Every night during the spring and fall migration seasons, thousands of birds are killed when they crash into illuminated windows, disoriented by the light. But a new study in PNAS shows that darkening only half of a building’s windows can make a big difference to birds. Using decades of data and birds collected by scientists at the Field Museum at the McCormick Place convention center in Chicago, the researchers found that on nights when half the windows were dark, there were 11 times fewer collisions. birds during the spring migration and 6 times less collisions in the fall. migration only when all windows were on.

“Our research provides the best evidence to date that migrating birds are attracted to building lights, often causing them to collide with windows and die,” says Benjamin Van Doren, postdoctoral associate at the Cornell Lab of Ornithology and senior author of the article. “This information was only possible thanks to more than 40 years of work by David Willard at the Field Museum, who led the collisions and light surveillance efforts.”

In 1978, Willard, the museum’s collections manager emeritus, overheard a flippant remark about birds hitting McCormick Place, North America’s largest convention center which is just a mile south of the museum. So he investigated.

“I went down early one morning, just out of curiosity, and I walked around and found four or five dead birds,” says Willard. “I might not have looked back if I hadn’t found anything on that first day, and now here we are, 40 years later and 40,000 birds later.”

Willard and his colleagues, including Field Museum co-author Mary Hennen and other Field staff and volunteers, visited the site daily before sunrise during migration season, sometimes as early as 3:30 a.m. morning. Some days there are no birds; other times there are as many as 200. Willard picks up the dead birds and brings them back to the museum, where he records each one in a register and adds them to the museum collection.

About twenty years ago, Willard started noticing a trend: On nights when the lights were out in McCormick Place, during vacations or construction work, there were fewer birds on the ground the next morning. As the building’s lighting patterns began to vary more, he began collecting data on the windows that were lit each night, in addition to collecting the birds he found on the sidewalk.

The new PNAS study is the most in-depth use of lighting model data to date, combining Willard’s specimens and lighting observations with other conditions that may play a role in bird mortality, including weather records and radar data revealing the number of birds in the sky on any given night. “We developed a statistical model based on the number of illuminated windows at McCormick Place, weather conditions, migration passage and time of season. This allowed us to isolate the relationship between window lighting and collisions while taking these other factors into account, ”says Van Doren. “By bringing these different data sources together, we were able to understand how lights, weather and migration each contribute to collision mortality.”

The team found that the total number of birds in the sky on a given night and the direction of the wind both played a role in mortality, but the biggest determining factor was light: when more windows were darkened, fewer birds were dying. “The sheer strength of the link between lighting and collisions was surprising,” says Van Doren. “This is testament to the exciting potential of saving birds simply by reducing light pollution.”

The researchers were able to quantify this potential for saving birds: they predict that halving the area of ​​lighted windows could reduce the number of collisions by 11 times in the spring and 6 times in the fall. By turning off half the lights during migration seasons, bird mortality at McCormick Place could be reduced by 59%.

Researchers note that McCormick Place is far from unique – it’s been guarded longer than any other building in Chicago, but, says Willard, “There is hardly any address in downtown Chicago that does not have any birds in the Field Museum collection, thanks to the efforts of the Chicago Bird Collision Monitors. ” However, there are a few factors that make the McCormick Center particularly unsafe for birds, including its massive size, isolation from other buildings, and proximity to Lake Michigan, which birds are sometimes reluctant to fly over.

“Buildings all over North America, all over the world, are killing birds, and it adds up,” says Doug Stotz, senior conservation ecologist at The Field. “What we’ve learned over the past 20 years about lights on has prompted the city of Chicago to create its Lights Out program, which requires exterior lights on buildings to be turned off during peak migration. article will show why it’s important to turn off internal lighting as well, especially in Chicago, which is the nation’s deadliest city for migratory birds. ”

Van Doren is also eager to see the results of the project applied. “Our study contains a message of hope: we can save birds just by turning off the lights for a handful of high-risk days each spring and fall,” he says. “By adapting our existing public migration forecasts to identify high collision risk nights, we will be able to issue targeted extinction advisories several days in advance.”

In addition to the study’s implications for bird conservation, she also talks about the importance of natural history collections in documenting global change. “This collision data is even more valuable because it is supported by specimens available for study at the Field Museum,” says Ben Winger, one of the lead authors of the article, assistant professor and curator at the University of Michigan and a Former graduate student of the Museum. “This will allow future scientists to go further and study the links between many aspects of avian biology and conservation issues.”

“It’s a classic museum dataset,” agrees Stotz. “We do a lot of collecting not knowing exactly what the specimens will be used for. But at the end of the day when people say, ‘I wish we had information on X, Y or Z’, we do – that’s in the museum .”

###

Warning: AAAS and EurekAlert! are not responsible for the accuracy of any press releases posted on EurekAlert! by contributing institutions or for the use of any information via the EurekAlert system.