A giant panda on loan from China to Austria has given birth to two naturally conceived twins, an exceptionally rare event for the endangered species, Vienna's famous Schoenbrunn Zoo said Tuesday.
Measuring around 15 centimeters (six inches), the pink, hairless cubs arrived on August 7, it announced in a statement.
Initially the zoo thought mother Yang Yang had only given birth to one panda because the delivery happened inside a dark nesting box and was only observed via an infrared camera.
More than a week passed before zookeepers realized there was a second one.
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"The cubs have little round bellies and panda mummy Yang Yang is very relaxed," zoologist Eveline Dungl said.
"You rarely see them because Yang Yang constantly warms them between her paws... What you can hear very clearly are their suckling and grunting noises when she feeds or licks them."