Since he observed pelicans in large numbers on the island he named the island as "Isla de los Alcatraces" meaning the "Island of Pelicans".
Even though the Native Indians of the San Francisco area are stated to be the original settlers on the island (they collected eggs from the large flock of birds that regularly gathered there), Alcatraz got its name during Spanish rule in 1775 when naval officer and explorer Juan de Ayala surveyed the harbor and the San Francisco Bay.