These buildings kill up to a billion birds a year. Architects want to save them

This story was originally published by The Guardian and appears here as part of the Climate Desk collaboration.

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. “It’s kind of designed to work for both humans and birds,” she said.

As many as 1 billion birds in the US die in building collisions each year. And Chicago, which sits along the Mississippi Flyway, one of the four major north-south migration routes, is among the riskiest places for birds. This year, at least 1,000 birds died in one day from colliding with a single glass-covered building. In New York, which lies along the Atlantic Flyway, hundreds of species traverse the skyline and tens of thousands die each year.

As awareness grows of the dangers posed by glistening towers and bright lights, architects are starting to reimagine city skylines to design buildings that are both aesthetically daring and bird-safe.

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.

“Many people think about bird-friendly design as yet another limitation on buildings, yet another requirement,” said Dan Piselli, director of sustainability at the New York-based architecture firm FXCollaborative. “But there are so many design-forward buildings that perfectly exemplify that this doesn’t have to limit your design, your freedom.”

How modern buildings put birds in danger

For Deborah Laurel, principal in the firm Prendergast Laurel Architects, the realization came a couple of decades ago. She was up for an award for her firm’s renovation of the Staten Island Children’s Museum when the museum’s director mentioned to her that a number of birds had been crashing into the new addition. “I was horrified,” she said.

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 develop a bird-safe building guide.

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.”

The changes that could save avian lives

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.

Earlier this year, Azadeh Omidfar Sawyer, an assistant professor in building technology in the Carnegie Mellon School of Architecture, working with student researchers, used open-source software to help designers create bespoke, bird-friendly glass patterns. A book of 50 patterns that Sawyer published recently includes intricate geometric lattices and abstract arrays of lines and blobs. “Any architect can pick up this book and choose a 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 perceptible to most birds. At night, conservationists and architects are encouraging buildings turn off lights, especially during migration season, when the bright glow of a city skyline can disorient birds.

And architects are increasingly integrating 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.

Gang’s work has incorporated structures that can also serve as blinds for birders, or perches from which to observe nature. A theater she designed in Glencoe, Illinois, for example, is surrounded by a walking path made of a wood lattice, where visitors can feel like they’re up in the canopy of trees.

Rejecting the idea of the iridescent, entirely mirrored-glass building, “where you can’t tell the difference between the habitat and the sky”, Gang aims for the opposite. “I always tried to make the buildings more visible with light and shadow and geometry, to have more of a solid presence,” she said.

Gang has been experimenting with adding bird feeders around her own home in an effort to reduce collisions with windows, and she encourages other homeowners to do the same.

“I’ve found that birds slow down and stop at feeders instead of trying to fly through the glass,” she said.

While high-rise buildings and massive urban projects receive the most attention, homes and low-rise buildings account for most bird collision deaths. “The huge challenge is that glass is everywhere.” said Christine Sheppard, who directs the glass collisions 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, ranked by how bird-safe they are.

Whether they’re large or small, the challenge of designing buildings that are safe for birds can be “liberating”, said Gang, who has become an avid birdwatcher and now carries a pair of binoculars on her morning jogs. “It gives you another dimension to try to imagine.”

The headline of this article was amended on 28 December 2023 because an earlier version said a billion birds were killed a year, when figures show the number to be up to a billion.