Millions of birds die every year from hitting glass. It's easy to save their lives.

These are some of the birds that died from bird strikes at Duke Kunshan University between 2019 and 2021.

Photo: Binbin Li from Duke Kunshan University

These birds unfortunately hit glass and other man-made structures during their flight. You may have seen such scenes in your life - maybe a bird hits the window of your home with a "bang", or a glass curtain wall is left with traces of bird impact. These "accidental phenomena" may seem funny at first glance, but in fact they are one of the most serious threats to the survival of wild birds today .

And those birds that flew towards the glass may just think that they were flying towards the bushes.

On October 23, 2022, a spotted dove died from a bird strike in Hangzhou | Life Observation

Bird strikes: The overlooked killer of birds

Most birds that are hit by birds will die from intracranial hemorrhage , and a small number will suffer skull injuries. Even if they survive a bird strike, the injured birds will experience varying degrees of corneal ulcers, head swelling, and beak fractures - such injuries will make it even more difficult for individuals to survive during a migration that is already extremely physically demanding.

It is estimated that bird strikes kill 16 to 42 million birds each year in Canada, and an astonishing 365 to 988 million birds in the United States. This number makes bird strikes the second-leading anthropogenic cause of bird mortality in North America, second only to predation by stray and domestic cats.

Ranking of anthropogenic causes of bird mortality in North America | Loss et al., 2015; Chinese translation: Species Calendar

Bird strikes are not uncommon in China. In the 2022 National Bird Strike Survey, volunteers from all over the country investigated nearly 700 buildings and found 231 bird strikes . Among the dead birds, there were many national second-level protected wild birds such as the Red-throated Robin and the Red-flanked White-eye.

A red-throated robin died from a bird strike in Beijing on June 9, 2022 | Life Observation

Even more heartbreaking are collective collision incidents. For example, in March last year, glass guardrails in an ecological park in Chengdu caused the death of many birds - fortunately, these glasses were later covered with film to prevent bird collisions from happening again. In another example, in November last year, more than 30 blue-winged thrushes died after collectively colliding with the glass curtain wall of a shopping mall in Guiyang, Guizhou.

A collective bird strike incident in a building in Guiyang last year | Cover News

Just last month, dozens of birds died after hitting glass guardrails in a park in Wuhu, Anhui Province... If we don't pay attention, there will be more shocking collective bird collision incidents in the future.

Why do bird strikes happen?

The main culprits that cause bird strikes are the reflection and light transmittance of building glass during the day and the lights at night.

There are two common reasons for bird strikes during the day. One is that birds see habitats or the sky reflected on reflective glass and mistakenly believe that the places on the glass are reachable, so they fly toward the glass. The other is that birds see plants or spaces on the other side through transparent glass and mistakenly believe that they can pass through the glass to the other side.

At night, artificial light not only makes birds lose their sense of direction, but also attracts birds, eventually causing large numbers of birds to gather around light source buildings, creating the risk of colliding with buildings and causing death.

A pavilion in the middle of a lake at Duke Kunshan University may have all three main causes of bird strikes (glass reflections, glass transparency, and night lights) | Wang Zifeng, Duke Kunshan University

Why is it that we can identify glass in buildings relatively easily, but birds can't?

Glass is a man-made building material that has only been widely used in modern times. With the rapid development of global urbanization since the Industrial Revolution, the appearance of the earth's surface has changed rapidly in a hundred years. However, birds have lived on the earth for tens of millions of years, but have never had the experience of coexisting with glass and have no concept of glass at all.

This is also related to the sensory characteristics of birds. Unlike humans, birds' side vision is stronger than their front vision. During flight, birds often need to turn their heads or look back to guard against predators and find prey. The visual resolution in the forward direction of flight is lower, which makes it difficult for them to effectively detect obstacles in front . In addition, birds are more sensitive to moving objects, which makes it more difficult for them to notice the deadly glass in front.

Comparison of the visual range of the Grey-necked Bustard, humans, and white storks. Compared to humans, birds have poor frontal vision, but better side vision｜Martin (2017)

Additionally, the season and the building's surroundings can affect bird strikes.

According to research in North America, bird strikes peak during the bird migration and breeding seasons . During the migration season, when a large number of migratory birds arrive in unfamiliar urban environments in a tired and hungry state, they are more likely to collide with buildings. During the breeding season, on the one hand, the risk of bird strikes increases as birds engage in more activities such as courtship, raising chicks, and guarding territories; on the other hand, young birds are still unfamiliar with flying skills, making bird strikes more likely.

What is even more worrying is the vegetation around buildings - these vegetation can provide suitable habitats for birds, increase the number of birds and the intensity of their activities, but at the same time, the presence of vegetation has led to an increase in bird strikes . A 10-year study in New York City found that up to 73% of bird strikes occurred in locations where the reflection of vegetation accounted for more than 50% of the glass area.

If you don’t look carefully, you might think that you can pass through the green plants reflected in the glass to the other side｜American Bird Consulting Christine Sheppard

Preventing Bird Strikes: What Can We Do?

Birds cannot realize that transparent glass is an impassable obstacle. Therefore, the most important way to avoid the tragedy of birds hitting glass is to let birds "see" the existence of glass .

Scientists from the American Bird Conservancy tested different types of glass and patterns by releasing birds from one side of a 23-foot-long tunnel and placing different types of glass on the other side for the birds to choose from.

Tunnel testing channel | American Bird Conservancy

The results showed that adding a dot matrix with a spacing of 5x5 cm and a diameter of 1 cm, or a vertical line with a spacing of 10 cm, to the glass can effectively prevent bird strikes. Moreover, compared with horizontal patterns, vertical patterns can provide better visual cues.

5 x 5 Matrix Sticker Principles | Bird-Safe Design Guidelines, Ottawa, Canada

This "5x5" or "5x10" standard has been adopted in bird strike prevention architectural guidelines and legislation in many North American cities. These patterns are best installed on the outside of the glass to avoid bird strikes caused by both transparency and reflection.

Canadian residents modify their own windows｜FLAP Canada

Duke Kunshan University dormitory sky corridors are renovated with bird-strike-proof stickers | Lü Chen, Duke Kunshan University

Bird-friendly buildings

However, will putting patterns on the glass affect the aesthetics and light transmittance?

The American Bird Conservancy has an online exhibition of a variety of bird-friendly buildings - it turns out that good design can not only prevent bird strikes, but also decorate glass and buildings .

Minimalist style: dot & line stickers

Regular dot-shaped or line-shaped stickers have a low presence and will not affect the original appearance of the glass . They can often only be discovered when you get close to the glass. This is one of the most commonly used modifications to glass.

Estero Llano Grande State Park in Texas, USA, has stickers on its windows to protect birds in the surrounding habitats. | Kate Sheppard

Consilium Towers in Toronto. You can only notice the dotted bird-strike stickers on the glass curtain wall when you get close to it. | Christine Sheppard

Art School: Opaque Patterns and Colors

This type of building usually chooses to decorate the glass with opaque patterns and colors , which can not only prevent bird strikes, but also beautify the building. For example, the art installation "Art for All" in Shanghai Henglong Plaza combines patterns visible to the human eye with ultraviolet paint that is only visible to birds. Not only can birds see the glass curtain wall, but also, with the cooperation of ultraviolet lights at night, it can also enable people to "experience the city from the perspective of birds."

Photo: Shanghai Plaza 66

Innovative: More than just glass

In addition to glass, innovative design changes to other parts of buildings can also have a bird-proofing effect, such as reducing the total amount of glass on a building’s exterior or using other types of visual cues to help birds spot a building.

Aqua Tower in Chicago, USA, with textured glass and windows hidden behind railings, forming a novel bird-friendly design｜Studio Gang

Tracy Aviary in Salt Lake City, USA, the decorative panels on the exterior of the building and the dotted stickers on the glass of the same color have the effect of preventing bird strikes｜AJC Architects

These designs can not only effectively reduce the tragedy of bird strikes, but also add color to the city's originally monotonous "concrete forest" and make people feel the warmth of a city's care for life.

★

The world's three most important migratory bird areas intersect in our country , but our attention and understanding of "bird strike" incidents are still insufficient, and actions to prevent bird strikes have just begun.

To effectively prevent the occurrence of "bird strike" tragedies and promote relevant actions and legislation to prevent bird strikes, we need to first understand how many bird strikes there are in China and where they occur. However, it is not easy to answer these questions - bird strikes may occur wherever there are buildings, but bird strikes are difficult to detect, so large-scale, long-term and continuous investigations are required .

Volunteers participate in bird strike investigation | Optimistic Earth

In 2021, Duke Kunshan University, Dr. Zhu Lei, Friends of Nature, Shanshui Conservation Center, Saving Wilderness, Mangrove Foundation, Optimistic Earth and other organizations jointly organized a national bird strike prevention action network . In the two years since the survey began, more than 800 volunteers from all over the country have completed more than 25,000 patrols and systematically recorded more than 350 bird strikes. The citizen science survey method not only collects valuable data, but also allows more people to "see" bird strikes.

References

[1] Machtans, Craig S., Christopher H. Wedeles, and Erin M. Bayne. “A First Estimate for Canada of the Number of Birds Killed by Colliding with Building Windows.” Avian Conservation and Ecology 8, no. 2 (2013). https://doi.org/10.5751/ace-00568-080206.

[2] Loss, Scott R., Tom Will, Sara S. Loss, and Peter P. Marra. “Bird–Building Collisions in the United States: Estimates of Annual Mortality and Species Vulnerability.” The Condor 116, no. 1 (February 2, 2014): 8–23. https://doi.org/10.1650/condor-13-090.1.

[3] Gelb, Yigal, and Nicole Delacretaz. “Windows and Vegetation: Primary Factors in Manhattan Bird Collisions.” Northeastern Naturalist 16, no. 3 (2009): 455–70. https://doi.org/10.1656/045.016.n312.

[4] Shi Danyang, Liao Shuyue, Zhu Lei, et al. Overview of bird strikes on buildings and systematic investigation case analysis. Biodiversity Science, 2022, 30(3): 1-20.

[5] Loss, Scott R., Tom Will, and Peter P. Marra. "Direct human-caused mortality of birds: Improving quantification of magnitude and assessment of population impact." Frontiers in Ecology and the Environment 10.7 (2012): 357-364.

[6] Loss, Scott R., Tom Will, and Peter P. Marra. "Direct mortality of birds from anthropogenic causes." Annual Review of Ecology, Evolution, and Systematics 46 (2015): 99-120.

[7] Veltri, Carl J., and Daniel Klem. "Comparison of fatal bird injuries from collisions with towers and windows." Journal of Field Ornithology 76, no. 2 (2005): 127-133.

[8] Horn, Lisa. “What Happens to the Birds that Survive a Window Collision?” FLAP Canada.

[9] Van Doren, Benjamin M., David E. Willard, Mary Hennen, Kyle G. Horton, Erica F. Stuber, Daniel Sheldon, Ashwin H. Sivakumar, Julia Wang, Andrew Farnsworth, and Benjamin M. Winger. "Drivers of fatal bird collisions in an urban center." Proceedings of the National Academy of Sciences 118, no. 24 (2021): e2101666118.

[10] Martin, Graham R. The sensory ecology of birds. Oxford University Press, 2017.

[11] Bayne, Erin M., Corey A. Scobie, and Michael Rawson-Clark. "Factors influencing the annual risk of bird–window collisions at residential structures in Alberta, Canada." Wildlife Research 39, no. 7 (2012): 583-592.

[12] Kahle, Logan Q., Maureen E. Flannery, and John P. Dumbacher. "Bird-window collisions at a west-coast urban park museum: analyzes of bird biology and window attributes from Golden Gate Park, San Francisco." PLoS one 11, no. 1 (2016): e0144600.

Author: Lv Yunfei

Editor: Mai Mai

Cover image source: Binbin Li, Duke Kunshan University

This article comes from the Species Calendar, welcome to forward

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