Curlew Sandpiper

The curlew sandpiper (Calidris ferruginea) is a slender, long-legged sandpiper that breeds only in the high Arctic of Siberia. Adults are about 18–23 cm long, have a wingspan of roughly 38–46 cm and weigh around 44–117 g. The slightly down-curved bill, long dark legs and completely white rump are useful identification features.

Breeding adults are transformed by deep rusty-red plumage across the head and underparts. Outside the breeding season they become much greyer above and white below. Juveniles have a neat, scaly-looking upperparts pattern caused by pale feather edges. Non-breeding birds can resemble dunlins (Calidris alpina), but curlew sandpipers are usually taller and more elegant, with a longer and more clearly curved bill and a white rump that is especially obvious in flight.

Breeding takes place in the treeless high-Arctic tundra of northern Siberia, especially in low-lying areas with wet hollows, pools and boggy ground created by melting snow over permafrost. The short summer provides an intense burst of insects and other invertebrates for adults and rapidly growing chicks.

For the rest of the year the species is primarily a wetland bird. Migrants and wintering birds use tidal mudflats, estuaries, lagoons, saltpans, shallow lakes, sewage ponds and other open wetlands where soft sediment provides rich feeding areas. Because the species migrates between continents, the condition of wetlands thousands of kilometres apart can affect the same population.

On the breeding grounds, insects and their larvae form a large part of the diet, together with other small invertebrates. During migration and winter, worms, small molluscs, crustaceans and aquatic insects become especially important. Seeds and other plant material may also be taken in smaller amounts.

The long bill is used to probe repeatedly into mud and shallow water, while visible prey is also picked from the surface. Curlew sandpipers can continue feeding after dark when tides expose productive mudflats.

Outside the breeding season, curlew sandpipers are strongly social and often feed or rest in dense mixed flocks with dunlins and other shorebirds. Group size changes with local food conditions and the amount of exposed wetland available.

Long-term ringing work also shows strong fidelity to non-breeding areas. Some individuals return to the same distant winter region year after year, even though they may show much less attachment to one exact breeding site.

The curlew sandpiper is an extreme long-distance migrant. Birds leave their Siberian breeding grounds and spread across several major flyways to non-breeding areas from West and southern Africa through India to Australia and New Zealand. Adults begin moving south first, followed later by juveniles, while spring migration brings the birds rapidly back toward Siberia.

A tracking study published in 2021 compared curlew sandpipers with red-necked stints (Calidris ruficollis) and followed birds travelling between Australia and the Russian Arctic. Curlew sandpipers used fewer stopover areas and depended more heavily on a small number of key sites, especially around the Yellow Sea. This concentrated migration strategy may help explain why the species has been especially vulnerable to rapid habitat loss along that flyway.

Pairs form during northward migration or soon after arrival in Siberia. Courtship is elaborate, with the male performing song flights, aerial chases and displays on the ground. The nest is a shallow depression lined with dry vegetation, and four eggs are typical.

Parental care is unusually one-sided. The male generally leaves the breeding area while the female is still laying eggs, leaving all incubation and chick care to her. Incubation lasts about 20 days. The chicks hatch covered in down, leave the nest quickly and can find much of their own food, while the female leads and defends them until they become independent after roughly 14–20 days.

Breeding success can vary sharply between years. An analysis published in 1987 linked productive breeding years to Arctic lemming cycles: when lemmings are abundant, Arctic foxes (Vulpes lagopus) and other predators concentrate more heavily on them, reducing predation pressure on nesting shorebirds. A field study from Taimyr published in 1998 found high chick survival in a lemming peak year and about two fledged young per female. Females moved their broods up to 2.4 km from the nest site during the first week, and several broods could gather in groups of two to six in which females cooperated in defending the chicks from predators.

The curlew sandpiper is classified as vulnerable on the IUCN Red List. The species was assessed as vulnerable in 2024 after the global population was estimated to have declined by more than 30% over three generations.

Loss and degradation of wetlands affect the species across its enormous migration system. Coastal development and conversion of tidal flats are particularly serious along the East Asian–Australasian Flyway, including around the Yellow Sea, where tracking studies show that many curlew sandpipers depend on a relatively small number of staging sites. Disturbance and hunting add further pressure at some stopover and wintering areas.

Climate-driven changes in the Arctic may alter snowmelt, invertebrate availability and the predator–lemming cycles that influence breeding success. Because different threats operate thousands of kilometres apart, deterioration at only a few important sites can affect birds from a much larger breeding population.

Curlew sandpipers depend on a connected network of wetlands throughout their flyways. Tidal flats, estuaries, saltpans and other staging areas are especially important where tracking and count data show that large parts of the population concentrate at a small number of key sites.

The annual cycle links breeding, migration and wintering areas across several continents. A population can therefore be affected even when one area remains intact if critical stopover sites elsewhere on the route are lost or degraded.