Zoo officials had thought mum Yang Yang had just given birth to one newborn a week ago but became suspicious after hearing sounds coming from the breeding box.

Their suspicions were confirmed last Friday when the camera filming the mother looking after the newborns caught both of them on film at the same time.

Photo: Tiergarten Schönbrunn

“As we believe in natural rearing, we will simply be watching via camera what is happening in the breeding box. It had sounded as if there were two young animals squeaking, but the pictures only ever showed one. On Friday the keepers could see two babies on the screen for the first time” explains Dagmar Schratter, the zoo's director.

The zoo says that it's quite common that Giant Pandas give birth to twins but the mother usually only rears the stronger of the two. Because the survival rate for pandas in the first few weeks is only 50 percent, the Chinese tradition is to only name the newborns after 100 days.

Nonetheless, experts say the two 15-centimetre-long pandas appear to be developing well with zoologist Eveline Dungl saying “both little pandas have fat little tummies and panda mother Yang Yang is totally relaxed.”

“The little ones can be rarely seen on the pictures because Yang Yang warms them between her large paws most of the time.”

Although born pink without fur, the zoo keepers can already make out the black and white markings as the first fluff appears.

Keepers say the latest additions to the family was probably conceived in March, when the mother Yang Yang and father Long Hui were spotted mating enthusiastically on several occasions.

Pandas mating in captivity is an extremely rare event and at the time the zoo described the moment between Yang Yang and Long Hui as “sensational”.  

Often pandas can only be bred by zoos using artificial insemination, which makes the latest arrivals - conceived naturally - a special and rare case.