Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2010, with observers at 41 nesting sites providing data. An estimated 6437-6699 California least tern breeding pairs established 6968 nests and produced 1971-2245 fledglings at 51 documented locations. The fledgling to breeding pair ratio was 0.29-0.35. Statewide, 12,826 eggs were reported, with a Site Mean clutch size of 1.82 eggs per nest (St Dev = 0.198) and the Statewide clutch size of 1.84 eggs (St Dev = 0.441) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Pt. Mugu, Batiquitos Lagoon, Bolsa Chica Ecological Reserve and Huntington Beach represented 73% of the breeding pairs while Camp Pendleton, Huntington Beach, Alameda Point, Naval Base Coronado and Batiquitos Lagoon Ecological Reserve produced 68% of the fledglings. The 2010 chick mortality rate of 18% is slightly greater than the last two years. Seal Beach, North Island Maintenance and Training Facility (NIMAT), Camp Pendleton, and Naval Base Coronado represented 73% of the total reported chick deaths, but only 56% of the total chicks. The predators responsible for the greatest number of depredated least terns in 2010 were gull-billed terns (Gelochelidon nilotica), common ravens (Corvus corax), coyotes (Canis latrans) and American crows (Corvus brachyrhynchos). Peregrine falcons (Falco peregrinus), great blue herons (Ardea herodias), common ravens, red-tailed hawks (Buteo jamaicensis), American crows, and western gulls (Larus occidentalis) were reported from the most sites. The monitoring effort of 2010 is scheduled to continue in 2011.