The California least tern (Sternula antillarum browni) is a subspecies of least tern that breeds primarily in bays of the Pacific Ocean within a very limited range of Southern California, in San Francisco Bay and in northern regions of Mexico. This migratory bird is a U.S. federally listed endangered subspecies. The total population of the subspecies amounted to 582 breeding pairs in 1974, when census work on this bird began. While numbers have gradually increased with its protected status, the species is still vulnerable to population decline through natural disasters, predation, and human disturbance.

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