Researchers track migratory birds in the region

Migrating birds on a radar screen look like doughnuts. Not individual Boston creams or anything like that, but a single giant yeast-raised doughnut inflating on the radar screen as flocks of birds lift off from their roosts and fly away.

"They take off shortly after sunset," Jeffrey Buler, at the University of Delaware's Aeroecology Lab, said. "You can almost track the path of the sun setting across the United States as you see this onset of bird migration."

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