Seabird Community Responses in the Northern California Current to the 2014-2015 NE Pacific Warm Anomaly

Previous warm temperature anomalies in the NE Pacific, including the 1997-1998 El Niño, had profound impacts on seabird communities in the northern California Current. Both physical forcing and biotic interactions impact seabirds from top-down effects of seabird predators to interactions between seabirds and their prey. We report on changes in diving seabird (common murre, Uria aalge, and pelagic and Brandt’s cormorants, Phalacrocorax spp.) breeding population sizes, reproductive success, phenology, and diets at breeding colonies (1998-2015) and at-sea seabird distribution and abundance (2013-2015) along the Oregon coast. Breeding seabird responses varied by species and breeding site. In 2014, reproductive success was mostly consistent with recent prior years for all species. In 2015, however, common murres and pelagic cormorants suffered colony-wide reproductive failures, while Brandt’s cormorants had the highest breeding success during our 8-yr time series. Breeding phenology in cormorants was delayed by 14 days in 2015 and the number of breeding pairs reduced compared to 2014. At-sea surveys revealed greater species diversity in 2015 compared to previous years, with sub-tropical and unusual migrant species observed in greater numbers. Overall, seabirds off Oregon appeared to suffer greater impacts from the 2014-2015 Pacific Ocean Anomalies during the 2015 breeding season.