How to Get Pandas to Mate Is Not Spelled Out in Black and White

SAN DIEGO —  They are the first couple of panda-dom, but theirs has not been a loving or (re)productive relationship.

She is young, frisky, fecund. He is middle-aged, sedentary, still potent but uninterested in launching his DNA delivery system.

There is not another couple like them in North America. They do not lack for visitors.

Since arriving in September 1996 from their native China, Bai Yun (White Cloud) and Shi Shi (Rock) have delighted visitors to the San Diego Zoo and kept zoo scientists busy trying to unravel the biological mysteries of this super-endangered species, whose numbers in the wild continue to dwindle perilously.

But what the pair has not done is produce a cub, much to the chagrin of the public and the zoo’s animal behaviorists.

The first year, panda keepers waited for Bai Yun and Shi Shi to do what comes naturally. They did not. The second year, keepers decided to attempt artificial insemination. It didn’t work.

Therein lies the sad tale of pandas both captive and wild: Females are in season only a day or two a year, males sometimes lose desire, and scientists know so little about the panda’s reproductive system that artificial insemination is a longshot.

No one really knows how many pandas live in the wild. Various estimates put the number at 200 to 1,000.

An additional 120 live in captivity in China and elsewhere, but few of those are reproducing. Even when offspring are born, infant mortality is high.

“For this species, the outlook is gloomy,” Don Lindburg, leader of the San Diego Zoo’s giant panda team, said recently during a State of the Panda address.

Still, scientists here and elsewhere soldier on, hoping to unlock the animals’ secrets through studying how they communicate by leaving urine markings. In San Diego, they also take Pap smears from Bai Yun to understand more about her estrus.

San Diego officials still hope that Shi Shi will impregnate Bai Yun when her estrus arrives in a few weeks--without the need to resort to artificial insemination.

Officials think they may have erred in two previous mating seasons by putting the pair into proximity too soon, so Shi Shi was bored by the time the big day arrived. He also seems not to smell Bai Yun’s scent markings.

“We noticed in the first two years he was not picking up her scent,” Lindburg said. “He did not have the kind of olfactory curiosity that pandas should have.”

With her biological clock ticking, Bai Yun backed aggressively into Shi Shi, her tail raised. He did not respond appropriately and a fur-flying spat broke out.

“She looked very frustrated,” Lindburg said. “She whirled around and grabbed a big flap of his skin.”

Last week, officials announced that the zoo and the World Wildlife Federation will host a panda summit next year in San Diego for scientists from around the world. The Pacific Bell Foundation has pledged a three-year gift of nearly $3 million to the save-the-panda campaign.

The San Diego Zoo has long worked with China to bolster efforts to study pandas in the wild and halt the destruction of their bamboo-thick habitat. Now the zoo is also linked with the Chapultepec Zoo in Mexico City, which has four giant pandas.

For years, Chapultepec was considered home of one of the few panda success stories. While the panda pair at the National Zoo in Washington were unable to produce surviving offspring, the Chapultepec pandas were absolutely prolific: six pregnancies that produced eight live births.

When the panda parents died, the zoo in 1990 switched to artificial insemination because it is not considered healthy for pandas of the same bloodline to reproduce. But so far artificial insemination has failed.

Rather than quit trying, Chapultepec officials arranged with San Diego officials to establish an endocrinology laboratory to test the females and determine the optimum moment for fertilization.

Frozen panda semen--some from a panda in the Bonn zoo, some from one in the London zoo--was then taken from San Diego, where it was being stored, to Mexico City. It will be months before it is known whether the effort was successful.

It is also possible that some of Shi Shi’s sperm may be shipped to the Chapultepec Zoo, but that would require approval from the Chinese. As part of the 12-year loan agreement that brought Shi Shi and Bai Yun to San Diego, the zoo promised to pay the Chinese $600,000 if a baby is born.

Shi Shi, who is pushing 20, and Bai Yun, 8, are on display each day at the San Diego Zoo from 10:30 a.m. to 3:30 p.m. in adjoining grottos. Zoo attendance is up 10% since their arrival.

They are not overly active animals. They eat (bamboo and high-fiber biscuits), sleep (in the trees), defecate (an average of four droppings an hour) and maintain an aloof mystique.

“Solitary mammals just have different rules than social mammals,” Lindburg said.