SPRING MIGRATION OF WESTERN SANDPIPERS ALONG THE PACIFIC COAST OF NORTH-AMERICA - A TELEMETRY STUDY

We studied the migratory movements of radio-equipped Western Sandpiper s (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; Bo linas Lagoon, CA; Fraser River Delta, British Columbia; and the Stikin e River Delta, AK. Daily aerial and ground monitoring from mid-April t o late May at banding sites as well as the Copper River Delta provided data on length of stay of individual shorebirds and migration times b etween study areas. Fifty-eight shorebirds were detected beyond bandin g sites for a 74% net relocation rate. The proportion of birds detecte d 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 p er site. We failed to detect differences in length of stay among sites or between sexes. A condition index calculated as body mass standardi zed 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 w ere never relocated suggesting that migrant birds use smaller disperse d wetlands as well as the major intertidal wetland complexes we studie d. We conclude that most spring migrant Western Sandpipers use a short -flight hopping migration strategy rather than a few sustained long fl ights. The short-flight strategy emphasizes the importance of maintain ing a continuous complex of intertidal wetland habitats along the migr ation route to ensure shorebird conservation.