If I kept the windows open I'd have a hawk in the house along with the bird that was trying to escape from the hawk. Not good lol. Not to mention all the cockatiels who'd be flying around outdoors acting like hawk bait.

What usually happens after they bounce of the window is that the hawk grabs them. There are a lot of Coopers hawks in my area, and they're smart enough to figure out that chasing birds into the window is an easy way to get lunch. I'm sure they didn't sit around thinking about what would happen if they did this. They simply noticed that birds that flew toward the house were easier to catch, so they kept chasing them in that direction.

I bought a brooder clamp lamp at Walmart and turned it into a swag light over the biggest cage. You can buy a swag light fixture from Feather Brite but my way is a lot cheaper.