Window markers reduce bird–window collisions in a real-world application

Abstract Bird–window collisions are a top source of direct anthropogenic mortality for birds worldwide. Although there are many commercially available products designed to reduce bird–window collisions, relatively few studies have included replicated field testing of such products to assess their effectiveness in real-world environments. We conducted a field study testing the effectiveness of Feather Friendly® white-dot window markers (5.1 × 5.1 cm-spaced, on the exterior) in reducing bird collisions at 2 buildings (6 total building façades) that were treated with the markers in comparison to several untreated buildings on the campus of Oklahoma State University in Stillwater, Oklahoma, USA. We included a before-after control-impact (BACI) design to evaluate collision rates at both treated and untreated buildings before and after the window markers were applied to the 6 glass façades in June 2023. Descriptive estimates based on collision data indicate that collision rates at treated façades were reduced by 67.2–71.6% in the post-treatment period compared to the pre-treatment period. We observed this reduction despite a 15.7% increase in collision rates at untreated façades from the pre-treatment to post-treatment periods. Although the formal BACI analysis found no significant effect of the interaction between treatment (treated versus untreated building façades) and period (pre- versus post-treatment periods), the above descriptive pattern suggests that this result may have been related to limited statistical power associated with the low replication of treated façades. Our results provide additional evidence indicating the effectiveness of this type of window marker in reducing bird collisions. Additionally, this study showcases a rigorous framework for conducting field tests of bird–window collision deterrent products that can be used for future evaluations of the effectiveness of similar products in real-world situations.