Upper-level predators are not distributed uniformly across the world's oceans. Instead, species ranges mirror large-scale ocean productivity patterns and the distributions of physically distinct water masses. Yet, relatively little is known about the mechanisms that restrict pelagic species to specific ocean domains, and whether habitat preferences are influenced by changing ocean climate.

This dissertation investigates how the distribution and abundance of marine birds reflects oceanographic variability off southern California. This research addresses a broad range of temporal (hours - years) and spatial (10's - 1000's km) scales, and combines three distinct perspectives of marine bird dispersion: Individual foragers, regional scales, and ocean domains. The objectives of this dissertation are to determine whether seabird habitat selection changes with scale, and whether distinct processes structure marine bird assemblages at different spatial and temporal scales. Marine birds are ideal biological indicators in marine systems because they are numerous and conspicuous predators sensitive to fluctuations in ocean climate, pelagic food-webs, and prey availability. Therefore, the study of seabird populations can provide insights into the potential impacts of fluctuations in ocean productivity and ecosystem structure on other upper trophic consumers such as salmonids, cetaceans, and tunas.

Studies of albatross foraging movements (Chapter 3) and seabird community structure (Chapter 4) suggest that marine birds respond to environmental variability over coarse - meso scales (10's - 100's km). Telemetry tracks revealed that individual albatrosses focused their foraging on specific areas of high productivity and prey aggregation such as continental shelves and frontal features. At-sea surveys of marine bird populations documented temporal shifts in the composition of coastal seabird assemblages, associated with a long-term (1987-99) decline in macro-zooplankton abundance and aggregation in onshore waters. Additionally, behavioral observations of albatross vessel-attraction (Chapter 2) illustrated how anthropogenic activities can influence marine bird dispersion over tens of kilometers.

Larger-scale studies of albatross foraging movements (Chapter 3) and seabird community structure (Chapter 5) support the notion that seabird species exploit particular water masses and ocean domains. The telemetry research revealed that two subtropical albatrosses foraged in highly productive Subarctic and California Current waters thousands of kilometers from their breeding colony. Long-term seabird surveys off southern California documented pervasive changes in marine bird feeding guilds, biogeographic assemblages, and warm-water and cold-water species groups, concurrent with a pronounced warming of near-surface (10m) and thermocline (100m) ocean temperatures.

This dissertation underscores the notion that distinct processes structure pelagic communities at diverse spatial and temporal scales. In particular, this research highlighted the notion that seabird communities are influenced by prey dispersion over coarse-meso scales (10's - 100's km), and by ocean productivity and water mass distributions over larger macro-mega scales (1000's km). Additionally, this dissertation revealed that seabird assemblages off southern California did not respond uniformly to environmental change. Instead, differences in ecology and natural history mediated the differential responses of individual species. These results have important implications for our understanding of the ecology of far-ranging marine species, and the biotic consequences of climatic variability in pelagic ecosystems.