Type: fact sheet

Article abstract: The California Least Tern (CLT) is a small seabird that nests in several protected nesting sites on the coast of California, USA, as well as parts of coastal Mexico. Following listing as an endangered species, the California population1 increased from 664 in 1976 to approximately 7,000 in 2009. The majority of the increase occurred during the 1990's, following the initiation of focused predator management. Despite ongoing protection efforts, egg and chick predation by several avian and mammalian species at many sites, as well as fluctuations in prey abundance and chronology, have resulted in low reported levels of productivity2 in recent years. Thus, although annual estimates of breeding pairs suggest a continued slow increase, many CLT researchers predict a sudden population decline. However, estimates of breeding pairs and fledglings are not systematically and consistently calculated. Thus, we analyzed several other breeding variables derived from field data. Results suggest large annual variations, but, aside from a statisticallysignificant decline in clutch size, no significant change over time in egg abandonment, egg predation, chick/fledgling mortality or chick/fledgling predation.