An investigation of Red Knot Calidris canutus spring migration at Grays Harbor and Willapa Bay, Washington

摘要

Red Knots Calidris canutus that migrate along the Pacific Flyway during spring are believed to belong to the roselaari subspecies, and in coastal Washington, USA, these knots aggregate in numbers not exceeded elsewhere in the flyway south of Alaska. In May 2010, as part of a continuing effort to investigate knot migration, including an effort to develop an estimate of abundance, we searched the northern areas of Grays Harbor and Willapa Bay, Washington, from airboats for flagged Red Knots originating from Baja California Sur, Mexico. We observed Red Knots roosting on sand or dredge-spoil islands, on estuarine shorelines, and at primary foraging areas. Red Knots were observed roosting primarily at shoreline and island locations, including sites that would not be available to them during extreme high tides or during storm events. The peak abundance of Red Knots occurred on 8 May, when 5,665 were in Grays Harbor and 1,314 in Willapa Bay. We documented 157 individually-marked Red Knots including 154 from Guerrero Negro, Baja California Sur, Mexico, one from the Yukon–Kuskokwim River Estuary in western Alaska, one from Wrangel Island, Russia, and one from Golfo de Santa Clara, Gulf of California, Mexico. We found a significant positive correlation between the dates of first observation of 43 individuals observed in both 2009 and 2010 (r = 0.42, P = 0.005) and this may reflect different timing of individual or cohort movements. Space use by knots changed during the migration period, with early migrants generally using areas near shore and late-season migrants using areas farther from shore. We observed 15 hunting flights by Peregrine Falcons Falco peregrinus directed at Red Knots, but none of these was successful. Key subjects requiring dditional investigation are identified.