| Summary: | Year-round habitat use of marine predators provides knowledge of important marine areas throughout different life stages. Large-scale, environmental variability, both in space and time, causes changes in the behavior and distribution of marine predators that are important to quantify for conservation. In the Northern California Current System (NCCS), common murres (Uria aalge) are widely distributed, however, regional gaps exist in information of seasonal movements and individual foraging behavior. My goal was to use individual tracking devices to relate distribution and behavior of common murres to conditions in the environment. I used satellite transmitters on non-breeding common murres captured at the Yaquina Head colony in Newport, Oregon and in the Columbia River plume over multiple years (2012- 2013, 2015-2017), which included the progression of a marine heatwave. I developed behavior-specific habitat models for three different movement groups: central-place foraging, non-central-place foraging, and dispersing during the non-breeding period. In addition, I quantified behavioral and distribution responses to increasing ocean variability between the summers of 2013 and 2015 using dive activity linear mixed models to determine the environmental influence on dive frequency and dive duration. I found habitat use was dependent on large-scale movement patterns of individual murres. During the breeding season, murres that engaged in central-place foraging had extremely large foraging ranges and non-linear, bimodal trends with ocean depth and salinity. Non-central-place foragers during the breeding period, engaged in more restricted foraging activity with decreasing ocean depths, during daylight hours, and spent more time foraging in 2015 than in any other year. During the non-breeding period, murres often foraged nearshore in waters masses associated with warm sea surface temperature, upwelling, and low salinity levels. These conditions were associated with productive bays and river mouths. Dive activity and dive ...
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