Something that hasn't mentioned here yet is that some of these parrots, usually the cockatoos and macaws, are rescued pets who can't fly either because their wings were restricted beforehand or their wing muscles atrophied, and that's why they're kept on perches. Obviously that doesn't apply to every parrot, but perhaps this will explain the situation for some of them.
Yeah, many of the zoos I've been to have mentioned that many of their parrots were former pets.
But in cases where the parrots can fly, I do agree that free-flight exhibits should be standard. Especially since a lot of zoos make it a point to tell visitors not to get pet parrots because they require so much work and stimulation.
