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SPRING MIGRATION OF SHOREBIRDS ON THE YAKUTAT FORELANDS, ALASKA

1998; Wilson Ornithological Society; Volume: 110; Issue: 3 Linguagem: Inglês

1938-5447

Brad A. Andres, Brian T. Browne,

Fire effects on ecosystems

During spring 1996 and 1997, we conducted ground surveys at high tide to determine species composition, numbers, and timing of spring shorebird migration on the Yakutat Forelands, Alaska. Western Sandpipers (Calidris mauri) and Dunlins (C. alpina) were the most abundant shorebirds we observed in the Seal Creek-Ahrnklin River estuary; we also observed large aggregations of Marbled Godwits (Limosa fedoa beringiae). Using information on turnover rates of radio-tagged Western Sandpipers, we estimated that about 101,000 small calidridine sandpipers used the Seal Creek-Ahrnklin River estuary as a spring migration stopover annually in 1996 and 1997. From previous aerial survey data on shorebird distribution, we estimated that the entire Yakutat Forelands supports a spring population of more than 350,000 migrant shorebirds. Therefore, the forelands is an important stopover site to migratory shorebirds and should be included in the network of international stopover sites needed to conserve shorebirds migrating along the Pacific coast. Received 22 Oct. 1997, accepted 30 Mar. 1998. Each spring, millions of shorebirds migrate north along the Pacific coast of North America to Arctic and sub-Arctic breeding grounds from temperate or tropical wintering grounds. To replenish depleted fat reserves during migration shorebirds congregate on coastal tidal flats that are often geographically restricted (Myers et al. 1987). Concentrations of shorebirds on large tidal flats can reach impressive numbers (Myers 1983). For example, most (>60%) of the world's Western Sandpipers (Calidris mauri), the most abundant shorebird migrant along the Pacific coast (Butler et al. 1996), stop at the Copper-Bering River Delta, Alaska, during spring migration; single-day counts in early May can exceed one million individuals (Isleib 1979, Iverson et al. 1996). Several other concentration areas along the Pacific coast annually support more than one million migratory shorebirds (e.g., Gray's Harbor, Washington; San Francisco Bay, California; Fraser River Delta, British Columbia; Page and Gill 1994, Gill et al. 1995). Protection of these primary concentration sites is critical to the conservation of migratory shorebirds and is central to the mission of the Western Hemisphere Shorebird Reserve Network (WHSRN) program (Finney 1995). Recent evidence from the Pacific Coast (Iverson et al. 1996) and Great Plains (Skagen and Knopf 1994) suggests that small, secondary wetlands also provide important shorebird stopover habitats. Radio-tagged Western Sandpipers used short flights (generally <1000 km) to migrate between a series of coastal wetlands along the Pacific Coast, and Great Plains migrants used alternative wetlands when environmental perturbations altered the quality and availability of traditionally-used wetlands. Although most primary stopover areas have been identified, information on the importance of secondary wetlands is still needed. Evidence from aerial surveys for radio-tagged Western Sandpipers (Bishop, unpubl. data) indicated that small estuaries on the Yakutat Forelands, heretofore thought to be of minor importance to migratory shorebirds, might provide stopover habitat for shorebirds that migrate along the Pacific coast of Alaska. In fact, when Senner and coworkers (1981) assessed patterns of spring migration of Western Sandpipers in southern Alaska, little information was available about their migration between the Fraser River Delta and the Copper-Bering River Delta, Alaska. Senner (1979) earlier suggested that Western Sandpipers might use a series of stopover sites but had no quantitative information from any site in southeastern Alaska to evaluate his hypothesis. Because no intensive study of estuaries on the forelands has been conducted, we initiated a project to determine species composition, numbers, and timing of spring shorebird migration on the Yakutat Forelands and to assess its importance as a stopover habitat. i U.S. Fish and Wildlife Service, Nongame Migratory Bird Management, 101 I East Tudor Rd., Anchor-