Thank you all for the advice, I do appreciate it a lot. You are right, he has been through a big transition recently, so I will just keep an eye on him and hope that he is healthy and settles in well. So far, I haven't seen him today yet (he has burrowed down into the bedding during the night) but I noticed most of the treats as well as seeds and nuts from his Harry Hamster mix gone, so he does seem to have an appetite