It was the second mating for Bai Yun and Gao Gao at the San Diego Zoo, which closed its panda exhibit to visitors and pointed its Internet "panda cam" elsewhere for the occasion. Bai Yun gave birth in 2003 to Mei Sheng and did not mate last year because she was nursing the cub.
Bai Yun will likely give birth to her third cub in about 4½ months, said Don Lindburg, the zoo's giant panda conservation team leader.
Lindburg said Saturday that Bai Yun had displayed signs of being receptive to mating in recent days, including yipping and raising her tail, walking through water and scraping pine tree bark onto her head and face.
"It's getting her perfume on for the date," Lindburg said.
Zoo officials then lifted the gate that separates the two for much of the year on Friday to let the mating begin. The pandas, both 13 years old, spent about 15 minutes mating in the same spot on Gao Gao's side of the exhibit where they mated in 2003.
Then, Lindburg said, "They pretty much ate and slept. They were pretty content to sleep most of the day, and try it again this morning."
The pandas mated for about a half-hour on Saturday. Researchers detected live sperm in Bai Yun's urine and determined that she had been successfully inseminated.
Female pandas are in heat for only a day or two a year. Natural mating attempts in recent weeks were unsuccessful at zoos in Atlanta and Washington, D.C. Both females were then artifically inseminated, but it is too soon to tell whether they are pregnant.
The recent amorous tendencies of the pair in San Diego are a relief for zoo officials who tried unsuccessfully from 1996 to 2002 to get Bai Yun to mate with Shi Shi, the zoo's first male.
Artificial insemination resulted in the 1999 birth of Hua Mei, the first giant panda to survive more than four days in the U.S.
About 1,600 giant pandas live in the wild in their native China and another 200 live in captivity there. Less than two dozen pandas live in captivity outside China.
Under the loan agreement with China, all pandas born at zoos outside the country must be returned to China after the animals mature.