Type: report

Article abstract: An estimated 4,141 to 4,182 pairs of California least terns nested at 39 nesting sites in 1998 and produced an estimated 2,686 to 2,810 fledglings. Statewide pair estimates increased 3.9%, but fledgling estimates decreased by 14.6% from 1997 estimates, likely due to high chick mortality at many sites. Seven sites (NAS Alameda, NAWS Point Mugu, Venice Beach, Huntington Beach, Santa Margarita River North Beach, Mariner's Point, and Delta Beach North) supported a combined total of 65% of statewide pairs and produced 66% of the state's fledglings in 1998. Fledglings per pair were 0.64 to 0.68, lower than 1997 (0.80). One of the more interesting findings of 1998 was a report of a nesting pair on evaporation pond dikes near Kettleman City in the San Joaquin Valley. Both eggs hatched and one chick apparently fledged. It is likely that monitors continue to underestimate renesting, as reported pair estimates are only 378 lower than statewide nest numbers of 4,541, despite 64 eggs lost to flooding, 900 observed dead chicks and minimum losses to predators of 147 eggs and 165 chicks. Another method of estimating pairs was requested and attempted by some monitors in 1998, based upon the number of renesters that a given site may generate, rather than the number of renesting pairs at that site. This estimate was 3,483 pairs, or 84% of estimates derived by the traditional method. Statewide mean clutch size was 1.66 eggs per nest, lower than for the previous three years, suggesting limitations in prey availability, as reported by several monitors. However, statewide mean hatching success was 0.80, similar to the previous two years. After a 54% increase in pairs and a 200% increase in fledglings between 1995 and 1997, pair numbers increased only 3.8% and fledgling numbers decreased by 14% from 1997. This is likely related to limitations in prey availability during 1998, as evidenced by high chick mortality, poor nest attendance, abnormal chick feeding and kleptoparasitism.