THE RELATIONSHIP BETWEEN REPRODUCTION AND SURVIVAL IN KNOWN-AGED CALIFORNIA GULLS

Data supported a hypothesis of increasing reproductive effort with age in Larus californicus. A flood during 1984 terminated breeding during the incubation phase of part of the colony, permitting an estimate of reproductive costs. Yearly survival of gulls whose nest flooded was 92% compared to 72% among gulls that carried out the reproductive cycle. Adult survival was inversely related to level of fledging success in 1984. Survival declined and fledging success increased with increasing age, but gulls of differing ages within the same fledging success category had the same probability of survival. Fledging success peaked at ages 16-19 and declined among gulls 20-23, suggesting senescence in extremely old gulls, but longitudinal data indicated that fledging success did not decline among old gulls. The few gulls surviving to extreme old age did so by consistently exerting low reproductive effort and fledging few offspring. -from Authors