DEMOGRAPHY OF A CALIFORNIA LEAST TERN COLONY INCLUDING EFFECTS OF THE 1982-1983 EL NINO

In a seven-year study (1983-1989) of banded California Least Terns (Sterna antillarum browni) breeding at Venice Beach, a number of demographic parameters were examined. Survival of breeding adults was found to be age-related, with young breeders age two and three years showing lower return rates than adults equal to or greater than four years. The return rate of banded hatchlings as breeding adults was 0. 16, and annual hatchling productivity per individual adult was 1.00. Combining the survival data with available information on intercolony exchange rates, we computed the expected breeding life of an adult (once it has bred) as 9.63 years, with a lifetime productivity of 1.49. The extraordinary El Nino (ENSO) of 1982-1983 had major adverse effects on the population dynamics of the colony for a period of five years. Values were computed for ''normal'' and ''ENSO'' years.