This species breeds in high and low Arctic and subarctic wet sedge or heath tundra, often near pools, rivers and lakes (del Hoyo et al. 1996). In the non-breeding season it is mainly coastal, favouring sandy beaches and intertidal mudflats, sometimes also shallow lagoons and saltmarsh (del Hoyo et al. 1996). On migration it is also found  at inland wetlands (del Hoyo et al. 1996). Food is mainly chironomid larvae in the breeding season, along with other small invertebrates and seeds. Various small aquatic, marine and terrestrial invertebrates are taken on migration, including horseshoe crab Limulus polyphemus eggs on spring migration in eastern USA (del Hoyo et al. 1996). Makes non-stop flights of up to 4,000 km on migration, with flocks of up to 350,000 gathering at key stopover sites (del Hoyo et al. 1996).

Calidris pusilla is a common breeder in the Arctic and subarctic from far-eastern Siberia (Russia) east across Alaska (USA) and northern Canada to Baffin Island and Labrador (Chandler 2009). In the non-breeding season the species uses coastal estuarine habitats, wintering on the Pacific coast from Mexico to Chile, and on the Atlantic coast from the Yucatan and the Caribbean south to central Argentina, with large non-breeding concentrations occurring along the coast of Suriname and French Guiana (del Hoyo et al. 1996, Chandler 2009, D. Mizrahi in litt. 2009).

Conservation Actions Underway
Protected under the Migratory Birds Act (1927). This species' non-breeding population is part-covered by the Christmas Bird Count (Meehan et al. 2022); it is covered by the International Shorebird Survey during migration (Brown et al. 2001, Smith et al. 2023); and partly covered by the International Waterbird Census during the non-breeding season (Wetlands International 2023). Breeding surveys are covered by PRISM monitoring (Bart et al. in prep.). The Eastern Flyway Shorebird Initiative (AFSI) has identified and undertaken a series of measures to address unsustainable harvest in the Caribbean and northern South America (AFSI 2016, 2017, 2020). An initial Potential Biological Removal estimate was generated (Watts et al. 2015) and subsequently a revision using a Prescribed Take Framework has been developed (Rivera-Milán et al. 2023). A preliminary estimate of the harvest in Guyana has been made (Andres et al. 2022), allowing an assessment of annual harvest level against likely sustainable take (Rivera-Milán et al. 2023).

Conservation Actions Proposed
Continue to carry out systematic monitoring in breeding areas, key staging sites and wintering sites to determine ongoing population trends. Implement actions to mitigate effects of key threats, in particular mortality from hunting. Increase capacity for better enforcement of hunting regulations and the introduction of these where they do not currently exist. Support adaptive management plan for horseshoe crab harvest in Delaware Bay.