Curlew Sandpiper

The curlew sandpiper (Calidris ferruginea) is a small wader. It is a long-distance migrant, breeding in the bogs and coastal lowlands of the Siberian Arctic, arriving there in June and staying until August or September. After the breeding season, it migrates south to spend the winter in Africa and along the coasts of Oceania and southern Eurasia, occupying tidal mudflats and saltpans. It has three main plumages that change with maturity and season. The non-breeding plumage shows brown-greyish upperparts and white underparts. The breeding plumage is much more striking, with the entire front tinted a deep rusty colour, more intensely so in males. The first-year bird does not migrate or breed, instead remaining in its overwintering range throughout the breeding season. It may occasionally moult into its breeding plumage, which is largely similar to that of an adult but with white spots on the...

The curlew sandpiper can occur throughout large swathes of Afro-Eurasia during migration. It is notably missing east of the Verkhoyansk Range in eastern Siberia during migration, along with southern inland Asia. It breeds exclusively in the Siberian extreme high Arctic tundra from the Yamal Peninsula to Kolyuchin Bay. It breeds in coastal lowlands and offshore islands, where the severe climate with harsh cold winds and short growing period prevents the growth of shrubs, and melting snow overlying the permafrost creates boggy conditions. The nest is typically placed on the margins of wet hollows or pools, or on the gentle slopes of hummocks, often close to the nests of Pluvialis plovers like grey plover or Pacific golden plover. Its non-breeding range includes coastal regions of west Africa (from Mauritania to Gabon and including Cape Verde) and southern Africa (inland throughout Mozambique to Namibia to South Africa, and north through Uganda to Kenya). It is additionally present, albeit more rarely, inland from Niger to Chad, along the Republic of the Congo to Angola, and the Nile from Sudan to Egypt and southeastern Tunisia. It is rarer along the coasts of Australasia, as well as inland Victoria and New South Wales. In New Zealand, it can be found on the southeastern coast of the South Island and the entire coastline of the North Island. It also overwinters in coastal South Asia and Southeast Asia. It does not overwinter in the rest of Eurasia. The curlew sandpiper is a scarce migratory vagrant in North America, especially along the Atlantic Seaboard. During the non-breeding season, it is commonly found along sheltered mudflats, as well as salt pans and wetland edges. While inland, it occupies the edges of various bodies of water, especially if they have muddy or sandy margins; it is also found along sewage ponds. It occupies coastal and inland wetlands during migration, and during breeding, it mostly remains in lowland tundra near bogs, depressions, or pools, away from scrub and other dense vegetation.

The curlew sandpiper can occur throughout large swathes of Afro-Eurasia during migration. It is notably missing east of the Verkhoyansk Range in eastern Siberia during migration, along with southern inland Asia. It breeds exclusively in the Siberian extreme high Arctic tundra from the Yamal Peninsula to Kolyuchin Bay. It breeds in coastal lowlands and offshore islands, where the severe climate with harsh cold winds and short growing period prevents the growth of shrubs, and melting snow overlying the permafrost creates boggy conditions. The nest is typically placed on the margins of wet hollows or pools, or on the gentle slopes of hummocks, often close to the nests of Pluvialis plovers like grey plover or Pacific golden plover. Its non-breeding range includes coastal regions of west Africa (from Mauritania to Gabon and including Cape Verde) and southern Africa (inland throughout Mozambique to Namibia to South Africa, and north through Uganda to Kenya). It is additionally present, albeit more rarely, inland from Niger to Chad, along the Republic of the Congo to Angola, and the Nile from Sudan to Egypt and southeastern Tunisia. It is rarer along the coasts of Australasia, as well as inland Victoria and New South Wales. In New Zealand, it can be found on the southeastern coast of the South Island and the entire coastline of the North Island. It also overwinters in coastal South Asia and Southeast Asia. It does not overwinter in the rest of Eurasia. The curlew sandpiper is a scarce migratory vagrant in North America, especially along the Atlantic Seaboard. During the non-breeding season, it is commonly found along sheltered mudflats, as well as salt pans and wetland edges. While inland, it occupies the edges of various bodies of water, especially if they have muddy or sandy margins; it is also found along sewage ponds. It occupies coastal and inland wetlands during migration, and during breeding, it mostly remains in lowland tundra near bogs, depressions, or pools, away from scrub and other dense vegetation.

While overwintering and migrating, the curlew sandpiper forages in large flocks (often mixed-species) of up to thousands on tidal flats, shallows, marshes, salt flats, and sewage lagoons, probing the ground for food, sometimes swimming while feeding. In mixed-species wader flocks, it is one of the dominant species, winning 83% of aggressive interactions with dunlin; individual birds feeding on detritus show significantly higher aggression toward dunlin than groups do. While breeding, it forages alone or in much smaller groups. Its diet consists of insects and other small invertebrates such as crabs, molluscs, and worms, supplemented with various seeds. In the High Arctic, chicks feed on Diptera (90%), with the majority belonging to families Chironomidae and Tipulidae. As the female is larger and longer-billed than the male, she is more likely to wade and tends to take larger, more calorically rewarding prey; in a study at Langebaan Lagoon, South Africa, she ate half as many gastropods, double the mass of crustaceans, and 25% fewer polychaetes. Juveniles forage significantly more slowly than adults, likely due to inexperience and reduced motivation. Unlike adults preparing to return to breeding grounds, juveniles typically remain on the overwintering grounds throughout the breeding season.

The curlew sandpiper appears to be largely monogamous; however, its breeding habits are not well studied. Its ground movements are similar to those of other waders: walking, running, and wading. Its flight speed during migration has been estimated to be around 70–75 km/h. It practices preening and bathing, sometimes scratching its head with its claws and dipping its head in the water to clean it. It mainly roosts at high tide in large mixed-species flocks on sandbars, lagoon islets, and occasionally dunes, reefs, or beach wrack. If disturbed while resting, it will often stretch its wings over its back before hopping on one leg or walking away.

The curlew sandpiper forms pairs during northward migration. Pairs usually arrive at their breeding site in early June and perform courtship in mid-June. The female moves around an area of a few hectares, feeding, and the male follows her attentively, trailing her 3–6 m away, occasionally giving partial or complete songs and conducting various types of courtship behaviour. During aerial courtship, the male pursues the female in long chases, occasionally catching up. When he catches up, he lifts his wings horizontally and glides towards the female while warbling and occasionally performing his chase call (the female also, although more rarely, performs the chase call). The aerial chase closely resembles chases during territorial conflicts, though the latter is more erratic, with sharper turns and gyrations. After the pair lands, the male then begins one of the ground courtship displays. During the pre-nesting period, the male intermittently assumes a "courtship" stance known as the ground courtship attitude (lowered head, ruffled scapulars and back feathers, and bent legs, resulting in a hunched appearance) during feeding. It is often followed by a full ground courtship display and seems to represent increased libido in males. The nest-cup display, one of two ground courtship displays, is often preceded by courtship attitude behaviour. The male, in short bursts, moves across the tundra, eventually stepping into a small depression. Once in the depression, he settles down as if it were a nest, folding his wings over his back and raising his tail. He proceeds to wag his wings and tail side to side, occasionally crouching and kicking up lichen and moss with his claws. He then stands up, picks various bits of vegetation from around him, and deposits them at his feet in the faux nest. Even if the bit of vegetation slips, he still mimes the motion of tossing it into the nest. This sequence is typically followed by him stamping his claws or repeating the crouching motion from earlier. During the sequence, he occasionally makes whine notes and trill calls. This display is not an act of nest-building, as the male performs it several times, each in different locations. Females are usually a few metres away but do not seem to pay full attention to the display. The precopulatory display precedes copulation and is described as elaborate, beginning with both birds standing near each other. The male raises the wing closer to the female, reaching an angle of about 60–70° with the horizontal, and raises the other wing to match it. He also raises his head and lowers and fans his tail. Following this, he gives a short series of warbling calls and sways back and forth, alternating between being behind her and in front of her. He attempts to display his fanned tail and rump to the female by keeping his back always facing her. The female, who has so far ignored him, dashes and thrusts her head towards the male's rump, occasionally overshooting such that her head ends up along the male's flank instead. After around a minute of this display, the female turns away, and the male, with his wings still held up high, approaches to mount and copulate. The breeding grounds are occupied from June until late August. Nesting sites are usually located at the edge of a marsh or pool or on dry patches of tundra, often near nests of other curlew sandpipers. Clutches consist of 3–4 eggs (average 3.76) and are typically laid over the course of three days. The first brood is regularly laid from late June to July, with especially early breeders laying eggs only 5–6 days after arriving and the majority of pairs finishing around the end of June. A second brood may occur for some birds nesting in the far south of their breeding range if the first is unsuccessful. Eggs are slightly pear-shaped and olive-coloured with large dark olive or brown splotches, with more splotches on the broad end, giving them a roughly continuous shade of olive-brown. The female incubates the egg…

The curlew sandpiper is a small wader 18–23 cm in length and weighing 44–117 g. It has a wingspan of 38–46 cm, a bill length of 32–44 mm, and a tarsus (the bone between the "knee" and the "ankle") length of 26–34 mm. It has a black bill, dark brown irises, and dark grey to black feet. All plumages have a large white patch on the rump, occasionally barred with red in some adults, and in flight show a distinctive white stripe going across the wing. Like most waders, the curlew sandpiper has seasonal plumages and moults yearly, shedding its old feathers and growing new ones. For example, to attain its breeding plumage, it will have to first complete the pre-breeding moult; to attain its non-breeding plumage, it will have to complete the post-breeding moult. The non-breeding plumage has greyish upperparts and white underparts with some pale grey streaks; however, as feather wear increases, it slowly becomes browner. The centres of its upperpart feathers are darker, especially on the top of the head, causing its upperparts to look mottled. The tail's underside and the rump are white, with broad, pale grey tail feathers. The largest feathers on its wing are dusky with white streaks along the shaft and a white tip. It has a distinctively white eyebrow, with grey-brown feathers between the base of the bill and the eyes and around the ear. The post-breeding moult, taking place from July to November and lasting as late as April the next year in some southern populations, is a complete moult, with all feathers being replaced. Occurring from January to May, the pre-breeding moult is partial, with all the body feathers and a few flight feathers being replaced. The plumage of a returning breeder differs by sex. In the female, the front side, the entire head, and the upper back are tinted variably reddish, with grey-to-dark streaks. The feathers above the wingstripe are tipped ruddy-silver with black centres, resulting in a spotty appearance. The upper tail, the rump, and most of the wing are all nearly identical to the non-breeding appearance, except for the central tail feathers and two to three of the innermost flight feathers, which are off-black with white or ruddy fringing. Male plumage is similar to that of the female, except with the rust-coloured tinting being almost completely opaque, and conspicuous spots above the eye and around the top of the head. The pre-juvenile moult of the chick occurs at the nest site from late June to July. The juvenile looks similar to the adult non-breeding plumage, but the wear marks and fringing on its feathers are more evenly spread out, resulting in a scaly and more buff-tinged appearance, and the tail feathers are slimmer. The top and back of its head are both dusky with pale creamy streaks, the back being slightly paler. The post-juvenile moult occurs from October to December (and can finish as late as April) and is a partial to incomplete moult, replacing all the body feathers and some wing feathers. This moult takes place almost entirely at stopover and overwintering sites, only rarely starting at breeding grounds. The pre-breeding moult of the first-year bird, which occurs from April to June, is absent or limited; the body feathers are largely or completely replaced, but few if any wing feathers are replaced. The plumage of the first-time breeder is similar to the adult summer plumage, with the primary differences being white spots on the underparts, which are fully and opaquely rust-coloured, not tinted. Sex differences are also similar to those of returning breeders.

BirdLife International, which provides the IUCN conservation status for birds, considers the curlew sandpiper to be a vulnerable species. Despite its vast extent of occurrence (3 million km2) and large population, the population has declined by an estimated 30–49% over the span of 15 years. The species is protected by the Agreement on the Conservation of African-Eurasian Migratory Waterbirds. The global population of the curlew sandpiper is estimated at 0.7–1.2 million individuals, including 420,000–960,000 mature birds. Approximately 300,000–400,000 individuals winter in South Africa, while another 400,000 winter across Southwest Asia, East Africa, and southern Africa. An estimated 200,000 winter in South Asia; however, this figure may be an overestimate. The East Asian–Australasian Flyway population is estimated at 120,000. The curlew sandpiper has experienced habitat loss throughout its wintering and migratory ranges. On the coast of the Yellow Sea, 65% of intertidal habitats have been lost over the past 50 years, and the area of reclaimed land exceeds the extent of the remaining intertidal mudflats, which may have been a major cause of the population decline. In China, the rate of reclamation has slowed since 2013 and has essentially ceased as of 2018. Reclamation has continued around the Korean Peninsula. Another major factor in habitat loss is the invasive smooth cordgrass, which may make occupied mudflats unsuitable habitats. The causes of the curlew sandpiper's declining breeding productivity are not fully understood; proposed factors include fewer lemming outbreaks, a mismatch between the timing of breeding and peak insect abundance, and breeding habitat alteration, all potentially resulting from climate change.

The curlew sandpiper was formally described in 1763 by the Danish ornithologist Erik Pontoppidan under the binomial name Tringa ferrugineus, later designated Tringa ferruginea by Morten Thrane Brünnich in 1764. Historically, it was often placed in the genus Tringa along with other small sandpipers; in 1816, Louis Pierre Vieillot even considered it the type species of that genus. It was later moved to the genus Calidris. The genus name is from Ancient Greek kalidris or skalidris, a term used by Aristotle for some grey waterside birds. The specific epithet ferruginea is from Latin ferrugo, ferruginis, "iron rust", referring to the bird's colour in breeding plumage. The curlew sandpiper has no recognised subspecies. Within the genus Calidris, the curlew sandpiper is most closely related to the stilt sandpiper; together, they form part of a small clade that also includes the spoon-billed sandpiper, Temminck's stint, red-necked stint, and long-toed stint. The curlew sandpiper occasionally hybridises with sharp-tailed and pectoral sandpipers, producing the hybrids Cooper's sandpiper and Cox's sandpiper, respectively. Hybrids with the dunlin and white-rumped sandpiper have also been observed, though they are rare.