A bird colliding with a window is an unfortunate event that occurs with distressing frequency, often resulting in injury or death. An estimated 365 to 988 million birds are killed annually in the United States alone due to strikes with glass on buildings and homes. Understanding why birds fail to perceive windows as barriers, how to respond immediately, and how to prevent future accidents is the most effective way to address this problem. This guide provides information on the causes of window strikes and practical measures to protect local avian populations.
Understanding Why Collisions Happen
Birds strike windows because of two primary optical illusions that interfere with their navigation and perception. The first illusion is transparency, which occurs when a bird sees clear glass as an open, unobstructed flight path. This often happens when windows are positioned across from one another or when vegetation is visible through the pane. This misperception causes them to fly straight ahead, believing the space is safe to traverse.
The second, and more common, illusion is reflection, where the glass acts like a mirror, reflecting the surrounding habitat, such as the sky, trees, or bushes. A bird flying toward what appears to be a safe landing spot cannot distinguish the reflection from the real environment. Birds lack the cognitive ability to recognize glass as a solid barrier, especially when it is perfectly clear or highly reflective.
Immediate Steps After a Bird Strike
If you find a bird that has just struck a window, assess whether it is stunned or seriously injured. Always wear gloves before attempting to handle any wild animal. If the bird is motionless but breathing, it is likely in shock or has a concussion and needs a quiet place to recover away from predators. Gently place the bird in a small cardboard box, such as a shoebox, lined with a soft cloth. Secure the lid after poking several small air holes.
The box should be moved to a dark, quiet, and temperature-controlled location, such as a garage or shed, to minimize stress. Check the bird after 30 minutes to two hours by taking the box outside and opening the lid to see if it flies away. Do not offer the bird any food or water, as they can easily inhale liquids or solids when in shock, which can lead to aspiration pneumonia. If the bird has visible injuries, such as a drooping wing or bleeding, or if it remains unresponsive after two hours, contact a local licensed wildlife rehabilitator immediately.
Strategies for Preventing Future Collisions
The most effective way to prevent strikes is by applying visual markers to the exterior surface of the glass. This breaks up the reflection and alerts birds to the barrier. Experts recommend using a dense pattern, often called the “2×4 rule,” where markings are spaced no more than two inches apart horizontally and four inches apart vertically across the entire window pane. This pattern ensures there is no gap large enough for a bird to fly through.
Suitable markers include high-contrast tape, decals, tempera paint, or UV-reflective stickers. Another solution is to install external insect screens, which soften the reflection and act as a physical buffer, potentially deflecting a bird mid-flight. When using bird feeders or baths, they should be placed either very close to the window (within three feet) or far away (greater than ten feet). Placing the feeder close to the glass ensures that if a bird is startled, it cannot build up enough speed to cause fatal injury upon impact.