Glass pane markings to prevent bird-window collisions: less can be more

To prevent birds from collisions with glass, markings on glass panes can be a valuable measure. However, to ensure public acceptance and widespread use of glass markings, maximum deterrent effect at minimum area covered has to be achieved. In this study we show that the efficacy of a deterring pattern does not necessarily depend on the size of the surface area of the marking but on orientation, spacing and dimension of the marking elements. We examined achromatic marking patterns in 1,428 choice experiments with wild birds (mostly songbirds) in a flight tunnel of seven meters length. A mist net ensured that the birds suffered no injury. Twelve markings were tested; of these, eleven effectively reduced collisions. However, considerable differences existed among the tested patterns. Covering less than 7%, 2 mm wide stripes were as effective as 13 mm wide stripes covering 50% of the glass surface. Vertical stripes 10 cm apart were significantly more effective than the same pattern in horizontal orientation. To create bird protection markings on glass, designers should consider both perceptional limits and pattern related behavioural responses of birds.