Differential timing in the use of the oceanographic features of the California current system by two pelagic seabirds.

The California Current System (CCS) is known for its extensive biodiversity along the western coast of North America. However, it remains difficult to understand the intricate relationship between environmental conditions within the CCS and the distribution patterns of species. This study focuses on two species of procellariform seabirds: the Black-vented Shearwater (Puffinus opisthomelas) and the Laysan Albatross (Phoebastria immutabilis). These bird species have different habitat preferences within the CCS: shearwaters prefer coastal areas, and albatrosses predominantly inhabit pelagic regions. However, there is limited knowledge about these species' foraging areas in the Mexican Pacific. To address this gap, we analyzed the movement tracks of Black-vented Shearwaters breeding on Natividad Island and Laysan Albatrosses breeding on Guadalupe Island throughout their breeding seasons. We used expectation-maximization binary clustering to identify the foraging areas of each species, and subsequently examined the oceanographic variables associated with these areas. The research revealed significant differences in the foraging environments of the two species. Shearwaters predominantly use coastal areas with higher temperatures and chlorophyll concentrations compared to the open ocean areas frequented by albatrosses for foraging. Furthermore, our research showed how important changes in the Ekman pumping rate are as a major factor affecting the presence of seabirds in their foraging areas, possibly acting as an early sign of the start of the food chain. These findings represent a notable advance in our understanding of the foraging habits of the Black-vented Shearwater and the Laysan Albatross. Furthermore, they highlight the critical importance of considering species-specific behaviors and conducting detailed investigations into various oceanographic phenomena that occur in foraging areas. These efforts will contribute to a broader understanding of the factors that shape each species' foraging areas.