Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2007, with observers at 35 nesting sites providing data. An estimated 6744-6989 California least tern breeding pairs established 7667 nests and produced 2293-2639 fledglings at 48 documented locations. The fledgling to breeding pair ratio was 0.33-0.39. Statewide, 12,238 eggs were reported, with a Site Mean clutch size of 1.67 eggs per nest (St Dev = 0.133) and the statewide clutch size of 1.62 eggs (St Dev = 0.493) 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 55% of the breeding pairs while Venice Beach, Camp Pendleton, Huntington Beach and Naval Base Coronado produced 52% of the fledglings. Although the state experienced a lower chick mortality rate (9%) for the third consecutive year, four of the largest sites (Alameda Point, Venice Beach, Batiquitos Lagoon and Camp Pendleton) experienced levels of chick mortality greater than the state average. These four sites reported 42% of the total chicks, but 79% of the dead chicks. The main predators of least terns in 2007 were unknown species, black-crowned night-herons (Nycticorax nycticorax) and gull-billed terns (Gelochelidon nilotica). Coyote (Canis latrans) and American crow (Corvus brachyrhynchos) predation was lower compared to previous years, but predation due to protected species appears to be increasing. Gulls (Larus sp.) and peregrine falcons (Falco peregrinus) were reported from the most sites. The monitoring effort of 2007 is scheduled to continue in 2008.