The Semipalmated Sandpiper (Calidris pusilla) is a small shorebird in the family Scolopacidae, distinguished by slight webbing between its front toes, black legs, and a straight dark bill. It breeds on wet sedge tundra in northern Canada and Alaska, winters on sandy beaches in South America, and undertakes long transatlantic migrations, relying heavily on horseshoe crab eggs during spring stopovers.
Learn to identify
Adult Semipalmated Sandpiper on spring migration, photographed in Connecticut on 29 May.
Learning lesson · openly licensed photographs, labelled by BirdBot; labels checked against the cited sources and approved by AI
Short, straight bill: dark and stout; looks blunt at the tip. Grey-brown above: greyer, less brown, than a Least Sandpiper. White below: white belly and flanks. Black legs: black or grey, not yellowish. Compare with Western and Least Sandpipers.
Leg colour is often hard to see in the field.
Sources: Audubon Guide to North American Birds: Semipalmated Sandpiper · Wikipedia: Semipalmated sandpiper (revision 1380704609)
Photo: Paul Danese, CC BY-SA 4.0, via Wikimedia Commons; labels added by BirdBot.
At 13 to 15 cm in length and weighing 21 to 32 g, the Semipalmated Sandpiper is one of the smaller sandpipers. Its most distinctive field mark is the slight webbing between the three front toes, which gives the species its name. The bill is straight, tubular, and dark, while the legs are black. Females are on average slightly larger than males.
Plumage changes significantly with season and age. During the breeding season, adults display a gray to brown upper body with a uniformly scaly pattern and a white belly with darker streaks along the upper breast. In nonbreeding plumage, the upper body fades to a lighter gray-brown, and the breast becomes mostly white with only faint streaking on the sides. Juveniles vary greatly but typically show a darker brown cap and a pronounced supercilium (eyebrow stripe).
In the field, the webbing on the toes is a key diagnostic feature, though it is often difficult to see without a close view. Therefore, plumage contrast and bill shape are the primary field marks for separation. The Semipalmated Sandpiper is often confused with the Least Sandpiper and the Western Sandpiper. Historical field guides, such as Reed (1916), note that the Semipalmated is generally less rusty above than the Western Sandpiper and has a breast that is only faintly streaked in nonbreeding plumage, unlike the more conspicuously streaked Least Sandpiper. These comparisons are based on historical references and should be verified against modern field guides for current taxonomic and plumage accuracy.
According to AviList v2026, the Semipalmated Sandpiper breeds on tundra from the eastern Chukotskiy Peninsula in northeastern Siberia through northern Alaska and eastward in northern Canada to northern Labrador, including southern Canadian Arctic islands from Banks to Baffin. It winters on coasts from the Isthmus of Tehuantepec and Yucatan Peninsula in southwestern Mexico and the Caribbean to far northern Chile and northeastern Brazil.
Breeding habitat consists of wet sedge or sedge-tundra along the shores of northern Canada and Alaska. These birds select open habitats well-suited for breeding displays and scrape nests. Foraging habitat includes pools close to lakes and rivers, shrubby river deltas, and sandy areas along the shore. During migration, stopover habitats may include wetlands, grassy fields, marshes, or edges of lakes and rivers. In winter, they inhabit sandy beaches and intertidal zones.
Semipalmated Sandpipers are migratory shorebirds with a very large range. Many amass to embark on 3,000 to 4,000 km transatlantic flights from northern Canada to South America. During the nonbreeding season, large flocks cooperate to deter predators such as falcons. In contrast, during the breeding season, adults behave in monogamous pairs that defend territory, nest, and young.
Upon arriving at the breeding grounds, males establish territories from which to display to females arriving about a week later. Males perform aerial displays at 5 to 9 m where they hover and produce "motorboat" calls. These displays are well suited to their relatively open habitat where visibility is high. Territory size varies, with estimates of 1 ha, though some nesting habitats have reported higher densities and thus smaller territories.
Semipalmated Sandpipers utilize a probing method to forage for small invertebrates on the ground, in mud, or occasionally under water. Their typical diet consists of chironomid larvae, arachnids, plant seeds, tipulid larvae, dolichopodid larvae, snails, and various beetle larvae and adults. They rely heavily on horseshoe crab eggs during spring migration, a behavior that has significant ecological implications.
Feeding behavior consists of running along the water's edge, pecking and probing in the ground along damp or flooded mud flats. When invertebrates are abundant, they also forage along marsh edges. They use both visual and tactile foraging to collect food, depending on the food source. Females will also eat small mammal bones as an extra source of calcium during egg laying.
Semipalmated Sandpipers breed from late May to July. The male excavates up to 10 to 12 scrapes among sparse vegetation within his territory for females to choose from. The female will then select 2 to 3 of these scrapes (although only one is used) to begin lining with vegetation and other organic matter. Females typically lay 3 to 4 eggs per brood in 24 to 32 hour intervals.
Incubation of the eggs, which is done by both parents, lasts 18 to 22 days. Like all scolopacids, semipalmated sandpipers are precocial at birth and begin actively foraging within hours of hatching. The young fledge 16 to 19 days after hatching. Both parents participate in feeding and protecting the young for up to 11 days. Between 6 to 11 days after the chicks hatch, the parents abandon the brood at separate times, with the female being the first to leave nearly 91% of the time. Semipalmated sandpipers reach sexual maturity at 1 year old.
Semipalmated Sandpipers use vocal and visual forms of communication. A soft 'cher' is often made from individuals of a large roosting flock to convey safety or lack of threat. This 'cher' is quickly replaced by a loud 'churt' when predators are detected. Other calls have been described for nest defense, chick defense, injury feigning, copulation, short-range communication between mates, calling chicks, and brooding.
Males use aerial displays to attract mates to established territories. These displays include a "motorboat" call given while hovering in midair. The species perceives auditory, tactile, visual, and chemical stimuli.
The Semipalmated Sandpiper is listed as Near Threatened (NT) in the IUCN Red List, as recorded in AviList v2026. Population surveys starting in 1986 have shown a slight decrease in overall population size, suspected to be driven by human activity. Key threats include the decline of horseshoe crab populations, which the species relies on heavily for eggs during spring migration. This dependence links directly to migration stopover sites where habitat loss and baitworm harvest further reduce food availability. Poaching on wintering grounds in South America also contributes to population pressure.
Observe flocks quietly from a distance on sandy shorelines or mudflats, watching for probing behavior and cooperative predator deterrence without approaching nests. During the breeding season, maintain a significant distance from nesting areas to avoid disturbing monogamous pairs defending their territories. In winter, observe large flocks from a respectful distance, noting their cooperative behavior when predators are present. Avoid disturbing horseshoe crab spawning areas during spring migration, as these are critical feeding grounds for the species.
Field Tip: When observing a flock on a sandy beach, look for the slight webbing between the front toes as the bird runs. This subtle feature is often the quickest way to confirm the species in the field, especially when plumage is worn or similar species are present.
