On Sunday, August 7, the Schönbrunn Zoo in Vienna, Austria announced that its female giant panda, Yang Yang, had given birth to a single cub. Now, the zoo has twice the cause for celebration: According to The Guardian, Yang Yang actually delivered twins—but animal keepers didn’t spot the second baby until days later, and confirmed on Friday, August 12.

The Schönbrunn Zoo relies on natural breeding, so they didn’t intervene during Yang Yang’s birthing process. Instead, they monitored her progress via camera. Pictures only showed one baby, ABC News reports, so the zoo initially assumed that Yang Yang— who’s also the mother of three other pandas, Fu Long, Fu Hu and Fu Bao—hadn’t produced additional offspring. 

Animal keepers suspected there might be another cub after they heard extra squeaks coming from the breeding box. However, the twin’s presence wasn’t officially verified until later on, when the camera captured Yang Yang cuddling the two infants, a zoo news release states.

The next few weeks are pivotal for the babies' survival. Female giant pandas give birth to twins around 50 percent of the time—but often, only one survives. (Experts think this is because the mother chooses to care for the stronger baby.) Plus, a baby panda’s survival rate for its first few years of life is only 50 percent. To play it safe, Schönbrunn Zoo officials say they’ll follow Chinese tradition, and won’t name the panda twins until after they’ve lived for more than 100 days.

In the meantime, the zoo says, the newborns are doing well. "Both pups have little fat bellies, and mother panda Yang Yang is very relaxed,” zoologist Eveline Dungl said in the zoo's news release. Yang Yang reportedly warms the babies between her paws, and they’re already sprouting their signature black-and-white fluff.

Members of the public will be able to visit the twins once they’re about four months old, the zoo says. Until then, you can watch the Associated Press’s video of the adorable newborns below. 

[h/t ABC News]

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