Type: report

Article abstract: Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2014, with observers at 41 nesting sites providing data. An estimated 4232-5786 California least tern breeding pairs established 6038 nests and produced 2136-2859 fledglings at 48 documented locations across California. The fledgling to breeding pair ratio was 0.37 to 0.68. Statewide, 10,827 eggs were reported, with a Site Mean clutch size of 1.7 eggs per nest (St Dev=0.29) and a Statewide clutch size of 1.8 eggs (St Dev = 0.45) for Type 1 sites where monitors walk within the colony. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Huntington Beach, Point Mugu, and Batiquitos Lagoon represented 60% of the breeding pairs. Fledgling numbers were also unevenly distributed as the sites with at least 90 fledglings each (Camp Pendleton, Alameda, Batiquitos, Huntington Beach, Point Mugu, Naval Base Coronado, and Hayward), contributed 74% of the state’s production, and the sites with greater than 35 fledglings each (including the seven aforementioned sites plus Bolsa Chica, Venice Beach, Mariner’s Point, Napa Sonoma Marsh, and Oceano Dunes), contributed 90% of the state’s production. The 2014 statewide nonpredation chick mortality rate was 20%, similar to that in 2013 (22%). With the exceptions of Camp Pendleton and Naval Base Coronado, the larger nesting colonies experienced nonpredation chick mortality rates less than the average, similar to that documented in 2013. The predators known to be responsible for the greatest number of depredated least terns in 2014 were common ravens (Corvus corax), followed by American crows (Corvus brachyrhynchos), peregrine falcons (Falco peregrinus), coyotes (Canis latrans), gull species, western meadowlarks (Sturnella neglecta), unknown species, corvid species, raptor species, great horned owls (Bubo virginianus), northern harriers (Circus cyaneus), opossums (Didelphis virginiana), unknown avian species, and American kestrels (Falco sparverius). The monitoring effort of 2014 is scheduled to continue in 2015.