Birds colliding with windows is a widespread issue, often resulting in injury or fatality for countless birds annually. Understanding the reasons behind these collisions and implementing effective prevention strategies can significantly mitigate this problem.
Understanding the Causes
Birds frequently fly into windows because glass can be imperceptible to them, creating a deceptive environment. One primary reason is reflections, where windows mirror the surrounding sky or vegetation. Birds perceive these reflections as open space or continuous habitat, leading them to fly directly into the glass at high speeds. This illusion is particularly dangerous during dawn, dusk, or migration seasons.
Another significant factor is transparency, where birds see through a building to habitat or open space on the other side. When windows are aligned on opposite sides of a structure, they can create a “tunnel effect,” making birds believe they can fly straight through. This can also occur if indoor plants are visible through the glass, attracting birds.
Artificial light pollution, especially at night, disorients migratory birds and draws them into urban landscapes. Nocturnal migratory birds are disoriented by city lights, pulling them off course and making them vulnerable to collisions with illuminated windows. Once drawn into these areas, they may collide with windows during the day due to reflections.
Birds can also become disoriented by sudden fright or unfamiliar surroundings, causing erratic flight paths that lead to window strikes. Sometimes, birds may attack their own reflections, particularly during breeding season when territorial instincts are high. While this “reflection aggression” is usually not fatal.
Effective Prevention Strategies
To reduce window strikes, various practical methods can make glass more visible to birds. Applying decals, tapes, or patterns directly onto the outside surface of windows is a common and effective approach. These markings should be spaced no more than two inches apart across the entire glass for effectiveness. White or light-colored materials often provide the best contrast for visibility.
Installing external window screens or netting can also prevent collisions by reducing reflections and providing a physical barrier that cushions any impact. These should be placed tautly at least two to three inches from the window. External shades or awnings also help minimize reflections.
Adjusting indoor and outdoor lighting, especially at night, significantly reduces the risk for migratory birds. Turning off non-essential lights, particularly during spring and fall migration periods, helps prevent disorienting birds. Using motion sensors or downward-facing lights can further minimize light spill.
The placement of bird feeders and baths also influences collision risk. Positioning feeders either very close to windows (within three feet) or far away (more than 30 feet) can help. When feeders are close, birds cannot build up enough speed to cause severe injury if they hit the glass.
Some specialized products, such as UV-reflective films or patterned glass, are designed to be visible to birds while remaining transparent to human eyes. While some birds can see ultraviolet light, UV reflectivity may be less effective during early morning hours when many collisions occur, so combining these with other strategies is recommended.
Responding to a Window Strike
If a bird strikes a window, assessing its condition safely is the first step. If the bird appears stunned but not severely injured, approach it calmly, ideally from behind. Small birds are fragile, so handle them gently without squeezing.
Creating a quiet, dark, and safe environment aids in recovery. Gently place the bird in a small, unwaxed paper bag or a cardboard box lined with a soft cloth. Ensure the container has air holes and is placed in a quiet, warm, dark location away from pets and children. This helps reduce external stimuli and allows the bird to recover.
Do not attempt to force-feed the bird or give it water, as this can cause aspiration and further harm. Check on the bird periodically, typically every 30 minutes to an hour. If the bird seems to have recovered, take the container outside to a sheltered spot and open it, allowing the bird to fly away when ready.
If the bird does not recover within two hours, appears visibly injured (e.g., broken bones, bleeding), or cannot fly away, contact a local wildlife rehabilitation center immediately. These professionals are equipped to provide the necessary care for internal injuries, which may not be immediately apparent but can worsen over time.