Leaf Medley Multi pack of 5 leaf decals. One Elm, Oak, Maple, and 2 Aspen leaves included. Window Alert decals help prevent wild birds from accidently striking windows. Each decal has a special coating that reflects ultraviolet sunlight. This ultraviolet light is invisible to humans, but birds see it as a brilliant glow much like a stoplight. To the human eye, the decals appear as frosted or etched glass. The decals measure approximately 4 inch across and are designed to be placed on the OUTSIDE of a window. As a rough guide, we recommend one decal for every 3 ft x 3 ft section of glass.