Western Sandpipers nest only in relatively dry tundra habitats, from coastal lowlands to the lower parts of mountains. Such areas are dominated by dwarf birch, willow, crowberry, and various sedges, grasses (especially cottongrass), and lichen. Their foraging habitats tend to be away from nest sites, in coastal lagoons and tundra ponds where water is always less than 4 inches deep (and usually less than 1 inch). They also catch insects near the nest site. During migration they use river deltas and tidal estuaries with fine mud. They also use sandflats, agricultural fields, muddy river and lake margins, sod farms, sewage treatment ponds, saltmarshes, and freshwater marshes. During high tide along the coast, they roost in dense flocks in saltmarsh or on beaches. Wintering birds south of the United States use similar habitats but also frequent salt evaporation ponds and abandoned shrimp farms. Some individuals winter in the interior of Mexico around high-elevation lakes.Back to top
Western Sandpipers eat tiny prey including insects, spiders, and aquatic invertebrates. Their diet changes through the course of the year. They mostly feed in or at the edge of shallow water, seldom more than two inches deep. On the breeding grounds, they eat insects and their larvae, which they pick from plants or water, and also aquatic invertebrates such as crustaceans, mollusks, and marine worms. These they find by probing into the mud or sand, then extracting. Because females have longer bills, they tend to probe more often than males, taking buried prey, while males more often hunt visually, foraging by pecking or gleaning. Males often use drier or shallower areas than females. On average, females also take larger prey items than males, which reduces competition between the sexes. In intertidal areas, Western Sandpipers, like other peep, eat “biofilm,” a frothy, scumlike mixture of diatoms, microbes, organic detritus, and sediment. They eat this material by skimming or slurping it. Documented food items include spiders, midges, craneflies, brine flies, shore flies, water beetles, marine worms, roundworms, amethyst gem clams, Baltic clams, blue mussels, eastern mudsnails, brine shrimp, and other tiny crustaceans such as amphipods and copepods.Back to top
The male prepares and the female selects the nest site, a scraped-out depression in a flat patch of dry tundra.
Both male and female arrange dry willow leaves, birch leaves, grasses, sedges, and lichens in the scrape, which often sits beneath a grass tussock or dwarf birch. The interior nest cup averages about 2.5 inches across and 2.2 inches deep.
|Clutch Size:||2-4 eggs|
|Number of Broods:||1 brood|
|Egg Length:||1.2-1.3 in (2.94-3.32 cm)|
|Egg Width:||0.8-0.9 in (2.14-2.35 cm)|
White, cream, or brown, densely spotted with brown.
|Condition at Hatching:|
Active and covered with down.
Males usually arrive before females on the breeding grounds, where they often must contend with snow and ice cover for several days or weeks. As soon as the tundra clears, they begin to establish territories (about 0.5–3.5 acres) by making display flights and calling frequently. Their displays include a typical shorebird “butterfly flight,” using slow, exaggerated wingbeats, and a fast, low, swooping flight ending with an abrupt ascent. Unlike Least and Semipalmated Sandpipers, they do not perform a hovering display. Western Sandpipers are very territorial, attacking other males that trespass on the territory and also many other species of small shorebird. Males perform courtship displays to females in their territory by approaching them sideways, cocking the tail, drooping and trembling the wings, and lowering the head, often giving a trilling call. Females seem to ignore them for several days, but eventually they follow males in flight to various scrapes (potential nest sites) that males make in flat areas of tundra. Mating usually occurs after the female has selected the final nest site; she indicates her approval by crouching and raising the tail. Western Sandpipers are monogamous in their mating system, and females usually repel advances by males other than their mate; nevertheless, some studies indicate that up to 8% of young birds are from extra-pair copulations. About half of returning adults re-pair with their mate from the previous season. Males and females share incubation and nest defense, but females depart before the young have fledged, leaving males to finish the work of chick-rearing. During migration and on wintering grounds, Western Sandpipers sometimes maintain feeding territories, but they are generally much less pugnacious than the smaller Semipalmated Sandpiper (though they sometimes chase away Least Sandpipers).Back to top
Partners in Flight estimates a global breeding population of 3.5 million and rates the species a 12 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Population trends are not known. The draining of wetlands in Middle America for shrimp farms and other purposes continues to reduce available habitat on the wintering grounds. In California, the spread of non-native cordgrass has also reduced habitat available for wintering and migrating Western Sandpipers. Pollutants pose conservation risks to this species throughout its range. The effects of climate change, including rising sea levels and changes to Arctic habitats and food webs, are forecast to reduce available foraging habitats and prey in the near future.Back to top
Franks, Samantha, David B. Lank and W. Herbert Wilson Jr. (2014). Western Sandpiper (Calidris mauri), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.
Lutmerding, J. A. and A. S. Love. (2019). Longevity records of North American birds. Version 1019 Patuxent Wildlife Research Center, Bird Banding Laboratory 2019.
Partners in Flight (2017). Avian Conservation Assessment Database. 2017.
Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.