Hundreds of millions of birds are killed in window collisions every year.
A common solution is to apply ultraviolet patterns that distinguish glass from reflected sky or trees. While glass panes containing UV-absorbing patterns are available commercially, field tests have yielded mixed results.
Scientists at the Swedish University of Agricultural Sciences and Uppsala University show that because birds differ strongly in how well they see ultraviolet light, the markings are only visible to species with the right type of color vision. These include birds like small perchers (passerines), gulls, and parrots. To these species, ultraviolet markings are clearly visible under a range of lighting conditions.
For geese, birds of prey, pigeons, and crows, however, these patterns can be difficult to detect. To be effective, the films would have to produce virtually perfect contrasts and be viewed against a scene with low color variation but a high ultraviolet content, such as a clear blue sky.
If a glass retrofit for bird safety isn’t decreasing collisions as you hoped, inventory the remaining affected species to see if additional films are necessary.