Instinct for survival. Wet feathers mean loss of number one defense, escape by flying as fast and far as possible. Going up high limits this. So heights are not only safe but warm from the sun to dry feathers as they are preened. I don't know where I read that it was around 40+ years ago when I got my first CAG. It instructed to aid in bird security provide a warm safe place for preening after baths. If a crochet hook isn't in my hand I am a compulsive reader. I read just to read, I retain some of the weirdest things. Like this fact. I don't remember the books. They were written by tropical bird avian specialists. Back then there wasn't much CAG specific literature., In a couple of places by different experts I read CAG's have a high need for calcium. A bit of cheese weekly will help out. I didn't. Dogs, cats, people often develop lactose intolerance as when adults. So how could a species not dependent up anything lactose thrive on cheese. I never got around to finding out why. A few years later this was disproved. If you read there are still articles out there that recommend cheese for CAG'S. Sometimes it is a specific type like white. I lost an old article dated from some time in the 1800's, Found it at a garage sale or library bargain basement somewhere. It was discussing the inability to breed beautiful eclectus in captivity. Infertile or no eggs were the only results. Different techniques and suggestions were recommended to aid infertility. I originally planned to look for the time when realization hit the world they were sexually dimorphic. I still prowl library bargain basements.