Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2011, with observers at 40 nesting sites providing data. An estimated 4826-6108 California least tern breeding pairs established 6435 nests and produced 1038-1195 fledglings at 49 documented locations. The fledgling to breeding pair ratio was 0.17-0.25. Statewide, 11,140 eggs were reported, with a Site Mean clutch size of 1.76 eggs per nest (St Dev = 0.111) and the Statewide clutch size of 1.75 eggs (St Dev = 0.459) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Batiquitos Lagoon Ecological Reserve, Huntington Beach, Pt. Mugu and Alameda Point represented 79% of the breeding pairs while Alameda Point, Camp Pendleton, Huntington Beach, Naval Base Coronado and Tijuana River NERR produced 55% of the fledglings. The 2011 chick mortality rate of 20% is slightly greater than the last three years. Alameda Point, Batiquitos Lagoon Ecological Reserve, Camp Pendleton, Huntington State Beach and Naval Base Coronado represented 87% of the total reported chick deaths, but only 70% of the total chicks. The predators responsible for the greatest number of depredated least terns in 2011 were unknown avian species, American crows (Corvus brachyrhynchos), gull species (Laris sp.), peregrine falcons (Falco peregrinus), gull-billed terns (Gelochelidon nilotica), and common ravens (Corvus corax). Common ravens, peregrine falcons, American crows, American kestrels (Falco sparverius), red-tailed hawks (Buteo jamaicensis), and coyotes (Canis latrans) were reported from the most sites. The monitoring effort of 2011 is scheduled to continue in 2012.