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 . 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 chest. The non-breeding juvenile plumage is also like that of an adult, except with creamy-coloured streaking on the breast and pale fringes on some of the wing feathers, leading to a scaly appearance. Adults superficially resemble the larger but shorter-billed red knot and the red phalarope in breeding plumage, and the dunlin and stilt sandpiper while not breeding. Juveniles may be confused with the larger and yellow-legged juvenile ruff, or the juvenile dunlin, which has a streaked chest.
The curlew sandpiper's courtship behaviour is complex and involves several distinct displays. In one, the male constructs a faux nest on the ground to present to the female. Another is a graceful aerial chase accompanied by frequent warbling calls. In a third, the male dances around the female on the ground, displaying his tail feathers and rump; this display sometimes culminates in copulation. The female almost always lays one clutch of eggs, usually around the end of June, which hatch after 20 days and fully fledge at 14–20 days. Chicks are relatively mature and mobile at birth. The curlew sandpiper's breeding success is linked to the lemming population; in years with many lemmings, its predators hunt them instead. It is omnivorous, foraging in large flocks in wetlands for various invertebrates, including crabs and insects.
The curlew sandpiper is listed as a vulnerable species on the IUCN Red List because land development and the invasive smooth cordgrass have caused significant habitat loss to its overwintering and migratory sites, and climate change has lowered its breeding productivity. The curlew sandpiper has an estimated annual survival rate of 75–80%.
Taxonomy and etymology 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. Published anonymously. The genus name is from Ancient Greek or , a term used by Aristotle for some grey waterside birds. The specific epithet ferruginea is from Latin , , "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.
Description
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 (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 , 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 , 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.. This source uses the Humphrey–Parkes moult terminology system, with Howell et al.'s 2003 modification. This means that, for example, the "pre-breeding moult of the yearling bird" would be called the "First Prealternate Molt". 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.
Similar species While in breeding plumage, the curlew sandpiper can be confused with the red knot, as both are reddish on the belly. Compared to the curlew sandpiper, the red knot is larger, and has paler orange-buff rather than rust-colored underparts, shorter, greenish legs, and a stockier bill, as well as a spotted and greyish rump. Compared to the red phalarope, the curlew sandpiper does not have black on the top of the head or a white patch around the face, nor does it have a straight and yellow beak or fully brick-red underparts.
The non-breeding or juvenile plumage looks similar to other species of its genus Calidris, such as the stilt sandpiper, which lacks the curlew sandpiper's distinctive white wing stripe and has longer, yellow legs and a flatter head, and the dunlin, which has less visible eyebrows and a straighter bill, along with a generally stouter appearance, and wingtips that barely, if at all, extend beyond the tip of its tail.
In juvenile plumage, the curlew sandpiper can be confused most easily with the juvenile female ruff, which is similar in body colour and build, though it is darker, larger, and has a shorter bill, and its legs are yellow instead of black. The dunlin also looks similar but can be slightly more compact in shape and is usually (though not always) shorter-billed; it can easily be distinguished by its streaked breast and flanks, and brown or black spots along the sides of its upper belly.; ; ; ; ;
Vocalisations
Only the male sings. Each song lasts for 10–15 seconds and consists of several parts, starting with several introductory notes, followed by multiple trilled doublets, a four-part phrase, and several drawn-out whine calls. Both genders vocalise calls. The alarm call is a whik, whik, whik repeated or wik-ki-ki-ki... used on the breeding grounds to warn of potential threats, and the chase call is a shrill, musical twittering given primarily by the male but occasionally by the female during courtship flights. The flight call is a chirrup that drops in the middle, usually uttered during takeoff. The whine call is a loud and ascending whaay, whaay, whaay, audible hundreds of metres away, nearly identical to the stilt sandpiper's whine. It is only given by the male and seems to be used to defend its territory.
Distribution and habitat
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.
Migration