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Looks like Bao Bao will be celebrating her second birthday with two new siblings.

After giving birth to a cub at around 5:30 p.m. on Saturday, Mei Xiang gave birth to a second at 10:07 p.m. According to the National Zoo, “a panda team of three keepers retrieved one of the cubs per the Zoo’s Giant Panda Twin Hand-Rearing protocol. The cub is now in an incubator and being cared for by veterinarians and panda keepers.”

The cubs will be swapped between Mei and the zoo team, “allowing one to nurse and spend time with Mei Xiang while the other is being bottle fed and kept warm in an incubator.” Giant pandas give birth to twins roughly half the time, the National Zoo explains; only two other female giant pandas have raised twins and “it required a lot of human support.”

Several details remain unknown about the panda family’s future. Jen Zoon, a spokesperson for the zoo, says keepers will determine the sex and paternity of the cubs about two weeks after their DNA is obtained from cheek swabs. (Mei Xiang was artificially inseminated in April with samples from two male giant pandas: Tian Tian, Bao’s father who lives at the National Zoo, and Hui Hui, who lives in China and whose sperm, the zoo explained in a statement last week, could help “preserve the genetic diversity of the panda population in human care.”) Zoon adds that the cubs don’t have names yet, and that their names may be put to a public vote, as was the case for Bao.

“Tian and Bao will remain solitary, just as they would in the wild,” Zoon says. The mother and her cubs will remain in the den for the next few weeks or even months—they’ll also be off-exhibit until the cubs receive all the necessary rabies vaccinations, at around five-months-old (January 2016).

Both cubs appear to be healthy: They’ve “vocalized” since yesterday and are being given nutrients consisting partly of human-baby and puppy formula. (The first cub zookeepers retrieved, according to a press release issued this morning, “has urinated and defecated—all good signs.” It’s been given a serum with antibodies since it hasn’t yet directly nursed on Mei Xiang.) As of today, one cub weighs 132.4 grams, while the other weighs 86.3 grams.

Many panda-watchers witnessed the births on the National Zoo’s online panda cam. Although the zoo doesn’t currently know how many people were watching live, Zoon says there were no apparent issues with streaming. If people have trouble playing the cams given the high volume of viewers tuning in, “they can refresh the page to reestablish a connection, or watch the cam uninterrupted via the Smithsonian’s National Zoo App,” Zoon explains.

Bao celebrated her second birthday today with “a frozen fruitsicle cake” that includes “honey, apple juice, apple sauce, bamboo, carrots, and beet juice.”

This post has been updated with additional details from the National Zoo.

Original post below

Bao Bao is a big sister.

Mei Xiang, the National Zoo’s adult female giant panda, gave birth to cub around 5:35 p.m. Saturday. The event was broadcast live via the zoo’s panda cam; viewers reported on Facebook hearing the cub cry.

From the zoo:

Mei Xiang reacted to the cub by picking it up. The panda team began preparing for a birth when they saw Mei Xiang’s water break at 4:32 pm and she was already having contractions. The sex of the cub won’t be determined until a later date.

The Zoo’s panda team is monitoring Mei Xiang and the cub via the Zoo’s panda cams. The panda team will perform a neonatal exam on the cub when they are able to retrieve it. That may take a few days.

“The cub’s been vocalizing,” Chief Veterinarian Don Neiffer said at a press conference, “showing us signs of being happy and healthy.”

Witness the miracle of panda birth below.

Photos via National Zoo; this post has been updated.