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How to prevent bird strikes

Updated: Jun 5, 2022

Birds are vital for healthy ecosystems: they pollinate flowers and disperse seeds, manage pest populations, and often act as “keystone” species that others rely upon. Unfortunately, bird populations have been hit hard by habitat loss, pesticides, invasive predators, and accidental injury, particularly in grassland areas like Illinois.

Hundreds of millions of birds die every year from collisions with windows and other large, uninterrupted panes of glass. Migratory birds — of which Chicago has many — are especially vulnerable. Birds see differently than us: reflections and interior lights prevent them from recognizing windows as barriers, which instead appear as open space that they can fly through. Fortunately, this problem is largely preventable by making windows more visible and less enticing to birds.

“Impact (Tennessee Warbler)” by Miranda Brandon.

Close curtains and blinds, and minimize artificial lights

During the day, keep interior blinds or shutters at least partially closed, or cover large windows with a sheer curtain. This reduces reflections in the glass and breaks up the illusion of clear passage with visible obstructions that deter birds, while still providing light and privacy.

At night, minimize the number and brightness of artificial lights visible through windows, including decorative lights such as candles, which both attract and disorient birds, leading to collisions. Turn off room lights when they’re not in use, and set to low levels when they are. Consider fully closing blinds and curtains.

Note that these solutions are particularly important during migration season; in Chicago, that’s March through June and then August through November.

Reposition indoor plants and outdoor feeders

Move indoor plants a few feet away from windows so that birds can’t see and mistake them for shelter or food. Move outdoor bird feeders and baths at least 30 feet from windows, so birds will be less likely to notice or even be near windows. Alternatively, and perhaps counterintuitively, these amenities may be placed directly on or within 3 feet of windows; if birds do fly into the glass, they’ll be moving more slowly, thus reducing the likelihood of injury. Likewise, planter boxes placed at the base of windows encourage birds to seek shelter there rather than through the glass.

Apply decals, films, or patterns to window surfaces

Minimize large areas of clear or reflecting glass with opaque decals or patterns that birds can see from a distance. Many options are available:

  • Apply thin, vertical strips of tape to exterior window surfaces. Specialty tapes can be purchased, but any tape will do, so long as it can hold up to the weather.

  • Place fun and/or decorative decals on windows. Many options are opaque, while some are specially made to reflect ultraviolet light; they’re mostly transparent to humans, but glow like stop lights for birds. Note that predator-shaped decals do not offer extra protection from bird strikes.

  • Apply a thin film to the outside of windows, covering the entire surface with subtle patterns or one-way opacity while still being mostly transparent. Avoid mirrored films, which can confuse birds and even lead to them attacking (their reflections in) the glass.

  • Use window markers/paints or even a thin layer of soap to make windows less transparent and less reflective. There’s also a very low-maintenance equivalent: let windows get dirty!

The important thing is that no large areas of glass are left uninterrupted. Birds will attempt to fly through spaces larger than about 3–4 inches, so these solutions must be spaced appropriately over the entire surface to be effective.

Install physical obstacles in front of windows

Similar to the previous set of solutions, physical obstacles installed in front of (outside) windows help birds to see windows as the barriers they are. Possible options include the following:

  • Hang wind chimes, wind socks, or other dangling objects in front of windows, ideally those that move and make noise in the wind. The added motion/noise makes birds cautious and less likely to fly through at speed.

  • Add general-purpose screens or bird-specific nets to window exteriors, which break up reflections and, in case of bird strike, significantly reduce the impact and likelihood of injury. Some versions are stretched taut, while others hang more loosely. Small mesh netting is best, so birds can’t become entangled.

  • Install evenly-spaced vertical cords that hang or are stretched taut over the window’s full height as a more permanent equivalent to applying thin strips of tape to the window surface.

  • Add exterior shutters to or sun shades/awnings above windows, reducing reflections while also keeping your home cooler on sunny days. Shutters may be fully closed for added protection and energy savings, especially when you’re out of the house.

Install new windows with bird-friendly glass

For a permanent solution, install new windows with ultraviolet, patterned glass that’s transparent to humans but visible to birds. The principle is similar to some of the pattern/decal options, but integrated specially into the glass itself. Alternatively, install frosted, etched, or fritted windows that are significantly less reflective while still allowing plenty of light through; some options can be quite artistic! Also, consider installing windows at a slight downward tilt, so that they reflect the ground rather than the sky and thus are not interpreted by birds as open airspace.

These solutions may be more expensive, but they require no maintenance and last for the entire life of the window — definitely worth considering when building or remodeling your home.

Acopian BirdSavers installed on a University of Chicago building.

What next?

  • Enjoy the views from your bird-safe windows — maybe even become a birdwatcher!

  • Make your private green spaces more welcoming to birds by planting shrubs, bushes, and hedges, and keeping your pet cat indoors where it can’t terrorize local wildlife.

  • Support policy change to protect birds more systematically, especially when it comes to large commercial buildings and skyscrapers.

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