VIENNA (Reuters) – Twin panda cubs born and raised at Vienna Zoo celebrated their first birthday very differently on Monday: one gorged on snacks in front of a crowd of admirers while the other slept in.

Fu Feng and Fu Ban have been brought up by their mother without human intervention, a first for twin cubs living in captivity, according to the zoo.

To mark their birthday, the zoo arranged an event at which the twins would tear open wrapped “presents” filled with their favorite treats — carrots and sweet potatoes.

Fu Ban, a male, and his mother Yang Yang played along. Fu Feng, a female, stayed away. The zoo said she was sleeping.

The young bears have drawn crowds at the zoo, which is set in the gardens of Schoenbrunn Palace, a former imperial summer residence.

On top of ticket sales, it has now found another way to cash in on their popularity — by releasing a 2018 calendar featuring pictures of the pair.