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The Panda Paradox
With so few pandas left in the world, the pressure on the National Zoo to deliver another cub is enormous. But the mysteries of the animal's reproductive system make that quest a race against time.

By Daniel Libit
Sunday, April 5, 2009

The National Zoo's panda Tai Shan turned 3 on a warm day last July. That morning, a few dozen members of Pandas Unlimited, the country's largest panda fan club, arrived at the zoo bright and early. With photo and video equipment in tow, they huddled together on the walkway of the Fujifilm Giant Panda Habitat, awaiting the annual spectacle of the birthday bear consuming his birthday treat.

Frances Nguyen, Pandas Unlimited's founder, stood next to Ed Ginn and his wife, who had driven from New York for the event the night before. Ed wore a T-shirt: "The more people I meet, the more I like pandas."

Craig Salvas, a NASA employee, who had set up his photo equipment a few paces away, was taking test shots with his camera and adjusting the zoom on his camcorder. Over the years, he said, he had snapped several hundred thousand digital photos of Tai Shan, filling two external hard drives with JPEGs. His explanation for this seemed almost instinctive.

"You can wake up and read a newspaper in the morning, or go to the zoo and watch a baby panda," he says.

Over the next half-hour, a throng of shutterbugs filled the exhibit's walkway. Funded with a $3.8 million donation from Fujifilm, the facility was refurbished in the fall of 2006, outfitted with big naturalistic enclosures for the animals and spacious pathways and seating areas for onlookers.

Several zoo staff members walked to the front of the centermost yard, lugging along two orange-colored pieces of ice that they stacked one on top of the other to form a giant "3."

"Hi, Lisa!" a woman called out toward the yard. The zoo's panda curator, Lisa Stevens, returned a sheepish wave. Among these devoted zoo patrons, Stevens had achieved a minor celebrity, unusual for a professional in the animal sciences. But Stevens's prior experience working with gorillas, which inspired their own, more modest level of fanaticism, had prepared her to a certain extent for managing pandas.

"People thought that primates needed to be taken from their mothers, put in diapers and clothes and given bottles and be treated like little human babies," says Stevens. "People think the same about panda cubs. So my staff and I, on a daily basis, get people who approach us because they perceive that the pandas are lacking something, or because we are not treating them like human children."

While jubilating over Tai Shan -- the first panda cub born at the National Zoo to survive infancy -- was the focus of the day, the fans' excitement was tempered with the understanding that in the not-so-distant future, the cub was slated for departure. The panda loan agreement between the Chinese government and the U.S. zoos was such that any cub born here would head east not long after it had been reared. Tai Shan had been weaned from his mother, Mei Xiang, almost a year before. The Chinese had extended his lease, but not for much longer. The zoo's sole consolation was the fervent hope that a new cub might at that very instant be growing inside Mei Xiang.

Pandas are a remarkable but mysterious species. In so many ways, they should have long ago ceased to exist. The animal's reproductive biology, viewed through a certain lens, seems counterproductive, starting with the fact that a female ovulates only once a year, bestowing an annual fertility window of 48 hours or less.

"Somebody once told me this species is an evolutionary dead end," says David Wildt, the head of the National Zoo's Center for Species Survival, and one of the leading giant panda experts in the United States. Wildt's goal -- and the zoo's -- was to prove that theory wrong, even after decades in which human activity had greatly diminished the chances for pandas' survival.

Throughout the 20th century, the Chinese, in their quest to turn forest into farmland, destroyed much of the pandas' natural habitat and isolated the population in the western mountains of China. There are now estimated to be 1,600 pandas in the wild, a precariously low sum.

One of the prime goals of the modern panda conservation effort over the last 20 years has been to forge a captive population healthy and diverse enough to serve as a backup in the event that disease, famine or natural disaster wiped out the remaining animals in the wild. This catastrophe seemed far more theoretical until May 12, 2008, when a 7.9-magnitude earthquake ripped through China's Sichuan province, killing tens of thousands of people. The disaster also laid waste to the China Giant Panda Protection and Research Center in Wolong, where scores of pandas had to be rescued: One died, two more were injured and six went missing, with five of those recovered.

Experts say that to replenish a decimated wild population for the next century, there must be 300 to 350 captive animals with diverse and robust genetic makeups. Last fall, there were only 241 pandas in captivity, all but a handful of them in China. Considering the recent history of breeding productivity, the target number seemed reachable within a few years. But in the world of panda production, nothing is guaranteed. "Every day in this business is a big experiment," says Wildt.

The enigmas of panda reproduction are as exasperating as they are fascinating, for experts and the devoted amateurs. Even determining if a female is pregnant can be elusive.

Back at the Panda Habitat on the celebratory morning last July, Craig Salvas thought he had figured out a fair amount. Salvas sidled up to fellow Pandas Unlimited member Bobby Hall to talk over Mei Xiang's gestational state.

"Obviously she is showing all the signs," said Salvas.

"Well," mused Hall, "she is twice as lethargic this year as she was last. I mean she doesn't do anything. Anything!"

Soon after, Tai Shan was released into the center yard and promptly plodded toward a bluff in the front while the crowd hoisted their cameras in rapt unison. He came to rest a paw on a rock, studied his iced treat for a moment, and then pivoted in the direction of a nearby thatch of downed bamboo, where he started gnawing on a stalk. The audience laughed, and the cameras clicked away. Tai Shan seemed to take no notice. It was all white noise to the panda, or so the zoo's scientists had concluded. They had done studies in the past to measure the stress-indicating cortisol hormone levels in the pandas' urine at times when the crowd size and noise were both great or small, and found only slight fluctuations. After a few more moments with the bamboo, Tai Shan got up and walked to the back of the yard, plunking down so that his hindquarters faced his fans.

***

Back in early spring 2008, there was more consternation around the panda house than celebration. Two empty incubators sat in the staff break room, ready to be converted into a cub nursery if and when the time came. Several staff members had suspended their vacation time until after the prospective birth. Hormone tests confirmed that if a cub were to come, it would be in a matter of weeks.

But everything empirical about the female -- her behavior, her appearance, her hormone readings -- could suggest she was pregnant when she was not. Scientists call this a "pseudopregnancy." The panda will stop eating and start building a nest; her vulva and mammary glands will enlarge; but nothing, in the end, will come of it. Higher-tech efforts to confirm actual pregnancy have been met with some success in recent years. The San Diego Zoo has picked up ultrasound images of panda fetuses in the latter stages of their female's pregnancies. But this is a difficult endeavor requiring luck, considering the uncooperativeness of a female panda near the end of gestation, the corresponding thickening of her uterine wall and the smallness of a panda fetus. If no image is visible, zookeepers are left to play a guessing game that can last from 21/2 to six months. The wide range owes, in part, to yet another reproductive curiosity: In female pandas, it can take up to a month after insemination for the embryo to attach to the uterine wall.

Wildt, who bears a striking resemblance to "Star Wars" creator George Lucas, arrived at the National Zoo in 1983, after helping to manage a bank of mice embryos at the National Institutes of Health. Before he concentrated on panda reproduction, Wildt worked with clouded leopards, another species that is highly challenging to breed in captivity, though two cubs were born in late March at the zoo's research facility. His experiences in wildlife procreation have made him a man of one mantra: "I never believe it until I see the offspring on the ground," he says. "There are so many variables. You might be a little early or late with respect to the sperm deposition. The animal might have had a little bit of stress, might have had a bad day. We don't know what's going on internally in the reproductive systems of all these animals."

But successful pregnancies are only part of the puzzle. Since 2001, Jonathan Ballou, a population geneticist at the zoo who advises the Chinese panda program, has been the keeper of the "stud book," a computer database containing the genetic information for every captive panda in the world. Using the information, Ballou determines which males and females should be bred together in a cycle to maintain a robust population. The key is having as wide a variety of genes as possible. Each panda is rated on a scale from 0 to 6, called the "mean kinship ratio." The lower the number, the more diverse the genes, and the more desirable for breeding. Among American pandas, San Diego's Gao Gao had the best mean kinship ratio last year at 0.4, said Ballou. The National Zoo's Tian Tian, Tai Shan's father, had a value of 4, which rated him 89th out of the 103 captive male pandas in the world. This made him a less than desirable breeder.

Any new cub with a middling mean kinship ratio would be of questionable value to the goal of long-term panda survival. Because the terms of the loan forbade the physical transfer of pandas from one U.S. zoo to another, Tian Tian had been Mei Xiang's only live breeding option. But this time the zoo sought a new opportunity -- and a novel way to contribute a cub to the general conservation effort.

In February, zoo director John Berry, its top reproductive scientist, Jo Gayle Howard, and Wildt began to work out travel arrangements to San Diego in hopes of bringing back Gao Gao's sperm. As it was drawn up, the plan was particularly intense, requiring multiple coast-to-coast trips and possibly the use of a standby private jet -- altogether an endeavor befitting a human organ transplant.

But in early March 2008, word came from San Diego that Gao Gao was ill, making sperm collection impossible.

Once again, Tian Tian and his common chromosomes would have to suffice. His testosterone levels had started their upward climb in November, and his behavior reflected it as the winter came to pass. In recent weeks, he was pacing incessantly. So on the morning of March 19, two lusting pandas were released into the outside yards. As if some hackneyed sitcom writer had thought up the scene, droves of schoolchildren on their spring break were just arriving at the zoo as Tian Tian's carnal instinct was cresting. He pursued his mate in the yard that morning with vigor. Occasionally, Mei Xiang would stop in place, allowing Tian Tian to thrust about her while he emitted high-pitched bleating sounds of a neck-hair-raising variety.

From the walkway, a teenager joyfully encouraged the display: "Hit that," he crowed. "Hit that."

"That panda's like, 'Oh yeah,' " said another boy.

A middle school-age girl curled her lip: "They're making noises. Ewwwww!"

Some parents and chaperones, unprepared for this, dug quickly into their wells of euphemism. A mother turned to her child and said, "Oh they're wrestling, honey ... Isn't that cute, sweetie?"

From a fenced-in view on the opposite side of the exhibit, Lisa Stevens remained stoic as she watched minutes of hapless humping turn into hours. Stevens took over the stewardship of pandas in 1987, following several cycles in which Ling Ling, the zoo's first female panda, had produced cubs that died in childbirth.

Only once, for a flickering moment, did it look like an actual copulatory event might occur, when Mei Xiang lifted her tail and backed up toward Tian Tian. But he happened not to be paying attention as she did this, and when he finally took notice, she had already pancaked to the ground. Undeterred, her mate proceeded to climb on her back, aiming himself at her side and then her back paw.

"He's only a foot or so off," Stevens said, trying to hide her frustration. "You just want to move him into position."

But the expectations for a successful natural breeding this day had never been high. The pandas had not succeeded in the past, although Stevens was quick to defend Tian Tian, who she felt had gotten a bad rap. "There's a lot of unfair language in terms of Tian Tian and his behavior," she said, referring to various Internet posts and newspaper stories over the years about his ineffectiveness. The real problem, as Stevens saw it, was that Mei Xiang tended to lie down during her peak ovulation period, and Tian Tian hadn't learned how to lift her up off the ground for mounting. Unlike male pandas in the wild, which have multiple mating possibilities a cycle, Tian Tian only had one female he could practice his technique on, and only for one day each year.

In 2005, the year Tai Shan was conceived, there was one significant copulatory event, where the pair aligned in what Stevens thought was the correct manner and made the right vocalizations. But just to make sure, the panda team ended up performing artificial insemination with Tian Tian's sperm. Given how much was riding on a birth, Stevens says, there was simply not enough confidence "for us to put all our eggs in that basket."

"There's something missing in the way in which we are keeping pandas --that individuals grow up and do not mate successfully, naturally," she says. "And we still have to figure that out." The pandas at the National Zoo "will never be a part of the reintroduction process," but they still play an important role. "Pandas at the National Zoo are ambassadors," Stevens says, "and they raise the much-needed funds to support the program in China." Still, the efforts to produce a new panda cub at the National Zoo do hold promise for the long-term conservation effort. Stevens says that while Tai Shan couldn't be introduced into the wild, he could potentially breed a female in one of the centers in China, and that cub, after being weaned naturally, could live on its own in the mountains of China.

By 10:30 a.m., the pandas had tired and took to their respective corners. Meanwhile, in a nondescript concrete building at the other end of the zoo, lab technician Dave Kersey was rubbing the sleep out of his eyes and waiting for a vile of panda urine. Kersey had been conducting Mei Xiang's hormone urinalysis since January. Fortnightly tests had turned into daily tests, and now the lab was running nonstop. The pandas' morning behavior suggested that Mei Xiang was in estrus, but the hormones were needed to confirm it. At the point that the ovary expels an egg, there is an instant drop in estrogen production.

As night began to fall on mating day, the zoo staff weighed its options. The Panda House had taken on the appearance of a makeshift hospital. There were long tables covered in blue sterile paper, monitors, microscopes, pipettes and a gray, missile-shaped object, which evoked a certain nervous gulp at the utterance of its name: the "electroejaculator."

Tian Tian was now pacing about the perimeter of his indoor enclosure, stopping every few moments to furiously sniff at the bottom of a door. Boxes of delivery pizza arrived for the staff, sustenance for a possible all-nighter. Howard and Stevens huddled to assess the hormone readings, which were a bit confusing. The morning sample showed a decrease in Mei Xiang's estrogen level, but the progesterone hormone hadn't correspondingly risen, as would be expected.

"I don't think she's quite ready," Howard concluded.

Back at the lab, Kersey was running the chemistry on the sample collected in the late afternoon; he'd know the results in a few hours. A few keepers would stay behind to collect additional samples through the night.

Early the next morning, Stevens coaxed Mei Xiang into the "squeeze cage," an outside pen that could be contracted and expanded. This allowed the animals to be moved into certain positions for medical examinations and blood draws. While distracting her with small pieces of pear and spoonfuls of honey, Stevens examined the panda's vulva, noting aloud that it was "a little less swollen and a little less pink" than the day before. It was one of those myriad observations made for future analysis, but it was inconclusive now. Could this mean that the panda's peak ovulation point had already come and passed? The hormones indicated otherwise.

While Mei Xiang was being examined, Tian Tian could be heard yelping on the other side of the wall. Stevens thought that this indicated his interest in one final attempt with his mate. The pandas were hastily corralled into an area of the exhibit called "the apron," where they were able to face each other through a fence, allowing the keepers to assess their level of mutual interest. But at once, Mei Xiang went incuriously supine, and Tian Tian let out a final, renunciatory yelp. Mating season was officially over.

***

The history of pandas in the United States began with the efforts of Ruth Harkness, a Manhattan socialite and designer of fine tea dresses whose husband, William Harkness, died in Shanghai while in search of the bears. Ruth took up her husband's unfulfilled dream and ended up bringing the first live panda into the country in 1936, claiming it as a dog on the customs voucher in China. Harkness attempted to sell the animal to any zoo, including Washington's, that could underwrite another expedition, but her price was too high. The panda, Su-Lin, eventually ended up in Chicago, where two years later she died of pneumonia. Over the next 15 years, a number of other pandas sent to Western zoos would die prematurely. After World War II and the Maoist revolution, the panda trade froze. It didn't thaw until 1972, when Mao Zedong presented President Richard Nixon with a diplomatic gift of two pandas, Ling Ling and Hsing Hsing, who were housed at the National Zoo for more than 20 years. Modern panda exportation had begun, though it would carry forward in a disorganized and sometimes harmful way. Relatively little was known about caring for the animals in captivity, and the conventional wisdom was often wrong. (Ling Ling died in 1992, Hsing Hsing in 1999.)

By the 1980s, China was offering three- to six-month loans of captive pandas to most any zoo with sufficient funds. Conservationists decried the flippancy of the "rent-a-panda" program. By the end of the decade, the U.S. government declared a moratorium on the animals' importation.

In the winter of 1996, a small team of American scientists received an invitation from the Chinese government to come to China and discuss panda conservation. David Wildt tagged along as the reproduction expert. He remembers entering a room filled with 60 scientists with folded arms. For five days, through translators, the scientists compared notes on the troubles that racked China's 100 or so captive pandas at the time. The largest concern was breeding: The females were inconsistent; pseudo pregnancies were rampant; and cubs frequently died in childbirth.

"They wanted help, but they were kind of cautious," Wildt says, "and we knew a top-down approach wasn't going to help. We were adamant we were not going to be perceived as missionaries."

Meanwhile, the U.S. Fish and Wildlife Service placed strict requirements on American zoos that desired pandas. Not only did the zoos have to prove their capacity to care for the bears, they had to commit to extensive research and conservation initiatives, often at great expense. For their part, the Chinese agreed to a series of 10-year leases. The San Diego Zoo got the first pair of pandas, in 1996, followed by Atlanta, Washington and Memphis zoos.

The National Zoo first tried to breed Mei Xiang back in 2002. The artificial insemination in the spring of 2005 finally took, and Tai Shan, the National Zoo's first surviving cub, sprung forth into the world five months later, at 3:41 a.m. on July 9. He was five inches long, squealing and, as one zoo staffer described it, looking like a "space rat." He became the third panda cub born in the United States that survived, the first two the offspring of the San Diego Zoo's Bai Yun. There have been four more births in this country since Tai Shan -- two more in San Diego and two in Atlanta -- bringing the grand total to seven.

To those staff members at the National Zoo who had toiled for years for a successful birth, Tai Shan felt like the lifting of a curse. On the first day the public was allowed to view him, back in November 2005, the 13,000 free tickets made available to the public were snatched up within two hours. The cub's inaugural press preview was covered by 59 media outlets and generated nearly 3,000 newspaper stories.

More visitors entered the zoo that month than during any previous month since 2001, when Mei Xiang and Tian Tian first went on display. By the end of the year, the Friends of the National Zoo signed up 9,000 new members, bringing in around $1 million; the zoo's "Adopt a Species" program raised three times more than its previous record; and 45 percent of the zoo's fourth-quarter merchandise sales of nearly $220,000 consisted of Tai Shan T-shirts and sweat shirts and panda plush toys.

The American public's clamor for pandas is said to befuddle the Chinese, and even Jo Gayle Howard finds herself at a loss sometimes when asked to explain it.

"I have no clue," she says, "and it's amazing, because people love the pandas, and it's like, there are other interesting animals."

True, but how many look like your favorite childhood stuffed animal? Plus, the panda exhibit's inviting accommodations, as well as the National Zoo's free general admission policy, encourage a singular devotion to the animals. While zoo staff members know it is their business to enliven passion and support of the zoo and its creatures, their patience is frequently tested on the panda front. There is an omnipresence of certain, highly scrutinizing panda fans, who, if they find anything amiss about the exhibit, quickly post it on the Internet. At times, this sets off a bombardment of panicked phone calls to the zoo.

When Tai Shan was weaned from Mei Xiang, an internecine squabble broke out in the Pandas Unlimited group. Members divided over those who supported the idea of the cub's separation and those who didn't. Shots were fired back and forth on the Web site, some splinter groups formed, and some members quit.

From her perch at the zoo, Stevens says, "You have to turn that off. I can't dwell on the blog sites, about what they say about us because we are taking Tai from his mother. I just can't go there."

The exhibit, Stevens says, is "our opportunity to educate people about endangered species, about pandas in particular and what giant pandas need to thrive in a captive environment and in the wild . . . I think we do have an impact. And in other cases, quite honestly, we have people who are nuts, and we're not going to change their minds."

But dealing with unbounded adulation is a minor concern, compared with the challenge, technical and financial, that the pandas represent. The cost has been steep. Collectively, the four U.S. zoos that hold pandas have sent $35 million in rental fees to China, and millions more to care for the pandas on loan. The National Zoo's $1 million annual rental fee is paid for by a donation from Fujifilm, which also provides an additional $350,000 a year to care for the three bears.

With the 10-year loans nearing completion, some American zoo directors have begun to consider whether the experience has been worth the costs.

"Probably not," Chuck Brady, director of the Memphis Zoo, said last year, adding that the decision to renew the loans at their current cost and terms would be "a difficult thing to justify."

"We're all losing our shirts," said the National Zoo's Berry. "People think: Oh, you're making money on these damn pandas. You're making a fortune. Every penny we make is plowed back into this species."

Then again, he added, "this is about advancing science and all biology . . . It's worth losing the money on. We lost money on Apollo, too, you know."

***

As the insemination procedure neared that March, the live panda Web feed was taken off the zoo's Web site -- in case something went awry-- and 20 vets and techs took their positions in the makeshift hospital. Wildt, Berry and Kersey had come down to observe the proceedings, along with a handful of other curious zoo employees. A placard was posted outside the panda house saying the facility was closed for the day.

Inside, all was silent. Tian Tian, anesthetized with a dart gun, was brought out swaddled in a tarp and splayed across the operating table. The electroejaculator was summoned and inserted. The panda's legs flailed. "I think it's urine," Howard said, holding the first sample up into the light as she walked over to the microscope. She was correct. The second sample was also polluted, as was the third. The sperm in the fourth sample was clean, but nearly lifeless. The fifth, however, showed promise. On a monitor hooked up to the microscope, the magnified visual looked like TV fuzz.

"This is the sample," Howard declared. "It's not sluggish like the other one."

After Tian Tian was returned to his den, the staff anesthetized Mei Xiang. An assisting vet took a set of electric hair clippers and shaved a small square patch on the panda's belly. In the coming months, this would serve as a window for the ultrasound machine. San Diego shaved the entire abdomen of their pregnant female panda, but the National Zoo decided against the full shave, partly out of concern for how the public might react to a bare-bellied panda.

"As soon as they see something abnormal," says zoo veterinarian Carlos Sanchez, "they immediately think it's sick, or that they have had an abdominal surgery. It needs more explanation for the public."

At the panda house, Howard navigated the tip of a specially made catheter into Mei Xiang's cervix.

"Okay, we're done," Howard finally said after injecting the semen.

The staff had done all that they could, and Howard was pleased with how it had gone. All hope now floated on 1.7 milliliters of white fluid.

***

Early last June, Kersey noticed a rise in Mei Xiang's progesterone levels and pegged the prospective delivery date to the end of July. From then on, each Wednesday morning, Mei Xiang would be cajoled by Stevens and Sanchez into the squeeze cage for an ultrasound reading.

In July, the evening of Tai Shan's birthday celebration and two months after the earthquake in China, 100 Pandas Unlimited members gathered together beneath a man-made grotto in the Asia Trail exhibit, bowed their heads in solemnity and prayed for the imperiled bears half the world away.

The pandas' post-cataclysmic plight instantly captured the Western media. It spawned tales of panda triumph, such as that of Guo Guo, a female who escaped from the wreckage to give birth to twins shortly after being found. Then there were the stories of panda tragedy. On June 11, the Associated Press reported on the funeral of Mao Mao, a mother of five who died after a wall collapsed on her:

"The center's director stood cap in hand and shoveled in a few spades of dirt. Then Mao Mao's keeper stepped forward crying and arranged two apples and a piece of bread by the grave. Three minutes of silence followed as workers gathered around the grave."

A thick pathos suffused the Pandas Unlimited party and fundraiser on that evening last July. The group had been keeping a more or less constant vigil on the pandas since the summer of 2005, just months after Tai Shan was born, when Frances Nguyen, a Web producer for a federal government agency, started posting pictures of the cub on the photo-sharing Web site Flickr. The page became a community portal for panda junkies, with membership eventually swelling to more than 2,600.

These days, it continues to serve as the Pandas Unlimited Web site. It is updated constantly, a widely collaborative effort that has members linking to news articles, dabbling in panda poetry, posting graphics and screen grabs from the zoo's "panda cam," and finely parsing and debating the animals' behavior. By the end of the day on Tai Shan's birthday last July, 151 comments were posted on the site's daily thread, many of which were written in a form of baby talk.

"Awwwwww dear Tai," chimed in one member, who went by the alias bumbkinbears. "We won't tell anyone that u wuz awake, don't u wowwwy now everwyone will be there soon for your bufday."

Another member, Unka Bobby, responded later in the thread, as if representing some anthropomorphized perspective of Tai Shan: "Fank you eveybody. . . . i twied to go back to sweep, but i culdent. Im eeting tum boo wite now, wooking out da window, wating fow aww my fwiends, Aunties, and Unkies."

And on it went.

The members' interest in panda bears was not simply confined to conservation or science or even pandas as ursine creatures of the wild. In many ways, that was all secondary to a certain emotional need the idea -- their idea -- of the panda met.

Though she had seen Tai Shan caper about online before, Nguyen's own interest didn't take hold until she gazed upon him in the flesh for the first time. Watching Mei Xiang care for her cub, Nguyen says, "was like a miracle to me." That first night after the encounter, she decided to stay at the house of a friend who lived closer to the zoo, so she could return all the earlier the next morning. She stayed away for a few months after that, alarmed by her own intense reaction, but after a few months returned regularly. She and her boyfriend now go practically every weekend, from 7 a.m. to midafternoon.

"I guess what bonds us," Nguyen says of the group, "is the need to express ourselves, to bring out what's in our heart to help the pandas. Because when you love something, you want to help it, too."

Sitting in the front row of the July gathering were Berry, Stevens and Howard, the honored guests. After the emcee got on with a few itinerary announcements, Berry took to a podium to thank the members for their passionate support, including, on this night, an $11,000 contribution to panda-related earthquake relief efforts, presented in the form of an oversize cardboard check.

Berry, a Washington native, had spent years on Capitol Hill and in the Interior Department during the Clinton administration before coming to the world of wildlife conservation. He displayed a bust of Teddy Roosevelt on his office desk and had an avuncular politician's mien about him. Later in December, his name would be mentioned as a possible nominee for secretary of the Interior in the new administration, and on this summer evening, he seemed ready-made for such a job.

"Persistence," he said, and let the word hang there for emphasis. "Persistence."

"Abraham Lincoln said: 'Give me persistence. I'll take it over arms, money and luck. Give me persistence. Whoever has it will take the day.' "

Those weren't precisely Lincoln's words, but the audience certainly absorbed the point.

"Well, Mother Nature handed us a big setback this year," Berry continued. "There is no question that this is one of the worst natural disasters ever suffered. It has dramatically impacted this program.

"Much of the investments that we and the other three holding institutions in the United States have made have now been destroyed. We are going to have to start over. We are not walking away from this species. My promise to you is we'll stay in there. What I ask of you is please stay with us."

It was obvious that the Pandas Unlimited members, accessorized to the extreme with all manner of buttons and hats, required no such appeal from Berry, who acknowledged this himself. He said he could see it in their eyes every time he ran into one of them at the zoo. He could see "the love."

"I see you share it with our animals here," he said, "the three today, and hopefully the four" -- with this, the crowd applauded -- "and maybe five."

Stevens, having exchanged her workday zookeeper uniform for a leopard-print dress and gold jewelry, was called to the podium next to accept the check.

"You are all truly the best," she told the crowd of panda fans, "and I don't know what else to say other than we can accomplish incredible things in this world with the commitment -- and yes -- the passion that you bring each day with this species, and I just applaud all of you."

***

As the summer passed, there was no sign of a fetus. Mei Xiang spent more and more time huddled up in den No. 3 -- possibly a sign of pregnancy. Zoo volunteers were now on round-the-clock watch, monitoring the panda's behavior.

On one morning, Susan Hughes sat before a bank of television monitors in a glassed-in room in the Panda House. Beside her were a joystick and a panel of buttons, which allowed Hughes to maneuver and toggle between the multitudes of cameras that surveyed the exhibit. She worked as a program analyst for the Federal Aviation Administration before retiring. She had been doing animal behavior watches as a volunteer for the zoo since back when Ling Ling was pregnant, and she was manning the cameras when Tai Shan was born.

On a clipboard next to Hughes was a check sheet. Every five minutes, she would make a notation: Was Mei Xiang moving, resting, feeding, cradling a toy, doing anything that was suggestive of nest-building or licking herself? There was also a place to note any signs of contractions or water breakage, but those boxes were conspicuously blank.

The hormone levels were dropping, which meant the potential birth was close at hand. Then the descent stopped, and throughout the final weekend of July and into the first week of August, staff members continued to hope that Mei Xiang was truly pregnant and about to deliver her second cub.

But in mid-August, the hormones hit baseline, and those hopes officially flamed out. The disappointing news was confirmed in a six-paragraph press release that morning, which stated: "National Zoo staff are recognized leaders in the study of giant panda reproduction, but they still have much to learn." Even though a fetus was never glimpsed on the ultrasound, the going hypothesis was that a fetus had been present but was reabsorbed into the lining of Mei Xiang's uterus.

A TV reporter asked Don Moore, the zoo's associate director of animal care, during a spur-of-the-moment news conference that morning, "How disappointing is it from a zoo perspective, the crowds and excitement that a baby panda generates?"

"You know," Moore said, "we're interested in the crowds, but our animals are like our family. So it's more like having the termination of a birth in a family member ... It's a very personal thing for us."

Afterward, Moore said that he wasn't just disappointed, but surprised. He recalled the visual of the sperm dancing about on the TV monitor during the artificial insemination back in March.

"It looked like the Olympic swim team," he said.

In the staff room of the Panda House a week later, Lisa Stevens echoed the general assessment: They thought they had done everything perfectly, but technical perfection could only take them so far.

***

In analyzing the collected hormone data over the months that followed, Dave Kersey brought something to the staff's attention. His readings suggested that peak ovulation time might be later than expected, if only by a few hours. In December, he left Washington to become an assistant professor of reproductive physiology at Western University in Pomona, Calif. But if Kersey was on to something, he may have left the National Zoo with a breakthrough.

The theory was put to the test in January, when Mei Xiang went into heat two months earlier than the previous year. There was no time to prepare for a collection of Gao Gao's sperm in San Diego. And so, on Jan. 15, Mei Xiang and Tian Tian engaged in their annual, ineffectual fling in the yards. Two days later, Jo Gayle Howard artificially inseminated Mei Xiang with Tian Tian's sperm. Howard performed two inseminations with anesthesia, as opposed to one, to take advantage of Kersey's discovery.

A cub could still be born this year, but as spring approached, Mei Xiang was keeping everyone guessing.

It now seems all but certain that Tai Shan won't be headed back to China this year, and maybe not even the following. As late as February, Dave Wildt had yet to have any conversations with the Chinese about a transport of the panda; he surmised that the earthquake's destruction would delay it indefinitely. Nevertheless, Wildt says the pressures of producing a new cub -- financial and conservational -- remain the same.

San Diego recently renegotiated the terms of its lease: five years for $500,000 per year; half the length of the previous deals, but for half the price. The National Zoo, whose lease is up in December 2010, has just begun its negotiations, but Wildt expects the terms to end up being the same as San Diego's.

***

In mid-January, Nguyen traveled to San Diego to see the zoo's now 21-month-old cub Zhen Zhen together with her mother for the last time before the weaning. Nguyen was accompanied by her boyfriend, and over the course of the six days she was in California, she got together with some other Pandas Unlimited members in the area. But for the most part, she spent her time at the exhibit, hours upon hours watching two pandas play. The experience, she says, wasn't quite the same as it is in Washington.

She is now beginning to plan for Tai Shan's next birthday party, though she worries that the economy may put a crimp in the attendance and the fundraising. Of course, what she's really hoping for is another birthday party to plan for in the years to come -- Tai Shan's still hypothetical sibling. But in light of the pandas' failure to produce last year, Nguyen is trying to steel herself with a cynic's detachment.

"I guess I don't want to be too hopeful this year," she says. "I don't want to be let down."

Daniel Libit is a staff writer for Politico. He can be reached at 20071@washpost.com.

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