Reducing Bird Strikes at Your Home

Introduction

Birds perceive reflections of vegetation, landscapes, and sky to be real.
Photo Credit: Danielle Blue

In 2016, 45 million birders in the United States spent $39 billion on travel and equipment to observe birds in the wild and their backyards. During the COVID-19 pandemic, the number of backyard birders increased significantly. While quarantined in their homes, many people discovered that birding is a great way to familiarize themselves with nature and a perfect activity for all ages. Many people put up birdfeeders to attract birds and enjoy watching feathered visitors throughout the day. Birding in your backyard is a great way to become more familiar with and learn the names of some common birds living in the area and visiting your backyard

Unfortunately, humans and wildlife don’t always coexist without problems. An example of one of those problems is bird collisions with windows, which is an all-too-frequent occurrence. While most people associate bird strikes with large skyscrapers that have reflective windows, nearly 50% of bird collisions occur at homes. It has been estimated that between 365 and 988 million birds are killed annually in the U.S. alone by building collisions (1). Of these collisions, approximately 56% occur at low-rises, 44% at residences, and 1% at high-rises. Of the types of human-caused mortality, this is second only to mortality from feral and free-ranging domestic cats.

Understanding the Problem

Birds cannot see glass. Instead, they see reflections of their surroundings, or they see the interior of a home or building if the light inside is brighter than outside. They do not recognize visual cues like door and window frames that humans learn to associate with glass, and they seldom survive a first collision to learn from their mistakes. Birds’ bodies are fragile. Even birds that can fly away after a collision die later from internal injuries or from predation because of their crippled condition.

Bird’s bodies, like this northern cardinal, are fragile and often do not survive window strikes.
Anthony (TJ) Savereno, ©2024, Clemson Extension

Birds perceive reflections of vegetation, landscapes, and sky to be real. As a result, they try to reach habitats seen as reflections. They are especially vulnerable when seeking escape cover after being frightened by predators (real or perceived) or by loud noises (2). Birds, particularly males, also strike windows when perceiving their own reflection as a competitor for territory and a mate. However, this is usually more of an annoyance to the homeowner than a threat to the bird.

Bird collisions with windows can happen at any time of year, although they are most common in spring and fall during migratory movements. Collision rates appear to be greater during fall migration than in spring, possibly due to the greater number of birds migrating in the fall. This increase in numbers is due to reproduction and recruitment (1). Young birds are also inexperienced flyers and may be more susceptible to collisions. Many of our songbirds migrate at night and fly into windows due to light from inside. Migratory birds are also less familiar with their surroundings than resident birds (3) and are, therefore, more likely to fly into a window. Collisions also increase in late spring when inexperienced fledglings leave the nest. The lowest rate of collisions generally occurs in winter (4). The reason is at least partly because once deciduous trees and shrubs have lost their leaves, the reflections in glass no longer resemble cover. As for the time of day, more collisions occur during the morning, when hungry birds are leaving their roosts and feeding more heavily.

Numerous researchers have shown that the frequency of bird collisions with windows is positively correlated to the density (number) of birds in the area. Factors acting as bird attractants include feeders, fruiting trees and shrubs, bird baths, nesting habitat, etc., which can increase density (5).

Identify Problem Windows

It is unlikely that every window in your house will pose equal risks of bird collisions. Identifying and fixing the windows that pose the greatest threats will have the most benefits. The American Bird Conservancy suggests treating the following windows:

1. Windows that have already caused collisions.
2. Large windows and glass doors, especially those that reflect habitat and sky.
3. Windows across from bird feeders, bird baths, fruit-bearing trees, and other vegetation that may be attractive to birds as escape, roosting, or nest cover.

If birds frequently or even occasionally fly into one or more of your windows, then there are numerous steps that you can take to reduce collisions. Even if you don’t have a current problem, there are still things that you can do to prevent a problem from developing. Take a walk around your house at different times throughout the day. Do any of your windows reflect vegetation or the sky? As discussed above, windows that reflect vegetation or sky could be perceived by a bird as the real thing. How far are bird attractants like bird feeders, bird baths, and fruit-bearing trees/shrubs from windows? What angle from the window are these attractants? What is reflected in that window as you stand in front of any attractants? If you notice vegetation or the sky, these windows may be potential threats to birds. To reduce the likelihood of bird/window collisions, try some of the following preventative measures.

Ways to Reduce the Likelihood of Bird Strikes

Relocate or Remove Attractant:

• Relocate attractants away from windows, if possible. Attractants include feeders, houses, baths, and cover. Obviously, it would be difficult to move a 15-foot cherry laurel that cedar waxwings flock to each winter, but it is possible to move a bird feeding station or bird bath. Moving them so that they are not facing a window is the safest option, but if you want to be able to watch them from the comfort of your home, within 3 feet of a window is the next best option. Birds flying quickly away from a feeder or bird bath within that distance do not have enough time to accelerate to a lethal speed before colliding with a window. If you insist on placing these attractants further away from your window, locate them more than 30 feet away so they have time to maneuver and avoid the house. Also, place the feeder at an angle to the window rather than perpendicular so that birds, if they do hit the window, will hit at an angle, resulting in a glancing blow rather than a full-frontal impact. If moving attractants is not an option, some treatments are outlined below that homeowners and business owners can try to prevent collisions.
• If you notice that most bird/window collisions happen during the spring or fall migration, consider taking your feeders down until migratory movements end. Another measure would be to close blinds or curtains at night so that migrating birds are not attracted to the light inside.

Make Glass Windows and Doors More Visible: As discussed previously, one of the reasons birds strike windows is because they cannot see the glass, only reflections. If those reflections are of sky or vegetation, birds can’t distinguish them from the real thing. As a result, they attempt to fly into it, especially if startled or being pursued by predators. Putting something on the outside of the window suddenly makes it visible to birds, if done correctly. This can be done in a number of ways, and the Cornell Lab of Ornithology and the Bird Collisions Program of the American Bird Conservancy provide some great suggestions.

Creating patterns or designs on windows helps break up reflections and appear as a barrier to birds. However, based on research, certain rules must be followed for this method to be effective:

• Markings must be applied to the outside of windows. Reflections on the outside of the window may obscure markings on the inside.
• Use white or light colors to maximize contrast and visibility.
• Markings should be visible from at least 10 feet away to give birds time to see them and react.
• Grids of dots or lines are very effective but should be placed no more than 2 inches apart over the entire window surface. Wider spacing creates apparent gaps that smaller birds may still try to fly through. Stripes should be at least one-eighth inch wide, and dots at least one-quarter inch in diameter. Bigger is better.
• Single decals of hawk silhouettes do little to deter birds. If applied to the outside of the window and spaced no greater than 2×2 inches, multiple decals, stickers, mylar strips, or masking tape are more effective.
• Tempera paint or soap can be used to create patterns or colorful artwork on the outside surfaces of windows. Again, keep spacings close as described above.

Many products are available commercially, including films that can be applied to the outside of a window and appear solid from the outside but can’t be seen looking out from the inside. Many of these products and do-it-yourself ideas are discussed on the American Bird Conservancy’s website.

Use Physical Barriers to Prevent Birds from Hitting Glass

• Window Screens: Window insect screens are familiar to many homeowners and are already found on many homes. These can be extremely effective at reducing bird strikes. Screens greatly reduce reflections, and the impact will be lessened if a bird does collide with the window.
• Shutters, Sunshades and Awnings: Shutters, such as Bahama shutters, awnings, and sunshades, can be added to new constructions or remodels to help prevent collisions. The addition of these features can reduce the amount of glass reflection.
• Bird Netting: Bird netting, which can be used to exclude birds from fruit trees and other crops, can also be used as a physical barrier against bird collisions. It can be mounted on a storm window frame or some other type of frame and placed at least 3 inches from the window. The netting should be stretched tight enough so that birds bounce off before impacting the glass. Ensure the netting mesh openings are no larger than about 5/8 inches to prevent birds from becoming entangled.

Other Methods

• Close Blinds and Curtains: Closing blinds and curtains in rooms that are not in use is a quick and easy way to reduce the likelihood of bird strikes. By doing this, you are reducing the reflection of outside vegetation. You can also close interior doors between rooms that could allow birds to see an open pathway or tunnel through a window on the other side of the house.
• Move Houseplants: Move houseplants away from windows to prevent birds from attempting to fly onto the plant.
• Turn off Lights: Reducing or eliminating the usage of lights is another easy way to reduce bird strike potential, particularly migrating birds that often fly at night. Turn off lights in rooms when not in use or dim them. You can also place exterior lights on a timer or add a motion sensor rather than keeping them on the entire night.

Conclusion

When it comes to bird collisions with windows, the good news is there are many preventative measures that homeowners, renters, and even businesses can take to reduce the likelihood of bird strikes. As mentioned above, many of these preventative measures cost little or no money and are simple behavior changes or modifications. Check around your house or business on a regular basis for injured birds so you can act accordingly and prevent future bird strikes from happening. Together, we can all play a role in aiding bird conservation by reducing bird collisions.

If you witness a bird strike or encounter an injured bird, remember that native songbirds are protected under the Migratory Bird Treaty Act. It is illegal to handle or keep a bird without a permit. Observe the bird or injured bird closely. It may just be stunned, and it will fly off on its own. If the bird is at risk, wear gloves to handle it and place it in a box to protect it from predators like house cats. If the bird is seriously injured, contact a licensed wildlife rehabilitator to receive further instructions on how to assist.

Additional Resources

HGIC 2900, Backyard Wildlife Enhancement

American Bird Conservancy Glass Collisions: Why Birds Hit Glass

American Bird Conservancy Birds Flying Into Windows? Truths About Birds & Glass Collisions from ABC Experts

American Bird Conservancy Glass Collisions: Preventing Bird Collisions at Home

Cornell Lab All About Birds: Why Birds Hit Windows-And How You Can Help Prevent It

American Bird Conservancy Glass Collisions: Products & Solutions Database

Audubon Society

Literature Cited:

1. Loss et al. Scott R. Loss, Tom Will, Sara S. Loss and Peter P. Marra. 2014. Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability. The Condor, Vol. 116, No. 1 (February 2014), pp. 8-23.
2. Erica H. Dunn. 1989. Bird mortality from striking residential windows in winter. Journal of Field Ornithology 64(3):302-309.
3. Lay G. Basilio, Daniele J. Moreno, and Augusto J. Piratelli. 2020. Main causes of bird-window collisions: a review. Anais da Academia Brasileira de Ciencias 92(1)
4. Kummer, J. A., and E. M. Bayne. 2015. Bird feeders and their effects on bird-window collisions at residential houses. Avian Conservation and Ecology 10(2):6.
5. Klem, D., Jr. 1989. Bird-window collisions. Wilson Bulletin 101:606–620.

Originally published 02/24