This small, moderately abundant, and widespread shorebird has the broadest and southernmost breeding distribution of all the Nearctic Calidris sandpipers. Breeding mainly in subarctic tundra and far northern boreal forest over much of North America, the Least Sandpiper prefers coastal wetlands or subalpine sedge meadows for nesting but will nest in sand dune habitats at the southern extremes of its range on Sable Island, Nova Scotia, and the Queen Charlotte Islands, British Columbia.
This species migrates on a broad front across North America, with eastern populations likely undertaking nonstop transoceanic migrations of 3,000 to 4,000 km from the Gulf of St. Lawrence and New England to wintering grounds in northeastern South America. Western populations migrate through interior North America to the Gulf Coast and Central America, or down the Pacific Coast to northwestern South America. The species occurs in mixed species flocks of small congeners during migration but tends to forage in drier microhabitats. Usually less numerous than other small, similar-looking sandpipers, it is often overlooked during surveys of staging and wintering sites; estimates of its populations may therefore be inadequate, although numerous migration and wintering surveys suggest significant declines in numbers in recent decades, especially along the east coast.
The Least Sandpiper is monogamous, lays a single clutch, and has a high degree of breeding-site fidelity. It defends nesting territories and is vocal during courtship. It is relatively tame compared to other shorebirds, often allowing close approach by humans. No subspecies have been described.
The key studies on breeding biology are from the Queen Charlotte Is., British Columbia (Cooper and Miller 1992, Cooper and Miller 1997) and Sable I., Nova Scotia (Miller 1979a, Miller 1979b, Miller 1983a, Miller 1985a). Particular attention has been paid to vocalizations on the breeding grounds (Miller 1986a). Butler and Kaiser (Butler and Kaiser 1995) described migration through British Columbia, and differential non-breeding distribution according to sex and body size was documented by Nebel (Nebel 2006). Rubega (Rubega 1997) discovered ‘surface tension transport' of prey in this species, a feeding mechanism employing surface tensions of water surrounding prey to transport prey from bill tip to mouth.