Frequently asked questions on Bird collisions with glass windows

The Frequently Asked Questions (FAQs) below are meant to provide Canadians information about causes of and solutions to prevent birds colliding with windows.

Disclaimer: Please be advised that the guidance provided here constitutes advice only. All persons must adhere to all pertinent laws (for example provincial or territorial laws), regulations and permit requirements including but not restricted to the Migratory Birds Convention Act, 1994 (MBCA) and the Migratory Birds Regulations (MBR). It is important to note that some species of birds protected under the MBCA have also been listed in Schedule 1 of the Species at Risk Act (SARA). These species receive protection from both the MBCA and SARA.

This advice does not provide an authorization for harming or killing migratory birds. It does not provide a guarantee that the activities will avoid contravening the MBR or other laws and regulations. The guidance provided is not intended to be relied on as official advice concerning the legal consequences of any specific activity. It is not a substitute for the MBCA, the MBR, or any other legislation.

Why is it important to prevent bird-window collisions?

Birds play vital roles in many ecosystems. They provide benefits like pest control, pollination, and seed dispersal. Protecting birds from collisions helps to conserve their populations, and can keep ecosystems healthy. This helps all species, including humans.

How many birds are killed by window collisions?

Window collisions are a significant threat to migratory birds. In Canada, window collisions kill 16 to 42 million birds a year. In the United States, collisions kill 365 to 988 million birds per year. It is one of the top sources of human-caused bird mortality, despite being easily preventable.

Most birds die on impact, but even birds who survive the initial impact will often be left with life threatening injuries. Collisions may result in concussions, shock, internal bleeding, broken bones or brain damage. Injured birds can have a harder time feeding, and also make for easier prey.

Why do birds collide with windows?

Glass is not a natural material, so birds do not understand that reflections of trees or sky are not real. Similarly, if they see the sky or indoor plants through glass, they try to access it and can not see that there is a transparent barrier in the way. Even dark glass, or a window into a dark room can look like a tunnel or hole through which the bird thinks it can fly.

Are some types of window glass more dangerous than others?

Highly reflective and clear materials (e.g., glass and acrylic) are the most dangerous to birds.

Does artificial light increase bird collisions?

Many birds migrate at night, using the moon and stars as guidance. Artificial light disorients birds and can draw them towards urban areas, where the risk of collision is greater. Bright lights can also affect a bird’s night vision, making them more likely to hit a building.

How can I tell if a building or window is dangerous?

How dangerous a window or building is depends on how reflective or transparent it is. This changes throughout the day. To determine if a window is dangerous, look at it from outside at different times of the day. Look at the window from many angles, and see if it reflects trees and other habitat. The window is dangerous as soon as it reflects vegetation.

Transparent deck railings and windows that face one another are also dangerous. Other structures made of glass or clear materials such as noise and wind barriers, bus and smoking shelters and walkways also can kill birds. Most collisions are not noticed, so even one injured or dead bird below a window shows there is a problem.

Does building height make a difference?

Most bird activity occurs between the ground and the treetops. So most collisions occur from heights between ground level and up to the height of the tallest nearby tree. A building’s location, square footage and general reflectivity are better signs of risk than height.

Only 1% of collisions occur at high rise buildings; most collisions occur at houses and low-rise buildings. This is because taller structures are less common, and found mostly in urban areas where there is less bird activity.

Can birds learn to avoid glass?

Birds that live around buildings year-round can usually coexist around glass safely. But other birds have less familiarity with buildings and are at risk of colliding with glass during migration, and in their wintering areas. Younger inexperienced birds are also at increased risk, since their first encounter with glass could easily be their last.

What should I do if a find a bird that has hit a window?

If you find a bird next to a building that doesn’t move as you approach, it probably has a concussion or other injury. It needs to be brought to a bird rehabilitator and taken away from light, noise, people and predators. Calmly approach the bird from behind and swiftly pick it up with both hands. Place the bird in an unwaxed paper bag or a box with breathing holes as quickly as possible. If you wait too long, the bird may try to fly away despite its injuries.

Close the bag or box securely. If it is a box, make sure there are a few air holes poked into the sides. If possible, place some paper towel or tissue on the bottom to cushion it. Do not try to feed the bird or give it water. Handle the bird only when necessary, too much stress can be lethal.

You can also help birds by reporting instances of collisions on Global Bird Collision Mapper.

For more information on what to do with an injured bird, consult FLAP Canada or Safe Wings Ottawa.

How can I prevent collisions?

Covering a window with a pattern can make it more visible to birds. You may create a pattern by hanging cord from the top of windows or with any visual markers, decals, window films, tape, cut-outs or paint you wish. But all patterns should follow these rules:

• the pattern must be applied across the entire glass surface
• there are no spaces greater than 5 cm between each component of the pattern (both horizontally and vertically)
• the pattern is applied to the outside surface of the window
• each component of the pattern is at least 5 mm wide
• the colour of the pattern contrasts well with the reflected vegetation, and is easily seen

Other solutions are to install exterior screens, solar shades or shutters. You may also install patterned, bird-friendly glass if you are replacing your windows. For more information and instructions on bird-friendly solutions, consult FLAP Canada, Safe Wings Ottawa or American Bird Conservancy.

Do UV decals or hawk silhouettes prevent collisions?

Any marker on the outside of the glass will help reduce collisions if they follow the rules above. One or two decals or silhouettes on a large window won’t work. This is because birds are good at finding gaps around vegetation and other obstacles in their natural environment. Birds may avoid the decal, but will fly into the unmarked area if they think the gap is large enough to fly through. Note that UV decals are difficult for birds to see under low light conditions, will fade, and need to be replaced regularly.

Won’t making windows bird-friendly ruin the view?

A uniform pattern covering the whole window should not affect the view. The human brain ignores a lot of the visual data it receives. The image created by the brain is based heavily on context, so small blanks are usually filled in based on what’s around them. This means a pattern will go mostly unnoticed by people. The eyes will look past the pattern and focus on what’s through the window, rather than what’s on it. Occupants of buildings with bird-friendly markers report that they do not notice the pattern within a short time after installation.

Are there easier ways to stop collisions?

Applying regularly spaced markers on glass tells birds that there is a barrier to avoid, and is the best way to prevent collisions. However, there are many small measures that can help to reduce collisions:

• turn off lights and close curtains or blinds when rooms are not in use
• keep houseplants away from windows
• reduce the frequency of window cleaning and avoid cleaning windows during the bird migratory seasons

I’ve heard that the best distance to keep feeders is less than 1 m or further than 10 m (30 feet) from windows. Is that true?

The risk of dying from collisions was studied at feeders placed less than 1 m from glass, at 5 m from glass and at 10 m from glass. Birds had a greater risk of death the further feeders were placed from glass. But because feeder distance was not tested beyond 10 m, we do not know if feeders farther than 10 m are safe for birds. Therefore, the current recommendation is that feeders should be kept less than 1 m from glass. This measure helps birds to escape safely if they are chased away by a predator. This is because panicked birds are less likely to hit glass at high speeds and hurt themselves if feeders are close to glass.

What if a bird keeps flying against a window?

A bird may think its reflection is a rival bird, especially during the breeding season. This can make the bird attack its reflection and hurt itself. If this happens, you may wish to cover the outside of the glass with waxed paper, newspaper, or something similar. The aggressive behaviour should pass in a week or two.

Are there long-term, large-scale solutions?

The easiest and cheapest solution is to design all buildings to be bird-friendly to begin with.

For more advice, see the Canadian Standards Association’s standards for bird-friendly design.