Every year, millions of birds migrating at night, often distracted by bright city lights, die by flying into American buildings. Now a study shows where they may be most at risk — and how efforts to save them might be honed.

Chicago, Houston and Dallas are the most dangerous cities for birds traveling at night based on their prime location along one of North America’s busiest migratory routes and the light pollution that they produce, according to the new research.

“The lights will pull those birds in, they’ll circle and they’ll become disoriented,” said Kyle Horton, a postdoctoral researcher at the Cornell Lab of Ornithology and the lead author of the study, published this month in the journal Frontiers in Ecology and the Environment.

Over all, scientists estimate that anywhere from 365 million to nearly a billion birds are killed in such accidents each year in the United States. And while researchers are still investigating the causes, experts believe that many can be attributed to the disorienting allure of artificial light.