Barton, Kathleen E.
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Large populations of diving seabirds are found in the San Juan Archipelago, an important overwintering region for many seabirds. Previous Pelagic Ecosystem Function Apprenticeships have focused on the relationships of various diving seabirds and tidal conditions. Cormorants are the second most abundant diving seabirds of the San Juan Channel yet their feeding ecology is not commonly investigated. My objectives were to contribute to the long term seabird database by studying the abundance of all seabirds seen in the San Juan Channel during fall 2014 and comparing this information to recent autumns. I also explored cormorants by relating their abundance to previous autumns and distribution along the six zones for fall 2014. I observed their flight direction and water interaction in the most tidally active area (zone 5) to determine during which tidal conditions they flew in and out of the channel. The population of cormorants increased as the season progressed, likely due to the migration of Brandt’s cormorants to the region, with numbers highest in areas containing rookeries and tidally influenced prey abundance. A significant correlation between cormorant flight direction and fast tidal currents was found at Cattle Pass although they flew in the opposite direction of the current flow. I examined cormorant water interactions within the channel and found they were indeed in the water (proxy for foraging) on fast ebbing tides, reinforcing the countercurrent flight direction I observed at Cattle Pass. My results suggest that cormorants are very different from other diving seabirds and must be studied carefully. Additionally, my analyses confirm population declines for gulls and alcids which are likely due to the anomalously warm offshore ocean water.