Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2006, with observers at 31 nesting sites providing data. An estimated 7006-7293 California least tern breeding pairs established 8173 nests and produced 2571-3644 fledglings at 45 documented locations. The fledgling to breeding pair ratio was 0.35-0.52. Statewide, 12,698 eggs were reported, with a site average of 1.57 eggs per nest (St Dev = 0.257) and an average clutch size of 1.62 eggs (St Dev = 0.494) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Los Angeles Harbor and Batiquitos Lagoon represented 58% of the breeding pairs while Camp Pendleton, Los Angeles Harbor, Bolsa Chica Ecological Reserve, Batiquitos Lagoon Ecological Reserve and Venice Beach produced 68% of the fledglings. Only two sites, Camp Pendleton and Los Angeles Harbor, produced 40% of the statewide fledgling total. Four large sites (Alameda Point, Camp Pendleton, Los Angeles Harbor and Batiquitos Lagoon) experienced levels of chick mortality greater than the state average. Weather and food shortage are suggested causes of the 22-55% chick death rate. The main predators of least tern chicks were American crows (Corvus brachyrhynchos), coyotes (Canis latrans) and gulls (Larus sp.) accounting for up to 334, 222 and 157 deaths, respectively. American crows and common ravens were reported from the most sites. The monitoring effort of 2006 is scheduled to continue in 2007.