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Providing evidence to improve practice

Action: Mark or tint windows to reduce collision mortality Bird Conservation

Key messages

Read our guidance on Key messages before continuing

  • Two randomised, replicated and controlled studies (one ex situ) found that marking windows did not appear to reduce bird collisions. However, when windows were largely covered with white cloth, fewer birds flew towards them.
  • A randomised, replicated and controlled study found that fewer birds collided with tinted windows than with un-tinted ones, although the authors noted that the poor reflective quality of the glass could have influenced the results.

Supporting evidence from individual studies


A randomised, replicated and controlled study over 52 days in Illinois, USA (Klem 1990), found that marking windows in various ways did not reduce the number of birds colliding with the windows, compared to an unmarked control window. Similarly, a randomised, repeated and controlled choice experiment in a flight cage found that dark-eyed juncos Junco hyemalis did not consistently avoid windows marked with wind chimes, silhouettes of falcons, plants, stickers of eyes or model owls. However, birds tended to avoid windows that were completely covered by white cloth, or covered by closely spaced cloth strips and meshes. Widely spaced cloth strips and flashing lights partially increased avoidance.


A randomised, replicated and controlled experiment between January and May 1991 in Pennsylvania, USA (Klem et al. 2004), found that a smaller proportion of collisions were with tinted windows (32% of 53 recorded collisions) than with clear windows (68% of collisions). The same study found that, when platform feeders were placed at varying distances in front of the windows (see ‘Provide supplementary food - Place feeders close to windows to reduce collisions’), only four of 52 fatal collisions (8%) occurred with tinted windows, the rest with clear glass windows. However, the authors note that the tinted glass was of a poor reflective quality and they believe this may have resulted in fewer fatalities than a highly reflective tinted glass. Experiments used six plate glass, wooden framed windows (1.4 x 1.2 m, 1.2 m off the ground, 15-43 m apart) on the edge of deciduous woodland and farmland.

Referenced papers

Please cite as:

Williams, D.R., Child, M.F., Dicks, L.V., Ockendon, N., Pople, R.G., Showler, D.A., Walsh, J.C., zu Ermgassen, E.K.H.J. & Sutherland, W.J. (2019) Bird Conservation. Pages 141-290 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.