Suburban idyll, green gardens, here and there a birdhouse. Black silhouettes of birds of prey are occasionally stuck to window panes. They are designed to prevent birds from flying into the glass. According to the German Nature Conservation Union (Nabu), however, this is of little use. Birds would only see a black spot instead of an enemy on the disc. They then usually crash right next to the invisible pane.
100 million birds die from glass death every year. This is the result of projections by the state working group of bird sanctuaries. At first glance, this figure sounds unrealistic. Catherina Schlueter, consultant for bird protection at NABU, explains how it came about: “Studies from the USA assume two glass victims per family home, that would be 32 million dead birds in Germany with 16 million single-family houses. In medium-sized houses, there are 22 victims of glass per year, and around 24 birds crash into each high-rise building every year.” The data can certainly be transferred to Germany. The domestic breeding population is estimated at 500 million birds, plus up to 500 million migratory birds.
A team led by Brendon Samuels, a PhD student in the Department of Biology at the University of Western Ontario in Canada, has now studied the behavior of the birds during the collisions and the Results in the journal peerJ published. Using motion detectors and cameras, the group spent two years bird-watching in a backyard in the city of London, Ontario. They recorded 29 collisions and 9 near misses of the birds with window panes. Only two of the collisions resulted in the immediate death of the animals, 23 birds flew away again after the collision. The researchers suspect that many died from injuries at a different location shortly after the impact.
The faster the birds flew and the more perpendicularly they hit the glass, the higher the likelihood that they would be injured or die. In 12 of the collisions, the cameras recorded that the birds were distracted before the collision. For example, they chased each other or kept an eye on nearby feeding sites. The type of bird does not play a role, writes the group. However, all of the birds recorded by the cameras were heavier than 40 grams – which may also have been due to the fact that smaller birds were not detected by the motion detectors.
The simplest solution is also highly effective: cleaning less windows
Reflections that reflect the surrounding nature are probably the main problem for the birds. And even if the desire for closeness to nature is understandable – a winter garden with plants in it represents a high risk of death, says Catherina Schlueter from Nabu.
When a bird hits the window and dies, it’s not only heartbreaking – it can also be expensive. In principle, §44 of the Federal Nature Conservation Act applies, the ban on killing and injuring wild animals. Violations of this prohibition can be punished with fines up to imprisonment. In concrete terms, this means that the neighbor may build his conservatory out of glass, but he has to make full use of bird protection measures. The competent nature conservation authority does not accept the argument that bird protection is not necessarily aesthetic.
In their paper, Brendon Samuels and his team recommend placing feeding stations or birdbaths near window panes. In this way, the animals would not hit the nearby pane with full force. This recommendation not only contradicts common sense – a guide from the Bavarian Federal Office for the Environment also expressly recommends the opposite. Catherina Schlueter also says: “The birdhouses create an attraction for birds, which then come dangerously close to the windows. Birdhouses should be placed far away from the window.”
The best thing is to work with bird protection markings such as frosted glass adhesive strips, which interrupt the reflection. According to Samuels and his team, bird-friendly materials should be used when building the windows, such as the milky-looking frit glass or window films. If adhesive films are used, they should be attached to the outside. Mounted on the inside of the glass, the animals usually could not see them sufficiently, wrote scientists at the William & Mary’s Institute for Integrative Conservation in the US state of Virginia recently also in the specialist journal peerJ. The simplest solution is also highly effective: cleaning less windows.