George has probably learned the whistles from some of the wild birds outside and may even be combining some of them inti new whistles and this is perfectly natural for them.
As far as George hanging out at the window screens, it is fine for him to do this, but I would keep a very close watch on the screens as he is strong enough to tear a hole in them at any time. If it were my bird and my windows I would mount some 1/2 inch hardware cloth in a frame and put that up on the outside on the house covering the window screens so that even if he were to tear open the normal screen wire he could not get out. This would also help to protect him from predatory birds outside as well as from cats and such. without the hardware cloth screen for additional protection, I think that I would be worried about escape or hawks and such predators.





