This thesis examines how physical processes associated with coastal waters affect the abundance and distribution of seabirds in these regions at different time-scales. At long time scales, I investigated the effect of physical processes on seabird abundance off Peru as a function of coastal upwelling. At short time scales, I examined the effect of physical processes on seabird distribution in the Bering Sea and Aleutian Islands with respect to particular physical features. In all cases, physical processes appear to determine the biological processes responsible for prey availability to the seabirds.

In the first chapter, I examined the hypothesis that change in the annual population size of guano-producing seabirds (cormorant, Phalacrocorax bougainvillii; booby, Sula variegata; pelican, Pelecanus thagus) is a response to changes in primary and secondary production of the Peruvian upwelling system. I tested this hypothesis by modeling nitrate input through upwelling to the upper layers of the ocean off Peru between 6° S and 14° S using data on wind stress and sea surface temperature. The model predicted a marked increase in primary production as a consequence of increasing wind stress. It closely predicted the growth of seabird populations from 1925 to the mid-1960s, and their decline thereafter, explaining about 94% of the variation in seabird numbers from 1925 to 2000.

In the second chapter, I examined the hypothesis that foraging short-tailed shearwaters (Puffinus tenuirostris) aggregate at the inner-front of the southeastern Bering Sea to prey on euphausiids that swarm near the surface. I tested this hypothesis by comparing primary production, and the distribution of euphausiids and shearwaters relative to the front during late spring and summer-fall of 1997, 1998 and 1999. We found enhanced primary production and high density of euphausiids at the front and offshore of the front during summer, but not during spring. Foraging shearwaters aggregated in high densities at the front during summer, but foraged close to shore during the spring. At the front, shearwaters foraged on euphausiids as expected, and on copepods that accumulated in the area. My results show that, during summer, the inner-front supports aggregations of euphausiids and their seabird predators.

In the third chapter, I examined the hypothesis that seabird distribution, abundance and diets are different in the eastern and central Aleutian Islands in response to distinct marine environments and energy pathways in each region. I tested this hypothesis by studying the distribution, abundance, diet and prey consumption of seabirds on research cruises conducted in June 2001 and May – June 2002. We found that distribution, abundance and diets of seabirds could be partitioned into two regions that correspond to marine environments determined by the extent of the Alaska Coastal Current. Short-tailed shearwaters were most abundant in the eastern Aleutian Islands, and northern fulmars (Fulmarus glacialis) were most abundant in the central Aleutian Islands. Seabird communities in the central and eastern Aleutian Islands were likely associated with different food webs. In the central Aleutian Islands, Short-tailed shearwaters and northern fulmars consumed oceanic euphausiids and copepods, respectively; in the eastern Aleutian Islands, both seabirds consumed shelf species of euphausiids. My study shows major zoogeographical differences in the marine environment between the central and eastern Aleutian Islands.