Birds, like humans, perceive obstacles visually. Unlike us, however, they do not take visual cues from structural components and cannot perceive untreated glass as an obstacle. This leads to frequent and often fatal collisions. Scientific studies have shown that treating glass properly makes it visible to birds, helping them avoid these dangerous encounters. The use of high contrast and application of treatment to the correct surface side are two of several critical scientific features of an effective treatment. For reflective glass, treat the external glass surface (Surface 1) to break up the reflection. Markers applied to internal surfaces will not be visible to birds during most of the day, especially when it is brighter outside and darker inside. For such glass, use white markers to enhance contrast and visibility. For fly-through glass, such as those in bus shelters and clear railings, applying black markers on either surface (Surface 1 or 2) can effectively interrupt transpare...