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Calidris mauri - Western Sandpiper

Western Sandpiper image

Geographic range:

Western Hemisphere

Key features:

This is a small shorebird with moderately long, black, and slightly decurved bill. Drab gray-brown back and white breast in winter, but colorful rufous highlights during breeding season.

Similar species:

Calidris minutilla -- Least Sandpiper


bay (sandy shore), estuary, exposed sandy beaches, protected sandy beaches

Primary common name:

Western Sandpiper

General grouping:

Seabirds and shorebirds

ITIS code:


Geographic Range

Range Description:

The Western Sandpiper is found on mudflats, wet meadows, grassy pools, and beaches in North America and as far south as northern Peru and Surinam in the winter. In MBNMS it may be found wintering on the mudflats of Elkhorn Slough, muddy areas throughout the Salinas Valley, and along the shoreline of the Monterey Peninsula south to Big Sur. During the breeding season they migrate to western Alaska and Siberia, as far north as Point Barrow at the convergence of the Beaufort and Chukchi Seas.


bay (sandy shore), estuary, exposed sandy beaches, protected sandy beaches

Habitat notes:

They are common in MBNMS as migrants and as winter residents, especially on estuarine mudflats.


Relative abundance:

Common in winter and rare in summer. Western Sandpipers are one of the most abundant shorebirds in North America, wintering along the Pacific coast of North America and the south Atlantic coast.

Species Description

General description:

The Western Sandpiper is small, similar in size to a sparrow, and is a member of the group known as peeps or stints. It has a short neck but moderately long bill and legs. It has chestnut-brown, scaled upperparts and white dotted rows of dark chevrons on its breast and back. In breeding plumage it has a deep rufous (reddish brown) crown and cheek patch, and rufous wings. This reddish brown color will fade by fall, when the plumage will appear drab grey above with a white breast. The bill is approximately 2.5 cm long, dark black, and is very slightly decurved at the tip. Legs and feet are black, with partial webbing between the toes. Thin white stripes are visible on dark wings when it flies, plus white on either side of their tails. Their flight is rapid on narrow, pointed wings. Juveniles appear similar to adults in breeding plumage, but their breasts are plain and without streaks or chevrons. The sexes look alike except the female has a slightly longer bill. Western Sandpipers are primarily terrestrial, with toes that are adapted for walking. They are able to walk or run during foraging. They often stand on one leg, occasionally hopping, causing observers to mistake them for cripples. Their call is a thin “jeet” sound. A group of sandpipers may be called a “bind”, “contradiction”, “fling”, “hill”, and “time-step” of sandpipers.

Distinctive features:

The Western Sandpiper is in MBNMS during winter, and their winter plumage is a drab grey and white. They have a moderately long, black, slightly decurved bill and black legs and feet that are partially webbed.


Length: 14-17 cm (5.5-6.6 in) Wingspan: 35-37 cm (13.65-14.4 in) Weight: 22-35 g (0.77-1.2 oz)

Natural History

General natural history:

The Western Sandpiper, one in the group of smaller sandpipers referred to as “peeps”, winters primarily along the Pacific coast from California to Peru, with a few wintering as far north as Washington. They also winter along the Atlantic coast from New Jersey southward to central Mexico, the Caribbean coast of Central America, Columbia, Venezuela, Surinam, and the West Indies. They prefer mudflats and beaches, where they forage and probe for their prey items, plus glean biofilm from the surface of mud. For breeding they migrate in large flocks to the Arctic tundra from eastern Siberia to northwest Alaska, from the mouth of the Kuskokwim River north to Point Barrow and Camden Bay.


On the breeding grounds red foxes (Vulpes vulper), Long-tailed Jaegers (Stercorarius longicaudus) and Parasitic Jaegers (S. parasiticus) prey on Western Sandpipers. During migration and on wintering grounds Merlins (Falco columbarius) and Peregrine Falcons (F. peregrinus) are the main predators of the Western Sandpiper.


On breeding grounds and inland stopover areas Western Sandpipers feed on freshwater benthic invertebrates, adult insects, and spiders. During migration along the coast and in the winter, marine benthic invertebrates, primarily arthropods, polychaete annelids, and bivalve mollusks are taken. There is new research from Japan, France, and Canada that has found that Western Sandpipers also ingest a biofilm that grows as a mat on the surface of mud. The very thin film is a thin sheet of microscopic bacteria, detritus, sediments, and compounds secreted by the bacteria. The researchers have found that Western Sandpipers and Dunlins have specialized bills that helps them graze on biofilms. (see Feeding Behavior for more details on biofilm feeding.)

Feeding behavior


Feeding behavior notes:

Western Sandpipers feed by pecking (when on dry sand or mud) or probing (when in wet, sandy habitats) and rarely forage in water deep enough to reach their bellies. They walk or run constantly and whistle at the water’s edge when foraging. They most often follow the receding and rising tide line. Along the central California coast they sometimes forage in areas lacking a surface film of water but more often will forage where there is a film of water, near the tidal edge. They frequently will forage in shallow intertidal pools and also in sand flats, mudflats, sewage ponds, salt marshes, sand beaches, tidal sloughs, and freshwater marshes. When arriving on their breeding grounds they will feed on insects taken from the snow and from partially melted streams. Both tundra and littoral habitats are used for foraging during breeding and post-breeding. New research has revealed that the Western Sandpiper and the Dunlin feed also on biofilms found on the surface of mud (Kuwae et al. 2008). Using high speed video, scientists from Japan, France, and Canada observed that the birds move more slowly when eating biofilm than when eating invertebrates, and speculate there is no need to sneak up on the immobile biofilm, so why rush? They simply collect a tiny ball of the film, raise their slightly open bill out of the mud and swallow the droplet. To prove that they were eating the biofilm and not minute invertebrates chemical assays were done, calculating how much of the sandpipers’ overall food energy was from biofilms. As primary producers, biofilms have unique chemical characteristics including a high abundance of proteins like chlorophyll that are not found in most invertebrates. These calculations showed that migrating Western Sandpipers get up to half of their daily energy requirements from eating biofilms. Western Sandpipers are one of the world’s most numerous shorebirds and mudflats in calm waters are ideal for growing biofilms. The researchers speculate that the abundance of Western Sandpipers may stem from their ability to feed on biofilms. For more information, see Kuwae et al. (2008) in Ecology 89(3):599–606.

March - May


Most Western Sandpipers migrate along the Pacific coast, although significant numbers migrate across interior North America also. They stage huge, spectacular flocks as they depart their wintering grounds (like Elkhorn Slough), especially from San Francisco Bay to the Copper River Delta in Alaska. As many as 6.5 million may pass through the Copper River Delta each spring, where they rest and feed before flying further northwest to their breeding grounds. Males begin their northward movement before the females, thus ensuring that they reach the breeding grounds and begin to establish a territory before the females arrive. Their migratory path seems to be a series of short flights, with stops of 1 to 5 days along the way for feeding. At coastal stopovers they frequent intertidal mudflats. At interior stopovers the margins of lakes and ponds are used. Along the central California coast migrating Western Sandpipers are seen most in mid-April, with individuals passing through until mid-May, when they will be in breeding plumage.

May - June


Most of the population of Western Sandpipers breeds in Alaska as far north as Point Barrow, in wet tundra areas with low shrub cover and nearby marshes. They favor habitat with dwarf birch (Betula), dwarf willow (Salix), crowberry (Empetrum), various ericaceous shrubs (Vaccinium spp., Arctostaphylos spp.), tussock grasses and bryophytes. It is necessary for the areas to be elevated for nesting but near wetland areas for feeding. On arrival in the spring, they are found in snow-free areas waiting for snowmelt to expose potential nesting sites.
Their breeding colonies are large and densely packed with nests. Males arrive first, and establish a territory, typically returning to the territory occupied the previous year. Females arrive a few days later and choose a mate. The male will display by flying to 20 feet with a little hovering and trilling. The male starts several nest scrapes (up to 6) near the water. The female will participate in this nest scraping also for 2 to 3 days until she selects one and lines it with leaves, lichen, moss, and sedge. Nests have an internal diameter of 5 to 8 cm and an internal depth of 3 to 8 cm.
The pair will remain monogamous throughout the season. Males aggressively defend their territory against all intruding males, with chasing among males being common until the young hatch. Fights are frequent and include ground charges and fluttering into the air, slapping with their wings and jabbing with their bills. Most fights last a few seconds although longer fights have been reported. Fight frequency is greatest early in the breeding season, although fights also occur just before hatching. Laying eggs begins a few days after snowmelt, which is usually late May. The female lays 4 cream to dark buff eggs marked with brown that are 1.2 in. (31mm) long. The eggs are laid in 23 to 28 hour intervals and arranged with the narrow ends of the eggs directed to the center of the nest cup. This snug fit maximizes heat retention.
Both parents incubate the eggs for 21 days, but do not start to incubate until the fourth egg has been laid. Both sexes have a pair of oblong incubation patches on either side of their ventral midline. The female incubates from late afternoon until the middle of the following morning; the male incubates during the middle of the day. Hatching is relatively synchronous with the clutch all hatching within 24 hours.
The chicks are precocious and will leave the nest within a few hours of hatching and begin to find their own food. However the family group remains together until the chicks can fly which occurs in 17 to 21 days. The female may desert a few days after the chicks hatch and join a flock of post-breeding females, in which case the male tends the young and broods them in cold weather. Adults will depart the breeding grounds in midsummer, with the chicks continuing to feed until they too depart in 2 to 3 weeks. The juveniles may occur singly or in flocks of up to 200 or more along river channels. Most begin their southward migration by early August.

June - October


Most Western Sandpipers migrate along the Pacific coast, but many also migrate across the continent to winter on the East and Gulf Coasts. In mid-July southbound migrants begin to be seen on wetlands along central California coasts. Since adults leave breeding grounds ahead of the juveniles there are two pulses of migration that appear in summer/fall. Within the adult migration the breeding females slightly precede the breeding males. The Yukon-Kuskokwim Delta is an important pre-migration staging area for Western Sandpipers and Dunlin during fall migration. Southward migration, beginning the third week of June and concluding in mid-October, is more protracted and leisurely than spring migration with frequent stops for feeding, often lasting from 5 to 30 days. Some migrate south along the Atlantic coast and others use the interior of the continent. At coastal stopovers they frequent intertidal mudflats. At interior stopovers the margins of lakes and ponds are preferred. Flocks may be as large as 10,000 birds.

October - March


Flocks of Western Sandpipers may be large on wintering grounds, where they have a preference for fine sand to muddy substrates. They will typically follow the receding and rising tide line along the Pacific Coast of North, Central, and South America as far south as Peru. They also winter along the Atlantic Coast from southern New Jersey to northern South America.

Listing Status:

There is some evidence suggesting a population decline in Western Sandpiper numbers. Nevertheless they remain one of the most abundant shorebirds in North America, numbering in the millions. There are varying estimates of the population ranging from 3,500,000 to 6,500,000. Although they are abundant they are vulnerable because a large percentage of the population gathers in few spots during migration. Development, human disturbance, and oil spills near these sites affect the population. The IUCN lists them as a species of Least Concern.

Cornell Lab of Ornithology
All About Birds

Monterey Audobon

Nature Canada

WWW Field Guide to Birds of North America.