Window collisions are one of the biggest bird killers in urban environments: birds can’t see the windows properly, and can fly straight into them.
People have tried a range of different things to stop birds killing themselves – including adding film or stickers to make the windows look different to their avian assailants.
It’s often a lot cheaper to apply these decals to the insides of windows, rather than the outside. But unfortunately, according to new research in PeerJ, that also renders them ineffective.
“Many people want to reduce bird-window collisions, as these unfortunate events kill hundreds of millions of birds each year,” says lead author Dr John P. Swaddle, a researcher at the University of William & Mary in the US.
“There are lots of decals and window films that will likely make glass surfaces more visible to birds, decreasing collision risk.”
The researchers analysed two different commercial bird films: Haverkamp and BirdShades. BirdShades funded the test of their window film, but were not otherwise involved in the study.
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The researchers added windowpanes with and without these films to an aviary filled with zebra finches. All windows had a fine net in front of them, to stop the finches from actually flying into the windows.
Then, they recorded the birds’ behaviour and counted the collisions.
“We were able to show that people must apply decals and films to the external surface of their windows to benefit the birds,” says Swaddle.
When they were on the outside of the window, BirdShades and Haverkamp increased window avoidance by 47% and 39%, respectively.
But when they were on the inside, neither film made any difference at all.
This means that, if you want to install a film to prevent bird collisions, it has to go on the outside of your building – even if it’s less convenient and more expensive to put it there.
“We want people to know this as we want their time and money to be well spent – protecting the birds we all love,” says Swaddle.