachievable dream.
By the end of last year, the team at Chengdu had produced 136.
68 pandas live at the base, including these, last year's cubs, being brought in for the night.
They'll grow up here, on the edge of the city, as China's other cities spread relentlessly into the wild.
Can the giant panda continue to compete? Half its habitat has been destroyed in two decades.
Humans, after all, have needs as well.
Forests have been cleared for farmland.
The wood cut for fuel.
What remains of the panda population has been pushed higher and higher into the mountains .
.
and divided by development into isolated groups, some too small to survive.
Efforts are now being made to protect the habitat that's left.
But, with so much damage done, there's no guarantee the slow-breeding panda will be able to rebuild its population without help.
So, here, at the Panda Base, they're making more.
The ultimate goal is to release them into the wild.
It's a risky and controversial plan.
It's been tried only once before, and it failed.
No-one knows if these pandas have the skills to survive in the wild.
So it's vital that there's a stable breeding population before they try to release any.
Experts put that number at 300.
When they reach it, re-introduction can start.
These pandas, however, are completely dependent on their keepers for survival.
The dream is that one day they could be free.
For now, the staff are busy with the day-to-day care and ongoing research.
And with none of the right kind of bamboo growing near Chengdu, the pandas can't even feed themselves here.
And they need vast amounts.
Finding the shoots and, after winter, the roots, involves a 100-mile round trip to small areas of forest on the edge of mountain farms.
The villagers climb high into the mountains to find the best patches.
Wild pandas spend at least ten hours a day selecting bamboo and the villagers put in the same amount of time.
Now begins the long descent.
Each bundle weighs around 60 kilos.
And the pandas, which are very fussy, will reject two-thirds of it.
More cutters carry bundles from the forest to the waiting truck where they're weighed.
THE BAMBOO CUTTERS TALK AMONGST THEMSELVES It's a good income for the farmers, and a regular one.
The quantity needed is huge.
This truckload will last the Chengdu pandas for just one day.
Spring, and last year's cubs are getting to grips with climbing.
It's the breeding season, the busiest time of Chengdu's year.
13 female pandas have been brought to the nursery for observation.
They hope that as many as possible will mate, but breeding pandas is far from easy.
Part of the problem is timing.
Pandas are on heat for only 72 hours a year.
Within that time, there is only a 12 to 24-hour window in which mating could produce a pregnancy.
Several show signs that they might be coming into heat, among them a young female, Ya Shuan.
Meanwhile, over in the males' enclosure a top spectacle for visitors - the dancing bears.
Tough work, and perhaps, for some of us, uncomfortable viewing.
But there's a serious purpose behind it.
These males, whose lives are more sedentary than those in the wild, have a daily sexercise to strengthen the leg muscles in preparation for the rigours of mating.
In the wild, they'll mate with as many females as they can, but the conditions in captivity simply turn them off.
Food, though, is something they always find interesting.
Mating is all they're required to do here at the research base, but most captive males have never succeeded in siring young.
In trying to persuade them to do so, the scientists have tried some imaginative solutions, from panda porn to Viagra.
But the most useful ideas have come from watching pandas in the wild.
By nature, pandas are solitary.
But during the breeding season they sniff out mates and discover who is around from communal scent-mark stations.
Scent plays a pivotal role in courtship.
Males go to great lengths to leave their urine as high above the ground as possible.
A clear, if perhaps deceptive, message about their size and virility.
Female scent carries information about their fertility.
For both sexes, the smells are clearly aphrodisiacs.
So keepers simply collect urine from the enclosure floor with a syringe and use science to interpret the messages it contains.
A sample provided by the young female, Ya Shuan, is being taken to the lab.
At four and a half years old, this panda is only just sexually mature.
They'll be able to tell from the hormones in her urine whether she's close to peak fertility.
This is one of the many breakthroughs that have come from collaborations with western zoos and has brought an end to guesswork.
The analyses are called up on-screen.
Ya Shuan is ready.
The team has only a few hours to match her with the right mate.
The best candidate is Pin Pin.
He's brought to the nursery and placed in an adjoining pen.
To help things along, one of the vets uses a stem of bamboo to touch the glands under Ya Shuan's tail.
Then it's held for Pin Pin to sniff, in the hope he'll find her scent arousing.
But he is more interested in the bamboo itself.
It's going to be a long session.
If the pandas are not attracted sexually to one another they will fight.
So the vets wait until interest picks up before opening the dividing gate.
For young Ya Shuan, this isn't just her first opportunity to mate, it's the first time she has even been close to another adult panda.
Neither of them seem to have any idea of how to go about things.
Most captive-born pandas seem to have lost the knowledge of how to get in the right position.
And position is crucial, because of the male's disproportionately short penis.
Even when things are going well, mating can take many attempts.
And things aren't going well.
They take time out.
Pin Pin's frustration is beginning to show.
After a bite to eat, they try again.
This time, both pandas seem more excited.
Pin Pin hangs onto Ya Shuan's neck in an effort to hold her in place.
A bit of aggression is normal, but after repeated attempts they are both tired and there is a risk of a serious fight.
Frustration and confusion are not a winning combination.
Mating is called off.
In the wild, with perfect conditions and a little foreplay, things are a lot easier.
It's a myth that pandas aren't interested in sex.
They're just picky about their partners.
There's no time to try Ya Shuan with another male.
So they're ready with an alternative.
Pin Pin, genetically, is a suitable mate, so they will collect his sperm and use it to artificially inseminate her.
Under sedation, the male panda's deficiencies are starkly exposed.
They rush to check that they have healthy sperm before they let him go.
The anaesthetist now prepares to dart Ya Shuan.
They have to act fast.
Miss this one opportunity, and they will have to wait a year for the next.
If the timing is spot on, there's a good chance she will conceive.
To increase the chances of conception, they'll often inseminate a female with sperm from a number of different pandas.
A team of 15 vets work with rehearsed precision.
They insert a catheter .
.
and use a syringe to inject the sperm into her womb.
The operation has gone well .
.
and it's all over in just five minutes.
Ya Shuan is returned to her pen to sleep off the effects .
.
and a couple of hours later, she is sitting outside, her appetite unaffected by events.
They won't know if she is pregnant until just before she gives birth.
And, remarkably, that can happen after about 11 weeks, or after nearly 11 months.
So, with a delivery date impossible to predict, all the staff can do is wait.
Meanwhile, over in the lab, the scientists are busy with a new problem - inbreeding.
A staggering 60% of today's total captive population is descended from just four male pandas.
As a result, there's a real risk of pandas being mated with their close relatives.
So Chengdu helps coordinate breeding programmes around the world.
One solution is sharing pandas.
A better one is sharing their sperm.
The scientists perfected a way of freezing panda sperm, and have created a sperm bank.
Now, they're able to pick and choose the best genetic match for female pandas, here and at foreign zoos.
And they're carrying out paternity testing for pandas, so each sample can be stored with its family history attached.
Their sperm bank is a priceless resource, protecting today's genetic diversity against a disaster that could wipe out a generation.
The remaining sperm taken from Pin Pin this morning will be frozen in liquid nitrogen, ready for use in years to come.
That may be long beyond his lifetime and on a far continent.
This advance could end the long history of taking pandas out of China.
The first person to bring a panda alive to the western world was a New York fashion designer, Ruth Harkness.
When asked how she did it, she said, "It behaved as a baby "and was treated as any human child would have been".
Su Lin arrived in 1937.
A second one came in the following year.
The cubs were taken to cocktail parties and press receptions, and slept in hotels before ending up at Brookfield Zoo, Chicago.
No-one in the western world had ever seen a living giant panda and they created a sensation.
Pandamania spread and with big money on offer, hunters travelled to Chengdu and went on up into the mountains in a great panda free-for-all.
Soon pandas were being shipped and flown to zoos across the west, despite attempts by the Chinese authorities to prevent it.
The plunder was forcibly banned by the newly founded People's Republic of China in 1949.
Under communism, pandas became the acceptable face of China - entertaining ambassadors from a secretive regime.
The giant panda had become a political animal.
Starting in 1953, the Chinese Government sent over 20 giant pandas overseas as gifts, initially to the Soviet Union and Korea, to reward alliances, and then to the West, in order to forge them.
Nixon's surprise visit to China in 1972 won America two pandas - Hsing-Hsing and Ling-Ling, from Chairman Mao.
Two years later, Edward Heath went to China, and received Chia-Chia and Ching-Ching for London Zoo.
Pandas were bringing hordes of paying visitors to foreign zoos.
Meanwhile in China, they were becoming increasingly scarce.
So the Chinese stopped handing out pandas as gifts and from the early 1990s adopted a new policy.
Pairs of pandas were now loaned to zoos for a million dollars a year, and the zoos' collaboration in research.
This influx of tens of millions of dollars and international expertise marked a turning point in the panda's survival.
When Zoo Atlanta received two pandas from Chengdu, it was on these terms.
And east-west teamwork led to the birth of a cub - Mei Lan.
Mei Lan! Mei Lan! Under the terms of the loan, all cubs born in foreign zoos have Chinese citizenship.
Mei Lan belongs to China.
And now she's nearly four, they want her back.
SIREN She is priceless cargo.
She travels in presidential style and has a private plane.
This VIP is returning to China to do her bit for her species.
Her arrival in China is greeted in quintessential Chinese style.
CHEERING A crowd is waiting for her at the research base.
She ends her journey at the quarantine house.
MEI LAN YAPS The transfer is inevitably traumatic for Mei Lan.
And for Heather, the American keeper who raised her from a cub.
After this inevitable upheaval, she will receive exceptional care.
And she has a new keeper of her own.
The following morning, Mei Lan's depression is only too clear.
MEI LAN BARKS Her food remains untouched.
Mei Lan.
For her keepers, old and new, it's a distressing sight.
They can only hope that she will soon adjust to her new life.
Six months later - late summer .
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And Mei Lan is now settled and content.
Next year she will join the breeding programme.
Over at the panda nursery meanwhile, everyone is waiting for this season's births to begin.
It seems that Ya Shuan, the panda that was inseminated, isn't pregnant.
But hopes are high that as many as eight of the others are.
The nursery boss, Wang Cheng-Dong makes a twice daily inspection.
But even he finds it hard to draw any conclusions.
Because of a biological quirk, pandas that come into heat but haven't actually conceived show all the same signs as those females who are actually pregnant, right down to the profiles of their hormones.
So all pandas are given the benefit of the doubt and extra rations.
It's two o'clock in the morning and the vets are woken to take a look at one of the pregnant females who seems a little agitated.
Li Li, a 17-year old, has in the past only given birth to stillborns or young that have died within days.
It seems she may be about to produce the first cub of the season.
PANDA CUB SQUEAKS There is enormous relief when she gives birth to a healthy baby.
Some panda mothers are frightened by all the fuss and panic or refuse to accept their newborn cubs.
But Li Li cradles hers.
With her first baby cub already suckling, she produces a second.
She can't deal with them both, so the second cub is taken to a warm incubator.
Newborns weigh little over a hundred grams, so the next ten days will be critical.
The vets hope that mothers will raise their cubs with little human intervention.
But if a mother abandons her newborn cub, or if the cub is weak, they step in.
These cubs receive intensive care in the incubators for the first five to six weeks.
But all newborns spend some time here so they can be monitored, and if necessary, given a supplementary feed.
The temperature is set to match the warmth of the mother's body deep within her fur.
They are weighed throughout the day and night to check that they're taking in enough of their mother's milk.
And over the course of two weeks, they begin to look a little bit more like pandas.
It has been 18 days since Li Li gave birth.
For her to produce twins is not unusual - half of all panda births result in them.
But for both twins to survive, certainly is.
Pandas almost always abandon one cub.
It's thought that they don't have sufficient milk or energy to care for two.
But the team at Chengdu have hit upon a cunning plan.
By removing one cub at birth and then switching them throughout the day and night, keepers are able to encourage panda mothers to feed both siblings, while being under the impression that they have only one.
Li Li is distracted with a bowl of honey water, but is reluctant to give up her cub.
Doing this successfully requires enormous patience from the keeper and great trust from the panda.
One twin is taken to the incubator where it will have a top-up of formula milk, and switched with the other, which will now get his share of his mother's milk.
The keeper will swap the twins up to ten times a day.
And Li Li will almost always have one cub with her.
Chengdu's technique of twin-swapping at last opens the way to a possible 100% survival rate in newborn captive cubs.
It's winter.
Li Li's cubs are four and a half months old.
They are as inquisitive about people as people are about them.
They spend part of the day supervised in a playpen together.
And with a third cub.
At two and a half months, he's crawling, but he prefers to sleep.
His sight, like his hearing, is still developing.
After 13 births last year, this year the breeding centre had only four.
The youngest is six weeks old.
Still helpless, but fat and healthy.
Her legs, however, aren't yet strong enough to support her weight.
So she will remain in the incubator for at least another week.
The cubs will stay here in the incubator room until they get their own pen at six months.
But they spend much of the day and night with their mothers.
The twins arriving in alternate deliveries.
Li Li's bond with her cubs is strong.
She's very maternal and restless when they're away.
In the wild, she would give birth every two or three years and keep her cub beside her for 18 months or more.
Her twins will soon be weaned, so she can build her strength for breeding next year.
It's a milestone day.
The twins are about to take their first steps into the outside world.
They are, understandably, somewhat wide-eyed.
Their very existence is a triumph for science and skill .
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Combined with love.
But unless captive-born pandas like these can be released, the extraordinary achievements of the Chengdu team will do little to help the plight of pandas in the wild.
And that continues to be their goal.
The first requirement was to build the worldwide population of captive pandas and produce that critical number of 300.
And, counting these twins, they've made it.
Now is the time for an even greater challenge - to wean the pandas off the human life-support and release them to the wild.
The road to freedom will be a long one.
What will the sociable, trusting pandas from the base make of a solitary life in the wild? They will need to establish and defend a territory, choose their mates, and the females raise their cubs alone.
Is that possible? The truth is no-one knows.
Almost all reintroduction programmes of any rare animal start with failure and death.
But the alternative is to abandon all hope and risk the total loss of a species.
But a new generation in China is waking up to the importance of panda conservation.
Chengdu's teachers visit schools to talk about wildlife.
Efforts are being made to protect panda habitat.
67 panda reserves, amounting to one and a half million hectares, have now been established.
Spending on conservation has doubled in ten years.
There are bans on logging and hunting.
And farmers who turn fields back to the wild are being properly rewarded.
China's first giant panda reintroduction centre is to be built above farmland inside the Sichuan Giant Panda Sanctuaries, a World Heritage site.
The site will have three different zones, each wilder, bigger and higher than the one before.
The pandas will be introduced gradually to the great outdoors.
Only the best-adapted will be freed.
The entire process will take at least 15 years.
There are signs that some wild pandas are still living high in the mountains.
One day those born at the base may find mates from among them.
It is perhaps fitting that the millions of dollars invested in returning the giant panda to the wild have come largely from the fees paid by zoos around the world, to exhibit them in captivity.
And the sanctuary into which the first panda will be released is within the very forest from which the western hunters first took one.
This is the first generation of captive-born giant panda cubs to have a real chance of life in the wild.
It's a bold and controversial move.
And it may not work.
There are those who argue that panda conservation is possibly one of the biggest wastes of conservation money in the last half century.
But we are, in a way, repaying man's debt, simply repairing what we shouldn't have broken, returning what we shouldn't have taken.
And we are using the knowledge and proceeds from pandas in captivity with which to do it.
It's a test case.
After all, if we cannot protect the long-term survival of the giant panda, the icon of global conservation, what chance do we have of protecting those species which do not intrigue us, entertain us and command such passionate adoration the world over?