I don't know when it comes to like south american hornbills or smaller softbills or other birds, but you can keep parrots outside pretty much all year around as long as they have a heated shelter, ice-free water and some other precautions like a lot of very wide perches so that they can cover the feet with feathers while they are resting etc.
I've seen a flock of budgies playing in the snow at -15 degrees Celsius. Same goes for macaws, it was a blast seeing them throwing snowballs around, haha.
Especially cockatoos and Australian/African parrots/parakeets seem to do very well in cold weather and even enjoy it if they get a chance to acclimatize during the fall.
