Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2009, with observers at 41 nesting sites providing data. An estimated 7130-7352 California least tern breeding pairs established 8037-8045 nests and produced 1734- 2132 fledglings at 51 documented locations. The fledgling to breeding pair ratio was 0.24-0.30. Statewide, 13,965 eggs were reported, with a Site Mean clutch size of 1.77 eggs per nest (St Dev = 0.110) and the Statewide clutch size of 1.76 eggs (St Dev = 0.455) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Batiquitos Lagoon, Pt. Mugu, and Huntington Beach represented 64% of the breeding pairs while Bolsa Chica Ecological Reserve, Alameda Point, and Batiquitos Lagoon Ecological Reserve produced 42% of the fledglings. The 2009 chick mortality rate of 15% is similar to the rate observed in 2004 (14%). LA Harbor, Camp Pendleton, and Batiquitos Lagoon Ecological Reserve represented 79% of the total reported chick deaths, but only 37% of the total chicks. The predators responsible for the greatest number of depredated least terns in 2009 were gull-billed terns (Gelochelidon nilotica) and American crows (Corvus brachyrhynchos). Gulls (Larus sp.), American crows, common ravens (Corvus corax), American kestrels (Falco sparverius), and peregrine falcons (Falco peregrinus) were reported from the most sites. The monitoring effort of 2009 is scheduled to continue in 2010.