Type: report

Article abstract: An estimated 3,451 to 3,674 pairs of California least terns nested at 36 nesting sites in 1999 and produced an estimated 671 to 711 fledglings. These estimates result in 0.18 to 0.21 fledglings per pair, the lowest productivity recorded since statewide censuses were initiated in 1976. Statewide pair estimates decreased 11% from 1998 values, but fledgling estimates declined by 74.9% due to exceedingly high predation and chick mortality at many sites. Over 30% of the nesting population was concentrated at two sites (Mission Bay Mariner's Point and Santa Margarita North Beach); ten sites supported a combined total of 76.6% of statewide pairs. One site (Los Angeles Harbor) contributed nearly 24% of the state's fledglings in 1999; Los Angeles Harbor and three other sites (NAS Alameda, Ormond Beach and Mission Bay Mariner's Point) produced over 50% of 1999 statewide fledglings. Four sites that supported least tern pairs in 1998 reported no nesting in 1999 (Batiquitos Lagoon W-1 and E-2; Mission Bay Fiesta Island, Mission Bay South Shores); four additional sites (Venice Beach, Seal Beach, Bolsa Chica, Chula Vista Wildlife Refuge) supported nesting but had no productivity in 1999. 1999 pair estimates were 18% lower than corresponding statewide nest numbers; in 1998 they differed by only 9%. Renesting may have occurred far less frequently in 1999 than in 1998 due to far higher predation (16.5% of all eggs and 7.7% of chicks hatched) and other factors contributing to chick mortality (26.5% of all hatched eggs) in 1999. The greatest egg losses in 1999 were attributed to coyotes, crows and ravens; highest chick/fledgling losses were to American kestrels, coyotes and peregrine falcons. Chick mortality due to factors other than predation was 26.5%, higher than 1997 and 1998 and is believed to be related to prey deficiencies and unknown factors.