A couple of bird-of-prey silhouettes, just like UV liquids, stickers and other invisible products, will effectively warn birds of danger.
Facts
Window stickers and UV products are very popular and widely sold in the Netherlands. This is a shame, because scientifically rigorous field testing has shown that such products are ineffective in preventing bird collisions.1 2 3
Birds that can easily manoeuvre through the dense branches of a tree will not view one or two stickers as an obstacle. They will simply fly around them. Testing has also shown that bird-of-prey stickers do not scare birds.
As for UV products, they are meant to reflect or absorb UV light that’s only visible to birds and not to humans. The first problem is that many bird species do not see UV light, or they do not see it well enough.4
The second problem is that UV light levels are lowest at the times of day when birds are most active and the risk of colliding the highest. That means UV products are least effective when they are most needed.
A good rule of thumb is: If you can’t see it, neither can birds.
- Trybus, T. 2003. Wirksamkeit von Greifvogelsilhouetten zur Verhinderung von Kleinvogelanprall an
Glasfronten. Die These des Masters, der Universität Wien. ↩︎ - Rössler, Martin, DI. 2018. “Bird collisions on glass surfaces – Dr. Kolbe Birdsticker® test report”, test
including reflections in Flight Tunnel II of the Hohenau-Ringelsdorf Biological Station, on behalf of the
Swiss Ornithological Institute in Sempach, February 2018. ↩︎ - Rössler, Martin. 2015. Bird collisions with glass surfaces – Test report birdpen®. Test according to ONR
191040 and WIN-Test in the flight tunnel II of the Biological Station Hohenau-Ringelsdorf. ↩︎ - Håstad O, Ödeen A. 2014. A vision physiological estimation of ultraviolet window marking visibility to birds. PeerJ 2:e621 https://doi.org/10.7717/peerj.621 ↩︎