Panda Cub Born at San Diego Zoo

The cub, which is about the size of a stick of butter, was born about 10 p.m. Tuesday after about three hours of labor. The cub's gender hasn't been determined because zoo officials don't want to disturb mother and cub.

Zoo officials are "absolutely excited," spokeswoman Yadira Galindo said.

With this addition, the San Diego Zoo has four giant pandas, the largest population outside China.

Bai Yun, whose name means White Cloud, had been pregnant with twins, but a veterinary check this month showed that the second fetus died and was reabsorbed into the womb -- a common occurrence in panda pregnancies.

Bai Yun gave birth in 1999 to a female, Hua Mei, and in 2003 to a male, Mei Sheng.

Her newborn hasn't been named, Galindo said, because the Chinese government traditionally names cubs after their 100th day.

Another giant panda was born at the National Zoo in Washington, on July 9.

Bai Yun and her cub can be seen at www.sandiegozoo.orgon a live "panda cam" from inside their den. Bai Yun probably won't be venturing out of the den with her cub until the baby is about 4 months old, Galindo said.