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