November 10, 2026, 5:01 am | Read time: 5 minutes
A dull thud against the window, and it’s happened: A bird has flown into the window and lies motionless on the ground. According to NABU, windows and glass facades are the most common cause of death for wild birds, with the nature conservation association estimating around 100 million bird deaths per year. The State Working Group of Bird Protection Stations (LAG VSW) suspects even more, as injured animals often die later in a bush. While large office buildings are more dangerous than private homes, windows at home can also be made bird-safe. PETBOOK explains why birds fly into windows and how to easily prevent it.
Overview
Why do birds fly into windows?
Birds–especially birds of prey–actually have excellent vision. For example, a kite can spot a grasshopper in a field or a mouse in a meadow from miles away. A blackbird also has excellent spatial vision. However, because their eyes are positioned on the sides, their forward-directed vision is limited. Additionally, glass surfaces have optical properties that prevent birds from recognizing them as obstacles.
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Reflection
The reflection of the surrounding nature and sky in the glass panes creates the illusion of an endless landscape for the bird. It only sees the reflection and continues flying, aiming to land in the next tree, for example. If the building is surrounded by lush vegetation where many birds are present, the risk of bird collisions increases significantly.
Transparency
There are also buildings constructed at angles or with particularly clean glazing that become a hazard for birds. These include conservatories, swimming halls, noise barriers, bus stops, or stairwells. Here, the bird sees the open sky or a group of trees on the other side, which it targets, only to be abruptly stopped by the glass facade.
Lighting
Especially in the evening or at night, buildings illuminated from the inside–and thus their glass panes–can pose a danger to migratory birds. These birds navigate their migration routes by the moon and stars, as well as the Earth’s magnetic field, which they can likely see with a receptor in their eyes. During their flight, they are attracted by the city lights, lose their orientation, and collide with the large glass facades of office buildings. However, due to energy savings, these artificial light sources will become less common in the future.
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Why Birds Fly Into Windows and How to Prevent It
Why you so rarely see dead birds
What should I do if a bird has flown into a window?
After a collision with a window, you should check whether the bird is dead from the impact or unconscious due to a traumatic brain injury.
First aid measures for a bird collision:
Check vital signs:
- Does the bird still have a pulse and is it breathing?
- Can you hear or see the heartbeat?
- Shine a flashlight into the eyes. If the pupils contract, the bird is alive.
- The bird can now be secured: The best option is a small box with a lid, with enough air holes cut into it. For a young bird, you can place a not-too-hot hot water bottle inside. The temperature should be 86 degrees Fahrenheit. An adult bird does not need a heat source. Then, carefully place the injured bird on a towel inside.
If no severe external injuries are visible, leave the bird alone for a while and place the box in a quiet, shady corner.
Warning: Do not give it water! If it has suffered a concussion, it could vomit and choke.
If it has not suffered serious injuries, the bird should recover after one to two hours, and you can take the box outside and release it. If it still appears unchanged after about two hours, please consult a veterinarian or a wild bird rescue center.
How can I prevent birds from flying into windows?
“With the right markings on the outside of the glass, the number of bird deaths can be significantly reduced,” says ornithologist Christa Glauser from Birdlife Switzerland. In her experience, traditional bird of prey silhouettes are not very effective. However, there are effective bird protection markings you can apply to your windows:
- Vertical lines and patterns are best perceived by birds
- Place the stripes or dots about a hand’s width apart. This prevents the bird from trying to fly through a perceived gap.
- The markings must cover the entire surface of the window.
- The markings must always be applied from the outside.
- The color orange is particularly well perceived by bird eyes.
- NABU recommends cost-effective solutions from the outside: fly screens, string curtains made of cords, window paints, and frosted adhesive strips.
- Inside, you can use light curtains, blinds, shades, or similar items.
Conclusion: Flying into windows is one of the most common causes of death for birds. Therefore, it is worthwhile to ensure that windows in private homes are bird-safe. Vertical lines and patterns are best perceived by birds. While this may not be aesthetically pleasing to humans, it reliably prevents birds from dying in accidents. Otherwise, curtains or blinds can also help reduce the risk of a bird flying into the window.
- Nabu.de, “Climate protection not at the expense of species and habitats” (accessed on 11/10/2026)
- Vogelglas.vogelwarte.ch, “Too many birds collide with glass” (accessed on 11/10/2026)
- Lbv.de, “How do I deal with injured birds?” (accessed on 11/10/2026)
- Srf.ch, “How the death of millions of birds can be prevented” (accessed on 11/10/2026)