As hundreds of millions of birds head south, the invisible danger is glass

Just after dawn in Washington, D.C., Stephanie Haley is walking a familiar downtown route, scanning the sidewalk next to office buildings. There, huddled on the ground, is a motionless olive-green songbird. It's an Acadian flycatcher, no doubt on its way to Central or South America before it slammed into a window.

Haley quietly sidles up to it, gently placing a net over the bird. Then she picks the bird up, using a gloved hand. It begins peeping in dismay.

"This is a good sign, the fluttering, which means that hopefully he's just stunned," says Haley, who volunteers with a local group called Lights Out DC , which urges people to turn off artificial lights during migration season, because these lights can attract birds and lead to deadly collisions.

"I'll take him to City Wildlife an