David Willard has been checking the grounds of Chicagos lakefront exhibition center for dead birds for 40 years. On Thursday morning he found something horrible: Hundreds of dead songbirds, so thick they looked like a carpet.

Nearly 1,000 songbirds perished during the night after crashing into the McCormick Place Lakeside Center s windows, the result, according to avian experts, of a deadly confluence of prime migration conditions, rain and the low-slung exhibition halls lights and window-lined walls.