The panda twins play at a research base in Chengdu, Sichuan province, Dec 6, 2016.[Photo by She Yi/ For China Daily]

All pandas coming from abroad have to be placed under quarantine for a month.

While some pandas can adapt to the new environment on the first day of quarantine, others are frightened and restless after the long flight.

"A few frightened cubs even climb to the window in their den," Wu said.

But researchers and keepers are experienced in helping the new arrivals.

"We can calm them down by giving them medicine and vitamins. All overseas returned pandas can adapt to their new home when the month-long quarantine is over," Wu said.