Large-scale nocturnal migratory movements of many hundreds of land birds were observed at distances of 100–400 km off the southern California mainland during the period 4–15 September 1975. These observations were made from on board the R/V Alexander Agassiz, of the Scripps Institution of Oceanography, La Jolla, California, in the course of a marine biological research cruise to an area just south of the San Juan Seamount (located approximately 350 km west of San Diego, California near 33°N, 121°W) 4–10 September and to the southern end of the San Clemente Basin (located 90–110 km west of northern Baja California, Mexico, in the vicinity of 32°N, 118°W) 11–15 September.