Population consequences of current and predicted ocean climate variability for the seabird Cassin's auklet Ptychoramphus aleuticus

Few studies have examined the effects of climate variability on population demography across species' ranges although such studies have become increasingly relevant due to anthropogenic climate change. This study examines the effects of current and predicted ocean climate variability on phenology, demographic rates, and population dynamics of the seabird Cassin's auklet across its range in the California Current coastal upwelling ecosystem. First, the effects of oceanographic conditions on timing of breeding, breeding success, and an index of prey abundance were assessed for Cassin's auklet populations in Canada, the United States, and Mexico over six years (Chapter 1). Timing of breeding was well-correlated between the northern and central populations that experience seasonally-variable, high-productivity environments and was asynchronous in the southern population that experiences an aseasonal, lower productivity environment. Breeding success was relatively well-correlated across populations. Timing of breeding for northern and central populations and breeding success across all populations were consistently related to local oceanographic indices that captured heterogeneity in physical processes important for production and auklet prey abundance. Next, the potential long-term effects of cohort-year oceanographic conditions on Cassin's auklet demographic rates were assessed using a 26-year data set from the central California population (Chapter 2). Cohort-year conditions influenced the age of first breeding where auklets reared under favorable conditions recruited earlier than auklets reared in poor conditions. Cohort-year conditions produced opposite effects on post-recruitment demographic rates where auklet cohorts reared under poor conditions subsequently demonstrated higher mean adult survival and breeding success. However, current-year oceanographic conditions explained more of the variance in post-recruitment demographic rates. Finally, ocean climate projections from a regional climate model were used to forecast changes in the population growth rate of the central California population and evaluate predicted oceanographic change across California seabird colonies (Chapter 3). The population growth rate decreased unsustainably by 8%--49% based on changes in sea surface temperature compared with moderate declines of 0.5%--2.5% based on changes in upwelling intensity. This study highlights the utility of coupling regional climate models with ecological data sets and suggests that the Cassin's auklet should be a priority for climate-integrated conservation strategies.