by Chicago’s 82-story Aqua Tower appears to wave in the wind. Its unusual, undulating façade has made it one of the most unique features of the Chicago skyline, distinct from the numerous right-angled glass towers that surround it.
When designing it, architect Jeanne Gang thought not only about how humans would see it, dancing against the sky, but also how birds flying by would see it. The irregularity of the building’s façade allows birds to see it more clearly and avoid fatal collisions. “It’s designed to work with both humans and birds,” she said.
In the United States, up to one billion birds die in building collisions each year. And Chicago, which lies along the Mississippi Flyway, one of four major north-south flyways, is among the highest-risk places for birds. This year, at least 1,000 birds died in one day when they collided with a single glass-covered building. In New York, which lies along the Atlantic Flyway, hundreds of species cross the horizon and tens of thousands die each year.
As awareness grows about the dangers posed by gleaming towers and bright lights, architects are beginning to reimagine city skylines to design buildings that are aesthetically bold and safe for birds.
Some are experimenting with new types of patterned or coated glass that birds can see. Others are reconsidering glass towers entirely, experimenting with exteriors that use wood, concrete or steel rods. By blurring the lines between inside and outside, some architects are creating green roofs and facades, inviting birds to nest inside the building.
“Many people think of bird-friendly design as just another limitation on buildings, just another requirement,” said Dan Piselli, director of sustainability at the New York-based architecture firm FXCollaborative. “But there are so many buildings of avant-garde design that perfectly exemplify that this does not have to limit your design, your freedom.”
How modern buildings endanger birds
For Deborah Laurel, director of the Prendergast Laurel Architects studio, the realization occurred a couple of decades ago. She was up for an award for her company’s renovation of the Staten Island Children’s Museum when the museum director mentioned that several birds had crashed into the new addition. “She was horrified,” she said.
He embarked on a research frenzy to learn more about bird strikes. After several years of research, she discovered there was little practical advice for architects, and partnered with the conservation group NYC Audubon to develop a bird-safe building guide.
The problem, he discovered, was that the technological and architectural advances of the last half century had somehow transformed New York City (and most other American skylines and suburbs) into death traps for birds.
Before the 1960s, much of the large sheets of glass used in buildings were made through a painstaking and expensive casting and polishing process. 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 transparent, uniform sheets, became widely available. “This new glass is very perfect: perfectly flat, perfectly smooth, and it’s also more reflective,” Laurel explained. In the decades that followed, builders also increasingly installed double-pane glass, which was intended to help insulate buildings and conserve energy, but which had the additional effect of making the glass even more reflective. “These two steps in technology have really significantly affected the birds.”
At certain times of the day, the tall glass towers almost merge with the sky. At other times, the windows appear so clear that they are imperceptible to birds, which might try to fly through them. During the day, trees and vegetation reflected in bright building facades can fool birds, while at night, brightly lit buildings can confuse and unnerve them.
In an unfortunate turn for birds, in the 1970s the shiny 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 have a feeling of openness,” Piselli said. “But the material has these multifaceted consequences.”
Changes that could save bird lives
About a decade ago, Piselli’s firm worked on a $500 million renovation of New York’s Jacob K Javits Convention Center, a gleaming glass-clad space structure that killed 4,000 to 5,000 birds a year. “The building was this black Death Star in the cityscape,” Piselli said.
To make it more bird-friendly, FXCollaborative (then called FXFowle) reduced the amount of glass and replaced the rest with porous glass, which has a baked-on ceramic pattern. The small textured dots in the glass are barely noticeable to people, but birds can see them. Porous glass can also help reduce heat from the sun, keeping the building cooler and reducing air conditioning costs. “This became kind of an example of bird-friendly design in the last decade,” Piselli said.
The renovation also included a green roof, monitored by 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 a reversal of the decades-old practice of fortifying buildings with bird spikes. In the Netherlands, the façade of the World Wildlife Fund headquarters, a futuristic structure that looks like an undulating mass of mercury, contains nest boxes and spaces for birds and bats to live.
The use of porous glass has also become more common as a way to save energy and birds.
Earlier this year, Azadeh Omidfar Sawyer, an assistant professor of construction technology at the Carnegie Mellon School of Architecture, developed open source software to help designers create custom, bird-friendly glass patterns. A book of 50 patterns that Sawyer recently published includes intricate geometric lattices and abstract arrays of lines and spots. “Any architect can pick up this book and choose the pattern they like, or they can customize it,” she said.
Builders have also been experimenting with UV-printed patterns, which are invisible to humans but noticeable to most birds. At night, conservationists and architects encourage buildings to turn off their lights, especially during migration season, when the bright glow of a city skyline can disorient birds.
And architects are increasingly integrating screens or bars that provide shade and visibility to birds. The 52-story New York Times building, for example, uses porous glass coated with ceramic rods. The distance between the rods increases towards the top of the building, to give the impression that the building dissolves into the sky.
Gang’s work has incorporated structures that can also serve as blinds for bird watchers or perches from which to observe nature. A theater she designed in Glencoe, Illinois, for example, is surrounded by a path made of wooden latticework, where visitors can feel as if they are high in the treetops.
Rejecting the idea of the iridescent building, entirely made of mirrored glass, “where you cannot distinguish between the habitat and the sky,” Gang aspires to the opposite. “I always tried to make buildings more visible with light, shadows and geometry, so they would have a stronger presence,” he said.
Gang has been experimenting with adding bird feeders around her own home in an effort to reduce window collisions, and encourages other homeowners to do the same.
“I’ve found that birds slow down and stop at the feeders instead of trying to fly through the glass,” he said.
While high-rise buildings and massive urban projects receive the most attention, homes and low-rise buildings account for the majority of bird strike deaths. “The big challenge is that glass is everywhere.” said Christine Sheppard, who directs the glass collision program at the American Bird Conservancy (ABC). “It’s hard to know what I know and not cringe when I look at it.”
Tips for improving your own home include using stained glass or patterned decals that can help birds see a window, she said. ABC has compiled a list of window treatments and materials, rated by how safe they are for birds.
Whether large or small, the challenge of designing buildings that are safe for birds can be “liberating,” said Gang, who has become an avid bird watcher and now carries a pair of binoculars on her morning runs. “She gives you another dimension to try to imagine.”
