Least Tern (Sternula antillarum) Science Article 4
The Atlantic race of the Least Tern (Sterna antillarum antillarum) breeds along the coastal beaches and bay systems of the Atlantic Ocean and Gulf of Mexico from Maine to southern Texas, while the Interior Least Tern (S. a. athalassos) breeds in the interior of the United States along the Mississippi River, its major tributary drainages, and portions of the Pecos and Rio Grande rivers (American Ornithologists Union 1957). Although various physical distinctions between these populations were suggested by Burleigh and Lowery (1942), none of these distinctions has been statistically verified, and separation of the races remains largely based on geographic separation of breeding areas.
ROGER L. BOYD, J. Field Ornithol: Vol56, No. 4