The San Diego Zoo's resident female panda, Bai Yun, gave birth to the first of twin cubs and researchers eagerly awaited the arrival of the second.

Bai Yun, a 13-year-old female giant panda on loan from China, delivered the cub at 1:15 pm on Tuesday, said Don Lindburg, head of the zoo's panda team.

"It's an exciting day for us," he told reporters. "Any moment now we could have a second cub on the ground."

Monitors were watching around the clock for the birth of the second cub, zoo spokesman Paul Garcia said, adding that nothing indicated there were problems with the pregnancy, as panda twins are sometimes born as much as 12 hours apart.

"This is typical at the end of a pregnancy," Garcia said. "She seems to be fine and providing proper care for the cub."

The birth occurred in a private pen, beyond the view of zoo visitors, where the 13-year-old Bai Yun had created a nest from shredded bamboo.

"We were all rather surprised ... including the mother," Lindburg said. "She showed a real startled reaction. There was no sign of a contraction and suddenly there's this very loudly vocalizing, slithering little animal.

"She immediately leaned over, as panda mothers do, picked it up in her mouth and put it on her body."

While delivery of the second cub was taking longer than expected, Lindburg said "we've every reason to believe everything is OK."

Researchers have closely monitored Bai Yun in recent weeks, but kept their distance to allow her to deliver on her own. They said it would be more than a week before they are able to examine the new cubs.

It is not uncommon for pandas to deliver twins, but typically a mother will choose to care for only one.

Lindburg said Bai Yun likely would choose one of the twins within minutes of the second birth. Researchers then would step in to care for the abandoned cub. Genetic testing will be done to determine which of two pandas is the father.

In 1999, Bai Yun gave birth to a female panda, named Hua Mei.

Hua Mei, the first US-born panda to survive into adolescence, is to be sent to China soon as part of the loan agreement.

Only 1,000 pandas remain in the wild in western and central China. Another 150 live in captivity.

(eastday.com August 21, 2003)