Birds chirp cheerfully heralding the start of the day, as free-flying entities in the sky. Birds, commonly seen around us, may appear small and insignificant, but they hold a crucial place in ecosystems and human lives. Birds reduce crop damage and prevent the spread of infectious diseases transmitted by insects and rodents by preying on a large amount on them, thereby controlling their population. Additionally, they serve as indicators of the overall health of nature.

As an example, in China from 1958 to 1960, an attempt to eradicate sparrows, which fed on crops during harvest season, resulted in the hunting of two billion sparrows. This disrupted the ecological food chain, causing a pest outbreak and leading to a catastrophic event where an estimated five million people died, making it one of the worst famines in human history recorded in the Guinness Book. In response, China had to import 200,000 sparrows from Russia and release them.

In the United States, it is estimated that every year, anywhere from hundreds of millions to as many as ten billion birds collide with glass windows and die. Canada similarly estimates an annual death toll of approximately 16 million to 42 million birds. The British Trust for Ornithology [BTO] identifies the three main causes of bird deaths as “cats, car collisions, and glass window collisions.”

Unlike nature, where survival favors the fit, man-made structures, including buildings and glass constructions, lead to the demise of all birds. Furthermore, the death of adult birds capable of laying eggs and raising offspring affects reproduction, making the consequences of wild birds and glass window collisions much more extensive than currently estimated.

Therefore, the international community recognizes collisions between wild birds and glass windows as a serious issue. Bird collisions with glass have become a significant problem that we need to address, from an ethical perspective and for preserving biodiversity.

 What Causes Birds to Collide With Glass Windows?

1. Characteristics of Glass

Two main characteristics of glass contribute to collisions: transparency and reflectivity. Birds cannot recognize structures with highly transparent glass. Moreover, glass windows reflect the sky and surrounding environment, causing birds to perceive them as their habitat and collide with them directly.

2. Vegetation Around Buildings

The vegetation around buildings also plays a role in the bird collision mortality rate. The height and density of plants growing around buildings are factors contributing to bird collisions with glass windows. The vegetation around buildings serves as habitat for birds and provides them with food. However, windows with high reflectivity in buildings reflect the surrounding vegetation, creating an illusion of foliage. Birds can’t distinguish between actual vegetation and the reflected illusion. As more birds gather around the greenery, the probability of collisions increases.

3. Migration

For migratory birds that move according to the seasons, they are not familiar with the migration routes and landscapes, compared with the birds that are familiar with the habitat, residing in the same area all year round. Consequently, it is challenging for them to recognize glass structures during flight. Additionally, for nocturnal birds that are active during the night, they navigate by referring to the stars in the night sky. The light emitted from glass windows can disrupt their sense of direction, leading to collisions with buildings.

4. Birds Anatomy

While humans may suffer minor injuries like bruises when colliding with glass windows, birds often sustain fatal or life-threatening injuries. Birds have a skeletal structure optimized for flight, making them extremely lightweight. Additionally, a bird’s skull is as rigid as an eggshell. Birds flying at high speeds find it challenging to absorb the impact of collisions. As a result, collisions with glass windows can cause severe harm or be fatal to birds.

Birds, unlike humans, have developed a vision that emphasizes the sides rather than the front. Unlike humans who focus both eyes on a single object, birds simultaneously focus each eye on different objects. While this vision is helpful for detecting predators, it makes it challenging for them to perceive glass windows directly in front of them.

How Can We Prevent Bird Collisions?

Multiple ways are available to avoid birds hitting structures. For instance, constructing buildings with bird safety in mind and employing devices to minimize collisions. Firstly, designing bird-friendly buildings can be instrumental in protecting birds. This involves altering the building’s features, such as using high contrast on surfaces, minimizing the glass surface area, and installing mesh nets near glass windows. Recently, companies are starting to produce safety glass designed especially for birds. Another effective method involves the use of anti-reflection devices to assist birds in recognizing glass structures. For instance, adding dots at 5*5 (cm) intervals on windows creates a pattern that birds perceive as a narrow space. This prompts them to avoid flying into the glass, ultimately preventing bird collisions.

Additionally, there is a method of turning off artificial lights at night to assist birds in their nocturnal movement. It is said that by removing and minimizing interior lights within buildings, making them darker, bird collisions can be reduced by 6 to 11 times.

In our world, various forms of life coexist. No life, no matter how small, should be treated with indifference. Especially in today’s heightened awareness of the importance of biodiversity, we must all make efforts to ensure that precious lives do not end tragically by colliding with glass windows. It is never something that has nothing to do with us. Let’s take interest and make efforts, starting from small actions.