If the map doesn t show where the bird is in the winter, the chances are that it leaves North America and heads for South America where the seasons are reversed, and it is spring during our fall, and summer during our winter. Some maps don't show where the birds go along the way, but if they nest on the East Coast, chances are good that you can see them as they head south. More good questions. Some people think birds know when the hours of daylight begin to get noticeably shorter, but no one knows for sure. As to how they get there, perhaps they follow the stars, or look for landmarks things on the ground they know.
Some birds travel in flocks, so the adults teach the young.
Truly a sight to see. Others find their way one at a time. When some birds migrate, they go no farther south than right here in Virginia. North say in Canada or Maine. In southern South America, and other places near the bottom of the world, birds that migrate go north.