On 23 April 1988, we observed a juvenile Masked Booby (Sula dactylatra) roosting on a small rock off the north end of Isla Coronado Sur, Baja California, Mexico. The Islas Los Coronados are situated 6 nautical miles (nm) off the west coast of northern Baja California, and 4 nm south of the United States/Mexico boundary.
We first noticed the bird at 12:50 as we cruised around the north end of the island. We slowly approached and observed it for 25 minutes at distances as close as 6 meters (photographs on file at the San Diego Natural History Museum). Throughout our observation, the bird seemed oblivious to our presence, despite several attempts to flush it by sounding our air horn.