[order] Charadriiformes | [family] Scolopacidae | [latin] Calidris mauri | [UK] Western Sandpiper | [FR] Bécasseau d'Alaska | [DE] Bergstrandläufer | [ES] Correlimos de Alaska | [IT] Piro-piro occidentale | [NL] Alaskastrandloper

Alaskastrandloper determination

copyright: Don DesJardin

In breeding plumage, it has a deep rufous crown and cheek patch, and rufous on the wings. It is heavily streaked and spotted on the breast and back. By fall, much of this color has faded or worn off. Its slightly drooping bill, black legs, and bright rufous patches in breeding plumage help distinguish it from similar species like the Least and Semipalmated Sandpipers. The adult in non-breeding plumage is drab grey with a white breast. Juveniles look similar to adults in breeding plumage, but their breasts are not streaked. They have rufous on their backs, but not on their heads or cheeks. Their plumage is not sexually dimorphic, but females have slightly longer bills than males. In flight, they show a white stripe down their wings and white on either side of their tails.

Most of the population of Western Sandpipers breeds in Alaska, in dry tundra areas with low shrub cover and nearby marshes. During migration, they are mostly coastal, but some migrate across land and stop over at inland wetlands. During coastal migration and in winter, they occur in most shoreline habitats, but prefer mudflats and sandy beaches.

The Canadian Wildlife Service estimates the population at 3,500,000 birds, but other estimates are of 6,500,000 birds. Although Western Sandpipers are abundant, they are vulnerable because such a large percentage of the population gathers in so few spots during migration. Development, human disturbance, and oil spills near these stopover sites could dramatically affect the population. Most of the population breeds in western Alaska, whereas during the nonbreeding season, its range extends along the American Pacific coast from southern Canada to Peru, and, to a lesser extent, along the east coast of the Americas. During winter, the largest concentrations occur in western central Mexico and in Panama. In Suriname an less common migrant from the north confined to the tidal flats along the coast.

During the breeding season, insect larvae are the food of choice. The migration and winter diet is primarily crustaceans, mollusks, marine worms, and other aquatic invertebrates.

This species has a large range, with an estimated global extent of occurrence of 50,000-100,000 km2. It has a large global population estimated to be 3,500,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Males typically arrive on the breeding grounds first and establish territories. Monogamous pair bonds form after the females arrive. The male starts several nest scrapes, and the female selects one and lines it with leaves, lichen, and sedge. Both parents incubate the four eggs for 21 days. The young leave the nest within a few hours of hatching and find their own food. The female often deserts the group within a few days of hatching, and joins other post-breeding females in a flock. The male tends the young, and broods them in cold weather until they can fly, at 17 to 21 days.

Unlike other small Calidris, migration appears as series of shorter flights; flight range c. 600 km. E Siberian birds join Nearctic population on migration. Most migrate down Pacific coast, although significant numbers move through interior North America, with Cheyenne Bottoms as most important interior stopover site, during both spring and autumn. During N migration Copper R Delta functions as key staging site, used by more than 90% of total population; other major spring stopover sites are San Francisco Bay, Grays Harbor, Fraser Delta, Chesterman Beach, Tofino mudflats and Stikine Delta; southbound, Yukon Delta, Kuskokwim Bay and Boundary Bay. On Atlantic coast, common autumn migrant to Puerto Rico. Males winter, on average, closer to breeding grounds, and predominate at start of N migration. In autumn, departure occurs Jul to early Aug; adults precede juveniles, and females slightly precede males. Migrates in huge flocks. Many immatures stay in non-breeding range all year. Arrival on breeding grounds May to mid-Jun.