We have a LOT of windows (46, DP counted one day whilst cleaning) and three bird feeders. A couple of things that have helped include: (1) rather than window stickers, hanging up a few glass decorations - the kind you use suction cups to attach to the window; and (2) putting our shades/blinds at different, staggered heights, especially for side by side windows. While these methods have not been foolproof, they have cut way down on the number of birds flying into the windows.