Nonrandom Bird-Glass Collision Pattern: Fewer Strikes Near Glass Edge

Abstract. Collisions with glass or glass-covered objects are an important source of bird mortality worldwide. In this study, we investigate bird-glass collision pattern with the help of novel method using marks left by birds on glass surfaces. We surveyed 85 glass bus shelters every 12 days over a year to evaluate which parts of glass surfaces have the highest risk of collision. Among 178 bird-glass collisions recorded only 3% took place within 10 cm from glass edge, although this glass band (i.e. 0–10 cm from edge) covers over 30% of the whole glass area, on average. More inner parts of glass (10–70 cm from glass edge) had collision frequency slightly higher than expected by their coverage or proportional to their coverage. Different collisions recorded at one glass seemed independent suggesting no spatial aggregations within single glass. This study is the first to demonstrate the non-random risk of bird collision in relation to position on the glass surface and may suggest that there is no need to implement mitigating measures, like visible markers placed on the glass, closer than 10 cm from the glass edge.