Bird window collisions are a common and distressing event. They result from a complex interaction between avian perception and human-built environments. Understanding why these collisions occur, their immediate consequences, how to assist an affected bird, and prevention strategies can help mitigate this widespread problem.
Why Collisions Occur
Birds frequently collide with windows due to a fundamental difference in how they perceive glass compared to humans. To a bird, transparent glass may appear as an unobstructed pathway, allowing them to see through to vegetation or open space on the other side. Alternatively, windows can act like mirrors, reflecting the surrounding environment, such as trees, sky, or habitat, which birds then mistake for a continuation of their natural surroundings.
The placement of windows and nearby vegetation often exacerbates these optical illusions. Birds, adapted to navigate by detecting edges and patterns, often do not register the clear, flat surface of glass as a solid barrier. Additionally, some birds may repeatedly strike windows during breeding season due to territorial aggression, perceiving their own reflection as a rival.
Immediate Consequences for Birds
Upon impact with a window, birds can sustain a range of severe injuries, even if they manage to fly away afterward. Concussions, a form of brain trauma, are common due to the blunt force of the collision. Birds may also suffer from broken bones, including fractures in their wings, legs, or beaks. Internal bleeding, which is not immediately visible, can also occur and may lead to delayed mortality.
Even if a bird appears stunned and recovers enough to fly, it remains highly vulnerable to predators. Their dazed state makes them slow to react and escape. Such birds may also have internal injuries that prove fatal later.
Assisting Stunned or Injured Birds
If a bird strikes a window, observing it from a distance is the first step. If the bird appears only stunned but otherwise uninjured, it might recover within a couple of hours. However, if it shows signs of injury, such as bleeding, an inability to stand or perch, seizures, or unresponsiveness, immediate intervention is necessary. For these cases, contacting a local wildlife rehabilitator is recommended, as they possess the expertise and resources for proper medical care.
To provide temporary care, gently approach the bird from behind and carefully place it into a small, unwaxed cardboard box with air holes. Line the bottom with tissue paper or a soft cloth for comfort. Keep the container in a dark, quiet, warm location, away from pets and excessive noise, allowing the bird to recover from shock. Do not offer food or water, as this could cause further harm. Check on the bird periodically, but avoid excessive handling.
If the bird recovers within an hour or two, take the box outside to a safe, sheltered area and open it, allowing the bird to fly away. If it does not fly away, or if it exhibits clear signs of injury, transport it to a wildlife rehabilitation facility as soon as possible.
Strategies to Prevent Strikes
Effective methods can reduce bird collisions with windows.
- Apply visible patterns to the outside of windows, such as decals, tapes, films, or tempera paint. These should be spaced closely, ideally in a grid pattern of no more than two inches by two inches, to make the glass discernible. Hawk silhouettes alone are generally ineffective unless applied in high density.
- Install external screens or netting over windows to create a physical barrier and break up reflections.
- Adjust blinds or curtains to be partially closed to reduce transparency and reflection.
- Place bird feeders and baths either within three feet of a window (to prevent speed gain) or more than 30 feet away.
- Reduce artificial light at night, especially during migration seasons, to prevent disorientation.