To humans, the twin blue beams shining upward from lower Manhattan each Sept. 11 evoke solemn memories of the 2001 terrorist attacks. But to migrating birds, they’re a potentially fatal attraction.

That’s the finding of a study published Monday that looked at seven years of annual tributes at the National September 11 Memorial and Museum.

Researchers noticed thousands of birds were drawn to the lights, causing them to waste precious energy circling and risking collisions with buildings or capture by predators.

The study published in the Proceedings of the National Academy of Sciences estimated that the light beams influenced more than a million birds. The authors recommend bright lights around homes, stadiums, offshore oil rigs and construction sites be turned off as much as possible during migration season.

(AP)