Transparent glass kills many birds, which crash into the windows and die. But changes in design are saving birds, without giving up sunlight. As a newspaper notes, “Chicago’s 82-story Aqua Tower appears to flutter with the wind. Its unusual, undulating facade has made it one of the most unique features of Chicago’s skyline, distinct from the many right-angled glass towers that surround it. In designing it, the architect Jeanne Gang thought not only about how humans would see it, dancing against the sky, but also how it would look to the birds who fly past. The irregularity of the building’s face allows birds to see it more clearly and avoid fatal collisions.”
A billion birds in America die each year in collisions with windows. Chicago is one of the biggest places for bird deaths, because it is in the Mississippi Flyway, one of the four principal north-south migration routes. In 2023, at least 1,000 birds died in a single day from colliding with a single glass-covered building. In New York, which is in the Atlantic Flyway, hundreds of species traverse the skyline and tens of thousands die every year.
So architects are changing building designs to make buildings bird-safe without sacrificing beauty:
Some are experimenting with new types of patterned or coated glass that birds can see. Others are rethinking glass towers entirely, experimenting with exteriors that use wood, concrete or steel rods. Blurring lines between the indoors and outdoors, some architects are creating green roofs and facades, inviting birds to nest within the building…..The New York Times building uses fritted glass clad with rods, which make its facade more visible to birds.
Architects feel guilty about how many birds their buildings killed, and this guilt has motivated change. Architect Deborah Laurel was up for an award for her firm’s renovation of the Staten Island Children’s Museum when the museum director told her that birds were crashing into the new addition. “I was horrified,” she says.
She embarked on a frenzy of research to learn more about bird collisions. After several years of investigation, she found there was little in the way of practical tips for architects, and she teamed up with the conservation group NYC Audubon, to write a manual on how to save birds:
The issue, she discovered, was that technological and architectural advancements over the last half-century had in some ways transformed New York City – and most other US skylines and suburbs – into death traps for birds.
Before the 1960s, much of the large sheet glass used in buildings was made via a painstaking and costly process of casting and polishing. The glass often contained bubbles or other imperfections that obscured its clarity.
Then, in the 1960s, float glass – made using a new technique that created uniform, clear sheets – became widely available. “This new glass is very perfect – perfectly flat, perfectly smooth and it’s also more reflective,” Laurel explained. In the following decades, builders also increasingly installed double-paned glass, which was intended to help insulate buildings and conserve energy but had the additional effect of making the glass even more reflective. “These two steps in technology have really affected birds significantly.”
At certain times of day, tall glass towers almost blend into the sky. At other times, windows appear so pristinely clear that they are imperceptible to birds, who might try to fly though them. During the day, trees and greenery reflected on shiny building facades can trick birds, whereas at night, brightly lit buildings can confuse and bewilder them.
In an unfortunate turn for the birds, in the 1970s, the lustrous glass look also became a popular design aesthetic, and the look has stuck around ever since. “It started with the good intention of wanting light-filled spaces, to help people feel a sense of openness,” said Piselli. “But the material has these multifaceted consequences.”
About a decade ago, Piselli’s firm worked on a half-billion-dollar renovation of New York’s Jacob K Javits Convention Center, a gleaming glass-clad space frame structure that was killing 4,000-5,000 birds a year. “The building was this black Death Star in the urban landscape,” Piselli said.
To make it more bird friendly, FXCollaborative (which was then called FXFowle) reduced the amount of glass and replaced the rest of it with fritted glass, which has a ceramic pattern baked into it. Tiny, textured dots on the glass are barely perceptible to people – but birds can see them. The fritted glass can also help reduce heat from the sun, keeping the building cooler and lowering air conditioning costs. “This became kind of the poster child for bird-friendly design in the last decade,” Piselli said.
The renovation also included a green roof, monitored by the NYC Audubon. The roof now serves as a sanctuary for several species of birds, including a colony of herring gulls. Living roofs have since become popular in New York and other major cities, in an inversion of the decades-long practice of fortifying buildings with anti-bird spikes. In the Netherlands, the facade of the World Wildlife Fund headquarters, a futuristic structure that looks like an undulating blob of mercury, contains nest boxes and spaces for birds and bats to live. The use of fritted glass has also become more common as a way to save the birds and energy.
Architects are exploring other ways of protecting birds as well. Some are experimenting with UV-printed patterns, which are invisible to humans but visible to a majority of birds. Some builders are adding screens or grates that provide shade as well as visibility for birds. “The 52-floor New York Times building, for example, uses fritted glass clad with ceramic rods. The spacing between the rods increases toward the top of the building, to give the impression that the building is dissolving into the sky.”
An architect has been adding bird feeders around her own home to reduce bird collisions with her windows. “I’ve found that birds slow down and stop at feeders instead of trying to fly through the glass,” she said. While office buildings and skyscrapers get the most attention, homes and low-rise buildings are the site of a majority of bird deaths. “The huge challenge is that glass is everywhere,” notes Christine Sheppard, head of the glass collisions program at American Bird Conservancy (ABC). “It’s hard to know what I know and not cringe when I look at it.”
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