A Multivariate Study of the Relationship of Parental Age to Reproductive Success in California Gulls

Breeding biology of a California gull population was investigated on Bamforth Lake, Albany County, Wyoming. Data on hatching success, Ist and 2nd wk survival, and fledging success were collected in 1979 and 1980 for 295 breeding pairs. Breeding success increased with parental age as a result of larger clutches and reduced offspring mortality. Linear regressions indicated that nest sites with shrub shelter, central location in the colony, and high nest densities correlated positively with many measures of breeding success. These types of nest sites were most commonly obtained by old parents. Multivariate analyses, however, indicated that while parental age had a major influence on breeding success, all other variables that correlated with breeding success did so through covaria- tion with parental age. Thus, results did not support a hypothesis that more experienced parents have greater breeding success because they obtain better nest sites.