Can’t find the report now, but the site of vogelwarte.ch has the following suggestions to prevent bird collision:
[quote (translated)]
- Only markings that have a large surface area and stand out from the surrounding area provide the necessary protection.
- Solutions with stripes are very effective; vertical lines are at least 5 mm wide at a maximum distance of 10 cm, horizontal lines at least 3 mm wide at a maximum distance of 5 cm.
- Use adhesive foils or tapes of good quality (e.g. strips for car tuning)
- Markings should be applied on the outside whenever possible.
Caution: foils can cause tension in the window panes, which in exceptional cases can lead to glass breakage; if in doubt, contact the glass manufacturer.
Under certain circumstances, good effects can also be achieved by the following (always apply on the outside, if possible):
- light curtains, blinds, roller blinds, cord tapes, foil tapes
- colored decorations, drawings with finger & window paints
- company logos, shop window decorations, decorative sprays
- grids, mosquito nets, nylon cords, cotton threads, coarse-meshed strong nets or perforated sheets
- strip curtains in winter gardens
[unquote]