Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sterna antillarum browni) continued in 2004, with observers at 32 sites providing data. An estimated 6354-6805 California least tern breeding pairs established 7977 nests and produced 1351-1624 fledglings at 48 documented locations. The fledgling to breeding pair ratio was 0.20-0.26. Statewide, 12,774 eggs were reported, with a site average of 1.56 eggs per nest (St Dev = 0.248) and an average clutch size of 1.625 eggs (St Dev = 0.50) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, LA Harbor, Naval Base Coronado, Pt. Mugu and Batiquitos Lagoon represented 65% of the breeding pairs while LA Harbor, Alameda Pt., Pt. Mugu and Batiquitos Lagoon produced 70% of the fledglings. Three large sites (LA Harbor, Camp Pendleton and Batiquitos Lagoon) in southern California experienced high levels of chick mortality. Starvation was believed to be the cause of 33-57% death rate of chicks. The main predators of least tern chicks were coyotes (Canis latrans) and American crows (Corvus brachyrhynchos), accounting for up to 676 and 1022 deaths, respectively. Gulls (Larus sp.), peregrine falcons (Falco peregrinus) and American crows were reported from the most sites. The monitoring effort of 2004 is scheduled to continue in 2005.