According to Cornell Lab of Ornithology, the overall population of birds have gone down by 2.9 billion since 1970. The leading causes of bird mortality are habitat loss, feral and outdoor cats, and collisions with structures and buildings. If we look more closely at the third cause, more than 30 birds a second are killed every year, or roughly a billion birds in a year. The collisions are with external glass surfaces of buildings and from light pollution. Glass surfaces can either be invisible, not detected as a solid boundary, or reflective, in which case, birds perceive the reflection as the extension of the habitat they are in. Light pollution due to artificial light disrupts or disorients the navigation senses of birds, especially during migration at night.
Recently, the City of Pittsburgh replaced some of its streetlights from high-pressure sodium lamps to LED versions that emit warmer light, which are directed downward. They also plan to dim the new lights between 11 pm and 4 am, resulting in substantial energy savings. We need more cities to take similar actions. To reduce the effects of light pollution at the household level, replacing white bulbs with yellow or amber-toned bulbs – light that does not correspond to moonlight – will help with the added benefit of reducing the number of insects attracted to outdoor lights, thus saving some of our moth pollinators.
For glass collisions, almost all the bird strikes occur below 100 feet above ground. 44% of them occur with low-rise structures (1-3 floors) and 55% occur with mid-rise structures (4-11 floors). Surprisingly, high rises make up a very small percentage of bird strikes. Below 100 feet is the area where most birds are normally active. Some glass bird strikes occur when birds startled and are trying to get away from a hawk.
The solution to prevent bird glass strikes is to make the glass visible or to break up the reflection. There are a few commercial products available that can be purchased to apply to or hang by windows of your home. Isolated stickers or stencils will not be sufficient. The pattern used must be closely spaced and cover the entire window.
One solution is hanging corded curtains (made with parachute cords), known as Acopian BirdSavers. Despite their minimalist design, BirdSavers are very effective at keeping birds from colliding with windows. They are also very cost effective. Jeff Acopian, who runs a successful power supply company, invented and perfected this technique. As a bird lover himself, he hand-makes these curtains to order, stringing together vertically hung parachute cords no more than 4-inches apart, but he encourages people to make their own and provides instructions on how to do so. These curtains hang on the outside of the glass. (Jeff generously donated a gift certificate for the silent auction at our 25th anniversary gala). There are almost 10,000 BirdSavers installed that he has made.
Another solution is applying special tape with a pattern or creating a pattern using the tape. ABC BirdTape is a white or light blue vinyl material that can be adhered to windows either in long strips or in a pattern of squares. The tape lasts an average of four years, and is translucent enough to allow natural light through and not impact the view outside. For BirdTape to be most effective, it should be applied on the outside of the window with no more than two inches of space between each strip or square.
Companies like Feather Friendly, CollidEscape, Solyx Decorative Films and others sell tapes with various patterns that can be applied to windows on the outside. A common pattern is a 2-inch by 2-inch dot grid. A comprehensive list of products can be found on the American Bird Conservancy site.
People who have installed the corded curtains or patterned tape found that these solutions did not obstruct or distract from the view from inside the house, and they quickly adjusted to not noticing them anymore. For those that installed Acopian BirdSavers, some found it soothing when the cords swayed in the breeze.
More information regarding how to prevent bird glass strikes can be found here.
You can listen to this webinar by Cornell Lab or Ornithology, the main reference for this article, that provides more details about bird glass strikes.