Seabirds are integral predators in marine ecosystems and ideal indicators of ocean health and productivity. Along the west coast of North America, the dynamic California Current Ecosystem (CCE) provides vital foraging habitat to a variety of resident and migratory marine birds. The CCE is a complex current system that is highly variable over different spatial and temporal scales. Within the CCE, there is a web of different marine protected areas, including five National Marine Sanctuaries (NMS). These NMSs are found in the southern, central and northern portion of the CCE and provide well-defined regions to compare patterns and changes in seabird distributions throughout the CCE. Although seabirds within the CCE are well studied, it is only recently that the majority of at-sea data on seabirds in the CCE have been consolidated into one dataset that spans from 1980 to 2017. In addition, there are broad spatial patterns and temporal trends that remain unresolved about seabirds within the CCE. Understanding such trends will provide valuable information on how seabird density, diversity, and community composition may change in association with natural environmental variability and long-term impacts from climate change. Here, I use the most extensive data available on seabirds at-sea in the CCE to: (1) describe broad spatial patterns of seabird indices of density, diversity and community composition, (2) determine fine scale temporal trends of these seabird indices within NMSs, and (3) use diverse sources of data, including citizen science, to investigate relationships between vagrant, tropical birds and environmental variables. I found higher seabird abundance and diversity within higher latitudes and nearshore habitats, and that west coast NMS capture important seabird habitat, with greater abundance and diversity than outside the sanctuary boundaries. However, I found that the abundance of avifauna within the NMS in the CCE has decreased since the 1980’s, with greater declines in south. Decreases were largely due to a decline in non-CCE breeding species, which had decreased in abundance within all five NMS. Relationships between the abundance of seabirds with environmental conditions varied among the NMS, indicating that there are distinct drivers within each of these regions. Through investigation into five tropical species, I found that all of these species had increased in the CCE and their rise in abundance was linked with the two intense marine heatwaves that occurred in the 2010’s. With these increases, there were some species that persisted at high abundances, and others that did not remain at high numbers after these warm water events. This research results in a detailed description of the spatial patterns of seabirds in the CCE, trends of seabirds within NMS, and documented the northward range expansion of five tropical species.