The Relationship between Reproduction and Survival in Known‐Aged California Gulls

Survival from 1984 to 1985 was compared among known—aged California Gulls 4—23 yr old. Data supported a hypothesis of increasing reproductive effort with age. A flood during 1984 terminated breeding during the incubation phase of part of the colony, thus 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. However, gulls of differing ages within the same fledging success category had the same probability of survival. No evidence supported the hypothesis that fledging success increased with age because disproportionately larger numbers of individuals with "good phenotypes" survived to old age. Cross—sectional data showed that fledging success peaked at ages 16—19 and declined among gulls 20—23, suggesting senescence in extremely old gulls. However, 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.