Various types of window film can be used to make windows bird-safe: creative designs applied to special weatherproof film, perforated vinyl film in a solid colour or printed with an image, and also off-the-shelf decorative films.
Perforated vinyl window film, which is often used for advertising, appears opaque from the exterior but almost entirely transparent from inside. It can be custom-printed or cut into dots, stripes or other shapes and applied in a bird-safe pattern.
But be aware that perforated film appears transparent from outside at night, if a building is lit from within, and is thus not suitable for all applications. Furthermore, clear perforated vinyl is not sufficiently effective and is not recommended for use in any situation.
Off-the-shelf decorative films, which are often used to provide privacy, stick to the glass with an adhesive backing or static electricity. They come in a wide variety of patterns, many of which are dense and visible enough to be bird-safe. However, these films are usually designed for interior application, where they will not prevent reflections but will usually block fly-through effects.
Depending on the specific window, the surroundings, and the amount of contrast, film applied on the interior surface may be sufficiently visible from outside to overcome reflections most of the time. To test this, tape the film in place temporarily, then look at the window from outside at various times of day, under different light and weather conditions, and from different angles.
