Buildings Are Hazardous to Migratory Birds, But There Are Solutions

Bird migration is a wondrous and majestic phenomenon. In North America, one may witness flocks of colorful songbirds sweeping the skies, geese gliding in a V-shape of beautiful symmetry, or a great hawk soaring above and diving for prey at 120 miles per hour.

About half of all birds in the world migrate, and even the smallest may travel remarkably long distances. Incredibly, the tiny hummingbird can fly nonstop 600 miles over the Gulf of Mexico. Some round-trip migrations can wind their way for as long as 44,000 miles.

Most songbirds migrate at night, and nocturnal travel makes their journey particularly perilous in light of human development. Birds face many obstacles along the way, including extreme weather events and lack of habitat. Yet, one particularly tragic and preventable peril stands out: human-made structures.

Scientists estimate an astounding upper-level figure of 1 billion birds that die in the U.S. each year from building collisions. Making matters worse, 40 percent of the world’s bird species are already in decline. In the last decade alone, four bird species became extinct and four more are “on the verge of extinction.” In the U.S., the Fish and Wildlife Service classifies 101 bird species as threatened or endangered as of 2019.

Artificial light from buildings draws migratory birds like a beckoning siren, luring them toward lit cities where skyscraper glass reflections are plentiful and deadly. What appear to be skies and trees turn out to be deceptive reflections, and as the birds glide toward the images, they slam into the glass. Many are killed instantly, while some are seriously wounded.

Scientists at the Cornell Lab of Ornithology have investigated light pollution and bird migration patterns in major U.S. cities to determine where collision risks are highest. They report that the median light exposure to birds in cities is 24 times higher than the countrywide average. Chicago tops the list of dangerous U.S. cities for birds, followed by Houston and Dallas. This is true for both fall and spring migrations. Other dangerous metropolises include New York, Minneapolis, St. Louis and Los Angeles.

The central region of the U.S. happens to be a superhighway for bird migrations. Every spring and fall, over 5 million migrating birds comprised of 250 species pass over Chicago, where the city’s glass skyscrapers and artificial light become a death trap. Scientists from the Field Museum in Chicago have been counting dead birds at just one building (McCormick Place) since 1978. By 2002, the numbers had totaled 29,842 birds from 140 species. Chicago clearly has to be a major focus for conservation efforts during migration periods, as also the other hazardous cities identified in the study.

Another useful lesson from the Cornell study is one of timing, and this can help birds in many geographic regions of the U.S. Particularly crucial is the ability to pinpoint specifically when the birds face the greatest risks in each region. Fine-tuning the weeks when help is most needed can have a substantial impact on saving birds.

Researchers discovered that while a migration may continue over a six-month period, it “occurs in sporadic waves,” with the vast majority of birds passing through dangerous locales on just a few nights. Half of all migratory birds each season passed a metro location on approximately seven to 10 nights during their migrations. This means helping birds, even for a period as short as a week, can have a significant impact. Really though, we must do more.

How Can We Lower the Rate of Bird Collisions?

For low-rises and high-rises, minimizing artificial window light is highly beneficial. This can be done by turning out the lights at night, drawing curtains and blinds, using a small lamp on a table rather than bright ceiling lights and introducing lights with motion sensors in office buildings.

Additionally, participating in Lights Out projects during peak migration times saves many birds. For the average reader, this is as simple as turning the lights out after 11 pm during fall and spring migration months. For building owners, minimizing exterior lighting is also essential. Lights Out programs are being organized in many major cities and have saved thousands of birds. A two-year study by the Field Museum using McCormick Place in Chicago found that turning off the lights resulted in an 83 percent reduction in bird window-collision deaths.

Chicago Bird Collision Monitors rescues injured birds and counts fatalities each morning during migration. Notably, they rescued an injured peregrine falcon (on the endangered list) that was restored to health and released. “We know that before all buildings were participating consistently in Lights Out, there was a foggy night in 2002 when many birds were migrating where a single building was reported to kill over a thousand birds in one evening,” said Annette Prince, the program’s director. “Chicago Bird Collision Monitors worked with buildings to get better participation in Lights Out and by 2004, saw 100 percent participation in light reduction so that subsequently we have never had a single building kill so many birds at once.”

The Cornell Lab of Ornithology has a live bird migration map, so one can view in real time when birds are migrating through one’s locale and be cognizant of light pollution during peak days. It is important to note that turning lights out whenever possible is also beneficial outside of migration periods, as scientists have shown that substantial numbers of collisions can and do occur outside of migration periods, even in winter.

Bird-friendly architecture for new construction is essential, as is mandatory legislation. Additionally, adding bird-safe architecture to green building certification standards is recommended by scientists. The extent to which architectural changes can affect bird collision incidence is illustrated by the recent renovation of New York’s Javits Center — a building previously responsible for the most bird deaths per year in New York. To help mitigate the problem, architects replaced dark-mirrored glass with glass that had a subtle fritted pattern, and also added a green roof for nesting. The project was a remarkable success, reducing bird collisions by 95 percent. Other architectural strategies are installation of UV-coated glass, translucent glass and indented windows with shutters. Legislation requiring implementation of these strategies is crucial to saving birds from collisions.

Chicago proposed bird-friendly building legislation at the beginning of the year. The ordinance would limit the percentage of transparent or reflective glass that can be used in new and renovated construction exteriors. Specifically, it would require that from the ground to 36 feet up, at least 95 percent of the exterior cannot be covered in glass, or must use glass containing frosting, etching or screens. Nonessential exterior lighting would also be required to automatically shut off after 11 pm. Chicago’s legislation was introduced by Alderman Brian Hopkins and is supported by Bird Friendly Chicago. It is expected that real estate developers will oppose the bill. Michael Cornicelli, executive vice president of the Building Owners and Managers Association of Chicago, communicated that the portion of the bill requiring adoption of bird-friendly architecture to renovations of existing buildings would be “a potential sticking point.” San Francisco and Toronto already have bird-friendly legislation in place to serve as a model.

On a national level, U.S. Rep. Mike Quigley, a Democrat who is also a Chicago resident, has reintroduced the Bird-Safe Buildings Act (H.R. 919), which he has tried four times to pass since 2010. Christine Sheppard, director of American Bird Conservancy’s Glass Collisions Program, notes, “The legislation would help address one of the greatest human-caused threats to birds. Although this legislation is limited to federal buildings, it’s a very good start that could lead to more widespread applications of bird-friendly designs and use of bird-smart glass solutions.”

When enacted, these bills will reduce bird collision deaths, and in the next few months, we will see how they fare. In the meantime, researchers recommend that residents take some of the following precautions to minimize window collisions: angling windows to reduce reflection, keeping indoor vegetation away from windows, installing netting, ultraviolet-reflecting glass or decals spaced closely together.

In the coming months, look to the sky and around you. Stop awhile and you will hear birdsong, more in the morning but also during the day: wee warblers with deceptively loud melodies, cardinals singing their sweet song, and if you look carefully you might catch a glimpse of a puff of bright yellow, the source of that surprising volume. These and others are growing families and enriching our lives before they prepare for the thousands of miles long autumn journey to their winter homes.