The Western Sandpiper (Calidris mauri) 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 the southern USA to Ecuador.
Western sandpipers feed on tiny marine invertebrates and biofilm in the organic layer of mudflats rich in organic matter.
Estimates are that about 3 to 4 million western sandpipers exist worldwide. 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 stay for a shorter time and are not counted on multiple days. The duration of stay decrease coincides with an increase in sightings of Peregrine Falcons on the delta beginning in the mid-1980s.
Western Sandpiper Threats
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 areas from industrial development of the mudflats, contamination of food supplies, and human disturbance.
Western Sandpipers land at many industrialized mudflats, including Humboldt, San Francisco bays, and Salton Sea in California.
The western sandpiper is present in large numbers during spring migration in April and May when adults migrate north to breed, and during summer migration 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 Sandpiper Feeding, Hunting & Foraging Behaviour
Western Sandpipers prey on marine invertebrates that burrow in mud and sand beaches, and among wracks of seaweed. They also eat diatoms and microscopic life living on the surface of mud.
Invertebrates that live in the mud and sand are caught using a sewing method where the bill is slipped rapidly up and down in the mud until a worm is found, or picked from the surface. The prey animal is then pulled from the mud and swallowed.
Biofilm – the living matter on the mud surface – is also eaten by Western Sandpipers by dabbing the tongue onto the muddy surface and slurping it into the mouth. During the breeding season, Western Sandpipers on the Alaskan tundra use their tweezer-like bills to pick emerging insects from plant stems.
Western Sandpipers fly with direct and steady wing beats while on migratory flights. They can glide for short distances while descending but most fly is steady and direct.
Around the foraging areas, flocks will take to the air in darting and weaving formation to avoid attacks from falcons. Shorebirds are capable of rapid turns in flight that to our eye appear as one but video of flocks when slowed reveals that the birds turn in sequence and occasionally collide.
On the breeding grounds, Western Sandpiper males hover in the air above the territory to attract the attention of potential mates.
Courtship & Breeding Behaviour of the Western Sandpiper
The breeding season begins in late May in western Alaska and ends in July or August when the young depart to the south for the winter. Adult males arrive on the breeding grounds first often while snow is still on the ground. They establish a territory where the females will lay eggs.
The females arrive soon after the males in late May or early June and the 24 hours of sunlight results in around-the-clock courting. To court a female, males hover in the air for long periods uttering a buzzing call.
This time of year is full of activity as males chase one another all the while attempting to lure a female to mate with them. Most Western Sandpipers produce 1 brood per year but they will attempt to relay a clutch if the first attempt fails early in the season. Many pairs return to the same territory or close by in successive years.
Shorebird biologists estimated the world’s population to be about 3.5 million Western Sandpipers making it the most numerous species on the northeast Pacific Coast. The majority of these tiny birds nest along the western shore of Alaska where biologists have studied breeding biology in detail.
The breeding range extends as far north as Barrow in Alaska and a small number nest along the extreme eastern Siberian shore in Russia. The nest is a tiny cup about the size of a tea cup made of dried grasses and plant stems hidden in the tundra vegetation.
The reddish brown with dark scrawl markings on the eggs matches the dried and dead stems of the tundra. The average clutch size is 4 eggs.
Adults feign a broken wing when an intruder approaches a nest or flutter in front of intruders who get close to their eggs and young. Both parents incubate the eggs which require about 18 to 21 days.
Eggs hatch into downy chicks with buff and chocolate markings, dark brown irises and black legs. Their mothers begin to depart the breeding grounds in mid-June leaving the care to their fathers.
The young are highly mobile within a few hours of hatching and they scamper off into the tundra. As the chicks age, their downy feathers are replaced with juvenile plumage, their fathers begin to depart for the winter quarters.
As a result, the adult males pass south on migration through British Columbia in late July ahead of their young. By late July the first young depart Alaska and most have gone by the middle of August.
Western Sandpipers, like many of the small sandpipers, utter a peeping call that has given rise to the colloquial name ‘peep’ for this group of birds. In a feeding flock, the peeping sounds like busy office chatter but when disturbed by an attacking falcon, it becomes a din of panicking, flapping shorebirds.
The territorial call is a buzzing sound. During migration, individuals departing for a long flight utter a ‘wreet’ call that is likely used to enlist flock mates to fly with them.
Some sandpipers also shriek when captured which draws the flock around for a second look.
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 58:103-111.
Butler, R. W., F. S. Delgado, H. De La Cueva, V. Pulido and B. K. Sandercock. 1996. Migration routes of the Western Sandpiper. Wilson Bull. 108:662-672.
Butler, R. W., T. D. Williams, N. Warnock and M. A. Bishop. 1997. Wind assistance: a requirement for migration of shorebirds? Auk 114: 456-466.
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 98:10-22.
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
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 33:47-56
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The American Dipper
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