The National Zoo's giant panda, Mei Xiang, gave birth to twins Saturday, almost two years to the day after giving birth to her daughter, Bao Bao.
Mei Xiang was seen picking up and licking her first cub at 5:35 p.m. Saturday, live on the zoo's panda cams. The cub could be heard squealing just after the birth, which zoo officials called a good sign.
The second cub was born just after 10 p.m. As is the zoo's practice, one of the two cubs was retreived from Mei Xiang's enclosure and placed in an incubator. That cub appears to be in good health, according to a post on the zoo's Facebook page.
Zoo veterinarians had not yet retrieved the other cub from Mei Xiang's enclosure late Saturday night. They will closely monitor both mom and that baby on the panda cams, waiting until they can retrieve the cub without distressing mom or cub.
The time after the birth is critical for bonding, but this is "still a very fragile time" for the cubs, said National Zoo Director Dennis Kelly.
In 2012, a female cub died a week after her birth. "We are very excited but we are very cautious," Kelly said at a press conference after the first birth.
There's a protocol for twin panda births, which happen about 50 percent of the time in the difficult and often-disappointing world of giant panda procreation. The Zoo's panda team will swap the cubs into the enclosure, allowing one to feed and bond with Mei Xiang while the other is bottle-fed and cared for in an incubator, the Zoo said.
The births came quickly on Saturday. Earlier that day, the Zoo's panda team said in a Facebook post that Mei is "restless, having contractions, body licking, and remains in her den." The team said those behaviors are consistent with an imminent birth.
Around 4:40 p.m., the zoo said the panda team confirmed that Mei Xiang's water broke.
Zoo personnel monitored Mei through their panda cams, which were overloaded from time to time due to the popularity of the pandas.
Mei was inseminated April 26 and 27 with frozen sperm from Hui Hui, a panda living in China, and with sperm from the zoo's male giant panda, Tian Tian, the Smithsonian Conservation Biology Institute said.
On Aug. 10, Mei's hormone levels were on the rise as she began to show typical signs of pregnancy or pseudopregnancy, including spending more time in her den, sleeping more, body licking and cradling objects.
On Tuesday, the National Zoo closed its giant panda exhibit as Mei entered her final final phase of her pregnancy due to her sensitivity to noise. Wednesday, Zoo vets detected her fetus on an ultrasound -- the first time they had ever seen a fetus on ultrasound, since Mei Xiang usually doesn't cooperate with scans.
At the time, zookeepers thought they might have spotted a second fetus, but they couldn't be sure, they said at the afternoon press conference.
This is the first time the National Zoo has had newborns and an older cub -- in this case, 2-year-old Bao Bao -- at the same time.
Mei Xiang has previously given birth to four cubs, two of whom survived: male Tai Shan, who was born at the zoo in 2005 and now lives in China, and female Bao Bao, who still lives at the National Zoo. In addition to the female cub that died in 2012, another female cub, Bao Bao's twin, was stillborn.
Tian Tian fathered all four cubs. It's not yet known which of the two possible fathers sired these cubs.
Following Chinese tradition that celebrates 100 days of life, panda cubs are named 100 days after their birth.