Spring Migration of Western Sandpipers along the Pacific Coast of North America: A Telemetry Study

Abstract

We studied the migratory movements of radio-equipped Western Sandpipers (Calidris mauri) along a 4,000 km stretch of the west coast of North America from California to Alaska during the 1992 spring migration. A total of 77 shorebirds were radio-tagged at San Francisco Bay, CA ; Bolinas Lagoon, CA ; Fraser River Delta, British Columbia ; and the Stikine River Delta, AK. Daily aerial and ground monitoring from mid-April to late May at banding sites as well as the Copper River Delta provided data on length of stay of individual shorebirds and migration times between study areas. Fifty-eight shorebirds were detected beyond banding sites for a 74% net relocation rate. The proportion ofbirds detected along the migration route increased with latitude : Grays Harbor, WA (3.4%) ; Fraser River, British Columbia (8.6%) ; Stikine River, AK (28.6%) ; and Copper River, AK (62.3%). Length of stay averaged three days per site. We failed to detect differences in length of stay among sites or between sexes. A condition index calculated as body mass standardized for body size was a poor indicator of length of stay at a site or migration time among sites. An estimated 26% of radio-equipped birds were never relocated suggesting that migrant birds use smaller dispersed wetlands as well as the major intertidal wetland complexes we studied. We conclude that most spring migrant Western Sandpipers use a short-flight hopping migration strategy rather than a few sustained long flights. The short-flight strategy emphasizes the importance of maintaining a continuous complex of intertidal wetland habitats along the migration route to ensure shorebird conservation.