Forster’s Tern is the only tern that is restricted almost entirely to North America throughout the year. Its highest breeding numbers are around south-central Manitoba, northern California-southern Oregon, and the Gulf Coast. Its centers of abundance in early winter match those of its Atlantic coastal breeding areas, particularly around the Virginia-North Carolina border, Texas, and Florida. Similar in appearance and ecology to several other terns, it is primarily a marsh bird, although also found along Atlantic, Pacific and Gulf coasts.
A “marsh tern,” this species breeds primarily in fresh, brackish, and saltwater marshes, including marshy borders of lakes, islands, or streams. It is found more often in open, deeper portions of marshes, generally in wetlands with considerable open water and large stands of island-like vegetation and/or large mats of floating vegetation. Along the Atlantic coast, Forster’s Tern breeds in marshy portions of beach and estuarine areas. The suitability of nesting habitat is often ephemeral, varying at a given site from year to year.