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They are agitated with boat distances of less than 30 meters when they are nesting, and less agitated during roosting (Ref. 94991). Nests on the surface of barren rocky islet or beach (Ref. 94991). Rocky-shore specialist concentrated along Pacific coast of northwestern North America (Ref. 87784). Feed mainly on intertidal marine invertebrates, primarily bivalves (clams and mussels) and other mollusks (limpets, whelks, and chitons); and secondarily, crabs, sea urchins, isopods, and barnacles. Contrary to its common name, oysters are rarely part of its diet (Ref. 95118). Uses rocky shores for nesting and rarely breed elsewhere. Nests prone to destruction by tides, particularly during storms; >10% of nests possibly lost to storm surges (Ref. 87784).
Chatwin, T.A. 2010 Set-back distances to protect nesting and roosting seabirds off Vancouver Island from boat disturbance. Thesis in MSc in Environment and Management, Royal Roads University, Victoria, British Columbia, Canada, 59p. (参照 94991)
IUCNのレッドリストの状況は
(参照 130435: Version 2025-2 (Global))
