The Western Sandpiper is the most numerous shorebird on the
Pacific Coast of North America. It migrates along the Pacific
Coast of North America each spring for breeding grounds in
western Alaska and eastern Siberia, and returns in summer and
early autumn to winter quarters from southern USA to Ecuador.
About 3 to 4 million western sandpipers are thought to exist
in the world. The number of Western Sandpipers has declined in
censuses made annually during the spring migration on the
Fraser River delta, British Columbia. Several million
sandpipers were estimated to use the delta in the early 1990s
but by 2004 the number had dropped to about 500,000
individuals. One hypothesis for the census decline is that
individual birds are staying for a shorter time and
consequently are not counted on multiple days. The decline in
the duration of stay coincides with an increase in sightings
of Peregrine Falcons on the delta beginning in the mid 1980s.
Like many species of shorebirds, the western sandpiper’s habit
of gathering in great numbers at a few sites makes them
vulnerable to single events such as an oil spill. However,
shorebirds are also impacted by the cumulative erosion of many
sites from industrial development of the mudflats,
contamination of food supplies, and human disturbance. Western
Sandpipers make land fall at many industrialized mudflats
including Humboldt and San Francisco bays and Salton Sea in
The western sandpiper is present in large numbers during
spring migration in April and May when adults migrate north to
breed, and during summer
from late June to September when adults, followed by
juveniles, migrate south for the winter. Each sandpiper stops
for only a few days to rest and refuel. Western sandpipers
feed on tiny marine invertebrates and biofilm in the organic
layer of mudflats rich in organic matter.
Butler, R.W., G.W. Kaiser and G.E.J. Smith.
1987. Migration, chronology, length of stay,
sex ratio, and weight of Western Sandpipers, (Calidris
mauri) on the south coast of
British Columbia. Journal of Field Ornithology
Butler, R. W., F. S. Delgado, H. De La Cueva,
V. Pulido and B. K. Sandercock.
Migration routes of the Western Sandpiper.
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Butler, R. W., T. D. Williams, N. Warnock and
M. A. Bishop. 1997. Wind assistance: a
requirement for migration of shorebirds? Auk
Clark, C. W. and R.W. Butler. 1999. Fitness
components of avian migration: a dynamic
model of western sandpiper migration.
Evolutionary Ecology Research 1: 443-457.
Iverson, G. C., S. E. Warnock, R. W. Butler, M.
A. Bishop And N. Warnock. 1996. Spring
migration of western Sandpipers (Calidris
mauri) along the Pacific Coast of North
America: a telemetry study. Condor
Sutherland, T. F., P. C. F. Shepherd and R. W. Elner. 2000.
Predation on meifaunal and
macrofaunal invertebrates by western sandpipers (Calidris
mauri): evidence for
dual foraging modes. Marine Biology (in press).
Warnock, N. and M. A. Bishop. 1998. Spring
stopover ecology of migrant Western
Sandpipers. Condor 100: 456-467.
Ydenberg, R.C., R.W. Butler, D. B. Lank, C.
Guglielmo, M. J. F. Lemon and N. Wolf.
2002. Trade-offs, condition dependence and stop over site selection
by migrant western sandpipers. Journal of Avian Biology