The Guardian reports that volunteers in Chicago continue to collect bird carcasses around the McCormick Place building, almost entirely surrounded by glass, three days after the collision.
"This is just the tip of the iceberg," said Annette Prince, director of the Chicago Bird Collision Observatory. Prince said this week's incident is the most bird deaths they have recorded in a single day due to a single building.
Between Wednesday, October 4 and Thursday, October 5, 1.5 million birds are thought to have flown over Cook County, home to Chicago's metropolitan area.
Brendon Samuels, who studies birds that crash into buildings at the University of Western Ontario, said, "Not every bird that crashes leaves a body behind," adding that some birds will fall after flying for hours.
Samuels said that the real death toll will be known after all bird bodies are collected from the surrounding area.