Curlew Sandpiper

Characterized as a medium-sized migratory shorebird, this wader exhibits a typical body length ranging from 19 to 21 cm, a wingspan of 38 to 46 cm, and a variable body mass spanning 45 to 85 g, which often doubles immediately prior to transcontinental migratory flights. It is distinguished morphologically by its slender, blackish bill that curves distinctly downward, paired with moderately elongated, dark slate legs. In adult breeding plumage, individuals display a prominent deep brick-red or chestnut hue covering the face, neck, breast, and belly, set against an upper mantle mottled with blackish-brown, buff, and white fringes. The non-breeding attire presents a striking shift toward understated tones, characterized by a pale ash-gray dorsum with subtle white margins, completely immaculate white underparts, and a faint white supercilium. Throughout all plumages and age classes, the prominent white rump patch serves as an indispensable field identification feature in flight, contrasting strongly with the gray tail and dark flight feathers.

Geographical distribution: Exhibiting one of the most extensive migratory flyways among waders, its circumpolar breeding range is confined strictly to the high-latitude Arctic tundra of northern Siberia, extending across the Yamal and Taymyr peninsulas eastward through maritime lowlands to the Chukchi Peninsula. During the boreal autumn, birds undergo vast southwards movements across multiple continental pathways, navigating interior Eurasia and the East Asian-Australasian Flyway. Its non-breeding wintering grounds encompass coastal and freshwater zones throughout sub-Saharan Africa, the Indian subcontinent, Southeast Asia, and broad coastal stretches of Australasia, with large concentrations established in Australia and New Zealand. Transatlantic or transpacific vagrants occasionally turn up along the Atlantic and Pacific seaboards of the Americas.

Habitat: Demonstrates marked seasonal shifts in macro- and microhabitat requirements throughout its annual lifecycle. Breeding activities occur exclusively within open Siberian Arctic lowland tundra, favoring wet peaty flats, low-lying hummocky moors, moss-sedge bogs, and gravelly slopes adjacent to river mouths and meltwater pools. In non-breeding and stopover quarters, the species is predominantly littoral, heavily frequenting intertidal mudflats and sandflats, sheltered coastal estuaries, mangrove fringes, saltmarshes, hypersaline coastal lagoons, and commercial solar saltworks. In addition to marine shorelines, it frequently utilizes shallow edges of ephemeral freshwater lakes, wastewater reservoirs, and river basins across continental stopover points.

Feeding: Operating as a tactile and visual predator, it sustains an invertebrate-dominated carnivorous diet adapted to sedimentary substrates. In estuarine and marine stopover environments, it uses its curved bill to probe into saturated sediments, actively extracting polychaete worms, small bivalves and gastropod mollusks, and diverse amphipod crustaceans. In its tundra nesting territories, its diet shifts markedly to capitalize on emergent terrestrial and aquatic insects, with larvae and adults of Chironomidae, Tipulidae, and Trichoptera forming the nutritional base. Beetles, small water bugs, arachnids, and occasional fragments of vegetative matter, including seeds of Arctic sedges, are ingested opportunistically during adverse weather conditions.

Behavior: Exceptionally gregarious outside the breeding period, it routinely integrates into large, compact conspecific and mixed flocks alongside dunlins, red knots, and sanderlings, coordinating communal flight maneuvers with remarkable synchronization. Foraging behavior involves energetic walking across unconsolidated sediments or wading belly-deep in shallow pools, driving the bill deeply into the mud with rapid, sewing-machine-like probe cycles. On northern breeding grounds, males adopt an opportunistic polygynous or promiscuous mating strategy, performing elaborate song flights wherein they rise rapidly, hover on shivering downcurved wings, and issue trilling, metallic calls before descending in a shallow glide. Long-distance migration occurs predominantly at high altitudes, often initiated in large, vocal flocks during late evening hours.

Nesting: Nest initiation takes place rapidly following snowmelt in mid-to-late June. The nest site is a meager, shallow depression pressed into the turf, strategically positioned on dry, elevated tundra hummocks, pingos, or lichen-rich gravel ridges that provide clear visibility and earlier drainage. The female lines the interior with a sparse layer of dry willow leaves, moss fragments, and lichen flakes. The typical clutch contains four sub-pyriform eggs, colored in olive-buff or pale greenish shades heavily blotched with dark sepia and chocolate markings, conferring excellent cryptic camouflage. Parental care is characterized by nearly exclusive maternal investment, as males generally desert the territory and mate shortly after clutch completion. The female incubates the eggs for 19 to 21 days. The newly hatched chicks are highly precocial and nidifugous, leaving the nest cup within hours to forage independently under maternal brooding, attaining full fledging status within 14 to 16 days.

Conservation status: Classified globally as Near Threatened (NT) on the IUCN Red List of Threatened Species, following persistent population reductions monitored over past decades. The primary driver of this trend is the widespread loss and degradation of crucial intertidal staging habitats, most acutely documented throughout the Yellow Sea region, where coastal land reclamation has severely restricted refuelling stopovers. Furthermore, anthropogenic climate change poses acute vulnerabilities to high-latitude tundra, transforming permafrost dynamics, altering prey emergence phenology, and disrupting the historic three-to-four-year population cycles of Arctic lemmings, which indirectly drives severe cyclical fluctuations in tundra nest predation by Arctic foxes and skuas.