The largest of the tern species, the Caspian Tern (Sterna caspia) breeds at both coastal and inland localities. The species was very localized in western North America until the 1940s, when a major expansion occurred. A second wave of colonization took place from the mid-1960s through the 1970s, and by the early 1980s, 20 colonies totaling approximately 6,000 pairs were known from California, Oregon, Washington, Idaho, Nevada, and Baja California (Gill and Mewaldt 1983).