Spring stopover ecology of migrant Western Sandpipers

We describe stopover ecology for 132 migrant radiomarked Western Sandpipers (Calidris mauri) relocated repeatedly along the Pacific Flyway of North America. Eighty-eight percent of radiomarked birds were detected at 1-5 sites north of their banding sites, at distances ranging from 240-4,000 km away. We compare length of stay and physical indices of Western Sandpipers banded at coastal sites (San Francisco Bay, California and Grays Harbor, Washington), and an interior, western Great Basin site (Honey Lake, California). Western Sandpipers radiomarked at the interior site had significantly shorter length of stays than birds radiomarked at coastal sites, and they had significantly lower fat scores. The ephemeral nature of Great Basin stopover sites and an increased risk of predation may explain some of this variation. Fat and body condition indexes explained little of the observed variation in length of stay of Western Sandpipers at banding and other stopover sites. Length of stay of birds radiomarked at Grays Harbor were significantly longer compared to birds radiomarked to the south that also stopped at Grays Harbor, suggesting a potential capture effect on length of stay of birds at banding sites. Mean length of stays at seven sites other than banding sites ranged from 1.1-3.3 days and were not significantly affected by sex of bird, year of study, or banding location. Length of stay of male Western Sandpipers at the Copper River Delta, Alaska became significantly shorter later in the migration period, but not for females. Coastal sites along the Pacific Flyway from San Francisco to the breeding grounds generally function as stopovers for Western Sandpipers instead of staging areas.