Learning from Tai Shan

The giant panda born at Washington, D.C.’s National Zoo has charmed animal lovers. Now he’s teaching scientists more than they had expected

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In a cramped, dimly lit room, three women stare at a bank of blinking video monitors. Each of the six screens shows, from a slightly different angle, a black-and-white ball of fluff—Tai Shan, the giant panda cub born last summer at Smithsonian’s National Zoo. Every two minutes, at the ring of a bell, the volunteer researchers write down what the cub is doing. Ding! Sleeping. Ding! A yawn. Ding! The right front paw twitches. For the first two months of Tai Shan’s life, Zoo staff and volunteers monitored him 24 hours a day. He is one of the most closely studied pandas in history.

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He’s also one of the capital’s biggest celebrities. In December, when the cub made his public debut, 13,000 free tickets to see him were snapped up on-line in two hours. Fans lined up in subfreezing temperatures before the ticket booth opened for a chance at the additional 60 tickets handed out each day. More than 200,000 people voted on the cub’s name—Tai Shan (tie-SHON) means “peaceful mountain”—while millions logged onto the Zoo’s live “panda cam” (nationalzoo.si.edu/Animals/GiantPandas).

The Zoo’s first surviving panda cub, and only the fourth nationwide, Tai Shan “is the culmination of a decade of collaborative research between the United States and China,” says David Wildt, chairman of the Zoo’s reproductive sciences department. In 2005, twenty-one cubs born in captivity survived (two in the United States, one in Japan and the rest in China), more than twice as many as survived in 2004 and more than any other year to date. That achievement, along with new panda reserves and other conservation measures in China, are upping the odds that one of the world’s most endangered—and most beloved—creatures will survive, not just in captivity but in the wild.

As recently as two decades ago, the panda’s future looked bleak. Restricted to remote, mist-shrouded bamboo forests in mountainous southwestern China, the bears had lost more than half of their habitat by the late 1980s. For centuries, logging and farming had pushed pandas to steeper and higher terrain. The species’ population was down to an estimated 1,000 animals scattered among two dozen isolated groups. Although another hundred or so pandas were kept in Chinese breeding centers, their reproductive rate was so low they offered little hope for replenishing dwindling numbers. By 1997, only 26 percent of captive pandas had ever bred.

Pandas are notoriously difficult to breed. Females ovulate just once a year and remain fertile for only one or two days. Most captive males, meanwhile, are either uninterested in sex or are so aggressive that they pose a danger to fertile females. Even when both partners seem willing, males are often unable to consummate the affair. It was a decade before the Zoo’s first panda pair, Ling-Ling and Hsing-Hsing, finally mated, in 1983, after years of fumbling, misdirected embraces. Ling-Ling and Hsing-Hsing—goodwill gifts from China commemorating President Richard Nixon’s 1972 visit—produced five cubs during their two decades together at the Zoo, but none lived longer than a few days.

In the 1970s, scientists at the Beijing Zoo pioneered techniques to artificially inseminate pandas, and they produced their first cub in 1978. But the procedure had a high failure rate, and only a small percentage of the cubs born in captivity in China, whether conceived artificially or naturally, survived as long as a year. The bear’s prospects began to look up in 1996, when Chinese officials invited a group of U.S. scientists experienced in breeding other endangered species to collaborate on giant panda research. The United States was to provide much of the science and technical know-how, while China would contribute knowledge gained through decades of panda studies and, of course, provide the actual animals. “We jumped at the opportunity,” recalls National Zoo reproductive physiologist JoGayle Howard, who had logged countless hours trying to make Ling-Ling a mom.

Beginning in 1998, U.S. scientists began traveling regularly to China, where they and their Chinese colleagues assessed the health, reproduction, genetics, behavior and nutrition of 61 animals at China’s three largest breeding centers, in Wolong, Chengdu and Beijing. The survey’s most surprising finding was that 80 percent of the pandas, even those that had been dismissed as “poor breeders,” were in fact “healthy, reproductively competent animals that had potential to contribute to the captive population,” says Wildt. A decade later, most of those animals are indeed contributing, thanks to the surge in panda science spawned by the collaboration. “Today,” Wildt adds, “we know more about the biology of the giant panda than we do about any other endangered species in the world.”

The giant panda is a biological oddity. A member of the bear family, Ailuropoda melanoleuca (“black and white cat-footed bear”) diverged from the main bear lineage 15 million to 25 million years ago. In addition to its bold markings, the panda has a larger and rounder head than any other bear. Like other bears, pandas are solitary creatures, except for mothers and their cubs, which stay together for up to two years. The most unusual thing about the giant panda is its diet. Unlike other ursids, which rely at least in part on insects, fish, mammals or other meat, pandas are vegetarians. Stranger still, 99 percent of the bear’s diet consists of bamboo, a grass. A panda might appear well suited to its bamboo diet. The animal’s large jaw is equipped with powerful chewing muscles and large, flat molars that grind down the tough grass. Its paws sport opposable “thumbs”—actually elongated wrist bones—allowing a panda to hold a bamboo stalk while munching it. (The animals usually do this while seated in a remarkably human-like position, one of the traits people find so appealing about pandas.) But a panda’s digestive system lacks the specialized gut that cows and deer have to break down grass efficiently. This means the bears must spend about 14 hours a day eating up to 40 pounds of bamboo. Adults weigh between 185 and 245 pounds. Because pandas aren’t able to accumulate much fat, they cannot afford to take the winter off to hibernate, unlike Asiatic black bears that live in the same habitat. “The panda’s dependence on bamboo drives its entire physiology and ecology,” says National Zoo animal nutritionist Mark Edwards.

Unlike polar bears and grizzlies, which travel long distances to find food, pandas can stay close to home. “Essentially, they’re living in their own salad bowl,” says Edwards. But the animal’s diet also makes it vulnerable to bamboo die-offs, which occur naturally every 40 to 100 years after the plants flower. In the past, when one bamboo stand died, pandas simply migrated to another. But most of the species’ habitat has been destroyed or fragmented, threatening to strand the bears.

The giant panda’s dependence on bamboo may even help explain its unusual reproductive system. When a female becomes pregnant, the fertilized egg does not immediately attach to the uterine wall, as it does in most mammal species. Instead, the embryo floats within the reproductive tract for many months, attaching only about 45 days before the cub’s birth. Edwards suspects a female cannot build up enough nutrients from bamboo to support a fetus for any longer. As a result, newborn cubs have only just begun to develop. Pink and hairless, they weigh about a quarter of a pound, or the same as a stick of butter. (Hence Tai Shan’s nickname, Butterstick.) Compared with the size of the mother, “no other non-marsupial mammal has a smaller offspring,” says Edwards.


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