Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sterna antillarum browni) continued in 2005, with observers at 28 nesting sites providing data. An estimated 6865-7341 California least tern breeding pairs established 8120 nests and produced 1721-2471 fledglings at 42 documented locations. The fledgling to breeding pair ratio was 0.23-0.36. Statewide, 13,752 eggs were reported, with a site average of 1.74 eggs per nest (St Dev = 0.111) and an average clutch size of 1.67 eggs (St Dev = 0.659) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Los Angeles Harbor, Naval Base Coronado, Batiquitos Lagoon and Pt. Mugu represented 68% of the breeding pairs while Los Angeles Harbor, Camp Pendleton, Bolsa Chica Ecological Reserve, Alameda Point, Naval Base Coronado and Batiquitos Lagoon Ecological Reserve produced 76% of the fledglings. Only two sites, Los Angeles Harbor and Camp Pendleton, produced 44% of the statewide fledgling total. Four large sites (Alameda Point, Los Angeles Harbor, Camp Pendleton and Batiquitos Lagoon) experienced high levels of chick mortality. Starvation is a suggested cause of the 33-49% chick death rate. The main predators of least tern chicks were American kestrels (Falco sparverius), American crows (Corvus brachyrhynchos) and coyotes (Canis latrans), accounting for up to 297, 287 and 170 deaths, respectively. Coyotes were reported from the most sites. The monitoring effort of 2005 is scheduled to continue in 2006.