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 shows that darkening just half of a building’s windows can make a big difference for birds.

Using decades’ worth of data and birds collected by Field Museum scientists at Chicago’s McCormick Place convention center, the researchers found that on nights when half the windows were darkened, there were 11 times fewer bird collisions during spring migration and six times fewer collisions during fall migration than when all the windows were lit.

 “Our research provides the best evidence yet that migrating birds are attracted to building lights, often causing them to collide with windows and die,” said Benjamin Van Doren, a postdoctoral associate at the Cornell Lab of Ornithology and the paper’s first author. “These insights were only possible thanks to over 40 years of work by David Willard at the Field Museum, who led collisions and light monitoring efforts.”

The study was published June 7, 2021 in Proceedings of the National Academy of Sciences. Benjamin Winger, an assistant professor in the University of Michigan Department of Ecology and Evolutionary Biology and assistant curator at the Museum of Zoology, is a senior author.

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

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

U-M’s Winger started working with the collision data in relation to lighting levels at McCormick Place in 2018, and a year later was lead author of a study that focused mainly on differences in collision rates among different bird species.

“It was quickly clear that there was a general correlation between the amount of light at McCormick Place and the number of collisions,” Winger said. “But to really understand the relationship between artificial light at night and collisions, a more sophisticated analysis that also involved data on migratory passage from radar and weather patterns was required.”

So, Winger contacted Van Doren and Andrew Farnsworth at Cornell and Kyle Horton at Colorado State University, who were doing cutting-edge research on analyzing bird migration with radar, and suggested a collaboration.

“Our study contains a hopeful message: We can save birds simply by turning off lights during a handful of high-risk days each spring and fall,” he said. “By adapting our existing public migration forecasts to identify nights with high collision risk, we will be able to issue targeted lights-out advisories several days in advance.”

In addition to the study’s implications for bird conservation, it also speaks to the importance of natural history collections in documenting global change, said U-M’s Winger.

“These collision data are even more valuable because they are backed up by specimens that are available for study in the Field Museum,” he said. “This will allow future scientists to go a step further and study the connections between many aspects of avian biology and conservation-relevant questions.”

Read full Michigan News press release

The research is receiving widespread media attention, including in Popular Science.