Maine Public Radio's Peter McGuire takes us out on a chilly morning to witness the change. (SOUNDBITE OF BIRDS CHIRPING) DOUG HITCHCOCK: These birds we're hearing right now are males. It tends to be ...

(SOUNDBITE OF BIRDS CHIRPING) DOUG HITCHCOCK: These birds we're hearing right now are males. It tends to be males that do most of the singing. PETER MCGUIRE, BYLINE: Maine Audubon's Doug Hitchcock ...