Care-guide
How to reduce bird collisions with glass in a home
Birds perceive glass as open space due to reflections. Applying patterns to the exterior surface and reducing artificial night lighting are effective measures to prevent these collisions.
Why glass is invisible to birds
For birds, glass acts as an invisible and deceptive threat. Because they do not perceive it as a solid barrier, individuals may be attracted by reflections showing elements of their natural habitat, such as vegetation or open sky. During the day, birds fly towards these reflections believing they can pass through the space. At night, artificial lighting attracts migratory birds, increasing their risk of colliding with buildings. Homes and buildings of fewer than four stories are an important factor in this problem, as their height reflects vegetation and sky, and the large number of windows makes them difficult to avoid.
Application of patterns on the exterior surface
The placement and spacing of deterrent elements are critical, as birds can pass through surprisingly small openings. Patterns should be applied to the exterior surface of windows to help birds see that glass is present. It is recommended that pattern elements have a diameter of at least 1/4 inch (approximately 6.35 mm) and be spaced no more than 2 inches (5.08 cm) apart. This spacing in a 2 x 2 inch grid is especially important for protecting small birds. Dark colors can be difficult to see when the window reflects dark tones, so it is preferable to use medium or light colors to improve visibility. One or two predator bird stickers are ineffective for preventing collisions.
Materials and treatment methods
There are several options for treating windows. Parachute cord curtains use 1/8 inch pieces spaced less than 4 inches apart, creating a visual barrier. Non-toxic tempera paint can be applied to the exterior surface of the glass following the 2 x 2 inch spacing; it is easy to remove with vinegar and water. External meshes and screens reduce reflections and alert birds that the window is a barrier; mesh openings should be 1/2 inch or smaller to prevent birds from getting entangled. Tapes, stickers, and exterior films are also available. In the case of construction or renovation, fritted, etched, or frosted glass is more effective when applied to the exterior surface, as it includes adhered ceramic lines or dots. Glass with ultraviolet patterns is invisible to humans but visible to many bird species.
Reduction of night lighting
Minimizing artificial light at night is one of the simplest and most effective actions. Although collisions occur throughout the year, they are more frequent during spring and autumn migration, when most birds migrate at night. Turning off unnecessary lights manually or using timers and motion sensors reduces attraction to the glass. The use of blinds, curtains, awnings, and shutters on windows helps reduce the amount of light escaping and allows birds to perceive the glass as a barrier. Limiting lighting to where and when necessary reduces light pollution and benefits birds and other nocturnal animals.
Monitoring and risk assessment
To determine if a home's windows are a problem, a monitoring program can be implemented. It is possible to hear a dull thud or see a dusty bird print on the window. Even if the bird appears stunned, there is a good probability that it has injuries from which it will not recover. Recording these incidents helps detect problematic windows and evaluate the effectiveness of measures taken. Appropriate solutions can prevent up to 95% of window collisions, although this percentage depends on the correct application of the measures described.
Sources
- Threats to Birds: Collisions (Buildings & Glass) · www.fws.gov
- Bird Safe Glass: What you Need to Know · www.nps.gov