Thanks, I totally know what it's like to live with no backyard, it sucks. Mind you mine is still just 12 ft by 12 feet but It still fits a thing or 2.
You know there are other ways to have similar experience without a backyard. Any public land like wetlands or lakes where you see birds chilling or even city parks where there are a lot of trees, learn to identify the species that visit and learn what they like to eat that would be part of their natural diet but not necessarily available in the area (obviously be mindful and use organic products with no pesticides or chemicals because they can be really sensitive to that)and bring some of that item regularly, scatter it in their hangout, just sit and wait near by, they catch on pretty quick if you are consistent. I do that with Canada geese and Ducks, I swear they remember us year after year and follow us all over with their babies even when we have no food.
I normally wouldn't trust cats around the birds too much either but he used to be bullied when he was feral and I think that traumatized him I don't think he wants to hurt anything living ever. Even the mice he hunts, he doesn't hurt or kill them, he catches them gently and wants to bring them live into the house. He's like a pay it forward kinda cat that wants to rescue everything. I do watch him the whole time tho.
RE: Backyard bird talk #2 : Hottest yard in the neighborhood & a bet