For generations, the sight of purple martin houses dotting American backyards has been a cherished symbol of spring’s return.

The purple martin is the largest swallow in North America ... mid-April in southern Canada, May in Arizona, early May in Montana. During fall, in the East, very large aggregations of thousands ...

The chatter belongs to the steady conversation of 50,000 or so purple martins gathering for the fall migration to South America. They have chosen again this year to roost in the trees lining the e ...