When 'Batu' first arrived at Twycross and went into 'seclusion' for a long period, he was about the same age as (his son) Tiga is now. He eventually came out of it so I'm sure Tiga will too- but it is a form of depression caused by the trauma of being moved. There have been a couple of cases on the Continent where after a transfer, Orangs had to be moved back to their home zoos as it was feared they would die otherwise.