Try some of the following ideas to make your windows safer. To deter small birds, vertical markings on windows need to be spaced no more than 4 inches apart and horizontal markings no more than 2 inches apart across the entire window. (If hummingbirds are a problem, the spacing should be reduced to a 2-inch by 2-inch grid.) All marking techniques should be applied to the outside of the window.
Decals. Put decals, stickers, sun catchers, mylar strips, masking tape, or other objects (even sticky notes) on the outside surface of the window. These are only effective when spaced very closely. Remember: placing just one or two window stickers on a large window is not going to prevent collisions—they must cover most of the glass with the spaces between too narrow for birds to fly through.
Screens. Installing mosquito screens over your windows is very effective, as long as they are on the outside of the window and cover the entire surface.
Netting. Cover the glass on the outside with netting at least 3 inches from the glass, taut enough to bounce birds off before they hit. Small-mesh netting (around 5/8″ or 1.6 cm) is best, so that birds don’t get their heads or bodies entangled but will bounce off unharmed. You can mount the netting on a frame, such as a storm-window frame, for easy installation and removal.