AGE-SPECIFIC SURVIVAL, BREEDING SUCCESS, AND RECRUITMENT IN COMMON MURRES (<i>URIA AALGE</i>) OF THE CALIFORNIA CURRENT SYSTEM

Abstract

Estimating age-specific vital rates and determining which of them have the greatest influence on population trajectory is very useful for conservation and management of at-risk species. We created multistate capture–recapture models to provide estimates of age-specific variation in survival, recruitment, breeding propensity, and breeding success of Common Murres (Uria aalge) breeding at Southeast Farallon Island, California. Model-averaged age functions indicated that a "plateauing" (inverse age) function best characterized recruitment probability (transition from nonbreeder to breeder state) and breeding success (fledglings per pair). Adult and juvenile survival and breeding propensity were best modeled as constant with age. We modeled the population using an extended Leslie matrix and determined elasticity values for each of our estimated parameters to determine which have the greatest influence on population growth. Elasticities indicated that variation in adult survival had the greatest influence on population growth rate, but juvenile survival was also important. Increased juvenile survival since 1999, a period of cooler and more productive oceanic conditions, is probably largely responsible for the population growth observed during this period.