The National Zoo's panda Mei Xiang gave birth yesterday to a squealing, squirming cub the size of a stick of butter, and elated zookeepers said she is giving it the tender care that befits its status as one of the world's most endangered animals.

Even as they rejoiced in their first panda birth after years of effort, zoo officials cautioned that the coming days would be critical to the cub's survival. They praised the mothering skills of Mei Xiang, who was holding a rubber toy at the moment of birth and at first seemed surprised by her squawking cub. But she quickly gave it her full attention.

"She looked kind of startled for all of about two minutes, and then she picked the cub up," said Lisa M. Stevens, associate curator for pandas and primates. "She picked it right up and began cuddling and cradling it. The cub responded immediately and settled in."

It might be weeks before keepers can get close enough to learn the cub's sex, because the mother will hold it close and the keepers will not intervene unless something goes wrong. A photo released by the zoo shows the newborn -- which weighs perhaps a quarter of a pound compared with its mother's 250 -- resting on Mei Xiang's arm in an indoor den at the Panda House as staff and volunteers watch via closed-circuit cameras in a nearby room.

The road to panda motherhood has been a three-decade cycle for the National Zoo marked by many hopeful springs and sad summers. The zoo's previous pair of pandas had five cubs during the 1980s, but none lived more than a few days. From the moment Mei Xiang and Tian Tian arrived from China in 2000, they have been celebrities and the subject of speculation about how soon they would add a cub to the tiny population of giant pandas worldwide.

The Panda House will be closed for at least three months to avoid disturbing mother and baby, zoo officials said, but the public will be able to monitor them on round-the-clock webcams. The outdoor panda yard will remain open, and zoo visitors will be able to see Tian Tian when he is outside, as he was for much of yesterday.

Mei Xiang was artificially inseminated March 11. She had recently been acting like a panda mother-to-be -- sleeping much of the day, eating little, building a bamboo nest in her den and cradling apples. Hormone tests showed that she could be pregnant, and volunteers with Friends of the National Zoo began a 24-hour watch last month. But pandas often have false pregnancies. Zoo veterinarians hoped to capture a pregnancy on a sonogram, but the panda had not sat still for one since June 20.

It was about 1 a.m. yesterday when volunteer Susan Hughes, watching a monitor, noticed that Mei Xiang seemed restless and unable to settle down. The animal was licking herself, grunting and honking. Hughes had seen videos of panda births and thought those were signs of labor, so she called Stevens, who asked longtime keeper Brenda Morgan to come in.

Hughes, who has been on panda watches since the 1980s, was so busy taking notes as part of her volunteer duty that she missed the birth. She heard the young panda's squeals, she said, and then became so excited that she couldn't write anymore. It was 3:41 a.m.

"There's a cub! There's a cub!" Morgan exclaimed to Stevens over the phone. Both are veteran zoo employees who were on the delegation that went to China to bring the pandas to Washington.

"She's doing a great job at being a mom," an exhausted Morgan said as she left the Panda House about 1 p.m. "She's cuddling the baby. If it's fussy, she repositions it.

"She's very bright," Morgan added. "First babies are dicey. She's paying close attention. I'm happy for her."

Morgan described the cub as "very vocal and fussy" -- like a newborn baby. "That means it's doing well, too."

The cub will not be named until it is 100 days old, a Chinese tradition. Under the zoo's 10-year, $10 million loan agreement with China, the cub will be sent there when it is 2 years old. Stevens said cubs generally stay with their mothers for 18 months.

The zoo's attempts to breed its first pair of giant pandas, a gift from the Chinese government to President Richard M. Nixon in 1972, were marked by repeated heartbreak. After a decade of false starts, Ling-Ling produced a cub in 1983, which died of pneumonia three hours later. She had a stillborn cub in 1984. In 1987, she bore twins; one died immediately, and the other died of an infection four days later. Her last cub died of pneumonia 23 hours after birth in 1989. Ling-Ling died in 1992, and the male, Hsing-Hsing, died in 1999.

Suzan Murray, the zoo's chief veterinarian, said that Ling-Ling and Hsing-Hsing were older when they began reproducing and that the female had chronic urinary tract infections that put her offspring at risk. But, she added, "The first couple of weeks are a tense time, and we'll be monitoring [Mei Xiang] very closely."

Mei Xiang, whose name means "beautiful fragrance," is 6. Tian Tian, whose name means "more and more," is 7. Pandas can reproduce from about 4 years old until about 20.

Tian Tian began trying in 2002, but Mei Xiang fled up a tree. The pair mated briefly in 2003 without result. They tried last year, after which Mei Xiang was vaginally inseminated and had a false pregnancy. This year, after the pair tried to mate several times but failed, a zoo reproductive scientist injected Tian Tian's sperm directly into the female's uterus, a technique that zoo officials say has a 55 percent success rate. Panda gestation periods range between 90 and 185 days; Mei Xiang's was 120 days.

Only about 1,600 giant pandas remain in China's bamboo forests, where they are endangered by poachers and by encroaching development. But pandas also are fussy breeders. The female is in heat only two or three days a year. In zoos, detecting a pregnancy is difficult, although experts hope that eventually a combination of behavior monitoring, hormone tests and other technology can improve the odds.

Only three other zoos in the United States exhibit giant pandas -- those in Atlanta, Memphis and San Diego. The San Diego Zoo has had two successful births.

The National Zoo's happy news comes as the animal park emerges from a troubled era in which its accreditation was on provisional status for a year before being restored, a National Academy of Sciences report criticized its management, and its director, Lucy H. Spelman, resigned.

Now, in addition to the panda birth, the zoo is drawing crowds to see five cheetah cubs, will open a new panda area with double the outdoor space next year and is undergoing a 10-year, multimillion-dollar renovation.

"Is it okay if I skip?" Stevens asked as she walked toward the microphones at the zoo's morning news conference to announce the birth.

"We've been waiting so long for another cub, you wonder if it is real," she said. "We're thrilled and a little scared because we want it to go perfectly."

Staff writer Yolanda Woodlee contributed to this report.

For more about the new cub and other panda information, go to

In a photo released by the National Zoo, Mei Xiang looks down over her cub (within the white box). The cub is as small as a stick of butter and likely weighs about four ounces.Dr. Suzan Murray, chief veterinarian, monitors the pandas from a distance.