Among-year site fidelity of Red Knots during migration in Washington; Fidelidad interanual del Playero rojizo al sitio de escala migratoria más importante del Corredor del Pacífico

ABSTRACT Many shorebirds exhibit within- and among-year site fidelity during their annual cycle. Little is known, however, about the migration ecology of Red Knots (Calidris canutus) that migrate along the Pacific Flyway and occur in Washington in numbers that exceed counts elsewhere on the flyway. At two large estuaries in coastal Washington, Grays Harbor and Willapa Bay, we searched for and recorded the locations of Red Knots (N= 547) that had been individually marked with leg flags at their wintering grounds in Baja California Sur, Mexico, during the period from October 2006 to April 2009. In 2010, we resighted 43 Red Knots at Grays Harbor and Willapa Bay that had been observed at these sites in previous years, primarily in 2009. We found a high degree of site fidelity between years, with birds observed in 2010 more likely to return to the same stopover site used in 2009 than to switch stopover sites. For knots that did not switch estuaries between years, the median nearest distance between locations where individuals were observed between years was 1.4 km at Grays Harbor and 0.6 km at Willapa Bay. Our results provide the first evidence of stopover site fidelity by Red Knots of the roselaari subspecies. Fidelity occurred at three spatial scales: coastal Washington, the two estuaries where we conducted our study, and specific mudflat areas within the estuaries. Because our study sites support high populations of bivalves, Red Knots may be returning to the same areas in subsequent years to exploit what we suspect is a predictable food resource. The abundance of Red Knots and high degree of site fidelity suggest that our study sites in Grays Harbor and Willapa Bay are important for the conservation of this species on the Pacific Flyway. RESUMEN No hay información sobre la fidelidad de los playeros rojizos del Pacífico (Calidris canutus roselaari) a las costas de Washington, pese a que en ellas sus números superan los de otras partes de la ruta migratoria. Investigaciones de fidelidad al sitio permitirán contextualizar la importancia de los estuarios de Washington para esta subespecie en su migración al norte. En las primaveras de 2009 y 2010 registramos, en Grays Harbor y Bahía Willapa, playeros rojizos marcados individualmente con banderas en las patas (N= 547). Las aves se marcaron en Baja California Sur, México, su principal zona de invernación, entre octubre de 2006 y abril de 2009. En 2010 observamos 43 playeros rojizos previamente registrados, sobre