These stickers are virtually invisible to the human eye, but are perceived by birds as obstacles due to the reflections on the special UV layer. These stickers are very durable and last a long time, even after multiple window washings.  For an optimal result, several stickers should be applied to the window surface. Results of the Birdsticker depend on lighting conditions and reflection of the window.  Not all “window collisions” can be prevented. This pack contains five silhouettes.