Peter, I take it you don't have a barn? We will always have barn cats, and always feed the birds. It's rare that the birds feed the cats, as much as the cats try.
edited to add: Our barn cats have always just showed up. They were not a result of our own irresponsibility because we always have them spayed, or neutered. I do agree that feral cats are a problem, but we don't contribute to that.